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BEGIN:VEVENT
SUMMARY:Diego Rubiera-Garcia (UCM\, Madrid\, Dept. Phys.)
DTSTART:20200929T131500Z
DTEND:20200929T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/1
DESCRIPTION:Title: Understanding space-time singularities inside black holes: a prop
osal for their resolution\nby Diego Rubiera-Garcia (UCM\, Madrid\, Dep
t. Phys.) as part of Theoretical physics seminar @ Tartu\n\nLecture held i
n Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nSpace-t
ime singularities are an ubiquitous prediction of Einstein's General Relat
ivity (GR). They represent (perhaps) the most important conundrum in our u
nderstanding of the nature of the gravitational interaction and\, moreover
\, are the pivotal point for our theoretical attempts to extend the theory
. In this talk I will describe one of such attempts - metric-affine gravit
y -\, and tackle the resolution of such singularities according to several
perspectives for detecting potentially pathological behaviours.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Yong Gao and Rui Xu (Peking University\, Beijing\, China)
DTSTART:20201006T131500Z
DTEND:20201006T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/2
DESCRIPTION:Title: Deformed neutron stars and their characteristics in electromagnet
ic and gravitational radiation\nby Yong Gao and Rui Xu (Peking Univers
ity\, Beijing\, China) as part of Theoretical physics seminar @ Tartu\n\nL
ecture held in Physicum room A101\, University of Tartu\, Estonia.\n\nAbst
ract\nThe shape of a neutron star (NS) is closely linked to its internal s
tructure and the equation of state of supranuclear matters. In the first p
art of the talk\, we will present the results that extend previous work an
d describe the free precession of a triaxially deformed NS. Such a NS is a
unique object that carries abundant information for multimessenger observ
ation\, as the free precession could manifest in\, (i) the spectra of cont
inuous gravitational waves\, and (ii) the timing behavior and pulse-profil
e of pulsars. Then\, in the second part\, we consider violation of Lorentz
invariance\, one of the fundamental principles in General Relativity\, as
one possible beyond-the-standard-model origin for the deformation of a NS
. An estimate for the continuous gravitational waves from such a source wi
ll be made\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantinos F. Dialektopoulos (Yangzhou University)
DTSTART:20201013T131500Z
DTEND:20201013T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/3
DESCRIPTION:Title: Recent developments in Horndeski theory and beyond\nby Konsta
ntinos F. Dialektopoulos (Yangzhou University) as part of Theoretical phys
ics seminar @ Tartu\n\nLecture held in Physicum room A101\, University of
Tartu\, Estonia.\n\nAbstract\nThe most general scalar-tensor theory with a
single scalar field\, in four dimensions\, leading to second order field
equations was introduced by Gregory Horndeski in 1974 and it took his name
since. Even though G. Horndeski abandoned physics to become a painter soo
n after he developed this theory\, in the late '00s the theory was redisco
vered as generalized Galileons. In this talk\, I will review its recent di
scovery and discuss why it is a powerful tool to explore cosmology and ast
rophysics beyond general relativity. I will also present its current statu
s after GW170817 and I will give a brief introduction in its generalizatio
ns\, i.e.\, Degenerate Higher Order Scalar Tensor (DHOST) theories.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Francisco José Maldonado Torralba (University of Cape Town and Un
iversity of Groningen)
DTSTART:20201020T131500Z
DTEND:20201020T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/4
DESCRIPTION:Title: Poincaré Gauge Gravity: stability\, phenomenology\, and prospect
s.\nby Francisco José Maldonado Torralba (University of Cape Town and
University of Groningen) as part of Theoretical physics seminar @ Tartu\n
\nLecture held in Physicum room A101\, University of Tartu\, Estonia.\n\nA
bstract\nPoincaré Gauge Gravity is a theory quadratic in both curvature a
nd torsion\, which is constructed by requiring that the gravitational theo
ry must be invariant under local Poincaré transformations. In this talk I
will present the main outcomes of my PhD thesis related to this theory. F
irst\, I will expose some results about the stability of the quadratic Poi
ncaré Gauge Lagrangian\, and prove that only the two scalar degrees of fr
eedom can propagate without introducing pathologies. I will make emphasis
on the form of the bi-scalar stable Lagrangian\, and give some application
s of this particular theory. Then\, in order to see which kind Black Hole
solutions we can expect in Poincaré Gauge theories\, I will study Birkhof
f's and no-hair theorems under physically relevant conditions. Finally\, I
will show an ultraviolet extension of Poincaré Gauge theories by introdu
cing non-local terms into the action\, which can ameliorate the singular b
ehaviour at large energies. I will present solutions of this theory at the
linear level\, and prove that such solutions are ghost- and singularity-f
ree\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kristjan Müürsepp (University of Tartu\, National Institute of C
hemical Physics and Biophysics)
DTSTART:20201027T141500Z
DTEND:20201027T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/5
DESCRIPTION:Title: The particle physics and astrophysical properties of dark compact
objects\nby Kristjan Müürsepp (University of Tartu\, National Insti
tute of Chemical Physics and Biophysics) as part of Theoretical physics se
minar @ Tartu\n\nLecture held in Physicum room A101\, University of Tartu\
, Estonia.\n\nAbstract\nThe detection of the Higgs boson in 2012 strongly
suggests that at least one fundamental scalar particle exists in the Natur
e. Moreover\, although no compact objects consisting of fundamental scalar
bosons have been observed\, there is\, as of now\, no fundamental princip
le ruling out the existence of compact objects consisting of scalar fields
. In this seminar\, I will present an introduction to a subset of the comp
act objects comprising of scalar fields that are known as boson stars. I w
ill discuss various astrophysical properties of boson stars and show how t
hose can markedly differ from the properties of neutron stars. Furthermore
\, I will highlight the mathematical formalism underlying a proper descrip
tion of these stars and briefly outline the first results I have obtained
on the topic. Finally\, contingent on time constraints\, I will briefly el
ucidate the possible connection between boson stars and dark matter.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Davi C. Rodrigues (Espirito Santo University)
DTSTART:20201103T141500Z
DTEND:20201103T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/6
DESCRIPTION:Title: Dark matter and gravity\nby Davi C. Rodrigues (Espirito Santo
University) as part of Theoretical physics seminar @ Tartu\n\nLecture hel
d in Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nDark
matter was introduced in the 30's as an additional kind of matter that co
uld not be directly detected from any electromagnetic waves\, but whose pr
esence could be inferred from gravitational phenomena. What was in the beg
inning a curious fact turned out to be the start of a solid\, although ind
irect\, evidence for an "invisible giant": it was far from an additional d
etail\, it was the main gravitational actor at the scales of galaxies and
beyond\, while no one could "see" it. It is therefore tempting to dismiss
this invisible giant as an illusion caused by using the wrong gravitationa
l theory. I will argue why this is even less likely. In particular\, I wi
ll talk about a well known proposal called "modified newtonian dynamics" a
nd why it is relevant as a phenomenological relation\, not as a theory for
gravity.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mir Faizal (Lethbridge University)
DTSTART:20201110T141500Z
DTEND:20201110T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/7
DESCRIPTION:Title: Quantum Gravity Beyond General Relativity\nby Mir Faizal (Let
hbridge University) as part of Theoretical physics seminar @ Tartu\n\nLect
ure held in Physicum room A101\, University of Tartu\, Estonia.\n\nAbstrac
t\nI will talk about different works done on quantum gravity. As quantum g
ravity is usually studied by quantizing general relativity\, I will highli
ght the new areas and open problems\, about the possibility of analyzing
quantization of other theories of classical gravity. My talk will include
but not be limited to string theory.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Maria Benito (NICPB\, Tallinn)
DTSTART:20201124T141500Z
DTEND:20201124T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/8
DESCRIPTION:Title: The Milky Way's Dark Matter halo\nby Maria Benito (NICPB\, Ta
llinn) as part of Theoretical physics seminar @ Tartu\n\nLecture held in P
hysicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nThe distri
bution of Dark Matter in galaxies is one remarkable output of structure fo
rmation in a cosmological context\, and an important input for searches of
the nature of Dark Matter. In this talk\, I will describe the sources of
uncertainty that affect the observational determination of the Dark Matter
content in the Milky Way\, and I will quantify their effect on the estima
ted Dark Matter density by means of a data-driven analysis. I will further
show that the uncertainties on the Dark Matter distribution\, and their i
mpact on searches of physics beyond the standard model\, stays sizable eve
n with state-of-the-art determinations of astrophysical quantities of rele
vance (such as the Sun’s circular velocity and its distance to the Galac
tic center).\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anna Pachol (Queen Mary University of London)
DTSTART:20201208T141500Z
DTEND:20201208T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/9
DESCRIPTION:Title: Observables and quantum spacetimes\nby Anna Pachol (Queen Mar
y University of London) as part of Theoretical physics seminar @ Tartu\n\n
Lecture held in Physicum room A101\, University of Tartu\, Estonia.\n\nAbs
tract\nNoncommutative geometry\, as the generalised notion of geometry\, c
an be helpful in providing the phenomenological models quantifying the eff
ects of quantum gravity. The noncommutative nature allows for obtaining qu
antum gravitational corrections to the classical solutions. One of the mos
tly studied possible phenomenological effects of quantum gravity is the mo
difications in wave dispersion.\n\nIn my talk I will introduce the mathema
tical framework for quantum spacetimes within the Hopf algebras and Drinfe
ld twists formalisms. Twisted differential calculus and twisting generator
s of the Hopf algebra symmetry allow on a fresh look on modifications in d
ispersion relations and offer a proper choice of physical observables as g
enerators of the quantum Lie algebra of symmetries. Wave equations on nonc
ommutative spaces are derived from a quantum Hodge star operator. The form
alism also allows for study of the curved backgrounds. I will present rece
nt results on propagation of waves in noncommutative cosmology and on the
modification of the dispersion relations due to noncommutativity combined
with curvature of spacetime.\n\nThe talk will base on the results develope
d in collaboration with P. Aschieri and A. Borowiec [Observables and Dispe
rsion Relations in k-Minkowski Spacetime J. High Energ. Phys. 2017\, 152 (
2017) arXiv:1703.08726\, Dispersion Relations in κ-Noncommutative Cosmolo
gy arXiv:2009.01051].\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Evgenii Strugovshchikov
DTSTART:20201215T141500Z
DTEND:20201215T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/10
DESCRIPTION:by Evgenii Strugovshchikov as part of Theoretical physics semi
nar @ Tartu\n\nLecture held in Physicum room A101\, University of Tartu\,
Estonia.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alejandro Jiménez-Cano (Universidad de Granada)
DTSTART:20210209T141500Z
DTEND:20210209T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/11
DESCRIPTION:Title: Gravitational wave solutions in metric-affine gravity\nby Al
ejandro Jiménez-Cano (Universidad de Granada) as part of Theoretical phys
ics seminar @ Tartu\n\nLecture held in Physicum room A101\, University of
Tartu\, Estonia.\n\nAbstract\nIn this work we derived exact gravitational
wave solutions in a general class of quadratic metric-affine gauge gravity
models. The Lagrangian includes all possible linear and quadratic invaria
nts constructed from the torsion\, nonmetricity and the curvature. The ans
atz for the gravitational wave configuration and the properties of the wav
e solutions are patterned following the corresponding ansatz and the prope
rties of the plane-fronted electromagnetic wave.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Swagat S. Mishra (Inter-University Centre for Astronomy and Astrop
hysics\, Post Bag 4\, Ganeshkhind\, Pune 411 007\, India)
DTSTART:20210216T141500Z
DTEND:20210216T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/12
DESCRIPTION:Title: Curing inflationary degeneracies using reheating predictions and
relic gravitational waves\nby Swagat S. Mishra (Inter-University Cent
re for Astronomy and Astrophysics\, Post Bag 4\, Ganeshkhind\, Pune 411 00
7\, India) as part of Theoretical physics seminar @ Tartu\n\nLecture held
in Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nAs a c
onsequence of the remarkable developments in cosmology over the past three
decades\, both in the theoretical as well as observational fronts\, cosmi
c inflation has emerged as the leading scenario of the very early universe
\, setting natural initial conditions for the standard cosmological model
prior to the commencement of the radiative hot Big Bang Phase. It is well
known that the inflationary scenario often displays different sets of dege
neracies in its predictions for the CMB observables. These degeneracies us
ually arise either because multiple inflationary models predict similar va
lues for the scalar spectral index n_s and the tensor-to-scalar ratio r\,
or because within the same model\, the values of {n_s\, r} are insensitive
to some of the model parameters\, making it difficult for the CMB observa
tions alone to constitute a unique probe of inflationary cosmology. Simila
rly another key aspect of inflationary cosmology\, namely the epoch of 're
heating'\, also remains observationally inaccessible at present\, despite
a profusion of theoretical progress in this direction. After providing a c
onsummate introduction of the inflationary cosmology\, the speaker will de
monstrate that by taking into account the constraints on the post-inflatio
nary reheating parameters such as the duration of reheating\, its temperat
ure and especially its equation of state (EOS)\, it is possible to break t
his degeneracy in certain classes of inflationary models. The relic gravit
ational wave (GW) spectrum provides us with another tool to break inflatio
nary degeneracies and probe the epoch of reheating. This is because the GW
spectrum is sensitive to the post-inflationary EOS of the universe. Indee
d a stiff EOS (w > 1/3) during reheating gives rise to a blue tilt in the
spectral index of the GWs while a soft EOS (w<1/3) results in a red tilt.\
n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Viktor Gakis (National Technical University of Athens\, Greece)
DTSTART:20210316T141500Z
DTEND:20210316T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/13
DESCRIPTION:Title: Generalised Proca theories in teleparallel gravity\nby Vikto
r Gakis (National Technical University of Athens\, Greece) as part of Theo
retical physics seminar @ Tartu\n\nLecture held in Physicum room A101\, Un
iversity of Tartu\, Estonia.\n\nAbstract\nGeneralised Proca theories of gr
avity represent an interesting class of vector–tensor theories where onl
y three propagating degrees of freedom are present. In 2012.11959\, we pro
pose a new teleparallel gravity analog to Proca theories where the general
ised Proca framework is extended due to the lower-order nature of torsion-
based gravity. We develop a new action contribution and explore the exampl
e of the Friedmann equations in this regime. We find that teleparallel Pro
ca theories offer the possibility of a much larger class of models in whic
h do have an impact on background cosmology.\n\nIn this talk we will revie
w how the Generalised Proca theories are constructed and then present a wa
y of adapting them in the teleparallel regime\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Celia Escamilla-Rivera (Universidad Nacional Autónoma de México)
DTSTART:20210323T141500Z
DTEND:20210323T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/14
DESCRIPTION:Title: Extended theories of gravity to explain the Hubble-Lemaitre tens
ion\nby Celia Escamilla-Rivera (Universidad Nacional Autónoma de Méx
ico) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Phy
sicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nThe current
cosmological probes have provided an extraordinary confirmation of the sta
ndard LCDM cosmological model\, that has been constrained with unprecedent
ed accuracy. However\, with the increase of the experimental sensitivity a
few statistically significant tensions between different independent cosm
ological datasets emerged. While these tensions can be in portion the res
ult of systematic errors\, the persistence after several years of accurate
analysis strongly hints at cracks in the standard cosmological scenario a
nd the need for new physics. In this talk I will list a few interesting ne
w physics models in the direction of extended theories of gravity that cou
ld solve this tension and discuss how the new computational techniques wil
l be crucial in this role.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Blixt (University of Tartu\,Estonia)
DTSTART:20210406T131500Z
DTEND:20210406T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/15
DESCRIPTION:Title: Hamiltonian analysis of covariant teleparallel gravity\nby D
aniel Blixt (University of Tartu\,Estonia) as part of Theoretical physics
seminar @ Tartu\n\nLecture held in Physicum room A101\, University of Tart
u\, Estonia.\n\nAbstract\nThe conventional action formulation for general
relativity is by the Einstein-Hilbert action\, which depends on the Levi-C
ivita connection and the metric. However\, a classically equivalent theory
can be done by formulating the action in terms of torsion (related to the
antisymmetric part of the affine connection) and tetrads. This is done in
the theory called teleperallel equivalent to general relativity. From thi
s formulation as a starting point it is not evident from a quick look that
this theory should be selected in favor of other modified teleparallel th
eories of gravity. This gives a motivation from a fundamental point of vie
w to investigate the theory further\, where the Hamiltonian analysis is us
eful since it can give insights of the canonical structure of a theory.\n\
nIn the literature there is some work on the Hamiltonian analysis for the
most basic teleparallel theories of gravity. However\, they are either inc
omplete\, contradicting to other work\, not formulated in a covariant way\
, or a combination of these. In this talk I will outline the derivation of
the so-called primary Hamiltonian for the most basic covariant teleparall
el theories of gravity. I explicitly write out these Hamiltonians without
putting the so-called spin connection to zero. Then\, I will briefly talk
about perturbations in the aforementioned theories and use this to show th
at they are most likely not viable theories. The irreducible decomposition
of the torsion scalar will be discussed in order to reach some insights o
n the fundamental relevance for the irreducible components and their relat
ion to propagating fields. If time allows I will spend some time on discus
sing future directions where a teleparallel bigravity construction might a
void theoretical pathologies while providing an interesting theory of grav
ity.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nico Benincasa (cNational Institute of Chemical Physics and Biophy
sics\, Tallinn\, Estonia)
DTSTART:20210427T131500Z
DTEND:20210427T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/16
DESCRIPTION:by Nico Benincasa (cNational Institute of Chemical Physics and
Biophysics\, Tallinn\, Estonia) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A101\, University of Tartu\, Estoni
a.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Priidik Gallagher (University of Tartu\,Estonia)
DTSTART:20210511T131500Z
DTEND:20210511T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/17
DESCRIPTION:by Priidik Gallagher (University of Tartu\,Estonia) as part of
Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room A101
\, University of Tartu\, Estonia.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Hardi Veermäe (NICPB\, Tallinn)
DTSTART:20210309T141500Z
DTEND:20210309T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/18
DESCRIPTION:Title: Probing primordial black holes with gravitational waves\nby
Hardi Veermäe (NICPB\, Tallinn) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A101\, University of Tartu\, Estoni
a.\n\nAbstract\nPrimordial black holes are hypothetical black holes that f
ormed within the first seconds of our Universe. They may form a part or ev
en all of dark matter. This talk will briefly review general aspects of gr
avitational wave astronomy and primordial black hole physics. In the secon
d half of the talk\, we will focus on gravitational waves signals associat
ed with primordial black holes and try to answer the question of how gravi
tational waves can be used to probe the existence of such black holes.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Aleksander Kozak (University of Wrocław)
DTSTART:20210330T131500Z
DTEND:20210330T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/19
DESCRIPTION:Title: Invariant quantities of scalar-tensor theories for stellar struc
utre\nby Aleksander Kozak (University of Wrocław) as part of Theoreti
cal physics seminar @ Tartu\n\nLecture held in Physicum room A101\, Univer
sity of Tartu\, Estonia.\n\nAbstract\nStars in the scalar-tensor theories\
, relativistic and non-relativistic\, have been widely\nstudied in the lit
erature\; however\, the formalism of conformal invariants has not yet been
\napplied to stellar objects. In my talk\, I will present a way to describ
e stellar structure in\na frame-independent way. This will be achieved by
expressing all relevant equations in\nterms of invariants. Such a procedur
e will allow us to easily compare dierent theories of\ngravity within one
framework. Also\, a non-relativistic limit of the Tolman-Oppenheimer-\nVo
lko will be presented\, and the formalism will be applied to Starobinsky
theory in the\nPalatini approach.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vladimir Hizhnyakov (University of Tartu)
DTSTART:20210608T131500Z
DTEND:20210608T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/20
DESCRIPTION:Title: Singular long-wave vibronic interaction in superfluid helium: ma
nifestation in zero-phonon line\nby Vladimir Hizhnyakov (University of
Tartu) as part of Theoretical physics seminar @ Tartu\n\nLecture held in
Physicum room A101\, University of Tartu\, Estonia.\n\nAbstract\nA theory
is proposed [1] that describes the vibronic transitions in impurity atoms
in superfluid helium\, based on a two-fluid model of helium II. It is show
n that\, owing to the Archimedes’ principle\, the linear vibronic intera
ction with low-frequency phonons in the liquid phase is singularly enhance
d. As a result of such a singular increase in the vibronic interaction\, a
macroscopic amount of phonons with an almost zero frequency is created du
ring the electronic transition in impurity atom\, which leads to a finite
broadening of the zero-phonon line (ZPL) in the optical spectrum already a
t the zero temperature limit. It is shown that the temperature dependence
of the ZPL has a discontinuity in the derivative at the temperature =2.17
K\, and above this dependence becomes linear.\nTheory is applied for th
e description of the studied in [2] temperature dependence of ZPL of the o
ptical spectrum of the inner shell transition of the Dy atom in superfluid
helium. A good agreement of the theory with experiment is achieved\, taki
ng into account\, in addition to the linear vibronic interaction\, the inh
omogeneous broadening of ZPL\, caused by slow fluctuations of the surface
tension of the bubbles of the surrounding helium atoms.\n\n\n\n[1] V.Hizhn
yakov\, V. Boltrushko\, G. Benedek\, Thermal broadening of zero-phonon lin
e in superfluid helium\, PRB\, 2021. \n\n[2] P. Moroshkin and K. Kono\, Ph
ysical Review B 99\, 104512 (2019).\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sebastian Schuster (University of Prague)
DTSTART:20210610T100000Z
DTEND:20210610T111500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/21
DESCRIPTION:Title: Wormholes\, Warp Drives\, Tractor Beam\nby Sebastian Schuste
r (University of Prague) as part of Theoretical physics seminar @ Tartu\n\
nLecture held in Physicum room A101\, University of Tartu\, Estonia.\n\nAb
stract\nThe solutions first encountered in studying general relativity (an
d its alternatives or modifications) are solutions for a given (or absent)
source. A different approach is to reverse engineer the source terms: One
posits a given metric and asks what source term this would require. This
kind of solution is frequently encountered when the metric is supposed to
“solve” a given problem\, like circumventing relativity's speed limit
by wormholes\, warp drives or hypertubes. So far\, all of these have ended
up with “odd” source terms in the sense that they violate energy cond
itions. While the precise physical standing of energy conditions is compli
cated\, their violation is usually still a warning sign. In this talk\, I
will present a general introduction to warp drives\, a new modification re
sulting in tractor beams\, and some discussion of energy conditions at lar
ge.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Erik Jensko (University College London)
DTSTART:20210907T131500Z
DTEND:20210907T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/22
DESCRIPTION:Title: Modifying General Relativity with boundary terms\nby Erik Je
nsko (University College London) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A101\, University of Tartu\, Estoni
a.\n\nAbstract\nIn this talk I present an outline of our recent work [2103
.15906 gr-qc] which looks at yet another modification of General Relativit
y (GR) of the form f(something). Here it’s based on a generalisation of
the first-order Einstein or Gamma-squared action\, which differs from the
Einstein-Hilbert action by a boundary term. The underlying geometry is the
usual Riemannian structure of GR (with vanishing torsion and nonmetricity
). However\, I look at some of the equivalences with the other popular geo
metric theories f(T) and f(Q) gravity\, set in different non-Riemannian ge
ometries. In the talk\, I focus on the importance of breaking the diffeomo
rphism invariance of the gravitational action and field equations\, and ho
w this differs from many current theories. The similarities with the Loren
tz non-invariance of modified teleparallel f(T) gravity are also highlight
ed. Lastly\, new boundary terms which differentiate between the gravitatio
nal actions of this theory and f(T) and f(Q) gravity are identified\, and
I look at how they can be used in a unified approach to modelling these ap
parently distinct theories.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlos Argüelles (ICRA\, Pescara)
DTSTART:20210914T131500Z
DTEND:20210914T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/23
DESCRIPTION:Title: Dark matter in the Milky Way: from SgrA* to the entire halo\
nby Carlos Argüelles (ICRA\, Pescara) as part of Theoretical physics semi
nar @ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\,
Estonia.\n\nAbstract\nRelaxation mechanisms of collisionless self-gravitat
ing systems of fermions\, can lead to spherical equilibrium states which a
re stable\, long-lived\, and able to explain the dark matter (DM) halos in
galaxies. The most general fermionic DM profile out of such a mechanism\,
develops a degenerate compact core which is surrounded by an extended hal
o. When applied to the Milky Way\, it is demonstrated that while the outer
halo can explain the rotation curve of our Galaxy\, the central DM-core e
xplain the dynamics of all the best resolved S-cluster stars orbiting SgrA
*\, without the need of assuming a central black hole (BH). Interestingly
\, when such a novel core-halo DM profiles are applied to larger galaxies\
, the dense DM core can reach the critical mass for gravitational collapse
into a BH of ∼ 10^8 Mo. This result provides a new mechanism for superm
assive BH formation in active galaxies directly from DM\, leading to a par
adigm shift in the understanding of galactic cores.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Soham Bhattacharyya (Hannover\, Max Planck Inst. Grav.)
DTSTART:20210928T131500Z
DTEND:20210928T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/24
DESCRIPTION:Title: Stumbling around in the modified gravity landscape\nby Soham
Bhattacharyya (Hannover\, Max Planck Inst. Grav.) as part of Theoretical
physics seminar @ Tartu\n\nLecture held in Physicum room A101\, University
of Tartu\, Estonia.\n\nAbstract\nParameters extracted from Gravitational
Wave (GW) data allow observers to quantify certain physical aspects of GW
producing sources\, like neutron stars (NS) and black holes (BH). In the c
ase of an isolated BH\, its physical shape in space\, as a freely falling
asymptotic observer would deduce from data\, combined with its inertial ma
ss\, gets encoded in GWs radiated from these sources. In classical terms\,
a multipolar structure of radiating sources can be established from the G
W data\, giving a freely falling observer a dynamic view of the 'horizon'
of a BH as it undergoes a damped oscillation towards a stable shape. Howev
er\, the dynamical behavior is the opposite when the source is a binary sy
stem. Two 'symmetric' bodies mutually deform each other to a maximally dis
torted single compact object\, radiating GWs that increase in frequency an
d amplitude (to specific maximum values) along with the distortion. Using
a Zangenbewegung approach towards the maximal distortion (known in GW lite
rature as the merger) from both sides (ring-down and inspiral\, respective
ly)\, I will talk about GR's predictions and the corresponding predictions
made by extended theories of gravitation like f(R) and dynamical Chern-Si
mons.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Emanuele Zappala (Institute of Mathematics and Statistics\, Univer
sity of Tartu)
DTSTART:20210921T131500Z
DTEND:20210921T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/25
DESCRIPTION:Title: Braided matter interactions in quantum gravity via 1-handle atta
chment\nby Emanuele Zappala (Institute of Mathematics and Statistics\,
University of Tartu) as part of Theoretical physics seminar @ Tartu\n\nLe
cture held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstr
act\nIn this talk I will present a topological description of elementary \
nmatter originally proposed by Bilson-Thompson\, where leptons\, quarks \n
and electroweak gauge bosons are represented by topological excitations\no
f trivalent ribbon networks. I will argue that utilizing handle attachment
of\nbraided networks in 3-space\, it is possible to preserve some of the
most\nappealing properties of Bilson-Thompson model\, while still overcomi
ng some\nof the hurdles that this theory has encountered\, regarding parti
cle interactions.\nIn addition\, I will explain how to derive some topolog
ical invariants\, from \nKauffman-Lins recoupling theory\, that distinguis
h topological configurations \nassociated to different particles. \nThe ta
lk will be self-contained\, and no previous knowledge of topology is \nreq
uired\, as I will introduce all the concepts used along the way.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Surajit Kalita (Indian Institute of Science\, Bangalore)
DTSTART:20211005T131500Z
DTEND:20211005T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/26
DESCRIPTION:Title: Probing violation of Chandrasekhar mass-limit through gravitatio
nal waves\nby Surajit Kalita (Indian Institute of Science\, Bangalore)
as part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicu
m room A102\, University of Tartu\, Estonia.\n\nAbstract\nEinstein’s the
ory of general relativity and quantum mechanics were among the most\nstart
ling discoveries in the 20th century. Based on these theories\, the maximu
m mass\nof a non-rotating non-magnetized white dwarf is found to be about
1.4 solar mass\,\nknown as the Chandrasekhar mass-limit. However\, over th
e past decades\, various\nresearchers have indirectly predicted many sub-
and super-Chandrasekhar limiting\nmass white dwarfs (white dwarfs which vi
olate the Chandrasekhar mass-limit) from\nthe luminosity-based observation
s of peculiar type Ia supernovae. Several research\ngroups worldwide\, inc
luding us\, have proposed different models based on magnetic\nfields\, rot
ation\, modified gravity\, noncommutative geometry\, etc.\, to explain the
se\npeculiar white dwarfs. However\, no such white dwarfs have so far been
observed\ndirectly in any observations. Hence to predict the correct theo
ry for white dwarfs is\nstill unclear. In my presentation\, I will show th
at if such white dwarfs rotate\nfollowing specific conditions\, they can e
mit continuous gravitational radiation\, which\nin the future\, various de
tectors\, such as LISA\, TianQin\, BBO\, DECIGO\, Einstein\nTelescope\, et
c.\, can detect with a significant signal-to-noise ratio. Thereby one can\
npredict the structure of the white dwarfs and single out the correct theo
ry of gravity.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adam Zadrożny (National Center for Nuclear Research\, Poland)
DTSTART:20211012T131500Z
DTEND:20211012T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/27
DESCRIPTION:Title: Gravitational Waves: what we learned so far\nby Adam Zadroż
ny (National Center for Nuclear Research\, Poland) as part of Theoretical
physics seminar @ Tartu\n\nLecture held in Physicum room A102\, University
of Tartu\, Estonia.\n\nAbstract\nIt took us almost a hundred years from E
instein’s publication to have observation-ready instruments. From the fi
rst detection GW150914\, we are able to observe the universe in gravitatio
nal waves. Currently\, after three observing runs of the LIGO-Virgo-KAGRA
detector network\, we were able to observe tens of mergers of binary black
holes and a bunch of mergers involving at least one neutron star. The mos
t interesting thing was what we can get from the data\, like rates of comp
act objects mergers\, constraints on neutron star equation of state\, test
s of GR in extreme regimes\, but also estimation of Hubble constant direct
ly from gravitational wave events observations.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/27/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantinos Pallikaris (University of Tartu)
DTSTART:20211019T131500Z
DTEND:20211019T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/28
DESCRIPTION:Title: Horndeski with axions: shaping black holes\nby Konstantinos
Pallikaris (University of Tartu) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, Estoni
a.\n\nAbstract\nWe discuss a ``user-friendly'' algorithm to systematically
and rapidly obtain exact planar black hole solutions in the Einstein-Maxw
ell theory deformed by the most general shift- and reflection-symmetric Ho
rndeski sector where the usual Galileon is replaced by a tuple of scalars
with profiles linear in the coordinates of the transverse manifold. Under
precise assumptions\, these axion backgrounds break the translational inva
riance of the system\, causing momentum dissipation in the holographically
dual field theory. The success of the method relies on the simple realiza
tion that the bulk equations of motion become more tractable when written
in terms of the axions kinetic terms\, instead of the radial coordinate. S
howcasing this particularly efficient recipe\, we derive novel asymptotica
lly AdS black holes\, and show that their extremal counterparts always flo
w to an AdS2×R2 infrared fixed point. Additionally\, we report an interes
ting family of new asymptotically Lifshitz black hole solutions with z>1.
Finally\, we discuss the DC transport properties of the dual relativistic
field theories in view of possible applications to condensed matter system
s.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kristjan Müürsepp (University of Tartu\, NICPB Tallinn))
DTSTART:20211102T141500Z
DTEND:20211102T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/29
DESCRIPTION:Title: Multispinor formalism for higher spin theory: particle physics p
henomenology\nby Kristjan Müürsepp (University of Tartu\, NICPB Tall
inn)) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Ph
ysicum room A102\, University of Tartu\, Estonia.\n\nAbstract\nThe Standar
d Model of particle physics\, despite its many triumphs\, still has flaws
that are yet to be convincingly addressed by new physics models. Among man
y other open questions\, the nature of dark matter and the recently update
d muon g-2 anomaly remain as some of the more pertinent examples. In this
talk\, I will review a possible explanation of these issues in light of a
recently proposed effective field theory for higher spin particles. I will
first highlight the problems of higher spin theories of the past and then
explain how one can construct a theory avoiding these obstacles. After th
at I will explain the phenomenological features of the new theory in detai
l\, covering issues related to dark matter\, collider physics\, the g-2 an
omaly\, and nuclear physics.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marek Biesiada (National Centre for Nuclear Research\, Warsaw\, Po
land)
DTSTART:20211109T141500Z
DTEND:20211109T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/30
DESCRIPTION:Title: Strong lensing of gravitational waves - new opportunities for mu
ltimessenger astronomy\nby Marek Biesiada (National Centre for Nuclear
Research\, Warsaw\, Poland) as part of Theoretical physics seminar @ Tart
u\n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n
\nAbstract\nDirect detections of gravitational waves (GW) opened a new era
of GW astronomy. Successful GW detection and observations of coalescing b
inary neutron star (NS-NS) system across a spectrum of electromagnetic wav
es (EM) elevated multimessenger astronomy to the next stage. Future genera
tions of GW detectors on the ground and in the space will yield a signific
ant statistics of such events reaching up to redshift z=5 and even deeper.
Non-negligible ammount of such events has a chance of being strongly lens
ed. In my talk I will review the issue of GW lensing and discuss new oppor
tunities emerging from future detections of lensed GW signals. Wave phenom
ena concerning lensed GW signals\, like diffraction fringes and beat patte
rns will be presented. An interesting idea of measuring dark matter self-i
nteractions due to bulk viscosity attenuating GW will be discussed.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Raissa F. P. Mendes (Universidade Federal Fluminense\, Brazil)
DTSTART:20211116T141500Z
DTEND:20211116T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/31
DESCRIPTION:Title: Probing general relativity with neutron star oscillations\nb
y Raissa F. P. Mendes (Universidade Federal Fluminense\, Brazil) as part o
f Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room A10
2\, University of Tartu\, Estonia.\n\nAbstract\nWith the dawn of the era o
f gravitational wave astronomy\, a new window has opened to probe general
relativity in the regime of strong gravitational fields. For this purpose\
, it is important to understand how predictions of modified theories of gr
avity compare to those of general relativity in this regime\, and whether
they can be discerned by observations. In this talk I will discuss some im
plications of modified theories of gravity for equilibrium and perturbativ
e properties of neutron stars\, focusing on their oscillation spectrum.\n(
Based on arXiv:1802.07847 and arXiv:2107.07036.)\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Marzo (NICPB\, Tallinn)
DTSTART:20211130T141500Z
DTEND:20211130T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/32
DESCRIPTION:Title: Radiatively stable unitarity in higher-spin models\, and applica
tions in metric-affine gravity\nby Carlo Marzo (NICPB\, Tallinn) as pa
rt of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room
A102\, University of Tartu\, Estonia.\n\nAbstract\nThe scrutiny of gravit
ational theories beyond Einstein-Hilbert enjoys a different standard than
flat models probed at collider-level energies. Of the proposed extensions\
, only a subset are explicitly required to be free of ghosts. Even in such
cases\, only dipole ghosts are usually targeted\, thus still allowing\, i
n general\, wrong-sign states to propagate. Moreover\, even in rare cases
where a thorough spectral analysis is performed\, the stability of the res
ulting action under radiative corrections is uncertain.\nIn this talk\, I
discuss the strong constraining power of requiring\, as standard for lower
-spin models\, a radiatively stable ghost- and tachyon-free action for the
paradigmatic scenario of metric-affine gravity. I will describe the role
of non-accidental symmetries and their interplay with diffeomorphism invar
iance. I will also provide\, in a more general way\, an overview of the co
mputational challenges on the way of the spectrum of higher-spin theories.
\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vladimir Hizhnyakov (University of Tartu)
DTSTART:20211207T141500Z
DTEND:20211207T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/33
DESCRIPTION:Title: Mechanisms of motion of vibrational solitons\nby Vladimir Hi
zhnyakov (University of Tartu) as part of Theoretical physics seminar @ Ta
rtu\n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.
\n\nAbstract\nPrevious studies of nonlinear dynamics have shown that local
vibrational excitations\, both stationary and moving\, can exist in ideal
anharmonic atomic lattices [1\,2]. These excitations are called vibration
al solitons\, intrinsic localized modes\, or discrete breathers (DBs). Lar
ge-size low-frequency DBs in atomic chains have high mobility. However\, w
hen the size of the DB is small\, the discreteness of the atomic lattice b
reaks the continuous symmetry and leads to the capture of the moving DB by
the Peierls-Nabarro potential barrier. Nevertheless\, as we have shown [3
\,4]\, DBs in metals Fe\, Cu\, Ni\, Nb and in some other crystals can move
on a long distance. DBs are most likely responsible for the transmission
of signals in biological chains.\nWe investigated in detail the mobility o
f DBs in the Fermi\, Pasta and Ulam lattice (FPU) and found that the odd (
cubic (k_3) and fifth (k_5)) anharmonicity strongly promotes the mobility
of DB. We also found that the mobility of BDs strongly depends on the line
ar localized modes (LLMs) previously predicted by us [6] – the phonons c
aptured by DB: these modes promote the interaction of DBs with phonon cont
inuum.\nMoreover\, we found that initially stationary or captured after mo
ving a DB of the high or medium frequency range is sooner or later convert
ed into a DB of medium frequency with a long service life\, propagating al
ong the chain over a long distance without capture. The process begins wit
h an increase in the amplitude of vibrations of the energy centers DB in t
ime\; the movement begins when this amplitude reaches half the distance be
tween the atoms. And in this case\, odd anharmonicity is also an important
factor – it greatly contributes to the mobility of DBs. The amplificati
on of the vibrations of the energy center and the subsequent movement occu
r due to the radiation of low frequency phonons with a momentum. This radi
ation is the result of the common nonlinear action of DB and LLM. Thus\, a
moving DB in the lattice is like a rocket: it emits particles (here low-f
requency phonons) with a pulse in the opposite direction\, which makes it
possible to overcome the braking caused by radiation processes. We also fo
und that a well-chosen fifth anharmonicity leads to the disappearance of t
he Peierls-Nabarro barrier and to an inversion of stability between bond-c
entered and site-centered DBs\, and\, in fact\, to essentially non-radiati
ve propagation of a DB along the chain.\n\n1. A.J. Sievers\, S. Takeno\, P
hys. Rev. Lett. 61\, 970 (1988).\n2. S. Flach and C. R. Willis\, Phys. Rep
ts. 295\, 181 (1998).\n3. M. Haas\, V. Hizhnyakov\, A. Shelkan\, M. Klopov
\, and A. J. Sievers\, Phys. Rev. B 84\, 144303 (2011).\n4. V. Hizhnyakov\
, M. Haas\; A. Shelkan\, M. Klopov\, Physica Scripta\, 89 (4) (2014).\n5.
A. Shelkan\, M. Klopov\, V. Hizhnyakov\, Phys. Lett. A 383\, 1893 (2019).\
n6. V. Hizhnyakov\, A. Shelkan\, M. Klopov\, S.A. Kiselev\, A.J. Sievers\,
Phys. Rev. B 73\, 224302 (2006).\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Joosep Pata (NICPB\, Tallinn)
DTSTART:20211214T141500Z
DTEND:20211214T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/34
DESCRIPTION:Title: Machine learning for data reconstruction at the LHC\nby Joos
ep Pata (NICPB\, Tallinn) as part of Theoretical physics seminar @ Tartu\n
\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\nA
bstract\nPhysics analyses at the CERN experiments rely on detector hits be
ing interpreted or reconstructed as particle candidates. The data reconstr
uction systems are built on decades of physics and detector knowledge and
must operate reliably on petabytes of data in diverse computing centers sp
read around the world. In the recent years\, machine learning (ML) is play
ing an increasingly important role at the LHC experiments for reconstructi
ng and interpreting the data\, from calibrating the detector readouts to t
he final interpretation for complex signal processes. We will discuss the
various aspects of ML at the LHC experiments\, focusing on data reconstruc
tion and particle identification approaches using modern machine learning
methods such as graph neural networks.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/34/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nico Alexis Benincasa (NICPB-KBFI\, Tallinn)
DTSTART:20220125T141500Z
DTEND:20220125T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/35
DESCRIPTION:Title: Multi-step phase transitions and gravitational waves in the iner
t doublet model\nby Nico Alexis Benincasa (NICPB-KBFI\, Tallinn) as pa
rt of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room
A102\, University of Tartu\, Estonia.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/35/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Flavio Bombacigno (University of Valencia)
DTSTART:20220208T141500Z
DTEND:20220208T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/36
DESCRIPTION:Title: Quasinormal modes of Schwarzschild black holes in projective inv
ariant Chern-Simons gravity\nby Flavio Bombacigno (University of Valen
cia) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Phy
sicum room A102\, University of Tartu\, Estonia.\n\nAbstract\nWe generaliz
e the Chern-Simons theory of gravity to the metric-affine case\, where pro
jective invariance is recovered by enlarging the Pontryagin density with h
omothetic curvature terms which do not spoil topologicity. This one is the
n broken by promoting the coupling to the Chern-Simons term to a dynamical
scalar field\, and we derive at the perturbative level the solutions for
torsion and nonmetricity\, showing that they can be iteratively obtained f
rom the background metric and the derivative of the scalar field. That all
ows us to describe the dynamics for the metric and the scalar field pertur
bations in a self-consistent way\, and we apply the formalism to the study
of quasinormal modes for a Schwarzschild black hole. By adopting numerica
l techniques\, we show that in the absence of the kinetic term for the sca
lar field the latter is still endowed with a proper dynamical character\,
contrary to non dynamical Chern-Simons theory in metric formalism. Finally
\, we compute the quasinormal frequencies and characterize the late-time p
ower law tails\, comparing the results with the outcomes of the purely met
ric approach.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/36/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sree Kanth Hari Kumar (NCBJ\, Warsaw)
DTSTART:20220215T141500Z
DTEND:20220215T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/37
DESCRIPTION:Title: Gravitational lensing of gravitational waves\nby Sree Kanth
Hari Kumar (NCBJ\, Warsaw) as part of Theoretical physics seminar @ Tartu\
n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\n
Abstract\nGravitational lensing has now become an unavoidable tool in astr
ophysics. Like lensing of electromagnetic waves\, matter distribution betw
een the gravitational wave (GW) source and the detector can act as a gravi
tational lens and produce multiple GW images. Lensing of GW signals leads
to the amplification of the signal and increases the signal to noise ratio
. Unlike EM waves\, the wavelength of the gravitational waves is comparab
le to the Schwarschild radius of the lens which leads to some interesting
effects such as interference and diffraction. In this talk I will discuss
such possible effects of lensing of gravitational waves that could be obse
rved with current and next generation gravitational wave detectors.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/37/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Francisco José Maldonado Torralba (University of Tartu)
DTSTART:20220222T141500Z
DTEND:20220222T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/38
DESCRIPTION:Title: Explaining Dark Matter with torsion\nby Francisco José Mald
onado Torralba (University of Tartu) as part of Theoretical physics semina
r @ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, Es
tonia.\n\nAbstract\nIn this talk I will explain how the pseudoscalar degre
e of freedom of the quadratic Poincaré Gauge theory of gravity can act as
a dark matter candidate. I will give the parameter space of the theory fo
r which such dark matter candidate can account for all predicted cold dark
matter\, and constrain such parameters based on current astrophysical obs
ervations.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/38/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Débora Aguiar Gomes (State University of Ceará\, Brazil)
DTSTART:20220301T141500Z
DTEND:20220301T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/39
DESCRIPTION:Title: Symmetric Teleparallel Equivalent of General Relativity\nby
Débora Aguiar Gomes (State University of Ceará\, Brazil) as part of Theo
retical physics seminar @ Tartu\n\nLecture held in Physicum room A102\, Un
iversity of Tartu\, Estonia.\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/39/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adrià Delhom I Latorre (University of Tartu)
DTSTART:20220308T141500Z
DTEND:20220308T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/40
DESCRIPTION:Title: Ghosts in curvature-based metric-affine gravity and the role of
projective symmetry\nby Adrià Delhom I Latorre (University of Tartu)
as part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum
room A102\, University of Tartu\, Estonia.\n\nAbstract\nWe will explicitl
y show how ghost degrees of freedom arise in a sub-class of metric-affine
theories unless projective symmetry is enforced. Then\, we will generalize
the techniques employed in that particular case to argue why ghosts will
arise in generic metric-affine theories of gravity around arbitrary backgr
ounds. We will also discuss some results on possible ways to avoid them.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/40/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sreekanth Harikumar (NCBJ\, Warsaw)
DTSTART:20220315T141500Z
DTEND:20220315T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/41
DESCRIPTION:Title: Moffat MOdified Gravity(MOG) / Scalar Tensor Vector Gravity (STV
G)\nby Sreekanth Harikumar (NCBJ\, Warsaw) as part of Theoretical phys
ics seminar @ Tartu\n\nLecture held in Physicum room A102\, University of
Tartu\, Estonia.\n\nAbstract\nScalar Tensor Vector Gravity / MOG is a metr
ic theory of gravity with dynamical scalar fields and a massive vector fie
ld introduced in addition to the metric tensor. In the weak field approxim
ation MOG modifies the Newtonian acceleration with a Yukawa like repulsive
term due to Maxwell-Proca type Lagrangian. This associates matter with a
fifth force and a modified equation of motion. MOG has been successful in
explaining galaxy rotation curves\, gravitational lensing\, cosmological o
bservations and all other solar system observation without the need of dar
k matter. In this talk I will discuss the key concepts of MOG theory. Then
I will discuss existing observational bounds on STVG weak field paramet
ers. In particular I will present the results obtained from X-COP sample o
f galaxy clusters.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/41/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alejandro Hernandez-Arboleda (Universidade Federal do Espírito Sa
nto\, Brazil)
DTSTART:20220322T141500Z
DTEND:20220322T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/42
DESCRIPTION:Title: Additional velocity Distribution: A fast sample analysis for dar
k matter or modified gravity models\nby Alejandro Hernandez-Arboleda (
Universidade Federal do Espírito Santo\, Brazil) as part of Theoretical p
hysics seminar @ Tartu\n\nLecture held in Physicum room A102\, University
of Tartu\, Estonia.\n\nAbstract\nWe propose a new complementary and fast a
pproach to study galaxy rotation curves straight from the sample data\, in
stead of individual rotation curve fits. It is based on the difference bet
ween the observational rotation curve and the expected one from the baryon
ic matter\, under certain normalization (𝛿𝑉2). The first step is to
find the observational data distribution of 𝛿𝑉2\, which is estimated
from the observational data from a 2D kernel density estimation. The esti
mate is then contrasted with specific model predictions for the same baryo
nic data. Here we consider the following five models: Burkert profile\, MO
ND\, Palatini 𝑓(𝑅) gravity\, Eddington-inspired-Born-Infeld (EiBI) m
odel and general relativity with renormalization group effects (RGGR). We
stress the following method properties: i) the method deals with the sampl
e behaviour\, not the individual galaxy fits: it provides quicker evaluati
on and it promptly presents sample properties\; ii) it studies the form of
the velocity curve added by the model\, not its magnitude (typically\, th
is implies one less parameter for the analysis)\; iii) it can be applied t
o modified gravity models even if the observational 3D baryonic matter dis
tribution is not known: it is based on the baryonic velocity contribution
to the rotation curve together with minimal hypothesis on the average 3D m
odeling. About the tested models\, and considering the tests that the meth
od can perform\, the Burkert profile\, MOND and RGGR have good sample beha
viour\, nonetheless\, the method points out specific difficulties for thes
e three cases. Palatini 𝑓(𝑅) and EiBI gravities cannot be used to re
place dark matter and\, if considered together with some dark matter halo\
, large amounts of the latter will be necessary.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/42/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sotirios Karamitsos (Pisa University)
DTSTART:20220405T131500Z
DTEND:20220405T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/43
DESCRIPTION:Title: Metric to Palatini (and vice versa): the strong limit and potent
ial reconstruction in attractor theories of inflation\nby Sotirios Kar
amitsos (Pisa University) as part of Theoretical physics seminar @ Tartu\n
\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\nA
bstract\nThe same model of inflation can be written in many different ways
\, often concealing its true physical degrees of freedom. In this talk\, I
will demonstrate how scalar-tensor theories of inflation are linked throu
gh equivalence classes in the absence of kinetic poles. When poles are int
roduced\, this equivalence is broken\, but the resulting "attractor" model
s give particularly robust predictions that do not depend on the inflation
ary potential\, in the so-called "strong coupling limit". However\, this i
ndependence may also be broken when switching to a different underlying fo
rmalism of gravity (metric or Palatini). I will discuss the conditions for
the strong limit to be maintained regardless the gravitational formalism
employed\, and the conditions for the potential to be reconstructed in a f
ormalism-independent way.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/43/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Arpan Chatterjee (University of Tartu)
DTSTART:20220419T131500Z
DTEND:20220419T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/44
DESCRIPTION:Title: A modern shape for the non-local Nambu Jona-Lasinio model\nb
y Arpan Chatterjee (University of Tartu) as part of Theoretical physics se
minar @ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\
, Estonia.\n\nAbstract\nThe Standard Model of Particle Physics is based on
two fundamental theories: the Electroweak theory of Glashow\, Weinberg an
d Salam\, and Quantumchromodynamics (QCD) developed by Gross\, Wilczek and
Politzer. Of these\, QCD has two features\, not common to the other inter
actions: Asymptotic Freedom\, which can be explained by the running of the
strong coupling due to renormalization\, and Quark Confinement which does
not allow us to “see” quarks as individual particles. The necessity t
o describe particles which have not and will never be “seen” as free p
articles led to the development of Effective Field Theories (EFTs). One of
these EFT approaches is the one developed by Nambu and Jona-Lasinio in 19
61\, based on the principles of the BCS theory of superconductivity develo
ped by Bardeen\, Cooper and Schrieffer. While the original approach replac
es the interaction vector bosons effectively by local four-fermion interac
tions (hence non-renormalisable)\, in our project we consider a non-local
version of the NJL model which has been shown to be both renormalisable an
d confining and hence much more appropriate to be used in elementary parti
cle physics. The main aim of our project is to present a modern and non-lo
cal version of the NJL model\, applied to particle physics phenomenology\,
in particular as an EFT approach for QCD.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/44/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alice Boldrin (NCBJ\, Warsaw)
DTSTART:20220503T131500Z
DTEND:20220503T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/45
DESCRIPTION:Title: Dirac procedure and the Hamiltonian formalism for cosmological p
erturbations in a Bianchi I universe\nby Alice Boldrin (NCBJ\, Warsaw)
as part of Theoretical physics seminar @ Tartu\n\nLecture held in Physicu
m room A102\, University of Tartu\, Estonia.\n\nAbstract\nWe apply the Dir
ac procedure for constrained systems to the Arnowitt–Deser–Misner form
alism linearized around the Bianchi I universe. We discuss and employ basi
c concepts such as Dirac observables\, Dirac brackets\, gauge-fixing condi
tions\, reduced phase space\, physical Hamiltonian\, canonical isomorphism
between different gauge-fixing surfaces and spacetime reconstruction. We
relate this approach to the gauge-fixing procedure for non-perturbative ca
nonical relativity. We discuss the issue of propagating a basis for the sc
alar-vector-tensor decomposition as\, in an anisotropic universe\, the wav
efronts of plane waves undergo a non-trivial evolution. We show that the d
efinition of a gravitational wave as a traceless-transverse mode of the me
tric perturbation needs to be revised. Moreover there exist coordinate sys
tems in which a polarization mode of the gravitational wave is given entir
ely in terms of a scalar metric perturbation. We first develop the formali
sm for the universe with a single scalar field and then extend it to the m
ulti-field case. The obtained fully canonical formalism will serve as a st
arting point for a complete quantization of the cosmological perturbations
and the cosmological background.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/45/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Laxmipriya Pati (BITS-Pilani Hyderabad)
DTSTART:20220607T131500Z
DTEND:20220607T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/46
DESCRIPTION:Title: Rip Cosmological Models in Extended Symmetric Teleparallel Gravi
ty\nby Laxmipriya Pati (BITS-Pilani Hyderabad) as part of Theoretical
physics seminar @ Tartu\n\nLecture held in Physicum room A102\, University
of Tartu\, Estonia.\n\nAbstract\nIn this work\, we have investigated some
rip cosmological models in an extended symmetric teleparallel gravity the
ory. We consider the form f(Q\,T)=aQm+bTf(Q\, T) = aQ^m+bT in the Einstein
–Hilbert action and express the field equations and the dynamical parame
ters in terms of the non-metricity QQ. Three rip models such as Little Rip
\, Big Rip\, and Pseudo Rip are presented\, also the energy conditions and
the cosmographic parameters are derived and analyzed for all these models
.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/46/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adrián Casado-Turrión (Complutense University of Madrid\, Spain)
DTSTART:20220920T131500Z
DTEND:20220920T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/47
DESCRIPTION:Title: (Im)possibility of gravitational collapse in f(R) gravity\nb
y Adrián Casado-Turrión (Complutense University of Madrid\, Spain) as pa
rt of Theoretical physics seminar @ Tartu\n\nLecture held in Physicum room
A102\, University of Tartu\, Estonia.\n\nAbstract\nGravitational collapse
is still poorly understood in the context of f(R) theories of gravity. Th
e archetypal Oppenheimer-Snyder model (which is an exact solution of Gener
al Relativity) is known to be\nincompatible with the junction conditions o
f f(R) models\, both in the metric and Palatini formalisms. In this talk\,
we shall explain how the Oppenheimer-Snyder construction must be generali
sed so as to fit within f(R) theories of gravity. By means of a systematic
analysis of the relevant junction conditions\, we will show that some par
adigmatic vacuum metrics cannot represent spacetime outside collapsing sta
rs in f(R) gravity.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/47/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fernando Izaurieta (University of Concepción\, Chile)
DTSTART:20220927T131500Z
DTEND:20220927T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/48
DESCRIPTION:Title: Gravitational Waves: A falsification Tool for Riemann-Cartan Gra
vity Theories?\nby Fernando Izaurieta (University of Concepción\, Chi
le) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Phys
icum room A102\, University of Tartu\, Estonia.\n\nAbstract\nWe develop ge
neral mathematical tools to study the propagation of waves on Riemann-Cart
an backgrounds in a way as model-independent as possible. Using this\, we
prove that torsional backgrounds can induce\nanomalous propagation of ampl
itude and polarization and assess whether it could allow using gravitation
al waves as a probe to detect torsion.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/48/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Adrián Casado Turrión (UCM\, Madrid\, Dept. Theor. Phys. II)
DTSTART:20221004T131500Z
DTEND:20221004T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/49
DESCRIPTION:Title: An 'Unruhduction' to particle creation by acceleration and Quant
um Field Theory in curved spacetimes\nby Adrián Casado Turrión (UCM\
, Madrid\, Dept. Theor. Phys. II) as part of Theoretical physics seminar @
Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, Eston
ia.\n\nAbstract\nThis talk will consist in a brief\, pedagogical introduct
ion to all the relevant concepts and techniques employed in Quantum Field
Theory in curved spacetimes. After reviewing the Unruh effect and its rela
tionship with the concept of particle in standard QFT in Minkowski spaceti
me\, we will move on to study particle creation due to the presence of cla
ssical gravitational fields. In particular\, we shall focus on Hawking rad
iation and black-hole thermodynamics.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/49/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Abdel Nasser Tawfik (Future University in Egypt)
DTSTART:20221101T141500Z
DTEND:20221101T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/50
DESCRIPTION:Title: Quantum-induced aspects imposed on Einstein tensor\nby Abdel
Nasser Tawfik (Future University in Egypt) as part of Theoretical physics
seminar @ Tartu\n\nLecture held in Physicum room A102\, University of Tar
tu\, Estonia.\n\nAbstract\nWhen generalized noncommutative Heisenberg alge
bra accommodating impacts of a finite gravitational field as specified by
doubly-special relativity\, loop quantum gravity\, and string theory\, is
extended to an eight-dimensional Finsler manifold\, quantum-induced aspect
s could be imposed on the Riemann curvature tensor and its unique contract
ions. In the same manner\, the Einstein tensor could be constructed. We f
ound that the covariant derivative of the Einstein tensor\, in which besid
es the quantization additional geometric structures have emerged\, vanishe
s.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/50/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marco Barsanti (Università di Pisa)
DTSTART:20221206T141500Z
DTEND:20221206T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/51
DESCRIPTION:Title: Baryons as topological solitons\nby Marco Barsanti (Universi
tà di Pisa) as part of Theoretical physics seminar @ Tartu\n\nLecture hel
d in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstract\nIn t
his talk\, I will discuss the mathematical and physical motivations that a
llow us to identify the solitonic solutions of a Mesonic Field Theory\, ca
lled the Skyrme model\, as Baryons in Large-N QCD. In the first part of th
e talk\, I will present the general idea of solitons in Physics\, giving a
simple example from Classical Mechanics. Then\, I will finally introduce
the Skyrme model\, a possible candidate for the low-energy QCD Lagrangian
at large N\, and I will show the existence of solitonic solutions\, known
as Skyrmions\, in that theory. These solutions are characterized by a cons
erved charge called topological index and for this reason are known as top
ological solitons. That conserved charge has been physically identified wi
th the baryon number and thus consequently the Skyrmions have been identif
ied with the Baryons. Physical predictions concerning baryon physics\, as
well as nuclear physics\, can be computed and compared with the experiment
s. In this regard\, I will present some good results and some problems of
the model.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/51/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Damianos Iosifidis (University of Tartu)
DTSTART:20230103T141500Z
DTEND:20230103T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/52
DESCRIPTION:Title: Non-Riemannian Effects in Cosmology\nby Damianos Iosifidis (
University of Tartu) as part of Theoretical physics seminar @ Tartu\n\nLec
ture held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstra
ct\nWe investigate the cosmological aspects of the most general parity pre
serving Metric-Affine Gravity theory quadratic in torsion and non-metricit
y in the presence of a cosmological hyperfluid.The latter is a generalizat
ion of the usual Perfect Fluid notion that includes also a non-vanishing h
ypermomentum tensor that is compatible with the Cosmological Principle and
encodes the microscopic characteristics of matter. Then\, the equations o
f motion are obtained by varying the action with respect to the metric and
the independent affine connection. Subsequently\, considering a Friedmann
-Lemaître-Robertson-Walker background\, we derive the most general form o
f the modified Friedmann equations for the full quadratic theory. We then
focus on a characteristic sub-case involving only two quadratic contributi
ons given in terms of torsion and non-metricity vectors. In this setup\, s
tudying the modified Friedmann equations along with the conservation laws
of the perfect cosmological hyperfluid\, we provide exact solutions both f
or purely dilation and for purely spin hypermomentum sources. We then disc
uss the physical consequences of our model and the prominent role of torsi
on and non-metricity in this cosmological setup.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/52/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tom Lawrence (Ronin Institute for Independent Scholarship)
DTSTART:20230124T141500Z
DTEND:20230124T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/53
DESCRIPTION:Title: The coset formulation of gravitational theories: understanding m
etric-preserving changes of basis\nby Tom Lawrence (Ronin Institute fo
r Independent Scholarship) as part of Theoretical physics seminar @ Tartu\
n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\n
Abstract\nThe requirement of distant parallelism implicitly defines a fiel
d of orthonormal frame bases. Such fields are related by a local Lorentz g
roup\, I(u). Meanwhile\, changes of coordinate basis form a wider group of
general linear transformations\, J(u). From this\, it can easily be shown
that the degrees of freedom contained in the metric are the parameters of
the coset space J/I. This separation of the parallelism degrees of freedo
m from the metric degrees of freedom allows a Cartan decomposition of the
Weitzenböck connection. Holonomic frames\, in which the Weitzenböck spin
connection vanishes\, are then found to be ones in which the frame basis
is related to the coordinate basis by a transformation matrix only contain
ing metric degrees of freedom. The transformation laws of such matrices
– coset space representatives – mean that this gauge choice is not con
sistent with general covariance. This formulation allows the correct relat
ionship between inertial effects and transformations in I(u) to be explore
d and identified. [The presentation is based on Sections 1-5 of arXiv:2211
.07586. It is an extended and rearranged version of that given to the Geom
etric Foundations of Gravity 2021 conference.]\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/53/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Orest Hrycyna (NCBJ\, Warsaw)
DTSTART:20230214T141500Z
DTEND:20230214T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/54
DESCRIPTION:Title: Structural stability and non-singular beginning of the universe<
/a>\nby Orest Hrycyna (NCBJ\, Warsaw) as part of Theoretical physics semin
ar @ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, E
stonia.\n\nAbstract\nTheory of gravity with a quadratic contribution of sc
alar curvature is investigated in terms of dynamical system approach. The
simplest Friedmann-Robertson-Walker metric is used to formulate dynamics i
n Jordan frame as well as in conformally transformed Einstein frame. In bo
th frames there are asymptotically stable de Sitter states for which the H
ubble function naturally gives terms corresponding to non-substantial dark
matter. Using invariant centre manifold I show that in the Einstein frame
there is a zero measure set of initial conditions leading from the unstab
le to the stable de Sitter state. The Jordan frame and the Einstein frame
formulation of the theory are physically nonequivalent.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/54/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ahmet Ilker Topuz (Tartu University)
DTSTART:20230221T141500Z
DTEND:20230221T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/55
DESCRIPTION:Title: Particle generation through energy discretization and restrictiv
e planes in GEANT4 simulations for potential applications of cosmic ray mu
on tomography\nby Ahmet Ilker Topuz (Tartu University) as part of Theo
retical physics seminar @ Tartu\n\nLecture held in Physicum room A102\, Un
iversity of Tartu\, Estonia.\n\nAbstract\nIn this study\, by attempting to
resolve the difficulties related to the angular distribution during the p
article generation for the muon tomography applications in the GEANT4 simu
lations\, we exhibit an unconventional methodology that is hinged on the d
irection limitation via the vectorial construction from the generation loc
ation to the restriction area rather than using a certain angular distribu
tion or interval. In other words\, we favor a momentum direction that is d
etermined by a vector constructed between an initial point randomly chosen
on a generative point/plane and a second point arbitrarily selected on a
restrictive plane of the same dimensions with the basal cross section of t
he volume-of-interest (VOI). On account of setting out such a generation s
cheme\, we optimize the particle loss by keeping an angular acceptance tha
t is directly dependent on the VOI geometry as well as the vertical positi
on of the restrictive plane for a tomographic system of a finite size. We
demonstrate our strategy for a set of target materials including aluminum\
, iron\, copper\, lead\, and uranium with a dimension of 40×10×40 cm^3 o
ver three restrictive planes of different positions by using a discrete en
ergy spectrum between 0.1 and 8 GeV and we compute the scattering angle\,
the number of absorption\, and the particle loss. Upon our simulation outc
omes\, we show that the particle generation by means of restrictive planes
is an effective strategy that is flexible towards a variety of computatio
nal objectives in the GEANT4 simulations.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/55/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Damianos Iosifidis (Tartu University)
DTSTART:20230912T131500Z
DTEND:20230912T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/56
DESCRIPTION:Title: Imperfect Fluids with Intrinsic Hypermomentum\nby Damianos I
osifidis (Tartu University) as part of Theoretical physics seminar @ Tartu
\n\nLecture held in Physicum room A102\, University of Tartu\, Estonia.\n\
nAbstract\nWe develop the Action Formulation of Relativistic Hyperfluids\,
namely fluids with intrinsic hypermomentum that describes the microproper
ties of matter (spin\, dilation and shear). By extending the Perfect Fluid
formulation we supplement the fluid action with matter-connection couplin
gs that reproduce the desired hypermomentum tensor of the recently develop
ed Perfect Hyperfluid. More specifically\, by considering the cases of pur
e spin\, dilation and shear hyperfluids separately\, we find the kinematic
s of each individual piece. A rather remarkable result is that for the pur
e spin and shear cases\, the corresponding energy-momentum tensor does not
have the usual Perfect Fluid form but rather that of an imperfect one who
se heat flux\, stresses and bulk viscosity are given in terms of the hyper
momentum variables. This ultimately indicates that the so-called constitut
ive relations for viscous fluids may naturally follow by the inclusion of
the micro-properties of matter (hypermomentum).\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/56/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Daniel Blixt (Scuola Superiore Merdionale\, Napoli\, Italy)
DTSTART:20230926T131500Z
DTEND:20230926T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/57
DESCRIPTION:Title: Teleparallelism\nby Daniel Blixt (Scuola Superiore Merdional
e\, Napoli\, Italy) as part of Theoretical physics seminar @ Tartu\n\nLect
ure held in Physicum room A102\, University of Tartu\, Estonia.\n\nAbstrac
t\nThis talk aims to give an introduction to teleparallelism and to presen
t some recent insights on the topic. Apart from delving into the concept o
f teleparallelism\, I will discuss general relativity and the (non)importa
nce of boundary terms\, to then show that teleparallelism allows us to ref
ormulate general relativity in terms of torsion and/or non-metricity inste
ad of curvature. From this formulation there are many ways for which one c
an depart from general relativity and look at modified theories of gravity
. In this context\, I will discuss symmetries and how they can be used to
simplify calculations and to count the number of degrees of freedom in the
theories. I will further argue that teleparallelism can be useful to solv
e theoretical and/or observational problems.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/57/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Alejandro Jiménez Cano (Tartu University)
DTSTART:20231114T141500Z
DTEND:20231114T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/58
DESCRIPTION:Title: Junction conditions: foundations and subtleties\nby Alejandr
o Jiménez Cano (Tartu University) as part of Theoretical physics seminar
@ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, Esto
nia.\n\nAbstract\nThis talk is an introduction to the junction conditions
formalism. I will provide the basic notions to understand the topic (tenso
r distributions\, regular plus singular decomposition\, etc.) and a genera
l procedure that we proposed to analyze particular theories. I will also u
nveil certain ambiguities that appear when dealing with distributions in t
his context.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/58/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Miguel Bezares (University of Nottingham)
DTSTART:20231121T141500Z
DTEND:20231121T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/59
DESCRIPTION:Title: Numerical Relativity - beyond General Relativity\nby Miguel
Bezares (University of Nottingham) as part of Theoretical physics seminar
@ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\, Esto
nia.\n\nAbstract\nWe will explore the long path from Einstein's equations
to computational simulations. I will discuss how Numerical Relativity (NR)
can serve as a tool to understand gravitational wave generation in dark e
nergy models and what challenges must be overcome to extend NR in these th
eories. In particular\, I will consider a class of alternative theories of
gravity known as k-essence. This cosmologically relevant scalar-tensor th
eory involves first-order derivative self-interactions\, which pass all ex
isting gravitational wave bounds and provide a screening mechanism. Specif
ically\, I will present our numerical simulations of this theory consideri
ng three different scenarios: nonlinear stellar oscillations\, gravitation
al collapse\, and binary neutron stars.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/59/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tomi Koivisto (Tartu University)
DTSTART:20231207T141500Z
DTEND:20231207T154500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/60
DESCRIPTION:Title: On the metageometric foundation of physics\nby Tomi Koivisto
(Tartu University) as part of Theoretical physics seminar @ Tartu\n\nLect
ure held in Physicum room A106\, University of Tartu\, Estonia.\n\nAbstrac
t\nFundamental interactions in the Standard Model of particle physics are
described by quantum gauge theory. I will present our novel approach to ga
uge interactions at the foundation of a new Standard Model which includes
General Relativity. It entails a completion of the latter theory and sugge
sts a possible rationale for the emergence of the Universe and its (appare
ntly\, mostly dark) contents. Rather than by adding new speculative assump
tions\, the proposed foundation arises by removing the scaffolding of obse
rver-independent spacetime ingrained into current formulations of fundamen
tal physics.\n\nPhysicum seminar - Physicum A106 (W. Ostwaldi str. 1)\n\nZ
oom link:\nhttps://ut-ee.zoom.us/j/91241051766?pwd=TTBQWmszbS9GV052alpXRmo
1VmFsdz09\n\nMeeting ID: 912 4105 1766\nPasscode: 370272\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/60/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Manuel Hohmann (Tartu University)
DTSTART:20240416T131500Z
DTEND:20240416T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/61
DESCRIPTION:Title: How to (not) break local Lorentz invariance in gravity theory\nby Manuel Hohmann (Tartu University) as part of Theoretical physics sem
inar @ Tartu\n\nLecture held in Physicum room A102\, University of Tartu\,
Estonia.\n\nAbstract\nLocal Lorentz invariance is one of the crucial feat
ures of general relativity which allows relating the reference systems\, a
nd hence the clocks\, of relatively moving observers. Several gravity theo
ries are claimed to break local Lorentz invariance\, including theories in
volving quantum corrections\, modified dispersion relations\, Finsler geom
etry and teleparallel gravity. I explain which of these correspond to an o
bservable violation of local Lorentz invariance and which\, despite their
name\, cannot be observed in nature\, even if they are present in the theo
ry.\n\nM. Hohmann\, Int. J. Geom. Meth. Mod. Phys. 19\, Supp. 1 2240001 (2
022) [arXiv:2112.15173 [gr-qc]]\nM. Hohmann\, C. Pfeifer and N. Voicu\, J.
Math. Phys. 63 032503 (2022) [arXiv:2106.14965 [math-ph]\nD. Läänemets\
, M. Hohmann and C. Pfeifer\, Int. J. Geom. Meth. Mod. Phys. 19 2250155 (2
022) [arXiv:2201.04694 [gr-qc]]\nM. Hohmann\, Class. Quant. Grav. 41 01502
5 (2024) [arXiv:2310.01487 [gr-qc]]\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/61/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tomi Koivisto (NICPB\, Tallinn)
DTSTART:20241015T131500Z
DTEND:20241015T144500Z
DTSTAMP:20260404T110822Z
UID:UTPhysics/62
DESCRIPTION:Title: Volume and gauge symmetry\nby Tomi Koivisto (NICPB\, Tallinn
) as part of Theoretical physics seminar @ Tartu\n\nLecture held in Physic
um room A102\, University of Tartu\, Estonia.\n\nAbstract\nTheories with a
preferred volume are called unimodular. Unimodularity has played subtle r
oles in theories of gravity since the inception of General Relativity [1]\
; it is well-known that unimodularity provides an alternative view to the
important problems with the cosmological constant Λ. This seminar\naims t
o clarify* unimodular physics from the perspective of relativity and gauge
symmetries\, and to present two relevant current developments. 1) Despite
various teleparallel modifications of gravity considered in the literatur
e\, the only known viable class of modifications can be understood in\nter
ms of a preferred volume [2]. In contrast to modifications of gravity\, lo
cal Lorentz symmetry is not speculative. 2) The incorporation of this symm
etry into a unimodular theory predicts the standard ΛCDM model of cosmolo
gy without postulating dark energy or dark matter [3]. It also facilitates
the coupling\nof the Standard Model gauge and Higgs fields into the theor
y [4].\n\n[1] Einstein\, A. (1916) The Foundation of the General Theory of
Relativity. Annalen der Physik\, 49\, 769-822.\n[2] Bello-Morales et al (
2024) A class of ghost-free theories in symmetric teleparallel geometry\,
e-Print: 2406.19355.\n[3] Gallagher\, P. and Koivisto\, T. (2021) The Λ a
nd the CDM as Integration Constants\, Symmetry 13 11\, 2076.\n[4] Wilczek
\, F. (1998) Riemann-Einstein structure from volume and gauge symmetry Ph
ys.Rev.Lett. 80 4851-4854.\n\n*In generally understandable terms\, avoidin
g exterior algebra and such modern notations.\n
LOCATION:https://stable.researchseminars.org/talk/UTPhysics/62/
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