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BEGIN:VEVENT
SUMMARY:Michalis Agathos (University of Cambridge & Friedrich-Schiller-Uni
versitat Jena)
DTSTART:20201217T120000Z
DTEND:20201217T130000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/1
DESCRIPTION:Title: Gravitational Waves as Probes of Strong-Field Gravity\nby Mic
halis Agathos (University of Cambridge & Friedrich-Schiller-Universitat Je
na) as part of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA
\n\n\nAbstract\nThe first observations of gravitational waves (GWs) from t
he coalescence of a black-hole binary in 2015 and a neutron-star binary in
2017 heralded the beginning of a new era in experimental gravity. In just
5 years\, the detection of GWs has evolved from virtually non-existent to
a weekly business and has led to a plethora of results with implications
for fundamental physics\, astrophysics and cosmology. In this talk\, I wil
l give an overview of the GW events detected so far by LIGO and Virgo and
will describe how these can be used to probe the true nature of gravity an
d test general relativity (GR) to unprecedented levels. I will focus on an
array of methods developed exactly for this purpose and will give an upda
te on their latest results\, with the analysis of signals from compact bin
aries\, detected in the first three observing runs of the Advanced LIGO-Vi
rgo network of detectors. If time allows\, I will briefly discuss the pros
pects of testing the predictions of GR with future GW detectors\, includin
g upgrades and extensions of the current network\, 3rd generation ground-b
ased interferometers and future space-bound detectors.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Pascal Anastasopoulos (U Vienna\, Dept. Math)
DTSTART:20210120T113000Z
DTEND:20210120T123000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/2
DESCRIPTION:Title: Emergent fields from Hidden sectors\nby Pascal Anastasopoulos
(U Vienna\, Dept. Math) as part of High Energy Theory\, Gravity and Cosm
ology Seminars @ NTUA\n\n\nAbstract\nHidden theories coupled to the SM may
provide emergent fields\, that are composites/bound-states of the hidden
fields. This is motivated by paradigms emerging from the AdS/CFT correspon
dence but it is a more general phenomenon. We explore the general setup an
d we focus on axions\, graviphotons (or dark photons) and neutrinos.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kristjan Kannike (NICPB\, Tallinn)
DTSTART:20210127T113000Z
DTEND:20210127T123000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/3
DESCRIPTION:Title: Minima of Classically Scale-Invariant Potentials\nby Kristjan
Kannike (NICPB\, Tallinn) as part of High Energy Theory\, Gravity and Co
smology Seminars @ NTUA\n\n\nAbstract\nWe define a matrix formalism to ana
lyze the minimum structure of classically scale-invariant effective potent
ials. We obtain general compact expressions for the minimum direction and
the mass matrix\, and derive a set of conditions on the running couplings
to have a minimum. If these conditions are satisfied at two or more places
along the RG-flow\, there can be two or more minima\, of which we give ex
amples in a toy model.\n\nhttps://arxiv.org/abs/2011.12304\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Kostas Filippas (Swansea University)
DTSTART:20210210T123000Z
DTEND:20210210T133000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/4
DESCRIPTION:Title: Holography in 2d N=(0\,4) quantum field theory\nby Kostas Fil
ippas (Swansea University) as part of High Energy Theory\, Gravity and Co
smology Seminars @ NTUA\n\n\nAbstract\nWe explore the duality between AdS3
massive IIA string theory vacua and two-dimensional N=(0\,4) quiver quant
um field theories. After categorizing all kinds of gravity solutions\, we
demystify the ones that seem to reflect anomalous dual gauge theories. In
particular\, we prove that there are bound states of D-branes on the bound
ary of the space which provide the dual quiver theory with exactly the cor
rect amount of matter in order to cancel its gauge anomalies. Then we prop
ose that the structure of the field theory should be complemented with add
itional bifundamental matter\, which we argue it may only be N=(4\,4) hype
rmultiplets. Finally\, we construct a BPS string configuration and use the
old and new supersymmetric matter to build its dual ultraviolet operator.
\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vasileios Letsios (York U.\, Dept. Math.)
DTSTART:20210203T113000Z
DTEND:20210203T123000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/5
DESCRIPTION:Title: The eigenmodes for spinor quantum field theory in global de Sitte
r space-time\nby Vasileios Letsios (York U.\, Dept. Math.) as part of
High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstract\
nThe de Sitter space-time is famous for being able to describe an expandin
g Universe and thus understanding physics in this space-time is of high im
portance. It is known that N-dimensional de Sitter space-time can be viewe
d as an ``analytic continuation'' of the N-dimensional sphere. Hence\, giv
en the solutions of the Dirac equation on the N-dimensional sphere\, one c
an obtain the solutions of the Dirac equation in de Sitter space-time by u
sing appropriate techniques. In this talk\, I will briefly explain how on
e can construct a spinor quantum field theory in de Sitter space-time by m
aking use of these techniques. This talk is based on https://arxiv.org/ab
s/2011.07875 .\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Georgios Karananas (LMU\, Munich)
DTSTART:20210217T113000Z
DTEND:20210217T123000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/6
DESCRIPTION:Title: Spontaneous Conformal Symmetry Breaking in the Fishnet CFT\nb
y Georgios Karananas (LMU\, Munich) as part of High Energy Theory\, Gravit
y and Cosmology Seminars @ NTUA\n\n\nAbstract\nQuantum field theories wit
h exact but spontaneously broken conformal invariance have an intriguing f
eature: their vacuum energy is equal to zero. Up to now\, the only known u
ltraviolet complete theories where conformal symmetry can be spontaneously
broken were associated with supersymmetry\, with the most prominent examp
le being the N =4 SYM. Interestingly\, its non-supersymmetric descendant\,
the ``Fishnet theory\,'' supports at the classical level a rich set of fl
at directions along which conformal symmetry is spontaneously broken. At l
east perturbatively\, some of these vacua survive in the full quantum theo
ry - in the planar limit - without any fine tuning. As a result\, the vacu
um energy vanishes along these flat directions\, providing the first non-s
upersymmetric example of a four-dimensional quantum field theory with “n
atural” breaking of conformal symmetry.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ilias Cholis (Oakland University)
DTSTART:20210224T113000Z
DTEND:20210224T133000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/7
DESCRIPTION:Title: Antimatter Cosmic-Ray Nuclei as a probe of Dark Matter\nby Il
ias Cholis (Oakland University) as part of High Energy Theory\, Gravity a
nd Cosmology Seminars @ NTUA\n\n\nAbstract\nAntimatter cosmic ray measurem
ents can advance our understanding of high-energy astrophysical phenomena
in our own Galaxy. Over the last years\, satellite experiments as the Alph
a Magnetic Spectrometer on board the International Space Station measure a
ntimatter cosmic ray fluxes\, including antiprotons and recently antimatte
r nuclei. These measurements provide a novel probe to search for new physi
cs including annihilations of dark matter in the Milky Way\, which I will
present.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ville Vaskonen (BIST\, Barcelona)
DTSTART:20210303T113000Z
DTEND:20210303T123000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/8
DESCRIPTION:Title: Primordial black holes in light of LIGO-Virgo observations\nb
y Ville Vaskonen (BIST\, Barcelona) as part of High Energy Theory\, Gravit
y and Cosmology Seminars @ NTUA\n\n\nAbstract\nAssuming that a fraction o
f dark matter is in primordial black holes (PBHs)\, a population of PBH bi
naries is formed before matter-radiation equality from large Poisson fluct
uations in their spatial distribution. Though many of these binaries are d
isrupted by a nearby PBH or a small cluster of PBHs\, a large fraction of
them survives until they merge. In this talk I will describe the calculati
on of the PBH merger rate and show that the LIGO-Virgo observations give s
trong constraints on the abundance of O(10) solar mass PBHs. I will also d
iscuss the possibility that some of the observed GW events are from PBH me
rgers.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fotis Koutroulis (National Technical University of Athens)
DTSTART:20210310T113000Z
DTEND:20210310T123000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/9
DESCRIPTION:Title: When a UV and Quantum 1st Order Phase Transition Gives the Soluti
on to the Higgs Fine-Tuning Problem\nby Fotis Koutroulis (National Tec
hnical University of Athens) as part of High Energy Theory\, Gravity and
Cosmology Seminars @ NTUA\n\n\nAbstract\nWe construct the zero temperature
(no compact dimensions) effective action for an SU (2) Yang–Mills theor
y in five dimensions\, with boundary conditions that reduce the symmetry o
n the four-dimensional boundary located at the origin to a U (1)-complex s
calar system. In order to be sen- sitive to the Higgs phase\, we need to i
nclude higher dimen- sional operators in the effective action\, which can
be naturally achieved by generating it by expanding the corresponding latt
ice construction in small lattice spacing\, taking the naive continuum lim
it and then renormalizing. In addition\, we build in the effective action
non-perturbative information\, related to a first order quantum phase tran
sition known to exist. As a result\, the effective action acquires a finit
e cut-off that is low and the fine tuning of the scalar mass is rather mil
d.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Guillem Domènech (INFN Padua)
DTSTART:20210324T113000Z
DTEND:20210324T123000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/10
DESCRIPTION:Title: Are induced gravitational waves gauge dependent?\nby Guillem
Domènech (INFN Padua) as part of High Energy Theory\, Gravity and Cosmo
logy Seminars @ NTUA\n\n\nAbstract\nPrimordial black hole formation is alw
ays accompanied by a large amount of induced gravitational waves (GWs)\, i
n principle observable by future GWs detectors. However\, the theoretical
expression of the induced GW spectral density is strictly speaking gauge d
ependent. This gauge dependence thus casts doubts on the theoretical predi
ctions of the induced GWs. In this talk\, I will investigate in detail th
e gauge issue of the induced GWs. I will show that\, under reasonable assu
mptions\, the induced GWs is for all practical purposes gauge independent.
Thus\, free of ambiguities\, induced GWs are an excellent source of info
rmation about the primordial universe.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Georgios Tringas (National Technical University of Athens)
DTSTART:20210331T103000Z
DTEND:20210331T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/11
DESCRIPTION:Title: From Type II to 3D flux vacua on G2 orientifolds\nby Georgio
s Tringas (National Technical University of Athens) as part of High Energy
Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstract\nWe discuss
flux compactifications of Type II supergravity on G2 structures and holon
omy to three dimensions. We construct the 3D vacua using smeared O-planes
and background NS and RR fluxes. Whether the internal manifold is Ricci fl
at or not is crucial for the consistent construction of the theory. For bo
th Type IIA and Type IIB we find supersymmetric Minkowski vacua and AdS3 v
acua with full moduli stabilization and indication for scale separation. A
dding SUSY breaking objects we find dS3 vacua and performing flux quantiza
tion we discuss the fate of each example.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stelios Karydas (National Technical University of Athens)
DTSTART:20210407T103000Z
DTEND:20210407T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/12
DESCRIPTION:Title: Successful (Higgs) inflation from combined non minimal and deriv
ative couplings.\nby Stelios Karydas (National Technical University of
Athens) as part of High Energy Theory\, Gravity and Cosmology Seminars @
NTUA\n\n\nAbstract\nWe discuss an inflationary scenario based on the con
current presence of non-minimal coupling (NMC) and generalized non-minimal
derivative coupling (GNMDC). The combined construction maintains the adva
ntages of the individual scenarios without sharing their disadvantages. A
long inflationary phase can be achieved due to the gravitational friction
effect owed to the GNMDC\, without leading to trans-Planckian values and u
nitarity violation. Additionally\, the tensor-to-scalar ratio remains low
due to the NMC contribution. Finally\, the instabilities related to the s
quared sound-speed of scalar perturbations\, which plague the Derivative C
oupling scenarios\, are now healed due to the domination of the NMC contri
bution and the damping of the GNMDC effects during the reheating era.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Konstantinos Kritos (National Technical University of Athens)
DTSTART:20210414T103000Z
DTEND:20210414T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/13
DESCRIPTION:Title: Black Holes merging with Low Mass Gap Objects inside Globular Cl
usters\nby Konstantinos Kritos (National Technical University of Athen
s) as part of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\
n\n\nAbstract\nRecently\, the LIGO-Virgo collaborations have reported the
coalescence of a binary involving a black hole and a low-mass gap object (
LMGO) with mass in the range $\\sim 2.5−5M_\\odot$. In this work we stud
y the dynamical formation of compact object pairs\, via multiple binary-si
ngle exchanges that occur at the cores of globular clusters. We find that
the exchanges are efficient in forming hard compact object binaries at the
cores of dense astrophysical stellar environments. Furthermore\, if the p
opulation size of the LMGOs is related to that of neutron stars\, the infe
rred merger rate density of black hole-LMGO binaries inside globular clust
ers in the local Universe is estimated to be about $0.1\\textrm{Gpc}^{−3
}\\textrm{yr}^{−1}$.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Maria Chira (Aristotle Univ. of Thessaloniki & National Observator
y of Athens)
DTSTART:20210421T103000Z
DTEND:20210421T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/14
DESCRIPTION:Title: Dependence of the dynamical properties of light-cone simulation
dark matter halos on their environment\nby Maria Chira (Aristotle Univ
. of Thessaloniki & National Observatory of Athens) as part of High Energy
Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstract\nWe study t
he dependence of a variety of DM halo properties (shape\, spin\, virialisa
tion status) on different environments in a whole-sky ΛCDM light-cone hal
o catalogue extending to z ∼ 0.65\, using a simple and well-defined halo
isolation criterion. Using this definition of the environment we study if
and how the DM halo-properties and their interrelations depend on their e
nvironment. We also study the relative orientations of the spin- and shape
- vectors of DM halos with their isolation\, as well as the alignment of t
he shape- and the spin- vectors of neighbouring DM halos for a vast range
of separations. Lastly\, we focus on halo pairs\, which are encountered in
a variety of isolation states in our catalogue and\, specifically\, we st
udy how the shape- and spin- alignments of halo-pairs is dependent on the
isolation of the pair. The latter can give insight in the formation and ev
olution of halos formed under the dynamical interaction of their nearest n
eighbour in a region devoid of other massive halos\, i.e. not affected by
the ambient tidal field.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/14/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fotis Farakos (University of Padova)
DTSTART:20210513T100000Z
DTEND:20210513T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/15
DESCRIPTION:Title: Supergravity and applications in string theory\nby Fotis Far
akos (University of Padova) as part of High Energy Theory\, Gravity and C
osmology Seminars @ NTUA\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Steven Cunnington (Queen Mary\, U. of London)
DTSTART:20210519T103000Z
DTEND:20210519T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/16
DESCRIPTION:Title: Large Scale Cosmology with 21cm Intensity Mapping\nby Steven
Cunnington (Queen Mary\, U. of London) as part of High Energy Theory\, Gr
avity and Cosmology Seminars @ NTUA\n\n\nAbstract\nNeutral hydrogen (HI)
has been shown to be a tracer of the underlying matter field in our Univer
se. Thus by probing the large-scale structure of HI\, we can indirectly pr
obe cosmic structure and from this\, infer constraints on cosmological par
ameters. 21cm intensity mapping with radio telescopes is an efficient meth
od for this purpose\, although the success of this novel technique relies
on overcoming a number of challenges which I will discuss. The ultra-large
scales of our Universe host potential signatures for new physics\, but co
nventional galaxy surveys struggle to probe these scales with statistical
significance. 21cm intensity mapping should be better suited to this task
since it can rapidly survey large cosmic volumes. However\, to access the
largest scales with the much anticipated Square Kilometre Array (SKA)\, th
e single-dish intensity mapping method will be relied on. I will therefore
also discuss the work being undertaken with MeerKAT (an SKA pathfinder te
lescope) to successfully demonstrate single-dish intensity mapping\, which
represents an important milestone for using SKA as a large-scale structur
e probe.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andreas Goudelis (CNRS-LPC\, Clermont-Ferrand)
DTSTART:20210520T100000Z
DTEND:20210520T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/17
DESCRIPTION:Title: Dark Matter in Cosmology and Particle Physics\nby Andreas Go
udelis (CNRS-LPC\, Clermont-Ferrand) as part of High Energy Theory\, Gravi
ty and Cosmology Seminars @ NTUA\n\n\nAbstract\nThe existence of dark mat
ter is very well-established observational. Despite the effort that has be
en dedicated\, both at the theoretical/phenomenological and at the experim
ental level\, in order to detect it through its potential non-gravitationa
l interactions\, its microscopic nature remains unknown. In these two lect
ures\, I will first present a brief overview of the evidence that corrobor
ates its existence\, I will discuss different ideas about what types of pa
rticles could constitute viable "dark matter candidates" and I will deline
ate different promising strategies in order to detect it non-gravitational
ly. Afterward\, I will focus mostly on scenarios in which dark matter inte
racts extremely weekly ("feebly") with the Standard Model particles. I wil
l discuss some types of models that could contain such Feebly Interacting
dark matter candidates and I will highlight some of the exiting phenomenol
ogy that they predict in particle and astroparticle physics experiments.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Andreas Goudelis (CNRS-LPC\, Clermont-Ferrand)
DTSTART:20210527T100000Z
DTEND:20210527T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/19
DESCRIPTION:Title: Dark Matter in Cosmology and Particle Physics\nby Andreas Go
udelis (CNRS-LPC\, Clermont-Ferrand) as part of High Energy Theory\, Gravi
ty and Cosmology Seminars @ NTUA\n\n\nAbstract\nThe existence of dark mat
ter is very well-established observational. Despite the effort that has be
en dedicated\, both at the theoretical/phenomenological and at the experim
ental level\, in order to detect it through its potential non-gravitationa
l interactions\, its microscopic nature remains unknown. In these two lect
ures\, I will first present a brief overview of the evidence that corrobor
ates its existence\, I will discuss different ideas about what types of pa
rticles could constitute viable "dark matter candidates" and I will deline
ate different promising strategies in order to detect it non-gravitational
ly. Afterward\, I will focus mostly on scenarios in which dark matter inte
racts extremely weekly ("feebly") with the Standard Model particles. I wil
l discuss some types of models that could contain such Feebly Interacting
dark matter candidates and I will highlight some of the exiting phenomenol
ogy that they predict in particle and astroparticle physics experiments.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ioanna Stamou (University of Athens)
DTSTART:20210526T103000Z
DTEND:20210526T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/20
DESCRIPTION:Title: Producing PBHs and Gravitational Waves by breaking the SU(2\,1)/
SU(2)xU(1) Symmetry\nby Ioanna Stamou (University of Athens) as part o
f High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstrac
t\nWe present a class of models in order to explaining the generation of P
rimordial\nBlack Holes (PBHs) and Gravitational Waves (GWs) in the Univers
e. These models\nare based on no-scale theory. By breaking the SU(2\,1)/SU
(2)×U(1) symmetry we\nfix one of the two chiral fields and we derive effe
ctive scalar potentials which are\ncapable of generating PBHs and GWs. Thu
s\, we derive scalar potentials which\,\non the one hand\, explain the pro
duction of PBHs and GWs and\, on the other\nhand\, they conserve the trans
formation laws\, which yield from the parametrization\nof the coset SU(2\,
1)/SU(2)×U(1) as well as they conserve the unification between\nthe model
s which yield by this coset. Moreover\, we generate PBHs by modifying\nthe
kinetic term of the Langrangian (or the Kahler potential) and we keep the
\nsuperpotentials unmodified. Furthermore\, we evaluate the fractional abu
ndances\nof PBHs in radiation dominated era by using and comparing two met
hods the\nPress–Schechter approach and the peak theory\, while focusing
on explaining the\ndark matter in the Universe. By using the resulting sca
lar power spectrum we\nevaluate the amount of GWs during the radiation epo
ch. All proposed models are\nin complete consistence with Planck constrain
ts.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fotis Koutroulis (NTUA)
DTSTART:20210528T150000Z
DTEND:20210528T160000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/21
DESCRIPTION:Title: On the Spontaneous and Simultaneous Breaking of Internal and Sca
le symmetry in Effective Field Theories of extra dimensional origin enhanc
ed with Higher Dimensional Operators: A New Approach to the Hierarchy Prob
lem\nby Fotis Koutroulis (NTUA) as part of High Energy Theory\, Gravit
y and Cosmology Seminars @ NTUA\n\n\nAbstract\nWay before the very recent
discovery of the Higgs boson the associated mechanism was under speculati
on due to a theoretical inconsistency\, the well known Higgs hierarchy pro
blem. The inconsistency refers to the sensitivity of the Higgs mass to the
ultra violet contributions which results in the need of a very strong fin
e tuning of the physical parameters in order to leave the mass almost unaf
fected by the quantum corrections. Many solutions have been proposed regar
ding the Higgs mass fine tuning problem during the past years\, however\,
none of them has given a confirmation signal. In this dissertation we prop
ose a novel solution to the Higgs hierarchy problem based on a specific ex
tra dimensional model with very special boundary conditions and higher tha
t four dimensional operators. This is the so called Non-perturbative gauge
Higgs unification model\, an SU(2) 5-d orbifold lattice model with obifol
d boundary conditions leading to a 4d boundary. On the latter lives a kind
of an Abelian Higgs model\, an ideal case for our purpose since it posses
ses a non-trivial effective potential sensitive to the UV corrections at f
irst glance and yet relieved of the complexity of the Standard Model’s h
igher gauge group contributions. Therefore\, our first step is to deal wit
h the usual Abelian Higgs model in four spacetime dimensions where we exam
ine its physicality and consistency under different gauge choices proving
that the associated effective potential is gauge invariant. Then we introd
uce the Non-perturbative gauge Higgs unification model under the assumptio
n that bulk and boundary are completely disconnected. Even though this hyp
othesis gives consistent results does not solve the fine tuning problem an
d the need to consider a connection between bulk and boundary becomes urge
nt. A consequence of this is that the insertion of higher dimensional oper
ators is unavoidable. Therefore\, before going back to our original model
we examine the effective potential of a real scalar field enhanced with di
mension six and eight operators. What we show is the various cases under w
hich such a potential is both stable and exhibits spontaneous and simultan
eous breaking of internal and scale symmetry as it reaches an interacting
or a Gaussian fixed point. Finally\, with these in our hands we turn back
to the 5-d orbifold model and take into account the bulk-boundary connecti
on which produces an effective action enhanced with higher that four dimen
sional operators\, at the 4-d boundary\, whose nature includes non-perturb
ative information related to a first order quantum phase transition. Under
these circumstances the effective action acquires a finite cut-off that i
s low and the fine tuning of the scalar mass is rather mild.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Theodoros Papanikolaou (APC\, Paris)
DTSTART:20210602T103000Z
DTEND:20210602T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/22
DESCRIPTION:Title: Constraining the early universe with ultralight primordial black
holes and vice-versa\nby Theodoros Papanikolaou (APC\, Paris) as part
of High Energy Theory\, Gravity and Cosmology Seminars @ NTUA\n\n\nAbstr
act\nIn our presentation\, we focus on ultralight PBHs\, not tightly const
rained in the literature\, produced naturally during the preheating insta
bility in the context of single-field inflationary models. In particular\,
we find that the PBH production mechanism can be so efficient that PBHs s
ubsequently dominate the content of the universe and reheating proceeds fr
om their evaporation. Taking into account observational constraints on the
PBH abundance one can constrain the energy scales at the end of inflation
and at the onset of the radiation era. Vice-versa\, by studying induced s
econd order gravitational waves generated by density perturbations underla
in by PBHs themselves and taking into account GW back-reaction effects one
can set constraints on the initial abundance of PBHs as a function of the
ir mass.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj (Turin U.)
DTSTART:20210604T100000Z
DTEND:20210604T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/23
DESCRIPTION:Title: A short introduction to superstring theory I\nby Carlo Angel
antonj (Turin U.) as part of High Energy Theory\, Gravity and Cosmology S
eminars @ NTUA\n\n\nAbstract\nIn this series of lectures I will give a sho
rt\, pedagogical\, introduction to superstring theory and its applications
. The first lecture is devoted to the quantisation of the superstrings and
the constructions of consistent superstring theories in D=10. A special e
mphasis will be put on the GSO projection and\nthe role of modular invaria
nce of the one-loop partition function. The second lecture will deal with
open strings and we shall introduce D-branes. Finally\, in the third lectu
re I shall discuss the problem of compactification.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj (Turin U.)
DTSTART:20210610T100000Z
DTEND:20210610T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/24
DESCRIPTION:Title: A short introduction to superstring theory II\nby Carlo Ange
lantonj (Turin U.) as part of High Energy Theory\, Gravity and Cosmology
Seminars @ NTUA\n\n\nAbstract\nIn this series of lectures I will give a sh
ort\, pedagogical\, introduction to superstring theory and its application
s. The first lecture is devoted to the quantisation of the superstrings an
d the constructions of consistent superstring theories in D=10. A special
emphasis will be put on the GSO projection and\nthe role of modular invari
ance of the one-loop partition function. The second lecture will deal with
open strings and we shall introduce D-branes. Finally\, in the third lect
ure I shall discuss the problem of compactification.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj (Turin U.)
DTSTART:20210617T100000Z
DTEND:20210617T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/28
DESCRIPTION:Title: A short introduction to superstring theory III\nby Carlo Ang
elantonj (Turin U.) as part of High Energy Theory\, Gravity and Cosmology
Seminars @ NTUA\n\n\nAbstract\nIn this series of lectures I will give a s
hort\, pedagogical\, introduction to superstring theory and its applicatio
ns. The first lecture is devoted to the quantisation of the superstrings a
nd the constructions of consistent superstring theories in D=10. A special
emphasis will be put on the GSO projection and\nthe role of modular invar
iance of the one-loop partition function. The second lecture will deal wit
h open strings and we shall introduce D-branes. Finally\, in the third lec
ture I shall discuss the problem of compactification.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/28/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Marco Scalisi (Max Planck Institute\, Munich)
DTSTART:20210623T103000Z
DTEND:20210623T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/29
DESCRIPTION:Title: The Gravitino and the Swampland\nby Marco Scalisi (Max Planc
k Institute\, Munich) as part of High Energy Theory\, Gravity and Cosmolo
gy Seminars @ NTUA\n\n\nAbstract\nWe propose a new swampland conjecture st
ating that the limit of vanishing gravitino mass corresponds to the massle
ss limit of an infinite tower of states and to the consequent breakdown of
the effective field theory. We test our proposal in large classes of mode
ls coming from compactification of string theory to four dimensions\, wher
e we identify the Kaluza-Klein nature of the tower of states becoming ligh
t. We point out a general relation between the gravitino mass and abelian
gauge coupling in models with extended supersymmetry\, which can survive a
lso in examples with minimal supersymmetry. This allows us to connect our
conjecture to other well established swampland conjectures\, such as the w
eak gravity conjecture or the absence of global symmetries in quantum grav
ity. We discuss phenomenological implications of our conjecture in (quasi-
)de Sitter backgrounds and extract a lower bound for the gravitino mass in
terms of the Hubble parameter.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/29/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Angelantonj (Turin U.)
DTSTART:20210624T100000Z
DTEND:20210624T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/30
DESCRIPTION:Title: A short introduction to superstring theory IV\nby Carlo Ange
lantonj (Turin U.) as part of High Energy Theory\, Gravity and Cosmology
Seminars @ NTUA\n\n\nAbstract\nIn this series of lectures I will give a sh
ort\, pedagogical\, introduction to superstring theory and its application
s. The first lecture is devoted to the quantisation of the superstrings an
d the constructions of consistent superstring theories in D=10. A special
emphasis will be put on the GSO projection and the role of modular invaria
nce of the one-loop partition function. The second lecture will deal with
open strings and we shall introduce D-branes. Finally\, in the third lectu
re I shall discuss the problem of compactification.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/30/
END:VEVENT
BEGIN:VEVENT
SUMMARY:E. Palti (Ben-Gurion University)
DTSTART:20210701T100000Z
DTEND:20210701T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/31
DESCRIPTION:Title: Introduction to the Swampland\nby E. Palti (Ben-Gurion Unive
rsity) as part of High Energy Theory\, Gravity and Cosmology Seminars @ N
TUA\n\n\nAbstract\nThe Swampland program aims to distinguish effective the
ories that can be completed into quantum gravity in the ultraviolet from t
hose which cannot. I will present an introduction to this field\, mainly b
y using ideas from string theory.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/31/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Eran Palti (Ben Gurion U. of Negev)
DTSTART:20210715T100000Z
DTEND:20210715T110000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/32
DESCRIPTION:Title: Introduction to the Swampland\nby Eran Palti (Ben Gurion U.
of Negev) as part of High Energy Theory\, Gravity and Cosmology Seminars
@ NTUA\n\n\nAbstract\nThe Swampland program aims to distinguish effective
theories that can be completed into quantum gravity in the ultraviolet fro
m those which cannot. I will present an introduction to this field\, mainl
y by using ideas from string theory.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/32/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stratos Pateloudis (Universität Regensburg)
DTSTART:20211103T120000Z
DTEND:20211103T130000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/33
DESCRIPTION:Title: Confinement/deconfinement transition in the D0-brane matrix mode
l—Appearance of M-theory?\nby Stratos Pateloudis (Universität Regen
sburg) as part of High Energy Theory\, Gravity and Cosmology Seminars @ N
TUA\n\n\nAbstract\nI will discuss the confinement/deconfinement transition
in the D0-brane matrix model (often called the BFSS matrix model) and its
one-parameter deformation (the BMN matrix model) by using lattice Monte C
arlo simulations. The results confirm general expectations from the dual s
tring/M-theory picture for strong coupling. In particular\, we observe the
confined phase in the BFSS matrix model\, which is a nontrivial consequen
ce of the M-theory picture. We suggest that these models provide us with a
n ideal framework to study the Schwarzschild black hole\, M-theory\, and f
urthermore\, the parameter region of the phase transition between type IIA
superstring theory and M-theory.\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/33/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Frans Klinkhamer (Institute for Theoretical Physics\, Karlsruhe In
stitute of Technology)
DTSTART:20221012T103000Z
DTEND:20221012T113000Z
DTSTAMP:20260404T100020Z
UID:HETatNTUA/34
DESCRIPTION:Title: Cosmological constant problem: Revisiting the unimodular-gravity
approach\nby Frans Klinkhamer (Institute for Theoretical Physics\, Ka
rlsruhe Institute of Technology) as part of High Energy Theory\, Gravity
and Cosmology Seminars @ NTUA\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/HETatNTUA/34/
END:VEVENT
END:VCALENDAR