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SUMMARY:Swagat Mishra (Inter-University Centre for Astronomy and Astrophys
ics\, Pune)
DTSTART:20200616T103000Z
DTEND:20200616T113000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/1
DESCRIPTION:Title: Primordial Black Holes from a tiny bump/dip in the Inflaton
potential\nby Swagat Mishra (Inter-University Centre for Astronomy and
Astrophysics\, Pune) as part of IACS Gravity Research Seminars\n\n\nAbstr
act\nScalar perturbations during inflation can be substantially amplified
by tiny features in the inflaton\npotential. A bump-like feature behaves l
ike a local speed-breaker and lowers the speed of the scalar\nfield\, ther
eby locally enhancing the scalar power spectrum. A bump-like feature emerg
es naturally\nif the base inflaton potential contains a local correction t
erm\, which leads to a large peak in the\ncurvature power spectrum and to
an enhanced probability of black hole formation. Remarkably this\ndoes not
significantly affect the scalar spectral index nS and tensor to scalar ra
tio r on CMB scales.\nConsequently\, such models can produce higher mass p
rimordial black holes (M_{PBH} ≥ 1 M☉ ) in\ncontrast to models with `n
ear inflection-point potentials' in which generating higher mass black\nho
les severely affects nS and r. With a suitable choice of the base potentia
l—such as the string\ntheory-based (KKLT) inflation or the α-attractor
models—the amplification of primordial scalar\npower spectrum can be as
large as ten million\, which leads to a significant contribution of\nprimo
rdial black holes (PBHs) to the dark matter density today\, Interestingly\
, our results remain\nvalid if the bump is replaced by a dip. In this case
\, the base inflaton potential contains a negative\nlocal correction term
which also leads to an enhanced probability of PBH formation. We conclude\
nthat primordial black holes in the mass range 10−17 M_☉ ≤ M_{PBH}
≤ 100 M_☉ can easily form in single-field inflation in the presence of
small bump-like and dip-like features in the inflaton potential.\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Amitabh Virmani (CMI)
DTSTART:20200623T103000Z
DTEND:20200623T113000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/2
DESCRIPTION:Title: Quasinormal modes of supersymmetric microstate geometries fr
om the D1-D5 CFT\nby Amitabh Virmani (CMI) as part of IACS Gravity Res
earch Seminars\n\n\nAbstract\nIn this talk\, I will describe the computati
on of the real and imaginary parts of the quasinormal modes of supersymmet
ric microstate geometry and show that in the parameter range when the geom
etries have large AdS region\, the spectrum is precisely reproduced from a
D1-D5 orbifold CFT analysis. The spectrum includes the slow decaying mode
s pointed out by Eperon\, Reall\, and Santos. I will also provide an overv
iew of the geometries known as "superstrata" and the very recent quasinorm
al modes computations for these geometries by Bena\, Eperon\, Heidmann\, a
nd Warner.\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jahanur Hoque (Charles University)
DTSTART:20200701T103000Z
DTEND:20200701T113000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/3
DESCRIPTION:Title: Peeling or not peeling?\nby Jahanur Hoque (Charles Unive
rsity) as part of IACS Gravity Research Seminars\n\n\nAbstract\nIn an asym
ptotically simple space-time using the conformal completion technique\, th
e peeling theorem shows that Weyl scalar $\\Psi_{n}$ falls off as $r^{n-5
}$ (r is affine parameter along null geodesic). In this talk\, we will dis
cuss peeling property with or without a positive cosmological constant. We
will also comment on the violation of the usual peeling property for a cl
ass of space-time. This talk is designed to be accessible for a broad audi
ence.\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jyotirmoy Bhattacharya (IIT Kharagpur)
DTSTART:20200707T103000Z
DTEND:20200707T113000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/4
DESCRIPTION:Title: An entropy current for dynamical black holes in four-derivat
ive theories of gravity\nby Jyotirmoy Bhattacharya (IIT Kharagpur) as
part of IACS Gravity Research Seminars\n\n\nAbstract\nI will begin with a
brief overview of black hole thermodynamics\, especially the second law\,
for two-derivative Einstein gravity. I will then briefly discuss Wald's en
tropy for higher derivative corrections to Einstein's gravity\, pointing o
ut the difficulty in proving a general second law for it. Subsequently\, I
shall review a recent attempt by Aron Wall at generalizing Wald entropy i
n linearized dynamic situations\, which obeys the second law. Through a cl
oser examination of this construction\, we shall demonstrate the existence
of a local current on the event horizon\, for four-derivative theories of
gravity. A local version of the second law can be conveniently expressed
in terms of this current. We will finally conclude with a discussion of th
e implications of this current\, with an outlook for future work.\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anupam Mazumdar (University of Groningen)
DTSTART:20200714T103000Z
DTEND:20200714T113000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/5
DESCRIPTION:Title: Spin Entanglement Witness for Quantum Gravity in a Laborator
y\nby Anupam Mazumdar (University of Groningen) as part of IACS Gravit
y Research Seminars\n\n\nAbstract\nUnderstanding gravity in the framework
of quantum mechanics and quantum field theory is one of the great challeng
es in modern physics. Along this line\, a prime question is to find whethe
r gravity is a quantum entity subject to the rules of quantum mechanics. I
t is fair to say that there are no feasible ideas yet to test the quantum
coherent behaviour of gravity directly in a laboratory experiment. Here\,
I will introduce an idea for such a test based on the principle that two o
bjects cannot be entangled without a quantum mediator. I will show that de
spite the weakness of gravity\, the phase evolution induced by the gravita
tional interaction of two micron size test masses (diamond/Rydberg atoms o
r completely a novel material) in adjacent matter-wave interferometers can
detectably entangle them even when they are placed far apart enough to ke
ep Casimir-Polder forces at bay. I will provide a prescription for witness
ing this entanglement\, which certifies gravity as a quantum coherent medi
ator\, through simple correlation measurements between two spins: one embe
dded in each test mass. Fundamentally\, the above entanglement is shown to
certify the presence of non-zero off-diagonal terms in the coherent state
basis of the gravitational field modes.\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Simone Speziale (CPT\, Aix Marseille University)
DTSTART:20200721T093000Z
DTEND:20200721T103000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/6
DESCRIPTION:Title: Boundary effects in general relativity with tetrads\nby
Simone Speziale (CPT\, Aix Marseille University) as part of IACS Gravity R
esearch Seminars\n\n\nAbstract\nTBA\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Chiranjeeb Singha (IISER Kolkata)
DTSTART:20200728T103000Z
DTEND:20200728T113000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/7
DESCRIPTION:Title: Hamiltonian-based derivation of the Hawking effect\nby C
hiranjeeb Singha (IISER Kolkata) as part of IACS Gravity Research Seminars
\n\n\nAbstract\nIn order to achieve a Hamiltonian-based canonical derivati
on of the Hawking effect\, one usually faces multiple hurdles. Firstly\, s
pacetime foliation using Schwarzschild time does not lead to hyper-surface
s which are always spacelike. Secondly\, the null coordinates which are fr
equently used in the covariant approach\, do not lead to a true matter Ham
iltonian. In order to overcome these difficulties\, We have introduced a n
ew set of near-null coordinates which allows one to perform an exact canon
ical derivation of the Hawking effect. However\, there too one faces the d
ifficulty of having to deal with non-vanishing matter diffeomorphism gener
ator as the spatial decomposition involves a non-zero shift-vector. Then w
e have introduced a new set of coordinates that allows one to perform an e
xact canonical derivation of the Hawking effect without having to deal wit
h matter diffeomorphism generator. These derivations open up an avenue to
explore the Hawking effect in the framework of different canonical quantiz
ation methods such as the polymer quantization. After that\, we have used
polymer quantization and shown that in polymer quantization the Hawking ef
fect is short-lived and it eventually disappears for an asymptotic future
observer.\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bibhas Majhi (IIT Guwahati)
DTSTART:20200804T103000Z
DTEND:20200804T113000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/8
DESCRIPTION:Title: Fluid-gravity correspondence: a new cut-off surface approach
\nby Bibhas Majhi (IIT Guwahati) as part of IACS Gravity Research Semi
nars\n\n\nAbstract\nFluid-gravity correspondence connects the Navier-Stoke
s (NS) equation with the Einstein’s equation on a particular hypersurfac
e. We propose an alternative to this. We show that the vanishing of the pr
ojected acceleration of a suitably chosen velocity field onto the flat tim
elike hypersurface corresponding to a particular constructed (p+2) dimensi
onal manifold requires the satisfaction of the incompressible NS equation
in (p+1) dimensions. Additionally\, the incompressibility condition of the
fluid arises from a vanishing expansion parameter. In this approach Einst
ein’s equations do not play any role and this can be regarded as an off-
shell description of fluid- gravity correspondence. We argue that our metr
ic effectively encapsulates the information of forcing terms in the govern
ing equations as if a free fluid is moving on this hypersurface. We finall
y discuss the implications of this interesting observation and its potenti
ality in helping us to understand hydrodynamical flows in a probable new s
etting.\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Debajyoti Sarkar (IIT Indore)
DTSTART:20200811T103000Z
DTEND:20200811T113000Z
DTSTAMP:20260404T110652Z
UID:virtualgravity/9
DESCRIPTION:Title: Endpoint contributions to excited-state modular Hamiltonians
\nby Debajyoti Sarkar (IIT Indore) as part of IACS Gravity Research Se
minars\n\n\nAbstract\nWe compute modular Hamiltonians for excited states o
btained by perturbing the vacuum with a unitary operator. We use operator
methods and work to first order in the strength of the perturbation. For t
he most part we divide space in half and focus on perturbations generated
by integrating a local operator J over a null plane. Local operators with
weight n>=2 under vacuum modular flow produce an additional endpoint contr
ibution to the modular Hamiltonian. Intuitively this is because operators
with weight n>=2 can move degrees of freedom from a region to its compleme
nt. The endpoint contribution is an integral of J over a null plane. We sh
ow this in detail for stress tensor perturbations in two dimensions\, wher
e the result can be verified by a conformal transformation\, and for scala
r perturbations in a CFT. This lets us conjecture a general form for the e
ndpoint contribution that applies to any field theory divided into half-sp
aces. This work is based on ArXiv:2006.13317 [hep-th] with Dan Kabat\, Gil
ad Lifschytz and Phuc Nguyen.\n
LOCATION:https://stable.researchseminars.org/talk/virtualgravity/9/
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