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SUMMARY:Swagat Mishra (Inter-University Centre for Astronomy and Astrophys
ics\, Pune)
DTSTART:20200616T103000Z
DTEND:20200616T113000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/1
DESCRIPTION:Title: Primordial Black Holes from a tiny bump/dip in the Inflaton potenti
al\nby Swagat Mishra (Inter-University Centre for Astronomy and Astrop
hysics\, Pune) as part of IACS Gravity Research Seminars\n\n\nAbstract\nSc
alar perturbations during inflation can be substantially amplified by tiny
features in the inflaton\npotential. A bump-like feature behaves like a l
ocal speed-breaker and lowers the speed of the scalar\nfield\, thereby loc
ally enhancing the scalar power spectrum. A bump-like feature emerges natu
rally\nif the base inflaton potential contains a local correction term\, w
hich leads to a large peak in the\ncurvature power spectrum and to an enha
nced probability of black hole formation. Remarkably this\ndoes not signif
icantly affect the scalar spectral index nS and tensor to scalar ratio r o
n CMB scales.\nConsequently\, such models can produce higher mass primordi
al black holes (M_{PBH} ≥ 1 M☉ ) in\ncontrast to models with `near inf
lection-point potentials' in which generating higher mass black\nholes sev
erely affects nS and r. With a suitable choice of the base potential—suc
h 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\nprimordial
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://researchseminars.org/talk/virtualgravity/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Amitabh Virmani (CMI)
DTSTART:20200623T103000Z
DTEND:20200623T113000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/2
DESCRIPTION:Title: Quasinormal modes of supersymmetric microstate geometries from the
D1-D5 CFT\nby Amitabh Virmani (CMI) as part of IACS Gravity Research S
eminars\n\n\nAbstract\nIn this talk\, I will describe the computation of t
he real and imaginary parts of the quasinormal modes of supersymmetric mic
rostate geometry and show that in the parameter range when the geometries
have large AdS region\, the spectrum is precisely reproduced from a D1-D5
orbifold CFT analysis. The spectrum includes the slow decaying modes point
ed out by Eperon\, Reall\, and Santos. I will also provide an overview of
the geometries known as "superstrata" and the very recent quasinormal mode
s computations for these geometries by Bena\, Eperon\, Heidmann\, and Warn
er.\n
LOCATION:https://researchseminars.org/talk/virtualgravity/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jahanur Hoque (Charles University)
DTSTART:20200701T103000Z
DTEND:20200701T113000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/3
DESCRIPTION:Title: Peeling or not peeling?\nby Jahanur Hoque (Charles University)
as part of IACS Gravity Research Seminars\n\n\nAbstract\nIn an asymptotica
lly simple space-time using the conformal completion technique\, the peeli
ng theorem shows that Weyl scalar $\\Psi_{n}$ falls off as $r^{n-5}$ (r i
s affine parameter along null geodesic). In this talk\, we will discuss pe
eling property with or without a positive cosmological constant. We will a
lso comment on the violation of the usual peeling property for a class of
space-time. This talk is designed to be accessible for a broad audience.\n
LOCATION:https://researchseminars.org/talk/virtualgravity/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jyotirmoy Bhattacharya (IIT Kharagpur)
DTSTART:20200707T103000Z
DTEND:20200707T113000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/4
DESCRIPTION:Title: An entropy current for dynamical black holes in four-derivative the
ories of gravity\nby Jyotirmoy Bhattacharya (IIT Kharagpur) as part of
IACS Gravity Research Seminars\n\n\nAbstract\nI will begin with a brief o
verview of black hole thermodynamics\, especially the second law\, for two
-derivative Einstein gravity. I will then briefly discuss Wald's entropy f
or higher derivative corrections to Einstein's gravity\, pointing out the
difficulty in proving a general second law for it. Subsequently\, I shall
review a recent attempt by Aron Wall at generalizing Wald entropy in linea
rized dynamic situations\, which obeys the second law. Through a closer ex
amination of this construction\, we shall demonstrate the existence of a l
ocal current on the event horizon\, for four-derivative theories of gravit
y. A local version of the second law can be conveniently expressed in term
s of this current. We will finally conclude with a discussion of the impli
cations of this current\, with an outlook for future work.\n
LOCATION:https://researchseminars.org/talk/virtualgravity/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Anupam Mazumdar (University of Groningen)
DTSTART:20200714T103000Z
DTEND:20200714T113000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/5
DESCRIPTION:Title: Spin Entanglement Witness for Quantum Gravity in a Laboratory\n
by Anupam Mazumdar (University of Groningen) as part of IACS Gravity Resea
rch Seminars\n\n\nAbstract\nUnderstanding gravity in the framework of quan
tum mechanics and quantum field theory is one of the great challenges in m
odern physics. Along this line\, a prime question is to find whether gravi
ty is a quantum entity subject to the rules of quantum mechanics. It is fa
ir to say that there are no feasible ideas yet to test the quantum coheren
t behaviour of gravity directly in a laboratory experiment. Here\, I will
introduce an idea for such a test based on the principle that two objects
cannot be entangled without a quantum mediator. I will show that despite t
he weakness of gravity\, the phase evolution induced by the gravitational
interaction of two micron size test masses (diamond/Rydberg atoms or compl
etely a novel material) in adjacent matter-wave interferometers can detect
ably entangle them even when they are placed far apart enough to keep Casi
mir-Polder forces at bay. I will provide a prescription for witnessing thi
s entanglement\, which certifies gravity as a quantum coherent mediator\,
through simple correlation measurements between two spins: one embedded in
each test mass. Fundamentally\, the above entanglement is shown to certif
y the presence of non-zero off-diagonal terms in the coherent state basis
of the gravitational field modes.\n
LOCATION:https://researchseminars.org/talk/virtualgravity/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Simone Speziale (CPT\, Aix Marseille University)
DTSTART:20200721T093000Z
DTEND:20200721T103000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/6
DESCRIPTION:Title: Boundary effects in general relativity with tetrads\nby Simone
Speziale (CPT\, Aix Marseille University) as part of IACS Gravity Research
Seminars\n\n\nAbstract\nTBA\n
LOCATION:https://researchseminars.org/talk/virtualgravity/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Chiranjeeb Singha (IISER Kolkata)
DTSTART:20200728T103000Z
DTEND:20200728T113000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/7
DESCRIPTION:Title: Hamiltonian-based derivation of the Hawking effect\nby Chiranje
eb Singha (IISER Kolkata) as part of IACS Gravity Research Seminars\n\n\nA
bstract\nIn order to achieve a Hamiltonian-based canonical derivation of t
he Hawking effect\, one usually faces multiple hurdles. Firstly\, spacetim
e foliation using Schwarzschild time does not lead to hyper-surfaces which
are always spacelike. Secondly\, the null coordinates which are frequentl
y used in the covariant approach\, do not lead to a true matter Hamiltonia
n. In order to overcome these difficulties\, We have introduced a new set
of near-null coordinates which allows one to perform an exact canonical de
rivation of the Hawking effect. However\, there too one faces the difficul
ty of having to deal with non-vanishing matter diffeomorphism generator as
the spatial decomposition involves a non-zero shift-vector. Then we have
introduced a new set of coordinates that allows one to perform an exact ca
nonical derivation of the Hawking effect without having to deal with matte
r diffeomorphism generator. These derivations open up an avenue to explore
the Hawking effect in the framework of different canonical quantization m
ethods such as the polymer quantization. After that\, we have used polymer
quantization and shown that in polymer quantization the Hawking effect is
short-lived and it eventually disappears for an asymptotic future observe
r.\n
LOCATION:https://researchseminars.org/talk/virtualgravity/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bibhas Majhi (IIT Guwahati)
DTSTART:20200804T103000Z
DTEND:20200804T113000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/8
DESCRIPTION:Title: Fluid-gravity correspondence: a new cut-off surface approach\nb
y Bibhas Majhi (IIT Guwahati) as part of IACS Gravity Research Seminars\n\
n\nAbstract\nFluid-gravity correspondence connects the Navier-Stokes (NS)
equation with the Einstein’s equation on a particular hypersurface. We p
ropose an alternative to this. We show that the vanishing of the projected
acceleration of a suitably chosen velocity field onto the flat timelike h
ypersurface corresponding to a particular constructed (p+2) dimensional ma
nifold 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 Einstein’s
equations do not play any role and this can be regarded as an off-shell d
escription of fluid- gravity correspondence. We argue that our metric effe
ctively encapsulates the information of forcing terms in the governing equ
ations as if a free fluid is moving on this hypersurface. We finally discu
ss the implications of this interesting observation and its potentiality i
n helping us to understand hydrodynamical flows in a probable new setting.
\n
LOCATION:https://researchseminars.org/talk/virtualgravity/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Debajyoti Sarkar (IIT Indore)
DTSTART:20200811T103000Z
DTEND:20200811T113000Z
DTSTAMP:20260422T225635Z
UID:virtualgravity/9
DESCRIPTION:Title: Endpoint contributions to excited-state modular Hamiltonians\nb
y Debajyoti Sarkar (IIT Indore) as part of IACS Gravity Research Seminars\
n\n\nAbstract\nWe compute modular Hamiltonians for excited states obtained
by perturbing the vacuum with a unitary operator. We use operator methods
and work to first order in the strength of the perturbation. For the most
part we divide space in half and focus on perturbations generated by inte
grating a local operator J over a null plane. Local operators with weight
n>=2 under vacuum modular flow produce an additional endpoint contribution
to the modular Hamiltonian. Intuitively this is because operators with we
ight n>=2 can move degrees of freedom from a region to its complement. The
endpoint contribution is an integral of J over a null plane. We show this
in detail for stress tensor perturbations in two dimensions\, where the r
esult can be verified by a conformal transformation\, and for scalar pertu
rbations in a CFT. This lets us conjecture a general form for the endpoint
contribution that applies to any field theory divided into half-spaces. T
his work is based on ArXiv:2006.13317 [hep-th] with Dan Kabat\, Gilad Lifs
chytz and Phuc Nguyen.\n
LOCATION:https://researchseminars.org/talk/virtualgravity/9/
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