91 research outputs found
Kinetic theory for scalar fields with nonlocal quantum coherence
We derive quantum kinetic equations for scalar fields undergoing coherent
evolution either in time (coherent particle production) or in space (quantum
reflection). Our central finding is that in systems with certain space-time
symmetries, quantum coherence manifests itself in the form of new spectral
solutions for the dynamical 2-point correlation function. This spectral
structure leads to a consistent approximation for dynamical equations that
describe coherent evolution in presence of decohering collisions. We illustrate
the method by solving the bosonic Klein problem and the bound states for the
nonrelativistic square well potential. We then compare our spectral phase space
definition of particle number to other definitions in the nonequilibrium field
theory. Finally we will explicitly compute the effects of interactions to
coherent particle production in the case of an unstable field coupled to an
oscillating background.Comment: 33 pages, 7 figures, replaced with the version published in JHE
"Double-trace" Deformations, Boundary Conditions and Spacetime Singularities
Double-trace deformations of the AdS/CFT duality result in a new perturbation
expansion for string theory, based on a non-local worldsheet. We discuss some
aspects of the deformation in the low energy gravity approximation, where it
appears as a change in the boundary condition of fields. We relate unique
features of the boundary of AdS to the worldsheet becoming non-local, and
conjecture that non-local worldsheet actions may be generic in other classes of
backgrounds.Comment: 21 pages, 2 figures, harvmac. v2: minor changes, references added,
version sent to JHEP. v3 minor correction
Non-linear corrections to inflationary power spectrum
We study non-linear contributions to the power spectrum of the curvature
perturbation on super-horizon scales, produced during slow-roll inflation
driven by a canonical single scalar field. We find that on large scales the
linear power spectrum completely dominates and leading non-linear corrections
remain totally negligible, indicating that we can safely rely on linear
perturbation theory to study inflationary power spectrum. We also briefly
comment on the infrared and ultraviolet behaviour of the non-linear
corrections.Comment: (v1) 14 pages, 2 figures; (v2) references added and discussions
expanded, including a new version of Figure 2, to appear in Journal of
Cosmology and Astroparticle Physic
Schwinger-Keldysh Propagators from AdS/CFT Correspondence
We demonstrate how to compute real-time Green's functions for a class of
finite temperature field theories from their AdS gravity duals. In particular,
we reproduce the two-by-two Schwinger-Keldysh matrix propagator from a gravity
calculation. Our methods should work also for computing higher point Lorentzian
signature correlators. We elucidate the boundary condition subtleties which
hampered previous efforts to build a Lorentzian-signature AdS/CFT
correspondence. For two-point correlators, our construction is automatically
equivalent to the previously formulated prescription for the retarded
propagator.Comment: 16 pages, 1 figure, references added; to appear in JHE
Mutated hybrid inflation in -gravity
A new hybrid inflationary scenario in the context of -gravity
is proposed. Demanding the waterfall field to 'support the potential from
below' [unlike the original proposal by Stewart in Phys. Lett. B345, 414
(1995)], we demonstrate that the scalar potential is similar to that of the
large-field chaotic inflation model proposed by Linde in Phys. Lett. B129, 177
(1983). Inflationary observables are used to constrain the parameter space of
our model; in the process, an interesting limit on the number of e-folds N is
found.Comment: 9 pages, 2 figures, LaTeX2e, v2: Sec.3 expanded and improved, 1 Fig.
added, a new result included, some Eqs. corrected, 2 References adde
Inflation with General Initial Conditions for Scalar Perturbations
We explore the possibility of a single field quasi-de Sitter inflationary
model with general initial state for primordial fluctuations. In this paper,
first we compute the power spectrum and the bispectrum of scalar perturbations
with coherent state as the initial state. We find that a large class of
coherent states are indistinguishable from the Bunch-Davies vacuum state and
hence consistent with the current observations. In case of a more general
initial state built over Bunch-Davies vacuum state, we show that the
constraints on the initial state from observed power spectrum and local
bispectrum are relatively weak and for quasi-de Sitter inflation a large number
of initial states are consistent with the current observations. However,
renormalizability of the energy-momentum tensor of the fluctuations constraints
the initial state further.Comment: Updated to match published version, 20 page
Phase Transition of Electrically Charged Ricci-flat Black Holes
We study phase transition between electrically charged Ricci-flat black holes
and AdS soliton spacetime of Horowitz and Myers in five dimensions. Boundary
topology for both of them is . We consider
Reissner-Nordstrom black hole and R-charged black holes and find that phase
transition of these black holes to AdS soliton spacetime depends on the
relative size of two boundary circles. We also perform the stability analysis
for these black holes. In order to use the AdS/CFT correspondence, we work in
the grand canonical ensemble.Comment: 33 pages, 9 figures, Version 2, References adde
Lodged in the throat: Internal infinities and AdS/CFT
In the context of AdS3/CFT2, we address spacetimes with a certain sort of
internal infinity as typified by the extreme BTZ black hole. The internal
infinity is a null circle lying at the end of the black hole's infinite throat.
We argue that such spacetimes may be described by a product CFT of the form
CFT-L * CFT-R, where CFT-R is associated with the asymptotically AdS boundary
while CFT-L is associated with the null circle. Our particular calculations
analyze the CFT dual of the extreme BTZ black hole in a linear toy model of
AdS3/CFT2. Since the BTZ black hole is a quotient of AdS3, the dual CFT state
is a corresponding quotient of the CFT vacuum state. This state turns out to
live in the aforementioned product CFT. We discuss this result in the context
of general issues of AdS/CFT duality and entanglement entropy.Comment: 11 pages, 2 figures; v2 - some typos corrected, minor revision
On time-dependent AdS/CFT
We clarify aspects of the holographic AdS/CFT correspondence that are typical
of Lorentzian signature, to lay the foundation for a treatment of
time-dependent gravity and conformal field theory phenomena. We provide a
derivation of bulk-to-boundary propagators associated to advanced, retarded and
Feynman bulk propagators, and provide a better understanding of the boundary
conditions satisfied by the bulk fields at the horizon. We interpret the
subleading behavior of the wavefunctions in terms of specific vacuum
expectation values, and compute two-point functions in our framework. We
connect our bulk methods to the closed time path formalism in the boundary
field theory.Comment: 19 pages, v2: added reference, JHEP versio
Brownian motion in AdS/CFT
We study Brownian motion and the associated Langevin equation in AdS/CFT. The
Brownian particle is realized in the bulk spacetime as a probe fundamental
string in an asymptotically AdS black hole background, stretching between the
AdS boundary and the horizon. The modes on the string are excited by the
thermal black hole environment and consequently the string endpoint at the
boundary undergoes an erratic motion, which is identified with an external
quark in the boundary CFT exhibiting Brownian motion. Semiclassically, the
modes on the string are thermally excited due to Hawking radiation, which
translates into the random force appearing in the boundary Langevin equation,
while the friction in the Langevin equation corresponds to the excitation on
the string being absorbed by the black hole. We give a bulk proof of the
fluctuation-dissipation theorem relating the random force and friction. This
work can be regarded as a step toward understanding the quantum microphysics
underlying the fluid-gravity correspondence. We also initiate a study of the
properties of the effective membrane or stretched horizon picture of black
holes using our bulk description of Brownian motion.Comment: 54 pages (38 pages + 5 appendices), 5 figures. v2: references added,
clarifications in 6.2. v3: clarifications, version submitted to JHE
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