48 research outputs found
Dynamics of false vacuum bubbles: beyond the thin shell approximation
We numerically study the dynamics of false vacuum bubbles which are inside an
almost flat background; we assumed spherical symmetry and the size of the
bubble is smaller than the size of the background horizon. According to the
thin shell approximation and the null energy condition, if the bubble is
outside of a Schwarzschild black hole, unless we assume Farhi-Guth-Guven
tunneling, expanding and inflating solutions are impossible. In this paper, we
extend our method to beyond the thin shell approximation: we include the
dynamics of fields and assume that the transition layer between a true vacuum
and a false vacuum has non-zero thickness. If a shell has sufficiently low
energy, as expected from the thin shell approximation, it collapses (Type 1).
However, if the shell has sufficiently large energy, it tends to expand. Here,
via the field dynamics, field values of inside of the shell slowly roll down to
the true vacuum and hence the shell does not inflate (Type 2). If we add
sufficient exotic matters to regularize the curvature near the shell, inflation
may be possible without assuming Farhi-Guth-Guven tunneling. In this case, a
wormhole is dynamically generated around the shell (Type 3). By tuning our
simulation parameters, we could find transitions between Type 1 and Type 2, as
well as between Type 2 and Type 3. Between Type 2 and Type 3, we could find
another class of solutions (Type 4). Finally, we discuss the generation of a
bubble universe and the violation of unitarity. We conclude that the existence
of a certain combination of exotic matter fields violates unitarity.Comment: 40 pages, 41 figure
Hawking's radiation in non-stationary rotating de Sitter background
Hawking's radiation effect of Klein-Gordon scalar field, Dirac particles and
Maxwell's electromagnetic field in the non-stationary rotating de Sitter
cosmological space-time is investigated by using a method of generalized
tortoise co-ordinates transformation. The locations and the temperatures of the
cosmological horizons of the non-stationary rotating de Sitter model are
derived. It is found that the locations and the temperatures of the rotating
cosmological model depend not only on the time but also on the angle. The
stress-energy regularization techniques are applied to the two dimensional
analog of the de Sitter metrics and the calculated stress-energy tensor
contains the thermal radiation effect.Comment: 13 pages, LaTex format, accepted for publication Astrophysics and
Space Science, Springer; Journal ID: 10509, Article ID: 606, Date 2011-01-1
Asymptotic symmetries on Killing horizons
We investigate asymptotic symmetries regularly defined on spherically
symmetric Killing horizons in the Einstein theory with or without the
cosmological constant. Those asymptotic symmetries are described by asymptotic
Killing vectors, along which the Lie derivatives of perturbed metrics vanish on
a Killing horizon. We derive the general form of asymptotic Killing vectors and
find that the group of the asymptotic symmetries consists of rigid O(3)
rotations of a horizon two-sphere and supertranslations along the null
direction on the horizon, which depend arbitrarily on the null coordinate as
well as the angular coordinates. By introducing the notion of asymptotic
Killing horizons, we also show that local properties of Killing horizons are
preserved under not only diffeomorphisms but also non-trivial transformations
generated by the asymptotic symmetry group. Although the asymptotic symmetry
group contains the subgroup, which results from the
supertranslations dependent only on the null coordinate, it is shown that the
Poisson bracket algebra of the conserved charges conjugate to asymptotic
Killing vectors does not acquire non-trivial central charges. Finally, by
considering extended symmetries, we discuss that unnatural reduction of the
symmetry group is necessary in order to obtain the Virasoro algebra with
non-trivial central charges, which will not be justified when we respect the
spherical symmetry of Killing horizons.Comment: 28 page
Surface Terms as Counterterms in the AdS/CFT Correspondence
We examine the recently proposed technique of adding boundary counterterms to
the gravitational action for spacetimes which are locally asymptotic to anti-de
Sitter. In particular, we explicitly identify higher order counterterms, which
allow us to consider spacetimes of dimensions d<=7. As the counterterms
eliminate the need of ``background subtraction'' in calculating the action, we
apply this technique to study examples where the appropriate background was
ambiguous or unknown: topological black holes, Taub-NUT-AdS and Taub-Bolt-AdS.
We also identify certain cases where the covariant counterterms fail to render
the action finite, and we comment on the dual field theory interpretation of
this result. In some examples, the case of vanishing cosmological constant may
be recovered in a limit, which allows us to check results and resolve
ambiguities in certain asymptotically flat spacetime computations in the
literature.Comment: Revtex, 18 pages. References updated and few typo's fixed. Final
versio
Particle production and classical condensates in de Sitter space
The cosmological particle production in a expanding de Sitter universe
with a Hubble parameter is considered for various values of mass or
conformal coupling of a free, scalar field. One finds that, for a minimally
coupled field with mass (except for ),
the one-mode occupation number grows to unity soon after the physical
wavelength of the mode becomes larger than the Hubble radius, and afterwards
diverges as , where . However, for a field with ,
the occupation number of a mode outside the Hubble radius is rapidly
oscillating and bounded and does not exceed unity. These results, readily
generalized for cases of a nonminimal coupling, provide a clear argument that
the long-wavelength vacuum fluctuations of low-mass fields in an inflationary
universe do show classical behavior, while those of heavy fields do not. The
interaction or self-interaction does not appear necessary for the emergence of
classical features, which are entirely due to the rapid expansion of the de
Sitter background and the upside-down nature of quantum oscillators for modes
outside the Hubble radius.Comment: Revtex + 5 postscript figures. Accepted for Phys Rev D15. Revision of
Aug 1996 preprint limited to the inclusion and discussion of references
suggested by the referee
Entropy of Lovelock Black Holes
A general formula for the entropy of stationary black holes in Lovelock
gravity theories is obtained by integrating the first law of black hole
mechanics, which is derived by Hamiltonian methods. The entropy is not simply
one quarter of the surface area of the horizon, but also includes a sum of
intrinsic curvature invariants integrated over a cross section of the horizon.Comment: 15 pages, plain Latex, NSF-ITP-93-4
Remarks on 't Hooft's Brick Wall Model
A semi-classical reasoning leads to the non-commutativity of the space and
time coordinates near the horizon of Schwarzschild black hole. This
non-commutativity in turn provides a mechanism to interpret the brick wall
thickness hypothesis in 't Hooft's brick wall model as well as the boundary
condition imposed for the field considered. For concreteness, we consider a
noncommutative scalar field model near the horizon and derive the effective
metric via the equation of motion of noncommutative scalar field. This metric
displays a new horizon in addition to the original one associated with the
Schwarzschild black hole. The infinite red-shifting of the scalar field on the
new horizon determines the range of the noncommutativ space and explains the
relevant boundary condition for the field. This range enables us to calculate
the entropy of black hole as proportional to the area of its original horizon
along the same line as in 't Hooft's model, and the thickness of the brick wall
is found to be proportional to the thermal average of the noncommutative
space-time range. The Hawking temperature has been derived in this formalism.
The study here represents an attempt to reveal some physics beyond the brick
wall model.Comment: RevTeX, 5 pages, no figure
Noncommutative geometry, Quantum effects and DBI-scaling in the collapse of D0-D2 bound states
We study fluctuations of time-dependent fuzzy two-sphere solutions of the
non-abelian DBI action of D0-branes, describing a bound state of a spherical
D2-brane with N D0-branes. The quadratic action for small fluctuations is shown
to be identical to that obtained from the dual abelian D2-brane DBI action,
using the non-commutative geometry of the fuzzy two-sphere. For some of the
fields, the linearized equations take the form of solvable Lam\'e equations. We
define a large-N DBI-scaling limit, with vanishing string coupling and string
length, and where the gauge theory coupling remains finite. In this limit, the
non-linearities of the DBI action survive in both the classical and the quantum
context, while massive open string modes and closed strings decouple. We
describe a critical radius where strong gauge coupling effects become
important. The size of the bound quantum ground state of multiple D0-branes
makes an intriguing appearance as the radius of the fuzzy sphere, where the
maximal angular momentum quanta become strongly coupled.Comment: 34 pages, Latex; v2: Minor correction in conformal transformation of
couplings, references adde
On The Problem of Particle Production in c=1 Matrix Model
We reconsider and analyze in detail the problem of particle production in the
time dependent background of matrix model where the Fermi sea drains away
at late time. In addition to the moving mirror method, which has already been
discussed in hep-th/0403169 and hep-th/0403275, we describe yet another method
of computing the Bogolubov coefficients which gives the same result. We
emphasize that these Bogolubov coefficients are approximately correct for small
value of the deformation parameter.
We also study the time evolution of the collective field theory stress-tensor
with a special point-splitting regularization. Our computations go beyond the
approximation of the previous treatments and are valid at large coordinate
distances from the boundary at a finite time and up-to a finite coordinate
distance from the boundary at late time. In this region of validity our
regularization produces a certain singular term that is precisely canceled by
the collective field theory counter term in the present background. The energy
and momentum densities fall off exponentially at large distance from the
boundary to the values corresponding to the static background. This clearly
shows that the radiated energy reaches the asymptotic region signaling the
space-time decay.Comment: 37 pages, 5 figures. Section 6 is modified to clarify main
accomplishments of the paper including a discussion comparing stress-tensor
analysis with those preexisted in literature. Other modifications include
minor changes in the text and addition of one reference. Version accepted for
publication in JHE
Charged AdS Black Holes and Catastrophic Holography
We compute the properties of a class of charged black holes in anti-de Sitter
space-time, in diverse dimensions. These black holes are solutions of
consistent Einstein-Maxwell truncations of gauged supergravities, which are
shown to arise from the inclusion of rotation in the transverse space. We
uncover rich thermodynamic phase structures for these systems, which display
classic critical phenomena, including structures isomorphic to the van der
Waals-Maxwell liquid-gas system. In that case, the phases are controlled by the
universal `cusp' and `swallowtail' shapes familiar from catastrophe theory. All
of the thermodynamics is consistent with field theory interpretations via
holography, where the dual field theories can sometimes be found on the world
volumes of coincident rotating branes.Comment: 19 pages, revtex, psfig, 6 multicomponent figures, typos, references
and a few remarks have been repaired, and adde