271 research outputs found
On the gravitational collapse in anti-de Sitter space-time
We study the semiclassical evolution of a self-gravitating thick shell in
Anti-de Sitter space-time. We treat the matter on the shell as made of
quantized bosons and evaluate the back-reaction of the loss of gravitational
energy which is radiated away as a non-adiabatic effect. A peculiar feature of
anti-de Sitter is that such an emission also occurs for large shell radius,
contrary to the asymptotically flat case.Comment: Changed to Elsevier style, 9 pages, 1 figure. Minor typos corrected.
Accepted for publication in Phys. Lett.
Particle Production in Tachyon Condensation
We study particle production in the tachyon condensation process as described
by different effective actions for the tachyon. By making use of invariant
operators, we are able to obtain exact results for the density of produced
particles, which is shown to depend strongly on the specific action. In
particular, the rate of particle production remains finite only for one of the
actions considered, hence confirming results previously appeared in the
literature.Comment: LaTeX, 6 pages, 3 figure
Thermodynamics of a collapsing shell in an expanding Universe
We describe the quasi-static collapse of a radiating, spherical shell of
matter in de Sitter space-time using a thermodynamical formalism. It is found
that the specific heat at constant area and other thermodynamical quantities
exhibit singularities related to phase transitions during the collapse.Comment: 9 pages, 2 figures, accepted for publication in Phys. Lett.
Minimal Composite Inflation
We investigate models in which the inflaton emerges as a composite field of a
four dimensional, strongly interacting and nonsupersymmetric gauge theory
featuring purely fermionic matter. We show that it is possible to obtain
successful inflation via non-minimal coupling to gravity, and that the
underlying dynamics is preferred to be near conformal. We discover that the
compositeness scale of inflation is of the order of the grand unified energy
scale.Comment: RevTeX 8 page
Trans-Planckian footprints in inflationary cosmology
We consider a minimum uncertainty vacuum choice at a fixed energy scale
Lambda as an effective description of trans-Planckian physics, and discuss its
implications for the linear perturbations of a massless scalar field in
power-law inflationary models. We find possible effects with a magnitude of
order H/\Lambda in the power spectrum, in analogy with previous results for
de-Sitter space-time.Comment: 4 pages, 1 figure, final version to appear in Physics Letters
Cosmological Unparticle Correlators
We introduce and study an extension of the correlator of unparticle matter
operators in a cosmological environment. Starting from FRW spaces we specialize
to a de Sitter spacetime and derive its inflationary power spectrum which we
find to be almost flat. We finally investigate some consequences of requiring
the existence of a unitary boundary conformal field theory in the framework of
the dS/CFT correspondence.Comment: 8 pages, 1 figure, to appear on Phys. Lett.
Gravitational Correction and Weak Gravity Conjecture
We consider the gravitational correction to the running of gauge coupling.
Weak gravity conjecture implies that the gauge theories break down when the
gravitational correction becomes greater than the contribution from gauge
theories. This observation can be generalized to non-Abelian gauge theories in
diverse dimensions and the cases with large extra dimensions.Comment: 8 pages; minor correction and refs adde
Thermal Unparticles: A New Form of Energy Density in the Universe
Unparticle \U with scaling dimension d_\U has peculiar thermal properties
due to its unique phase space structure. We find that the equation of state
parameter \omega_\U, the ratio of pressure to energy density, is given by
1/(2d_\U +1) providing a new form of energy in our universe. In an expanding
universe, the unparticle energy density \rho_\U(T) evolves dramatically
differently from that for photons. For d_\U >1, even if \rho_\U(T_D) at a
high decoupling temperature is very small, it is possible to have a large
relic density \rho_\U(T^0_\gamma) at present photon temperature ,
large enough to play the role of dark matter. We calculate and
\rho_\U(T^0_\gamma) using photon-unparticle interactions for illustration.Comment: 5 pages; v3, journal version
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
Signatures of black holes at the LHC
Signatures of black hole events at CERN's Large Hadron Collider are
discussed. Event simulations are carried out with the Fortran Monte Carlo
generator CATFISH. Inelasticity effects, exact field emissivities, color and
charge conservation, corrections to semiclassical black hole evaporation,
gravitational energy loss at formation and possibility of a black hole remnant
are included in the analysis.Comment: 13 pages, 7 figure
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