218 research outputs found
Quantum backreaction in evolving FLRW spacetimes
Quantum fluctuations of a nonminimally coupled scalar field in D-dimensional
homogeneous and isotropic background are calculated within the operator
formalism in curved models with time evolutions of the scale factor that allow
smooth transitions between contracting and expanding and between decelerating
and accelerating regimes. The coincident propagator is derived and used to
compute the one-loop backreaction from the scalar field. The inflationary
infrared divergences are absent in Bunch-Davies vacuum when taking into account
a preceding cosmological era or spatial curvature which can be either positive
or negative. It is found that asymptotically, the backreaction energy density
in the minimally coupled case grows logarithmically with the scale factor in
quasi-de Sitter space, and in a class of models decays in slow-roll inflation
and grows as a power-law during super-inflation. The backreaction increases
generically in a contracting phase or in the presence of a negative nonminimal
coupling. The effects of the coupling and renormalization scale upon the
quantum fluctuations together with the novel features due to nontrivial time
evolution and spatial curvature are clarified with exact solutions and
numerical examples.Comment: 23 pages, 6 figure
Born-Infeld type Gravity
Generalizations of gravitational Born-Infeld type lagrangians are
investigated. Phenomenological constraints (reduction to Einstein-Hilbert
action for small curvature, spin two ghost freedom and absence of Coulomb like
Schwarschild singularity) select one effective lagrangian whose dynamics is
dictated by the tensors g_{\mu\nu} and R_{\mu\nu\rho\sigma}(not R_{\mu\nu} or
the scalar R).Comment: 7 pages, 3 figures, revte
Metric-scalar gravity with torsion and the measurability of the non-minimal coupling
The "measurability" of the non-minimal coupling is discussed by considering
the correction to the Newtonian static potential in the semi-classical
approach. The coefficient of the "gravitational Darwin term" (GDT) gets
redefined by the non-minimal torsion-scalar couplings. Based on a similar
analysis of the GDT in the effective field theory approach to non-minimal
scalar we conclude that for reasonable values of the couplings the correction
is very small.Comment: 10 pages, LaTex. Accepted for publication in Mod. Phys. Lett.
Quantum effects in Acoustic Black Holes: the Backreaction
We investigate the backreaction equations for an acoustic black hole formed
in a Laval nozzle under the assumption that the motion of the fluid is
one-dimensional. The solution in the near-horizon region shows that as phonons
are (thermally) radiated the sonic horizon shrinks and the temperature
decreases. This contrasts with the behaviour of Schwarzschild black holes, and
is similar to what happens in the evaporation of (near-extremal)
Reissner-Nordstrom black holes (i.e. infinite evaporation time). Finally, by
appropriate boundary conditions the solution is extended in both the asymptotic
regions of the nozzle.Comment: 23 pages, latex, 1 figure; revised version, to appear in Phys. Rev.
Dynamics of Interacting Scalar Fields in Expanding Space-Time
The effective equation of motion is derived for a scalar field interacting
with other fields in a Friedman-Robertson-Walker background space-time. The
dissipative behavior reflected in this effective evolution equation is studied
both in simplified approximations as well as numerically. The relevance of our
results to inflation are considered both in terms of the evolution of the
inflaton field as well as its fluctuation spectrum. A brief examination also is
made of supersymmetric models that yield dissipative effects during inflation.Comment: 36 pages, 12 figures. Version published in the Physical Review
Bound states due to an accelerated mirror
We discuss an effect of accelerated mirrors which remained hitherto
unnoticed, the formation of a field condensate near its surface for massive
fields. From the view point of an observer attached to the mirror, this is
effect is rather natural because a gravitational field is felt there. The
novelty here is that since the effect is not observer dependent even inertial
observers will detect the formation of this condensate. We further show that
this localization is in agreement with Bekenstein's entropy bound.Comment: Final version to appear in PR
Quantization of massive scalar fields over static black string backgrounds
The renormalized mean value of the corresponding components of the
Energy-Momentum tensor for massive scalar fields coupled to an arbitrary
gravitational field configuration having cylindrical symmetry are analytically
evaluated using the Schwinger-DeWitt approximation, up to second order in the
inverse mass value. The general results are employed to explicitly derive
compact analytical expressions for the Energy-Momentum tensor in the particular
background of the Black-String spacetime. In the case of the Black String
considered in this work, we proof that a violation of the weak energy condition
occur at the horizon of the space-time for values of the coupling constant,
that include as particular cases the most interesting of minimal and conformal
coupling.Comment: 4 page
Semiclassical zero-temperature corrections to Schwarzschild spacetime and holography
Motivated by the quest for black holes in AdS braneworlds, and in particular
by the holographic conjecture relating 5D classical bulk solutions with 4D
quantum corrected ones, we numerically solve the semiclassical Einstein
equations (backreaction equations) with matter fields in the (zero temperature)
Boulware vacuum state. In the absence of an exact analytical expression for
in four dimensions we work within the s-wave approximation. Our
results show that the quantum corrected solution is very similar to
Schwarzschild till very close to the horizon, but then a bouncing surface for
the radial function appears which prevents the formation of an event horizon.
We also analyze the behavior of the geometry beyond the bounce, where a
curvature singularity arises. In the dual theory, this indicates that the
corresponding 5D static classical braneworld solution is not a black hole but
rather a naked singularity.Comment: 26 pages, 4 figures; revised version (title changed, conclusions
shortened), published as Phys. Rev. D73, 104023 (2006
Space-time correlations in inflationary spectra, a wave packet analysis
The inflationary mechanism of mode amplification predicts that the state of
each mode with a given wave vector is correlated to that of its partner mode
with the opposite vector. This implies nonlocal correlations which leave their
imprint on temperature anisotropies in the cosmic microwave background. Their
spatial properties are best revealed by using local wave packets. This analysis
shows that all density fluctuations giving rise the large scale structures
originate in pairs which are born near the reheating. In fact each local
density fluctuation is paired with an oppositely moving partner with opposite
amplitude. To obtain these results we first apply a ``wave packet
transformation'' with respect to one argument of the two point correlation
function. A finer understanding of the correlations is then reached by making
use of coherent states. The knowledge of the velocity field is required to
extract the contribution of a single pair of wave packets. Otherwise, there is
a two-folded degeneracy which gives three aligned wave packets arising from two
pairs. The applicability of these methods to observational data is briefly
discussed.Comment: revised version, accepted for publication in PRD ; the
complementarity and the usefullness of wave packet analysis have been
emphasized ; 32 pages, 6 figure
Canonical quantization of the relativistic particle in static spacetimes
We perform the canonical quantization of a relativistic spinless particle
moving in a curved and static spacetime. We show that the classical theory
already describes at the same time both particle and antiparticle. The analyses
involves time-depending constraints and we are able to construct the
two-particle Hilbert space. The requirement of a static spacetime is necessary
in order to have a well defined Schr\"odinger equation and to avoid problems
with vacuum instabilities. The severe ordering ambiguities we found are in
essence the same ones of the well known non-relativistic case.Comment: Revtex, 9 page
- …