2,186 research outputs found
Decoherence without Dissipation
That decoherence can take place in the presence of energy conservation seems
to be a poorly known fact. That lack of knowledge has for example bedevilled
the discussion of the "black hole information" problem. I present a simple
model which illustrates such energy free decoherence.Comment: 4 pages-- To appear in Phil Trans Roy Soc in special issue on
Decoherence, ed. A. Haga
Long-wavelength metric backreactions in slow-roll inflation
We examine the importance of second order corrections to linearized
cosmological perturbation theory in an inflationary background, taken to be a
spatially flat FRW spacetime. The full second order problem is solved in the
sense that we evaluate the effect of the superhorizon second order corrections
on the inhomogeneous and homogeneous modes of the linearized flucuations. These
second order corrections enter in the form of a {\it cumulative} contribution
from {\it all} of their Fourier modes. In order to quantify their physical
significance we study their effective equation of state by looking at the
perturbed energy density and isotropic pressure to second order. We define the
energy density (isotropic pressure) in terms of the (averaged) eigenvalues
associated with timelike (spacelike) eigenvectors of a total stress energy for
the metric and matter fluctuations. Our work suggests that that for many
parameters of slow-roll inflation, the second order contributions to these
energy density and pressures may dominate over the first order effects for the
case of super-Hubble evolution. These results hold in our choice of first and
second order coordinate conditions however we also argue that other
`reasonable` coordinate conditions do not alter the relative importance of the
second order terms. We find that these second order contributions approximately
take the form of a cosmological constant in this coordinate gauge, as found by
others using effective methods.Comment: Submitted to Phys. Rev.
On the origin of the particles in black hole evaporation
We present an analytic derivation of Hawking radiation for an arbitrary
(spatial) dispersion relation as a model for ultra-high energy
deviations from general covariance. It turns out that the Hawking temperature
is proportional to the product of the group and phase
velocities evaluated at the frequency of the outgoing radiation far
away, which suggests that Hawking radiation is basically a low-energy
phenomenon. Nevertheless, a group velocity growing too fast at ultra-short
distances would generate Hawking radiation at ultra-high energies
(``ultra-violet catastrophe'') and hence should not be a realistic model for
the microscopic structure of quantum gravity.Comment: 4 pages RevTe
On the Universality of the Hawking Effect
Addressing the question of whether the Hawking effect depends on degrees of
freedom at ultra-high (e.g., Planckian) energies/momenta, we propose three
rather general conditions on these degrees of freedom under which the Hawking
effect is reproduced to lowest order. As a generalization of Corley's results,
we present a rather general model based on non-linear dispersion relations
satisfying these conditions together with a derivation of the Hawking effect
for that model. However, we also demonstrate counter-examples, which do not
appear to be unphysical or artificial, displaying strong deviations from
Hawking's result. Therefore, whether real black holes emit Hawking radiation
remains an open question and could give non-trivial information about Planckian
physics.
PACS: 04.70.Dy, 04.62.+v, 04.60.-m, 04.20.Cv.Comment: 11 pages RevTeX, 6 figure
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