405 research outputs found
Primordial Density Perturbation in Effective Loop Quantum Cosmology
It is widely believed that quantum field fluctuation in an inflating
background creates the primeval seed perturbation which through subsequent
evolution leads to the observed large scale structure of the universe. The
standard inflationary scenario produces scale invariant power spectrum quite
generically but it produces, unless fine tuned, too large amplitude for the
primordial density perturbation than observed. Using similar techniques it is
shown that loop quantum cosmology induced inflationary scenario can produce
scale invariant power spectrum as well as small amplitude for the primordial
density perturbation without fine tuning. Further its power spectrum has a
qualitatively distinct feature which is in principle falsifiable by observation
and can distinguish it from the standard inflationary scenario.Comment: 33 pages, revtex4, few typos and a confusing notation changed;
several clarifications, references added, to appear in CQ
Loop quantum gravity corrections to gravitational wave dispersion
Cosmological tensor perturbations equations are derived for Hamiltonian
cosmology based on Ashtekar's formulation of general relativity, including
typical quantum gravity effects in the Hamiltonian constraint as they are
expected from loop quantum gravity. This translates to corrections of the
dispersion relation for gravitational waves. The main application here is the
preservation of causality which is shown to be realized due to the absence of
anomalies in the effective constraint algebra used.Comment: 27 page
New coordinates for a simpler canonical derivation of the Hawking effect
In order to achieve a Hamiltonian-based canonical derivation of the Hawking
effect, one usually faces multiple hurdles. Firstly, the spacetime foliation
using Schwarzschild time does not lead to hyper-surfaces which are always
spacelike. Secondly, the null coordinates which are frequently used in
covariant approach, do not lead to a true matter Hamiltonian. Recently, an
exact canonical derivation was presented using the so-called near-null
coordinates. However, there too one faces the difficulty of having to deal with
non-vanishing matter diffeomorphism generator as the spatial decomposition
involves a non-zero shift vector. Here we introduce a new set of coordinates
which allows one to perform an exact canonical derivation of Hawking effect
without having to deal with matter diffeomorphism generator.Comment: 6 pages, 1 figure, revtex
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