425 research outputs found
Perturbations in k-inflation
We extend the theory of cosmological perturbations to the case when the
``matter'' Lagrangian is an arbitrary function of the scalar field and its
first derivatives. In particular, this extension provides a unified description
of known cases such as the usual scalar field and the hydrodynamical perfect
fluid. In addition, it applies to the recently proposed k-inflation, which is
driven by non-minimal kinetic terms in the Lagrangian. The spectrum of quantum
fluctuations for slow-roll and power law k-inflation is calculated. We find,
for instance, that the usual ``consistency relation'' between the tensor
spectral index and the relative amplitude of scalar and tensor perturbations is
modified. Thus, at least in principle, k-inflation is phenomenologically
distinguishable from standard inflation.Comment: 12 pages, LaTe
Supercurvaton
We discuss observational consequences of the curvaton scenario, which
naturally appears in the context of the simplest model of chaotic inflation in
supergravity. The non-gaussianity parameter f_NL in this scenario can take
values in the observationally interesting range from O(10) to O(100). These
values may be different in different parts of the universe. The regions where
f_NL is particularly large form a curvaton web resembling a net of thick domain
walls, strings, or global monopoles.Comment: 17 pages, 1 figure. Non-perturbative effects related to
non-gaussianity in the curvaton scenario are discussed, some references are
added. This is the version accepted in JCA
Spectroscopy of the quantum black hole
We develop the idea that, in quantum gravity where the horizon fluctuates, a
black hole should have a discrete mass spectrum with concomitant line emission.
Simple arguments fix the spacing of the lines, which should be broad but
unblended. Assuming uniformity of the matrix elements for quantum transitions
between near levels, we work out the probabilities for the emission of a
specified series of quanta and the intensities of the spectral lines. The
thermal character of the radiation is entirely due to the degeneracy of the
levels, the same degeneracy that becomes manifest as black hole entropy. One
prediction is that there should be no lines with wavelength of order the black
hole size or larger. This makes it possible to test quantum gravity with black
holes well above Planck scale.Comment: RevTeX, 9 page
Inflation and String Cosmology
Inflationary theory is already 20 years old, and it is impossible to describe
all of its versions and implications in a short talk. I will concentrate on
several subjects which I believe to be most important. First of all, I will
give a brief review of the first versions of inflationary theory, from
Starobinsky model to new inflation. Then I will describe chaotic inflation, the
theory of quantum fluctuations and density perturbations, the theory of eternal
inflation, and recent observational data. In the second part of the talk I will
discuss the recently proposed ekpyrotic scenario and argue that in its present
form it does not provide a viable alternative to inflation.Comment: 22 pages, contribution to the Proceedings of PASCOS 200
Inflationary Theory and Alternative Cosmology
Recently Hollands and Wald argued that inflation does not solve any of the
major cosmological problems. We explain why we disagree with their arguments.
They also proposed a new speculative mechanism of generation of density
perturbations. We show that in their scenario the inhomogeneities responsible
for the large scale structure observed today were generated at an epoch when
the energy density of the hot universe was 10^{95} times greater than the
Planck density. The only way to avoid this problem is to assume that there was
a stage of inflation in the early universe.Comment: 17 pages, 1 fig, a discussion of a canonical measure of probability
of inflation is adde
Constraining the Inflationary Equation of State
We explore possible constraints on the inflationary equation state: p=w\rho.
While w must be close to -1 for those modes that contribute to the observed
power spectrum, for those modes currently out of experimental reach, the
constraints on w are much weaker, with only w<-1/3 as an a priori requirement.
We find, however, that limits on the reheat temperature and the inflationary
energy scale constrain w further, though there is still ample parameter space
for a vastly different (accelerating) equation of state between the end of
quasi-de Sitter inflation and the beginning of the radiation-dominated era. In
the event that such an epoch of acceleration could be observed, we review the
consequences for the primordial power spectrum.Comment: 12 pages, 2 figur
Optimal dataset combining in f_nl constraints from large scale structure in an idealised case
We consider the problem of optimal weighting of tracers of structure for the
purpose of constraining the non-Gaussianity parameter f_NL. We work within the
Fisher matrix formalism expanded around fiducial model with f_NL=0 and make
several simplifying assumptions. By slicing a general sample into infinitely
many samples with different biases, we derive the analytic expression for the
relevant Fisher matrix element. We next consider weighting schemes that
construct two effective samples from a single sample of tracers with a
continuously varying bias. We show that a particularly simple ansatz for
weighting functions can recover all information about f_NL in the initial
sample that is recoverable using a given bias observable and that simple
division into two equal samples is considerably suboptimal when sampling of
modes is good, but only marginally suboptimal in the limit where Poisson errors
dominate.Comment: 6 pages, 5 figures; v2: comment on weighting for PS determination,
fixed a couple of typos; v3: revised, matches version accepted by JCA
Density Perturbations in the Ekpyrotic Scenario
We study the generation of density perturbations in the ekpyrotic scenario
for the early universe, including gravitational backreaction. We expose
interesting subtleties that apply to both inflationary and ekpyrotic models.
Our analysis includes a detailed proposal of how the perturbations generated in
a contracting phase may be matched across a `bounce' to those in an expanding
hot big bang phase. For the physical conditions relevant to the ekpyrotic
scenario, we re-obtain our earlier result of a nearly scale-invariant spectrum
of energy density perturbations. We find that the perturbation amplitude is
typically small, as desired to match observation.Comment: 36 pages, compressed and RevTex file, one postscript figure file.
Minor typographical and numerical errors corrected, discussion added. This
version to appear in Physical Review
Imprints of Short Distance Physics On Inflationary Cosmology
We analyze the impact of certain modifications to short distance physics on
the inflationary perturbation spectrum. For the specific case of power-law
inflation, we find distinctive -- and possibly observable -- effects on the
spectrum of density perturbations.Comment: Revtex 4, 3 eps figs, 4 page
Computing the Primordial Power Spectra Directly
The tree order power spectra of primordial inflation depend upon the
norm-squared of mode functions which oscillate for early times and then freeze
in to constant values. We derive simple differential equations for the power
spectra, that avoid the need to numerically simulate the physically irrelevant
phases of the mode functions. We also derive asymptotic expansions which should
be valid until a few e-foldings before first horizon crossing, thereby avoiding
the need to evolve mode functions from the ultraviolet over long periods of
inflation.Comment: 11 pages, uses LaTex2
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