498 research outputs found
Second Order General Slow-Roll Power Spectrum
Recent combined results from the Wilkinson Microwave Anisotropy Probe (WMAP)
and Sloan Digital Sky Survey (SDSS) provide a remarkable set of data which
requires more accurate and general investigation. Here we derive formulae for
the power spectrum P(k) of the density perturbations produced during inflation
in the general slow-roll approximation with second order corrections. Also,
using the result, we derive the power spectrum in the standard slow-roll
picture with previously unknown third order corrections.Comment: 11 pages, 1 figure ; A typo in Eq. (38) is fixed ; References
expanded and a note adde
The Power Spectrum for a Multi-Component Inflaton to Second-Order Corrections in the Slow-Roll Expansion
We derive the power spectrum of the density perturbations
produced during inflation up to second-order corrections in the standard
slow-roll approximation for an inflaton with more than one degree of freedom.
We also present the spectral index up to first-order corrections including
previously missing terms, and the running to leading order.Comment: 11 pages, no figure. KAIST-TH 2002/0
Holography of Gravitational Action Functionals
Einstein-Hilbert (EH) action can be separated into a bulk and a surface term,
with a specific ("holographic") relationship between the two, so that either
can be used to extract information about the other. The surface term can also
be interpreted as the entropy of the horizon in a wide class of spacetimes.
Since EH action is likely to just the first term in the derivative expansion of
an effective theory, it is interesting to ask whether these features continue
to hold for more general gravitational actions. We provide a comprehensive
analysis of lagrangians of the form L=Q_a^{bcd}R^a_{bcd}, in which Q_a^{bcd} is
a tensor with the symmetries of the curvature tensor, made from metric and
curvature tensor and satisfies the condition \nabla_cQ^{abcd}=0, and show that
they share these features. The Lanczos-Lovelock lagrangians are a subset of
these in which Q^{abcd} is a homogeneous function of the curvature tensor. They
are all holographic, in a specific sense of the term, and -- in all these cases
-- the surface term can be interpreted as the horizon entropy. The
thermodynamics route to gravity, in which the field equations are interpreted
as TdS=dE+pdV, seems to have greater degree of validity than the field
equations of Einstein gravity itself. The results suggest that the holographic
feature of EH action could also serve as a new symmetry principle in
constraining the semiclassical corrections to Einstein gravity. The
implications are discussed.Comment: revtex 4; 17 pages; no figure
An Open Inflationary Model for Dimensional Reduction and its Effects on the Observable Parameters of the Universe
Assuming that higher dimensions existed in the early stages of the universe
where the evolution was inflationary, we construct an open, singularity-free,
spatially homogeneous and isotropic cosmological model to study the effects of
dimensional reduction that may have taken place during the early stages of the
universe. We consider dimensional reduction to take place in a stepwise manner
and interpret each step as a phase transition. By imposing suitable boundary
conditions we trace their effects on the present day parameters of the
universe.Comment: 5 pages, accepted for publication in Int. J. of Mod. Phys.
Time evolution of a non-singular primordial black hole
There is growing notion that black holes may not contain curvature
singularities (and that indeed nature in general may abhor such spacetime
defects). This notion could have implications on our understanding of the
evolution of primordial black holes (PBHs) and possibly on their contribution
to cosmic energy. This paper discusses the evolution of a non-singular black
hole (NSBH) based on a recent model [1]. We begin with a study of the
thermodynamic process of the black hole in this model, and demonstrate the
existence of a maximum horizon temperature T_{max}, corresponding to a unique
mass value. At this mass value the specific heat capacity C changes signs to
positive and the body begins to lose its black hole characteristics. With no
loss of generality, the model is used to discuss the time evolution of a
primordial black hole (PBH), through the early radiation era of the universe to
present, under the assumption that PBHs are non-singular. In particular, we
track the evolution of two benchmark PBHs, namely the one radiating up to the
end of the cosmic radiation domination era, and the one stopping to radiate
currently, and in each case determine some useful features including the
initial mass m_{f} and the corresponding time of formation t_{f}. It is found
that along the evolutionary history of the universe the distribution of PBH
remnant masses (PBH-RM) PBH-RMs follows a power law. We believe such a result
can be a useful step in a study to establish current abundance of PBH-MRs.Comment: To appear in Int. J. Mod. Phys.
Universes inside a black hole
We address the question of universes inside a black hole which is
described by a spherically symmetric globally regular solution to the Einstein
equations with a variable cosmological term , asymptotically
as with of the scale of symmetry
restoration. Global structure of spacetime contains an infinite sequence of
black and white holes, vacuum regular cores and asymptotically flat universes.
Regular core of a white hole models the initial stages of the
Universe evolution. In this model it starts from a nonsingular nonsimultaneous
big bang, which is followed by a Kasner-type anisotropic expansion. Creation of
a mass occurs mostly at the anisotropic stage of quick decay of the initial
vacuum energy. We estimate also the probability of quantum birth of baby
universes inside a black hole due to quantum instability of the de
Sitter vacuum.Comment: REVTEX, 9 pages, 13 figures. To appear in Physics Letters
The warm inflationary universe
In the past decade, the importance of dissipation and fluctuation to
inflationary dynamics has been realized and has led to a new picture of
inflation called warm inflation. Although these phenomena are common to
condensed matter systems, for inflation models their importance has only
recently started to be appreciated. The article describes the motivation for
these phenomenon during inflation and then examines their origins from first
principles quantum field theory treatments of inflation models. Cosmology today
is a data intensive field and this is driving theory to greater precision and
predictability. This opens the possibility to consider tests for detecting
observational signatures of dissipative processes, which will be discussed. In
addition it will be discussed how particle physics and cosmology are now
working in tandem to push the boundaries of our knowledge about fundamental
physics.Comment: 20 pages, 8 figure
Triple-horizon spherically symmetric spacetime and holographic principle
We present a family of spherically symmetric spacetimes, specified by the
density profile of a vacuum dark energy, which have the same global structure
as the de Sitter spacetime but the reduced symmetry which leads to a
time-evolving and spatially inhomogeneous cosmological term. It connects
smoothly two de Sitter vacua with different values of cosmological constant and
corresponds to anisotropic vacuum dark fluid defined by symmetry of its
stress-energy tensor which is invariant under the radial boosts. This family
contains a special class distinguished by dynamics of evaporation of a
cosmological horizon which evolves to the triple horizon with the finite
entropy, zero temperature, zero curvature, infinite positive specific heat, and
infinite scrambling time. Non-zero value of the cosmological constant in the
triple-horizon spacetime is tightly fixed by quantum dynamics of evaporation of
the cosmological horizon.Comment: Honorable Mentioned Essay - Gravity Research Foundation 2012;
submitted to Int. J. Mod. Phys.
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