4,045 research outputs found
Origin of the inflationary Universe
We give a consistent description of how the inflationary Universe emerges in
quantum cosmology. This involves two steps: Firstly, it is shown that a
sensible probability peak can be obtained from the cosmological wave function.
This is achieved by going beyond the tree level of the semiclassical expansion.
Secondly, due to decoherence interference terms between different semiclassical
branches are negligibly small. The results give constraints on the particle
content of a unified theory.Comment: LATEX, 6 pages, selected for honorable mention in the 1999 Essay
Competition of the Gravity Research Foundation. To appear in Mod. Phys. Lett.
Operator ordering and consistency of the wavefunction of the Universe
We demonstrate in the context of the minisuperspace model consisting of a
closed Friedmann-Robertson-Walker universe coupled to a scalar field that
Vilenkin's tunneling wavefunction can only be consistently defined for
particular choices of operator ordering in the Wheeler-DeWitt equation. The
requirement of regularity of the wavefunction has the particular consequence
that the probability amplitude, which has been used previously in the
literature in discussions of issues such as the prediction of inflation, is
likewise ill-defined for certain choices of operator ordering with Vilenkin's
boundary condition. By contrast, the Hartle-Hawking no-boundary wavefunction
can be consistently defined within these models, independently of operator
ordering. The significance of this result is discussed within the context of
the debate about the predictions of semiclassical quantum cosmology. In
particular, it is argued that inflation cannot be confidently regarded as a
"prediction" of the tunneling wavefunction, for reasons similar to those
previously invoked in the case of the no-boundary wavefunction. A synthesis of
the no-boundary and tunneling approaches is argued for.Comment: 9 pages, epsf, revTeX-3.1, 1 figure. In revised version (v2) a new
section etc with additional arguments increases the length of paper by 3
pages of Physical Review; several references added. v3: small typos fixe
Space for Both No-Boundary and Tunneling Quantum States of the Universe
At the minisuperspace level of homogeneous models, the bare probability for a
classical universe has a huge peak at small universes for the Hartle-Hawking
`no-boundary' wavefunction, in contrast to the suppression at small universes
for the `tunneling' wavefunction. If the probability distribution is cut off at
the Planck density (say), this suggests that the former quantum state is
inconsistent with our observations. For inhomogeneous models in which
stochastic inflation can occur, it is known that the idea of including a volume
factor in the observational probability distribution can lead to arbitrarily
large universes' being likely. Here this idea is shown to be sufficient to save
the Hartle-Hawking proposal even at the minisuperspace level (for suitable
inflaton potentials), by giving it enough space to be consistent with
observations.Comment: LaTeX, 20 pages, no figures, blank lines removed, page break inserte
Creation of a Compact Topologically Nontrivial Inflationary Universe
If inflation can occur only at the energy density V much smaller than the
Planck density, which is the case for many inflationary models based on string
theory, then the probability of quantum creation of a closed or an infinitely
large open inflationary universe is exponentially suppressed for all known
choices of the wave function of the universe. Meanwhile under certain
conditions there is no exponential suppression for creation of topologically
nontrivial compact flat or open inflationary universes. This suggests, contrary
to the standard textbook lore, that compact flat or open universes with
nontrivial topology should be considered a rule rather than an exception.Comment: 9 pages 2 figures, new materials and references adde
Gravitational waves from stochastic relativistic sources: primordial turbulence and magnetic fields
The power spectrum of a homogeneous and isotropic stochastic variable,
characterized by a finite correlation length, does in general not vanish on
scales larger than the correlation scale. If the variable is a divergence free
vector field, we demonstrate that its power spectrum is blue on large scales.
Accounting for this fact, we compute the gravitational waves induced by an
incompressible turbulent fluid and by a causal magnetic field present in the
early universe. The gravitational wave power spectra show common features: they
are both blue on large scales, and peak at the correlation scale. However, the
magnetic field can be treated as a coherent source and it is active for a long
time. This results in a very effective conversion of magnetic energy in
gravitational wave energy at horizon crossing. Turbulence instead acts as a
source for gravitational waves over a time interval much shorter than a Hubble
time, and the conversion into gravitational wave energy is much less effective.
We also derive a strong constraint on the amplitude of a primordial magnetic
field when the correlation length is much smaller than the horizon.Comment: Replaced with revised version accepted for publication in Phys Rev
Inflation from Susy quantum cosmology
We propose a realization of inverted hybrid inflation scenario in the context
of n=2 supersymmetric quantum cosmology. The spectrum of density fluctuations
is calculated in the de Sitter regimen as a function of the gravitino and the
Planck mass, and explicit forms for the wave function of the universe are found
in the WKB regimen for a FRW closed and flat universes.Comment: 9 pages, one figure, to appear in Phys. Rev.
On the Infrared Behavior of the Pressure in Thermal Field Theories
We study non-perturbatively, via the Schwinger-Dyson equations, the leading
infrared behavior of the pressure in the ladder approximation. This problem is
discussed firstly in the context of a thermal scalar field theory, and the
analysis is then extended to the Yang-Mills theory at high temperatures. Using
the Feynman gauge, we find a system of two coupled integral equations for the
gluon and ghost self-energies, which is solved analytically. The solutions of
these equations show that the contributions to the pressure, when calculated in
the ladder approximation, are finite in the infrared domain.Comment: 20 pages plus 4 figures available by request, IFUSP/P-100
Mutated Hilltop Inflation : A Natural Choice for Early Universe
We propose a model of inflation with a suitable potential for a single scalar
field which falls in the wide class of hilltop inflation. We derive the
analytical expressions for most of the physical quantities related to inflation
and show that all of them represent the true behavior as required from a model
of inflation. We further subject the results to observational verification by
formulating the theory of perturbations based on our model followed by an
estimation for the values of those observable parameters. Our model is found to
be in excellent agreement with observational data. Thus, the features related
to the model leads us to infer that this type of hilltop inflation may be a
natural choice for explaining the early universe.Comment: 22 pages, 7 figures, 2 tables. Matches published version in JCA
Inflation in minimal left-right symmetric model with spontaneous D-parity breaking
We present a simplest inflationary scenario in the minimal left-right
symmetric model with spontaneous D-parity breaking, which is a well motivated
particle physics model for neutrino masses. This leads us to connect the
observed anisotropies in the cosmic microwave background to the sub-eV neutrino
masses. The baryon asymmetry via the leptogenesis route is also discussed
briefly.Comment: (v1) 4 pages, 1 figure; (v2) typos corrected; (v3) title and abstract
changed, numerical estimates given, minor changes; (v4) 5 pages, relations
between the neutrino masses and the CMB fluctuations become more explicit,
miscellaneous changes, to appear in Physical Review
Braneworld effective action and origin of inflation
We construct braneworld effective action in two brane Randall-Sundrum model
and show that the radion mode plays the role of a scalar field localizing
essentially nonlocal part of this action. Non-minimal curvature coupling of
this field reflects the violation of AdS/CFT-correspondence for finite values
of brane separation. Under small detuning of the brane tension from the
Randall-Sundrum flat brane value, the radion mode can play the role of
inflaton. Inflationary dynamics corresponds to branes moving apart in the field
of repelling interbrane inflaton-radion potential and implies the existence
acceleration stage caused by remnant cosmological constant at late (large brane
separation) stages of evolution. We discuss the possibility of fixing initial
conditions in this model within the concept of braneworld creation from the
tunneling or no-boundary cosmological state, which formally replaces the
conventional moduli stabilization mechanism.Comment: 18 pages, LaTeX, the effective action form factor is corrected for
small separation between branes and new references are adde
- …