1,727 research outputs found
Quantum cosmology of the brane universe
We canonically quantize the dynamics of the brane universe embedded into the
five-dimensional Schwarzschild-anti-deSitter bulk space-time. We show that in
the brane-world settings the formulation of the quantum cosmology, including
the problem of initial conditions, is conceptually more simple than in the
3+1-dimensional case. The Wheeler-deWitt equation is a finite-difference
equation. It is exactly solvable in the case of a flat universe and we find the
ground state of the system. The closed brane universe can be created as a
result of decay of the bulk black hole.Comment: 4 pages, revte
Dark matter component decaying after recombination: lensing constraints with Planck data
It has been recently suggested~\cite{Berezhiani:2015yta} that emerging
tension between cosmological parameter values derived in high-redshift (CMB
anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can
be reconciled in a model which contains subdominant fraction of dark matter
decaying after recombination. We check the model against the CMB Planck data.
We find that lensing of the CMB anisotropies by the large-scale structure gives
strong extra constraints on this model, limiting the fraction as at
2\, confidence level. However, investigating the combined data set of
CMB and conflicting low- measurements, we obtain that the model with
\% exhibits better fit (by 1.5-3\, depending on the
lensing priors) compared to that of the concordance CDM cosmological
model.Comment: 5 pages, 4 figures; v2: journal version, pages++, figures+
Non-Thermal Production of Dangerous Relics in the Early Universe
Many models of supersymmetry breaking, in the context of either supergravity
or superstring theories, predict the presence of particles with weak scale
masses and Planck-suppressed couplings. Typical examples are the scalar moduli
and the gravitino. Excessive production of such particles in the early Universe
destroys the successful predictions of nucleosynthesis. In particular, the
thermal production of these relics after inflation leads to a bound on the
reheating temperature, T_{RH} < 10^9 GeV. In this paper we show that the
non-thermal generation of these dangerous relics may be much more efficient
than the thermal production after inflation. Scalar moduli fields may be
copiously created by the classical gravitational effects on the vacuum state.
Consequently, the new upper bound on the reheating temperature is shown to be,
in some cases, as low as 100 GeV. We also study the non-thermal production of
gravitinos in the early Universe, which can be extremely efficient and overcome
the thermal production by several orders of magnitude, in realistic
supersymmetric inflationary models.Comment: 21 pages, 4 Postscript figure
Thermal and Non-Thermal Production of Gravitinos in the Early Universe
The excessive production of gravitinos in the early universe destroys the
successful predictions of nucleosynthesis. The thermal generation of gravitinos
after inflation leads to the bound on the reheating temperature, T_{RH}< 10^9
GeV. However, it has been recently realized that the non-thermal generation of
gravitinos in the early universe can be extremely efficient and overcome the
thermal production by several orders of magnitude, leading to much tighter
constraints on the reheating temperature. In this paper, we first investigate
some aspects of the thermal production of gravitinos, taking into account that
in fact reheating is not instantaneous and inflation is likely to be followed
by a prolonged stage of coherent oscillations of the inflaton field. We then
proceed by further investigating the non-thermal generation of gravitinos,
providing the necessary tools to study this process in a generic time-dependent
background with any number of superfields. We also present the first numerical
results regarding the non-thermal generation of gravitinos in particular
supersymmetric models.Comment: 31 pages, 7 Postscript figures. New references adde
The Cosmological Moduli Problem and Preheating
Many models of supersymmetry breaking, in the context of either supergravity
or superstring theories, predict the presence of particles with
Planck-suppressed couplings and masses around the weak scale. These particles
are generically called moduli. The excessive production of moduli in the early
Universe jeopardizes the successful predictions of nucleosynthesis. In this
paper we show that the efficient generation of these dangerous relics is an
unescapable consequence of a wide variety of inflationary models which have a
preheating stage. Moduli are generated as coherent states in a novel way which
differs from the usual production mechanism during parametric resonance. The
corresponding limits on the reheating temperature are often very tight and more
severe than the bound of 10^9 GeV coming from the production of moduli via
thermal scatterings during reheating.Comment: 17 pages, 5 Postscript figures, corrected some typo
GUT baryogenesis after preheating: numerical study of the production and decay of X-bosons
We perform a fully non-linear calculation of the production of supermassive
Grand Unified Theory (GUT) bosons during preheating, taking into account
the fact that they are unstable with a decay width . We show that
parametric resonance does not develop if is larger than about
. We compute the nonthermal number density of superheavy bosons
produced in the preheating phase and demonstrate that the observed baryon
asymmetry may be explained by GUT baryogenesis after preheating if
is smaller than about .Comment: 13 pages, LaTeX file, 3 figures. One reference added and minor
change
- …