3,410 research outputs found

### Prethermalization Production of Dark Matter

At the end of inflation, the inflaton field decays into an initially
nonthermal population of relativistic particles which eventually thermalize. We
consider the production of dark matter from this relativistic plasma, focusing
on the prethermal phase. We find that for a production cross section
$\sigma(E)\sim E^n$ with $n> 2$, the present dark matter abundance is produced
during the prethermal phase of its progenitors. For $n\le 2$, entropy
production during reheating makes the nonthermal contribution to the present
dark matter abundance subdominant compared to that produced thermally. As
specific examples, we verify that the nonthermal contribution is irrelevant for
gravitino production in low scale supersymmetric models ($n=0$) and is dominant
for gravitino production in high scale supersymmetry models ($n=6$).Comment: 12 pages, 4 figure

### Enhancement of the Dark Matter Abundance Before Reheating: Applications to Gravitino Dark Matter

In the first stages of inflationary reheating, the temperature of the
radiation produced by inflaton decays is typically higher than the commonly
defined reheating temperature $T_{RH} \sim (\Gamma_\phi M_P)^{1/2}$ where
$\Gamma_\phi$ is the inflaton decay rate. We consider the effect of particle
production at temperatures at or near the maximum temperature attained during
reheating. We show that the impact of this early production on the final
particle abundance depends strongly on the temperature dependence of the
production cross section. For $\langle \sigma v \rangle \sim T^n/M^{n+2}$, and
for $n < 6$, any particle produced at $T_{\rm max}$ is diluted by the later
generation of entropy near $T_{RH}$. This applies to cases such as gravitino
production in low scale supersymmetric models ($n=0$) or NETDM models of dark
matter ($n=2$). However, for $n\ge6$ the net abundance of particles produced
during reheating is enhanced by over an order of magnitude, dominating over the
dilution effect. This applies, for instance to gravitino production in high
scale supersymmetry models where $n=6$.Comment: 16 pages, 5 figure

### Gravitational Wave Emission from Collisions of Compact Scalar Solitons

We numerically investigate the gravitational waves generated by the head-on
collision of equal-mass, self-gravitating, real scalar field solitons
(oscillatons) as a function of their compactness $\mathcal{C}$. We show that
there exist three different possible outcomes for such collisions: (1) an
excited stable oscillaton for low $\mathcal{C}$, (2) a merger and formation of
a black-hole for intermediate $\mathcal{C}$, and (3) a pre-merger collapse of
both oscillatons into individual black-holes for large $\mathcal{C}$. For (1),
the excited, aspherical oscillaton continues to emit gravitational waves. For
(2), the total energy in gravitational waves emitted increases with
compactness, and possesses a maximum which is greater than that from the merger
of a pair of equivalent mass black-holes. The initial amplitudes of the
quasi-normal modes in the post-merger ring-down in this case are larger than
that of corresponding mass black-holes -- potentially a key observable to
distinguish black-hole mergers with their scalar mimics. For (3), the
gravitational wave output is indistinguishable from a similar mass,
black-hole--black-hole merger.Comment: 8 Pages, 8 figures, movies :
https://www.youtube.com/playlist?list=PLSkfizpQDrcahgvc5TvBk5qtXAzkSyHP

### No-Scale Inflation

Supersymmetry is the most natural framework for physics above the TeV scale,
and the corresponding framework for early-Universe cosmology, including
inflation, is supergravity. No-scale supergravity emerges from generic string
compactifications and yields a non-negative potential, and is therefore a
plausible framework for constructing models of inflation. No-scale inflation
yields naturally predictions similar to those of the Starobinsky model based on
$R + R^2$ gravity, with a tilted spectrum of scalar perturbations: $n_s \sim
0.96$, and small values of the tensor-to-scalar perturbation ratio $r < 0.1$,
as favoured by Planck and other data on the cosmic microwave background (CMB).
Detailed measurements of the CMB may provide insights into the embedding of
inflation within string theory as well as its links to collider physics.Comment: Invited contribution to the forthcoming Classical and Quantum Gravity
focus issue on "Planck and the fundamentals of cosmology". 22 pages, 7
figures, uses psfra

### A No-Scale Inflationary Model to Fit Them All

The magnitude of B-mode polarization in the cosmic microwave background as
measured by BICEP2 favours models of chaotic inflation with a quadratic $m^2
\phi^2/2$ potential, whereas data from the Planck satellite favour a small
value of the tensor-to-scalar perturbation ratio $r$ that is highly consistent
with the Starobinsky $R + R^2$ model. Reality may lie somewhere between these
two scenarios. In this paper we propose a minimal two-field no-scale
supergravity model that interpolates between quadratic and Starobinsky-like
inflation as limiting cases, while retaining the successful prediction $n_s
\simeq 0.96$.Comment: 25 pages, 12 figure

### Phenomenological Aspects of No-Scale Inflation Models

We discuss phenomenological aspects of no-scale supergravity inflationary
models motivated by compactified string models, in which the inflaton may be
identified either as a K\"ahler modulus or an untwisted matter field, focusing
on models that make predictions for the scalar spectral index $n_s$ and the
tensor-to-scalar ratio $r$ that are similar to the Starobinsky model. We
discuss possible patterns of soft supersymmetry breaking, exhibiting examples
of the pure no-scale type $m_0 = B_0 = A_0 = 0$, of the CMSSM type with
universal $A_0$ and $m_0 \ne 0$ at a high scale, and of the mSUGRA type with
$A_0 = B_0 + m_0$ boundary conditions at the high input scale. These may be
combined with a non-trivial gauge kinetic function that generates gaugino
masses $m_{1/2} \ne 0$, or one may have a pure gravity mediation scenario where
trilinear terms and gaugino masses are generated through anomalies. We also
discuss inflaton decays and reheating, showing possible decay channels for the
inflaton when it is either an untwisted matter field or a K\"ahler modulus.
Reheating is very efficient if a matter field inflaton is directly coupled to
MSSM fields, and both candidates lead to sufficient reheating in the presence
of a non-trivial gauge kinetic function.Comment: 41 pages, 6 figure

### Calculations of Inflaton Decays and Reheating: with Applications to No-Scale Inflation Models

We discuss inflaton decays and reheating in no-scale Starobinsky-like models
of inflation, calculating the effective equation-of-state parameter, $w$,
during the epoch of inflaton decay, the reheating temperature, $T_{\rm reh}$,
and the number of inflationary e-folds, $N_*$, comparing analytical
approximations with numerical calculations. We then illustrate these results
with applications to models based on no-scale supergravity and motivated by
generic string compactifications, including scenarios where the inflaton is
identified as an untwisted-sector matter field with direct Yukawa couplings to
MSSM fields, and where the inflaton decays via gravitational-strength
interactions. Finally, we use our results to discuss the constraints on these
models imposed by present measurements of the scalar spectral index $n_s$ and
the tensor-to-scalar perturbation ratio $r$, converting them into constraints
on $N_*$, the inflaton decay rate and other parameters of specific no-scale
inflationary models.Comment: 33 pages, 14 figure

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