1,054 research outputs found
A model for fluctuating inflaton coupling: (s)neutrino induced adiabatic perturbations and non-thermal leptogenesis
We discuss an unique possibility of generating adiabatic density
perturbations and leptogenesis from the spatial fluctuations of the inflaton
decay rate. The key assumption is that the initial isocurvature perturbations
are created in the right handed sneutrino sector during inflation which is then
converted into adiabatic perturbations when the inflaton decays. We discuss
distinct imprints on the cosmic micro wave background radiation, which can
distinguish non-thermal versus thermal leptogenesis.Comment: 4 pages, version to be published in PR
Numerical simulations of fragmentation of the Affleck-Dine condensate
We present numerical simulations of fragmentation of the Affleck-Dine
condensate in two spatial dimensions. We argue analytically that the final
state should consist of both Q-balls and anti-Q-balls in a state of maximum
entropy, with most of the balls small and relativistic. Such a behaviour is
found in simulations on a 100x100 lattice with cosmologically realistic
parameter values. During fragmentation process, we observe filament-like
texture in the spatial distribution of charge. The total charge in Q-balls is
found to be almost equal to the charge in anti-Q-balls and typically orders of
magnitude larger than charge asymmetry. Analytical considerations indicate
that, apart from geometrical factors, the results of the simulated two
dimensional case should apply also to the fully realistic three dimensional
case.Comment: 28 pages, 39 figure
Solitosynthesis of Q-balls
We study the formation of Q-balls in the early universe, concentrating on
potentials with a cubic or quartic attractive interaction. Large Q-balls can
form via solitosynthesis, a process of gradual charge accretion, provided some
primordial charge assymetry and initial ``seed'' Q-balls exist. We find that
such seeds are possible in theories in which the attractive interaction is of
the form , with a light ``Higgs'' mass. Condensate formation
and fragmentation is only possible for masses in the sub-eV range;
these Q-balls may survive untill present.Comment: 9 pages, 1 figur
Effect of Background Evolution on the Curvaton Non-Gaussianity
We investigate how the background evolution affects the curvature
perturbations generated by the curvaton, assuming a curvaton potential that may
deviate slightly from the quadratic one, and parameterizing the background
fluid density as \rho\propto a^{-\alpha}, where a is the scale factor, and
\alpha depends on the background fluid. It turns out that the more there is
deviation from the quadratic case, the more pronounced is the dependence of the
curvature perturbation on \alpha. We also show that the background can have a
significant effect on the nonlinearity parameters f_NL and g_NL. As an example,
if at the onset of the curvaton oscillation there is a dimension 6 contribution
to the potential at 5 % level and the energy fraction of the curvaton to the
total one at the time of its decay is at 1 %, we find variations \Delta f_NL
\sim \mathcal{O}(10) and \Delta g_NL \sim \mathcal{O}(10^4) between matter and
radiation dominated backgrounds. Moreover, we demonstrate that there is a
relation between f_NL and g_NL that can be used to probe the form of the
curvaton potential and the equation of state of the background fluid.Comment: 14 pages, 8 figure
Scale-dependence of Non-Gaussianity in the Curvaton Model
We investigate the scale-dependence of f_NL in the self-interacting curvaton
model. We show that the scale-dependence, encoded in the spectral index
n_{f_NL}, can be observable by future cosmic microwave background observations,
such as CMBpol, in a significant part of the parameter space of the model. We
point out that together with information about the trispectrum g_NL, the
self-interacting curvaton model parameters could be completely fixed by
observations. We also discuss the scale-dependence of g_NL and its implications
for the curvaton model, arguing that it could provide a complementary probe in
cases where the theoretical value of n_{f_NL} is below observational
sensitivity.Comment: 14 pages, 5 figures, Eq.(10) correcte
Determination of the freeze-out temperature by the isospin thermometer
The high-resolution spectrometer FRS at GSI Darmstadt provides the full
isotopic and kinematical identification of fragmentation residues in
relativistic heavy-ion collisions. Recent measurements of the isotopic
distribution of heavy projectile fragments led to a very surprising new
physical finding: the residue production does not lose the memory of the N/Z of
the projectile ending up in a universal de-excitation corridor; an ordering of
the residues in relation to the neutron excess of the projectile has been
observed. These unexpected features can be interpreted as a new manifestation
of multifragmentation. We have found that at the last stage of the reaction the
temperature of the big clusters subjected to evaporation is limited to a
universal value. The thermometer to measure this limiting temperature is the
neutron excess of the residues.Comment: 8 pages, 6 figures, corrected some misprints in the abstract, to be
published in "Yadernaya Fizika" as a proceeding of the "VII International
School Seminar on Heavy-Ion Phyics", Dubna (Russia), May 27 - June 1, 200
Production of Neutron-rich Heavy Residues and the Freeze-out Temperature in the Fragmentation of Relativistic 238U Projectiles Determined by the Isospin Thermometer
Isotope yields of heavy residues produced in collisions of 238U with lead at
1AGeV show indications for a simultaneous break-up process. From the average
N-over-Z ratio of the final residues up to Z = 70, the average limiting
temperature of the break-up configuration at freeze out was determined to T
approximately 5 MeV using the isospin-thermometer method. Consequences for the
understanding of other phenomena in highly excited nuclear systems are
discussed.Comment: 22 pages, 9 figures, accepted by Nucl. Phys.
Q-ball formation: Obstacle to Affleck-Dine baryogenesis in the gauge-mediated SUSY breaking ?
We consider the Affleck-Dine baryogenesis comprehensively in the minimal
supersymmetric standard model with gauge-mediated supersymmetry breaking.
Considering the high temperature effects, we see that the Affleck-Dine field is
naturally deformed into the form of the Q ball. In the natural scenario where
the initial amplitude of the field and the A-terms are both determined by the
nonrenormalizable superpotential, we obtain only very a narrow allowed region
in the parameter space in order to explain the baryon number of the universe
for the case that the Q-ball formation occurs just after baryon number
production. Moreover, most of the parameter sets suited have already been
excluded by current experiments. We also find new situations in which the
Q-ball formation takes place rather late compared with baryon number creation.
This situation is more preferable, since it allows a wider parameter region for
naturally consistent scenarios, although it is still difficult to realize in
the actual cosmological scenario.Comment: 27 pages, RevTeX, 21 postscript figures included. The version to be
publishe
Non-metric chaotic inflation
We consider inflation within the context of what is arguably the simplest
non-metric extension of Einstein gravity. There non-metricity is described by a
single graviscalar field with a non-minimal kinetic coupling to the inflaton
field , parameterized by a single parameter . We discuss the
implications of non-metricity for chaotic inflation and find that it
significantly alters the inflaton dynamics for field values , dramatically changing the qualitative behaviour in this regime.
For potentials with a positive slope non-metricity imposes an upper bound on
the possible number of e-folds. For chaotic inflation with a monomial
potential, the spectral index and the tensor-to-scalar ratio receive small
corrections dependent on the non-metricity parameter. We also argue that
significant post-inflationary non-metricity may be generated.Comment: 7 pages, 1 figur
Non-Gaussianity from Instant and Tachyonic Preheating
We study non-Gaussianity in two distinct models of preheating: instant and
tachyonic. In instant preheating non-Gaussianity is sourced by the local terms
generated through the coupled perturbations of the two scalar fields. We find
that the non-Gaussianity parameter is given by ,
where is a coupling constant, so that instant preheating is unlikely to be
constrained by WMAP or Planck. In the case of tachyonic preheating
non-Gaussianity arises solely from the instability of the tachyon matter and is
found to be large. We find that for single field inflation the present WMAP
data implies a bound on the scale of tachyonic
instability. We argue that the tachyonic preheating limits are useful also for
string-motivated inflationary models.Comment: 12 pages, 1 figure, additional discussion, improved constraint on the
scale of tachyonic preheatin
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