5,653 research outputs found
A new study on the emission of EM waves from large EAS
A method used in locating the core of individual cosmic ray showers is described. Using a microprocessor-based detecting system, the density distribution and hence, energy of each detected shower was estimated
Microprocessor-based single particle calibration of scintillation counter
A microprocessor-base set-up is fabricated and tested for the single particle calibration of the plastic scintillator. The single particle response of the scintillator is digitized by an A/D converter, and a 8085 A based microprocessor stores the pulse heights. The digitized information is printed. Facilities for CRT display and cassette storing and recalling are also made available
Identifying the curvaton within MSSM
We consider inflaton couplings to MSSM flat directions and the thermalization
of the inflaton decay products, taking into account gauge symmetry breaking due
to flat direction condensates. We then search for a suitable curvaton candidate
among the flat directions, requiring an early thermally induced start for the
flat direction oscillations to facilitate the necessary curvaton energy density
dominance. We demonstrate that the supersymmetry breaking -term is crucial
for achieving a successful curvaton scenario. Among the many possible
candidates, we identify the flat direction as a viable MSSM
curvaton.Comment: 9 pages. Discussion on the evaporation of condensate added, final
version published in JCA
Supersymmetric Thermalization and Quasi-Thermal Universe: Consequences for Gravitinos and Leptogenesis
Motivated by our earlier paper \cite{am}, we discuss how the infamous
gravitino problem has a natural built in solution within supersymmetry.
Supersymmetry allows a large number of flat directions made up of {\it gauge
invariant} combinations of squarks and sleptons. Out of many at least {\it one}
generically obtains a large vacuum expectation value during inflation. Gauge
bosons and Gauginos then obtain large masses by virtue of the Higgs mechanism.
This makes the rate of thermalization after the end of inflation very small and
as a result the Universe enters a {\it quasi-thermal phase} after the inflaton
has completely decayed. A full thermal equilibrium is generically established
much later on when the flat direction expectation value has substantially
decareased. This results in low reheat temperatures, i.e., , which are compatible with the stringent bounds arising from the
big bang nucleosynthesis. There are two very important implications: the
production of gravitinos and generation of a baryonic asymmetry via
leptogenesis during the quasi-thermal phase. In both the cases the abundances
depend not only on an effective temperature of the quasi-thermal phase (which
could be higher, i.e., ), but also on the state of equilibrium
in the reheat plasma. We show that there is no ``thermal gravitino problem'' at
all within supersymmetry and we stress on a need of a new paradigm based on a
``quasi-thermal leptogenesis'', because in the bulk of the parameter space the
{\it old} thermal leptogenesis cannot account for the observed baryon
asymmetry.Comment: 53 pages. Final version published in JCA
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
A-term inflation and the smallness of the neutrino masses
The smallness of the neutrino masses may be related to inflation. The minimal
supersymmetric Standard Model (MSSM) with small Dirac neutrino masses already
has all the necessary ingredients for a successful inflation. In this model the
inflaton is a gauge-invariant combination of the right-handed sneutrino, the
slepton, and the Higgs field, which generate a flat direction suitable for
inflation if the Yukawa coupling is small enough. In a class of models, the
observed microwave background anisotropy and the tilted power spectrum are
related to the neutrino masses.Comment: 13 pages, 1 figure, uses JHEP3.cls, minor modifications, final
version accepted for publication in JCA
Separable and non-separable multi-field inflation and large non-Gaussianity
In this paper we provide a general framework based on formalism to
estimate the cosmological observables pertaining to the cosmic microwave
background radiation for non-separable potentials, and for generic \emph{end of
inflation} boundary conditions. We provide analytical and numerical solutions
to the relevant observables by decomposing the cosmological perturbations along
the curvature and the isocurvature directions, \emph{instead of adiabatic and
entropy directions}. We then study under what conditions large bi-spectrum and
tri-spectrum can be generated through phase transition which ends inflation. In
an illustrative example, we show that large and
can be obtained for the case of separable and
non-separable inflationary potentials.Comment: 21 pages, 6 figure
Coexisting orders in the quarter-filled Hubbard chain with elastic deformations
The electronic properties of the quarter-filled extended
Peierls-Holstein-Hubbard model that includes lattice distortions and molecular
deformations are investigated theoretically using the bosonization approach. We
predict the existence of a wide variety of charge-elastic phases depending of
the values of the Peierls and Holstein couplings. We include the effect of the
Peierls deformation in the nearest-neighbor repulsion V, that may be present in
real materials where Coulomb interactions depend strongly on the distance, and
we show that the phase diagram changes substantially for large V when this term
is taken into account.Comment: 6 pages, 3 figure
Affleck-Dine baryogensis in large extra dimensions
Baryogenesis in the models where the fundamental scale is as low as TeV in
the context of large extra dimensions is a challenging problem. The requirement
for the departure from thermal equilibrium necessarily ties any low scale
baryogenesis with that of a successful inflationary model which automatically
provides the out of equilibrium condition after the end of inflation. However,
it is also noticeable that in these models the reheat temperature of the
Universe is strongly constrained from the overproduction of Kaluza-Klein modes,
which enforces a very low reheat temperature. In this paper we describe a
possible scenario for baryogenesis which has a similar characteristics of an
Affleck-Dine field. We notice that in order to have an adequate baryon to
entropy ratio one requires to promote this Affleck-Dine field to reside in the
bulk.Comment: 4 pages, LaTeX file, no figures. Important improvements on the paper.
Conclusions unchanged. References adde
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