1,439 research outputs found
The Fate of SUSY Flat Directions and their Role in Reheating
We consider the role of supersymmetric flat directions in reheating the
Universe after inflation. One or more flat directions can develop large vevs
during inflation, which can potentially affect reheating by slowing down
scattering processes among inflaton decay products or by coming to dominate the
energy density of the Universe. Both effects occur only if flat directions are
sufficiently long-lived. The computation of their perturbative decay rate, and
a simple estimate of their nonperturbative decay have led to the conclusion
that this is indeed the case. In contrast, we show that flat directions can
decay quickly through nonperturbative channels in realistic models. The mass
matrix for MSSM excitations around flat directions has nondiagonal entries,
which vary with the phase of the (complex) flat directions. The quasi-periodic
motion of the flat directions results in a strong parametric resonance, leading
to the rapid depletion of the flat direction within its first few rotations.
This may preclude any significant role for the flat directions in reheating the
Universe after inflation in models in which the inflaton decays perturbatively.Comment: 30 pages, 6 .ps figures. Final published versio
Scalar-Scalar, Scalar-Tensor, and Tensor-Tensor Correlators from Anisotropic Inflation
We compute the phenomenological signatures of a model (Watanabe et al' 09) of
anisotropic inflation driven by a scalar and a vector field. The action for the
vector is U(1) invariant, and the model is free of ghost instabilities. A
suitable coupling of the scalar to the kinetic term of the vector allows for a
slow roll evolution of the vector vev, and hence for a prolonged anisotropic
expansion; this provides a counter example to the cosmic no hair conjecture. We
compute the nonvanishing two point correlation functions between physical modes
of the system, and express them in terms of power spectra with angular
dependence. The anisotropy parameter g_* for the scalar-scalar spectrum
(defined as in the Ackerman et al '07 parametrization) turns out to be negative
in the simplest realization of the model, which, therefore, cannot account for
the angular dependence emerged in some analyses of the WMAP data. A g_* of
order -0.1 is achieved when the energy of the vector is about 6-7 orders of
magnitude smaller than that of the scalar during inflation. For such values of
the parameters, the scalar-tensor correlation (which is in principle a
distinctive signature of anisotropic spaces) is smaller than the tensor-tensor
correlation
Production of Massive Fermions at Preheating and Leptogenesis
We present a complete computation of the inflaton decay into very massive
fermions during preheating. We show that heavy fermions are produced very
efficiently up to masses of order 10^{17}-10^{18} GeV; the accessible mass
range is thus even broader than the one for heavy bosons. We apply our findings
to the leptogenesis scenario, proposing a new version of it, in which the
massive right-handed neutrinos, responsible for the generation of the baryon
asymmetry, are produced during preheating. We also discuss other production
mechanisms of right-handed neutrinos in the early Universe, identifying the
neutrino mass parameters for which the observed baryon asymmetry is reproduced.Comment: 29 pages, 4 figure
Fermion production from preheating-amplified metric perturbations
We study gravitational creation of light fermions in the presence of
classical scalar metric perturbations about a flat Friedmann-Lemaitre-
Robertson-Walker (FLRW) background. These perturbations can be large during
preheating, breaking the conformal flatness of the background spacetime. We
compute numerically the total number of particles generated by the modes of the
metric perturbations which have grown sufficiently to become classical. In the
absence of inhomogeneities massless fermions are not gravitationally produced,
and then this effect may be relevant for abundance estimates of light
gravitational relics.Comment: 17 pages, 7 figures, accepted for publication in Nuclear Physics
Uma alternativa de uso da RENPAC para a EMBRAPA.
O NTIA tem se preocupado em experimentar alternativas para implementação de recursos para comunicação de dados que, de alguma maneira, viabilizem por parte das unidades descentralizadas, a colocação de informações de competência do centro de pesquisa disponíveis para acesso público. A RENPAC tem demonstrado ser um meio viável para colocação de bases de dados disponíveis a um grande número de usuários. Várias instituições já vem usando com sucesso, entre elas podemos citar o IBICT e o IBGE (veia anexo 1 - Bases de Dados disponíveis). A seguir faremos uma descrição das alternativas de uso da rede e como as unidades poderiam fazer uso da RENPAC. Veia o anexo III para uma noção de custos e alternativas de uso de cada modelo de acesso.bitstream/item/76665/1/CNPTIA-COM.TEC.-8806-88.pd
Post-Inflationary Gravitino Production Revisited
We revisit gravitino production following inflation. As a first step, we
review the standard calculation of gravitino production in the thermal plasma
formed at the end of post-inflationary reheating when the inflaton has
completely decayed. Next we consider gravitino production prior to the
completion of reheating, assuming that the inflaton decay products thermalize
instantaneously while they are still dilute. We then argue that instantaneous
thermalization is in general a good approximation, and also show that the
contribution of non-thermal gravitino production via the collisions of inflaton
decay products prior to thermalization is relatively small. Our final estimate
of the gravitino-to-entropy ratio is approximated well by a standard
calculation of gravitino production in the post-inflationary thermal plasma
assuming total instantaneous decay and thermalization at a time . Finally, in light of our calculations, we consider potential
implications of upper limits on the gravitino abundance for models of
inflation, with particular attention to scenarios for inflaton decays in
supersymmetric Starobinsky-like models.Comment: 34 pages, 7 figures, uses psfra
Equation of state and Beginning of Thermalization After Preheating
We study the out-of-equilibrium nonlinear dynamics of fields after
post-inflationary preheating. During preheating, the energy in the homogeneous
inflaton is exponentially rapidly transfered into highly occupied
out-of-equilibrium inhomogeneous modes, which subsequently evolve towards
equilibrium. The infrared modes excited during preheating evolve towards a
saturated distribution long before thermalization completes. We compute the
equation of state during and immediately after preheating. It rapidly evolves
towards radiation domination long before the actual thermal equilibrium is
established. The exact time of this transition is a non-monotonic function of
the coupling between the inflaton and the decay products, and it varies only
very weakly (around 10^(-35) s) as this coupling changes over several orders of
magnitude. This result is applied to refine the relation between the number of
efoldings N and the physical wavelength of perturbations generated during
inflation. We also discuss the implications for the theory of modulated
perturbations from preheating. We finally argue that many questions of the
thermal history of the universe should be addressed in terms of
pre-thermalization, illustrating this point with a calculation of perturbative
production of gravitinos immediately after chaotic inflation. We also highlight
the effects of three-legs inflaton interactions on the dynamics of preheating
and thermalization in an expanding universe.Comment: 15 pages, 13 figure
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