1,054 research outputs found
Large-scale Perturbations from the Waterfall Field in Hybrid Inflation
We estimate large-scale curvature perturbations from isocurvature
fluctuations in the waterfall field during hybrid inflation, in addition to the
usual inflaton field perturbations. The tachyonic instability at the end of
inflation leads to an explosive growth of super-Hubble scale perturbations, but
they retain the steep blue spectrum characteristic of vacuum fluctuations in a
massive field during inflation. The power spectrum thus peaks around the
Hubble-horizon scale at the end of inflation. We extend the usual delta-N
formalism to include the essential role of these small fluctuations when
estimating the large-scale curvature perturbation. The resulting curvature
perturbation due to fluctuations in the waterfall field is second-order and the
spectrum is expected to be of order 10^{-54} on cosmological scales.Comment: 10 pages, 4 figures; v2 comments added on application of delta-N
formalism including Hubble scale fluctuation
Local Features with Large Spiky non-Gaussianities during Inflation
We provide a dynamical mechanism to generate localized features during
inflation. The local feature is due to a sharp waterfall phase transition which
is coupled to the inflaton field. The key effect is the contributions of
waterfall quantum fluctuations which induce a sharp peak on the curvature
perturbation which can be as large as the background curvature perturbation
from inflaton field. Due to non-Gaussian nature of waterfall quantum
fluctuations a large spike non-Gaussianity is produced which is narrowly peaked
at modes which leave the Hubble radius at the time of phase transition. The
large localized peaks in power spectrum and bispectrum can have interesting
consequences on CMB anisotropies.Comment: 22 pages, 2 figure
Contribution of the hybrid inflation waterfall to the primordial curvature perturbation
A contribution to the curvature perturbation will be generated
during the waterfall that ends hybrid inflation, that may be significant on
small scales. In particular, it may lead to excessive black hole formation. We
here consider standard hybrid inflation, where the tachyonic mass of the
waterfall field is much bigger than the Hubble parameter. We calculate
in the simplest case, and see why earlier calculations of
are incorrect.Comment: Simpler and more complete results, especiallly for delta N approac
Issues on Generating Primordial Anisotropies at the End of Inflation
We revisit the idea of generating primordial anisotropies at the end of
inflation in models of inflation with gauge fields. To be specific we consider
the charged hybrid inflation model where the waterfall field is charged under a
U(1) gauge field so the surface of end of inflation is controlled both by
inflaton and the gauge fields. Using delta N formalism properly we find that
the anisotropies generated at the end of inflation from the gauge field
fluctuations are exponentially suppressed on cosmological scales. This is
because the gauge field evolves exponentially during inflation while in order
to generate appreciable anisotropies at the end of inflation the spectator
gauge field has to be frozen and scale invariant. We argue that this is a
generic feature, that is, one can not generate observable anisotropies at the
end of inflation within an FRW background.Comment: V3: new references added, JCAP published versio
Curvature perturbation and waterfall dynamics in hybrid inflation
We investigate the parameter spaces of hybrid inflation model with special
attention paid to the dynamics of waterfall field and curvature perturbations
induced from its quantum fluctuations. Depending on the inflaton field value at
the time of phase transition and the sharpness of the phase transition
inflation can have multiple extended stages. We find that for models with mild
phase transition the induced curvature perturbation from the waterfall field is
too large to satisfy the COBE normalization. We investigate the model parameter
space where the curvature perturbations from the waterfall quantum fluctuations
vary between the results of standard hybrid inflation and the results obtained
here.Comment: V2: Minor revisions, references added, JCAP published versio
Stationary solutions for the parity-even sector of the CPT-even and Lorentz-covariance-violating term of the standard model extension
In this work, we focus on some properties of the parity-even sector of the
CPT-even electrodynamics of the standard model extension. We analyze how the
six non-birefringent terms belonging to this sector modify the static and
stationary classical solutions of the usual Maxwell theory. We observe that the
parity-even terms do not couple the electric and magnetic sectors (at least in
the stationary regime). The Green's method is used to obtain solutions for the
field strengths E and B at first order in the Lorentz- covariance-violating
parameters. Explicit solutions are attained for point-like and spatially
extended sources, for which a dipolar expansion is achieved. Finally, it is
presented an Earth-based experiment that can lead (in principle) to an upper
bound on the anisotropic coefficients as stringent as
Comment: 8 pages, revtex style, revised published version, to appear in EPJC
(2009
X-wave mediated instability of plane waves in Kerr media
Plane waves in Kerr media spontaneously generate paraxial X-waves (i.e.
non-dispersive and non-diffractive pulsed beams) that get amplified along
propagation. This effect can be considered a form of conical emission (i.e.
spatio-temporal modulational instability), and can be used as a key for the
interpretation of the out of axis energy emission in the splitting process of
focused pulses in normally dispersive materials. A new class of spatio-temporal
localized wave patterns is identified. X-waves instability, and nonlinear
X-waves, are also expected in periodical Bose condensed gases.Comment: 4 pages, 6 figure
Unravelling the genetics of non-random fertilization associated with gametic incompatibility
In the dairy industry, mate allocation is dependent on the producer’s breeding goals and the parents’ breeding values. The probability of pregnancy differs among sire-dam combinations, and the compatibility of a pair may vary due to the combination of gametic haplotypes. Under the hypothesis that incomplete incompatibility would reduce the odds of fertilization, and complete incompatibility would lead to a non-fertilizing or lethal combination, deviation from Mendelian inheritance expectations would be observed for incompatible pairs. By adding an interaction to a transmission ratio distortion (TRD) model, which detects departure from the Mendelian expectations, genomic regions linked to gametic incompatibility can be identified. This study aimed to determine the genetic background of gametic incompatibility in Holstein cattle. A total of 283,817 genotyped Holstein trios were used in a TRD analysis, resulting in 422 significant regions, which contained 2075 positional genes further investigated for network, overrepresentation, and guilt-by-association analyses. The identified biological pathways were associated with immunology and cellular communication and a total of 16 functional candidate genes were identified. Further investigation of gametic incompatibility will provide opportunities to improve mate allocation for the dairy cattle industry
Evolution of fNL to the adiabatic limit
We study inflationary perturbations in multiple-field models, for which zeta
typically evolves until all isocurvature modes decay--the "adiabatic limit". We
use numerical methods to explore the sensitivity of the nonlinear parameter fNL
to the process by which this limit is achieved, finding an appreciable
dependence on model-specific data such as the time at which slow-roll breaks
down or the timescale of reheating. In models with a sum-separable potential
where the isocurvature modes decay before the end of the slow-roll phase we
give an analytic criterion for the asymptotic value of fNL to be large. Other
examples can be constructed using a waterfall field to terminate inflation
while fNL is transiently large, caused by descent from a ridge or convergence
into a valley. We show that these two types of evolution are distinguished by
the sign of the bispectrum, and give approximate expressions for the peak fNL.Comment: v1: 25 pages, plus Appendix and bibliography, 6 figures. v2: minor
edits to match published version in JCA
- …