2,917 research outputs found
Non-linear metric perturbation enhancement of primordial gravitational waves
We present the evolution of the full set of Einstein equations during
preheating after inflation. We study a generic supersymmetric model of hybrid
inflation, integrating fields and metric fluctuations in a 3-dimensional
lattice. We take initial conditions consistent with Eintein's constraint
equations. The induced preheating of the metric fluctuations is not large
enough to backreact onto the fields, but preheating of the scalar modes does
affect the evolution of vector and tensor modes. In particular, they do enhance
the induced stochastic background of gravitational waves during preheating,
giving an energy density in general an order of magnitude larger than that
obtained by evolving the tensors fluctuations in an homogeneous background
metric. This enhancement can improve the expectations for detection by planned
gravitational waves observatories.Comment: 5 pages, 4 eps figures, matches Phys. Rev. Lett. versio
Constraining New Physics with D meson decays
Latest Lattice results on form factors evaluation from first principles
show that the standard model (SM) branching ratios prediction for the leptonic
decays and the semileptonic SM branching ratios of the
and meson decays are in good agreement with the world average
experimental measurements. It is possible to disprove New Physics hypothesis or
find bounds over several models beyond the SM. Using the observed leptonic and
semileptonic branching ratios for the D meson decays, we performed a combined
analysis to constrain non standard interactions which mediate the transition. This is done either by a model independent way through
the corresponding Wilson coefficients or in a model dependent way by finding
the respective bounds over the relevant parameters for some models beyond the
standard model. In particular, we obtain bounds for the Two Higgs Doublet Model
Type-II and Type III, the Left-Right model, the Minimal Supersymmetric Standard
Model with explicit R-Parity violation and Leptoquarks. Finally, we estimate
the transverse polarization of the lepton in the decay and we found it
can be as high as .Comment: 28 pages, 8 figures, 3 tables. Improved and extended analysis with
updated form factors from Lattice QC
A Study of the Effects on Dropout Migrant Students, Relative as to How it Affects Their Lives
A survey was conducted of 15 migrant students and their parents. Students and their parents were interviewed with a list of questions. These students attended two secondary and two senior high schools in Yakima, Washington. It was determined that because of continued migration of families, students get behind in their studies and therefore lose interest because of the frustration and low self-esteem these students feel. Families still migrate from Yakima, Washington, to other states in search of seasonal work, farm labor is still a way of life for migrant families from schools in the Yakima School District. It\u27s sad to say, but many migrant families will never know any other way of life, except farm labor. Most of the migrant families from schools in Yakima are of Mexican decent
Scattering processes could distinguish Majorana from Dirac neutrinos
It is well known that Majorana neutrinos have a pure axial neutral current
interaction while Dirac neutrinos have the standard vector-axial interaction.
In spite of this crucial difference, usually Dirac neutrino processes differ
from Majorana processes by a term proportional to the neutrino mass, resulting
in almost unmeasurable observations of this difference. In the present work we
show that once the neutrino polarization evolution is considered, there are
clear differences between Dirac and Majorana scattering on electrons. The
change of polarization can be achieved in astrophysical environments with
strong magnetic fields. Furthermore, we show that in the case of unpolarized
neutrino scattering onto polarized electrons, this difference can be relevant
even for large values of the neutrino energy.Comment: 12 pages, 5 figure
Non-linear Preheating with Scalar Metric Perturbations
We have studied preheating of field perturbations in a 3-dimensional lattice
including the effect of scalar metric perturbations, in two generic models of
inflation: chaotic inflation with a quartic potential, and standard hybrid
inflation. We have prepared the initial state for the classical evolution of
the system with vanishing vector and tensor metric perturbations, consistent
with the constraint equations, the energy and momentum constraints. The
non-linear evolution inevitably generates vector and tensor modes, and this
reflects on how well the constraint equations are fulfilled during the
evolution. The induced preheating of the scalar metric perturbations is not
large enough to backreact onto the fields, but it could affect the evolution of
vector and tensor modes. This is the case in hybrid inflation for some values
of the coupling and the height of potential . For example with
GeV, preheating of scalar perturbations is such that
their source term in the evolution equation of tensor and vector becomes
comparable to that of the field anisotropic stress.Comment: 15 pages, 12 eps figure
The scalar sector in the Myers-Pospelov model
We construct a perturbative expansion of the scalar sector in the
Myers-Pospelov model, up to second order in the Lorentz violating parameter and
taking into account its higher-order time derivative character. This expansion
allows us to construct an hermitian positive-definite Hamiltonian which
provides a correct basis for quantization. Demanding that the modified normal
frequencies remain real requires the introduction of an upper bound in the
magnitude |k| of the momentum, which is a manifestation of the effective
character of the model. The free scalar propagator, including the corresponding
modified dispersion relations, is also calculated to the given order, thus
providing the starting point to consider radiative corrections when
interactions are introduced.Comment: Published in AIP Conf.Proc.977:214-223,200
QFT results for neutrino oscillations and New Physics
The CP asymmetry in neutrino oscillations, assuming new physics at production
and/or detection processes, is analyzed. We compute this CP asymmetry using the
standard quantum field theory within a general new physics scenario that may
generate new sources of CP and flavor violation. Well known results for the CP
asymmetry are reproduced in the case of V -A operators, and additional
contributions from new physics operators are derived. We apply this formalism
to SUSY extensions of the Standard Model where the contributions from new
operators could produce a CP asymmetry observable in the next generation of
neutrino experiments.Comment: 6 pages, 3 figures, version to be published in Phys.Rev.
Limits to differences in active and passive charges
We explore consequences of a hypothetical difference between active charges,
which generate electric fields, and passive charges, which respond to them. A
confrontation to experiments using atoms, molecules, or macroscopic matter
yields limits on their fractional difference at levels down to 10^-21, which at
the same time corresponds to an experimental confirmation of Newtons third law.Comment: 6 pages Revtex. To appear in Phys. Rev.
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