46,384 research outputs found
Impact of radiative corrections on sterile neutrino scenarios
In sterile neutrino scenarios, radiative corrections induce mass splittings
proportional to the top Yukawa coupling, in contrast to the three active
neutrino case where the induced splittings are proportional to the tau Yukawa
coupling. In view of this, we have analyzed the stability of the four-neutrino
schemes favored by oscillation experiments, consisting in two pairs of nearly
degenerate neutrinos separated by the LSND gap. Requiring compatibility with
the measurements of the abundances of primordial elements produced in Big Bang
Nucleosynthesis, we find that when the heaviest pair corresponds to the solar
neutrinos (mainly an admixture of nu_e - nu_s) the natural mass splitting is
3-5 orders of magnitude larger than the observed one, discrediting the scenario
from a theoretical point of view. On the contrary, the scheme where the
heaviest pair corresponds to the atmospheric neutrinos (mainly an admixture of
nu_mu - nu_tau) is safe from radiative corrections due to the small sterile
component of these mass eigenstates.Comment: 14 pages, LaTeX, 2 figures. Discussion enlarged, references added and
typos correcte
The Vector Curvaton
We analyze a massive vector field with a non-canonical kinetic term in the
action, minimally coupled to gravity, where the mass and kinetic function of
the vector field vary as functions of time during inflation. The vector field
is introduced following the same idea of a scalar curvaton, which must not
affect the inflationary dynamics since its energy density during inflation is
negligible compared to the total energy density in the Universe. Using this
hypothesis, the vector curvaton will be solely responsible for generating the
primordial curvature perturbation \zeta. We have found that the spectra of the
vector field perturbations are scale-invariant in superhorizon scales due to
the suitable choice of the time dependence of the kinetic function and the
effective mass during inflation. The preferred direction, generated by the
vector field, makes the spectrum of \zeta depend on the wavevector, i.e. there
exists statistical anisotropy in \zeta. This is discussed principally in the
case where the mass of the vector field increases with time during inflation,
where it is possible to find a heavy field (M >> H) at the end of inflation,
making the particle production be practically isotropic; thus, the longitudinal
and transverse spectra are nearly the same order which in turn causes that the
statistical anisotropy generated by the vector field is within the
observational bounds.Comment: LaTex file in Aipproc style, 6 pages, no figures. Prepared for the
conference proceedings of the IX Mexican School of the DGFM-SMF: Cosmology
for the XXIst Century. This work is entirely based on Refs. [23-26] and is
the result of Andres A. Navarro's MSc thesi
Consistency in NLO analyses of inclusive and semi-inclusive polarized DIS data
We perform a detailed study of the consistency between different sets of
polarized deep inelastic scattering data and theory, from the standpoint of a
next to leading order QCD global analysis, and following the criteria proposed
by Collins and Pumplin. In face of recent suggestions that challenge the usual
assumption about parent parton spin independence of unpolarized fragmentation
functions, we specially focus on polarized semi-inclusive data.Comment: 17 pages, 5 figure
Constraints on gluon polarization in the nucleon at NLO accuracy
We compare constraints on the gluon polarization in the nucleon obtained in
next to leading order global QCD fits to polarized deep inelastic scattering
data with those coming from observables more directly linked to the gluon
polarization, such as the double spin asymmetry measured by Phenix at RHIC, and
high-pT hadron production studied by COMPASSComment: 4 pages, 3 figures, 1 tabl
- âŠ