546 research outputs found
Leptogenesis, Z' bosons, and the reheating temperature of the Universe
We study the impact for leptogenesis of new U(1) gauge bosons coupled to the
heavy Majorana neutrinos. They can significantly enhance the efficiency of
thermal scenarios in the weak washout regime as long as the Z' masses are not
much larger than the reheating temperature (), with the
highest efficiencies obtained for Z' bosons considerably heavier than the heavy
neutrinos (). We show how the allowed region of the parameter
space is modified in the presence of a Z' and we also obtain the minimum
reheating temperature that is required for these models to be successful.Comment: 14 pages, 6 figures; One figure added, discussion on the reheating
temperature extende
Neutrinos and the matter-antimatter asymmetry in the Universe
The discovery of neutrino oscillations provides a solid evidence for nonzero
neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny
constitutes a puzzling problem in particle physics. From the theoretical
viewpoint, the smallness of neutrino masses can be elegantly explained through
the seesaw mechanism. Another challenging issue for particle physics and
cosmology is the explanation of the matter-antimatter asymmetry observed in
Nature. Among the viable mechanisms, leptogenesis is a simple and
well-motivated framework. In this talk we briefly review these aspects, making
emphasis on the possibility of linking neutrino physics to the cosmological
baryon asymmetry originated from leptogenesis.Comment: 8 pages, 1 table, 1 figure; Based on talk given at the Symposium
STARS2011, 1 - 4 May 2011, Havana, Cuba; to be published in the Proceeding
Addendum to Finite-size effects on multibody neutrino exchange
The interaction energy of the neutrons due to massless neutrino exchange in a
neutron star has recently been proved, using an effective theory, to be
extremely small and infrared-safe. Our comment here is of conceptual order: two
approaches to compute the total interaction energy density have recently been
proposed. Here, we study the connection between these two approaches. From CP
invariance, we argue that the resulting interaction energy has to be even in
the parameter , which expresses the static neutrino
potential created by a neutron medium of density .Comment: Latex file (Revtex), 9 pages, 1 figure, one reference change
Minimal Lepton Flavour Violation and Leptogenesis with exclusively low-energy CP Violation
We study the implications of a successful leptogenesis within the framework
of Minimal Lepton Flavour Violation combined with radiative resonant
leptogenesis and the PMNS matrix being the only source of CP violation, which
can be obtained provided flavour effects are taken into account. We find that
the right amount of the baryon asymmetry of the universe can be generated under
the conditions of a normal hierarchy of the light neutrino masses, a
non-vanishing Majorana phase, sin(theta_{13})>0.13 and m_{nu,lightest}<0.04 eV.
If this is fulfilled, we find strong correlations among ratios of charged LFV
processes.Comment: published in JHEP, small change
Leptogenesis with exclusively low-energy CP Violation in the Context of Minimal Lepton Flavour Violation
We analyze lepton flavour violation (LFV) and the generation of the observed
baryon-antibaryon asymmetry of the Universe (BAU) within a generalized minimal
lepton flavour violation framework with three quasi-degenerate heavy Majorana
neutrinos. The BAU which is obtained through radiative resonant leptogenesis
can successfully be generated widely independent of the Majorana scale in this
scenario and flavour effects are found to be relevant. Then we discuss the
specific case in which CP violation is exclusively present at low-energies (a
real R matrix) in the flavour sensitive temperature regime. Successful
leptogenesis in this case leads to strong constraints on low-energy neutrino
parameters.Comment: Contrubution to the proceedings of the EPS HEP 2007 conference,
Manchester (UK). 3 pages, 3 figure
Lepton flavor violation in low-scale seesaw models: SUSY and non-SUSY contributions
Taking the supersymmetric inverse seesaw mechanism as the explanation for
neutrino oscillation data, we investigate charged lepton flavor violation in
radiative and 3-body lepton decays as well as in neutrinoless
conversion in muonic atoms. In contrast to former studies, we take into account
all possible contributions: supersymmetric as well as non-supersymmetric. We
take CMSSM-like boundary conditions for the soft supersymmetry breaking
parameters. We find several regions where cancellations between various
contributions exist, reducing the lepton flavor violating rates by an order of
magnitude compared to the case where only the dominant contribution is taken
into account. This is in particular important for the correct interpretation of
existing data as well as for estimating the reach of near future experiments
where the sensitivity will be improved by one to two orders of magnitude.
Moreover, we demonstrate that ratios like BR()/BR() can be used to determine whether the supersymmetric contributions
dominate over the and contributions or vice versa.Comment: 75 pages, 7 figures. v3: references and comments added. Matches
published versio
Infrared Behavior of High-Temperature QCD
The damping rate \gamma_t(p) of on-shell transverse gluons with ultrasoft
momentum p is calculated in the context of next-to-leading-order
hard-thermal-loop-summed perturbation of high-temperature QCD. It is obtained
in an expansion to second order in p. The first coefficient is recovered but
that of order p^2 is found divergent in the infrared. Divergences from
light-like momenta do also occur but are circumvented. Our result and method
are critically discussed, particularly regarding a Ward identity obtained in
the literature. When enforcing the equality between \gamma_t(0) and
\gamma_l(0), a rough estimate of the magnetic mass is obtained. Carrying a
similar calculation in the context of scalar quantum electrodynamics shows that
the early ultrasoft-momentum expansion we make has little to do with the
infrared sensitivity of the result.Comment: REVTEX4, 55 page
A Two-Singlet Model for Light Cold Dark Matter
We extend the Standard Model by adding two gauge-singlet %
-symmetric scalar fields that interact with visible matter only through the
Higgs particle. One is a stable dark matter WIMP, and the other one undergoes a
spontaneous breaking of the symmetry that opens new channels for the dark
matter annihilation, hence lowering the mass of the WIMP. We study the effects
of the observed dark matter relic abundance on the annihilation cross section
and find that in most regions of the parameters space, light dark matter is
viable. We also compare the elastic scattering cross-section of our dark matter
candidate off nucleus with existing (CDMSII and XENON100) and projected
(SuperCDMS and XENON1T) experimental exclusion bounds. We find that most of the
allowed mass range for light dark matter will be probed by the projected
sensitivity of XENON1T experiment.Comment: 30 pages, 17 figure
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