89 research outputs found
F-term inflation in Superstring Theories
A supersymmetric inflationary stage dominated by an -term has the problem
that the flatness of the potential is spoiled by supergravity corrections, that
is the slow-roll parameter gets contributions of order unity. We show
that in -term inflationary models based on strings there is natural way of
obtaining small values of . This happens in models of hybrid inflation
based on orbifold constructions, in which a modulus field is responsible
for the large value of the potential during inflation, and a second field
with appropriate modular weight is responsible for the roll-over. We
illustrate the mechanism with a model in which the inflaton potential is
provided by gaugino condensation, leading to succesful inflation.Comment: 9 pages, LaTe
Gamma-Ray Constraints on Maximum Cosmogenic Neutrino Fluxes and UHECR Source Evolution Models
The dip model assumes that the ultra-high energy cosmic rays (UHECRs) above
10 eV consist exclusively of protons and is consistent with the spectrum
and composition measure by HiRes. Here we present the range of cosmogenic
neutrino fluxes in the dip-model which are compatible with a recent
determination of the extragalactic very high energy (VHE) gamma-ray diffuse
background derived from 2.5 years of Fermi/LAT data. We show that the largest
fluxes predicted in the dip model would be detectable by IceCube in about 10
years of observation and are within the reach of a few years of observation
with the ARA project. In the incomplete UHECR model in which protons are
assumed to dominate only above 10 eV, the cosmogenic neutrino fluxes
could be a factor of 2 or 3 larger. Any fraction of heavier nuclei in the UHECR
at these energies would reduce the maximum cosmogenic neutrino fluxes. We also
consider here special evolution models in which the UHECR sources are assumed
to have the same evolution of either the star formation rate (SFR), or the
gamma-ray burst (GRB) rate, or the active galactic nuclei (AGN) rate in the
Universe and found that the last two are disfavored (and in the dip model
rejected) by the new VHE gamma-ray background.Comment: 19 pages, 16 figures, JHEP3.cls needed to typese
Do solar neutrinos decay?
Despite the fact that the solar neutrino flux is now well-understood in the
context of matter-affected neutrino mixing, we find that it is not yet possible
to set a strong and model-independent bound on solar neutrino decays. If
neutrinos decay into truly invisible particles, the Earth-Sun baseline defines
a lifetime limit of \tau/m \agt 10^{-4} s/eV. However, there are many
possibilities which must be excluded before such a bound can be established.
There is an obvious degeneracy between the neutrino lifetime and the mixing
parameters. More generally, one must also allow the possibility of active
daughter neutrinos and/or antineutrinos, which may partially conceal the
characteristic features of decay. Many of the most exotic possibilities that
presently complicate the extraction of a decay bound will be removed if the
KamLAND reactor antineutrino experiment confirms the large-mixing angle
solution to the solar neutrino problem and measures the mixing parameters
precisely. Better experimental and theoretical constraints on the B
neutrino flux will also play a key role, as will tighter bounds on absolute
neutrino masses. Though the lifetime limit set by the solar flux is weak, it is
still the strongest direct limit on non-radiative neutrino decay. Even so,
there is no guarantee (by about eight orders of magnitude) that neutrinos from
astrophysical sources such as a Galactic supernova or distant Active Galactic
Nuclei will not decay.Comment: Very minor corrections, corresponds to published versio
Classical Nambu-Goldstone fields
It is shown that a Nambu-Goldstone (NG) field may be coherently produced by a
large number of particles in spite of the fact that the NG bosons do not couple
to flavor conserving scalar densities like . If a flavor
oscillation process takes place the phases of the pseudo-scalar or flavor
violating densities of different particles do not necessarily cancel each
other. The NG boson gets a macroscopic source whenever the total (spontaneously
broken) quantum number carried by the source particles suffers a net increase
or decrease in time. If the lepton numbers are spontaneously broken such
classical NG (majoron) fields may significantly change the neutrino oscillation
processes in stars pushing the observational capabilities of neutrino-majoron
couplings down to GeV.Comment: 11 pages, updated, to appear in PR
A review of the discovery reach of directional Dark Matter detection
Cosmological observations indicate that most of the matter in the Universe is Dark Matter. Dark Matter in the form of Weakly Interacting Massive Particles (WIMPs) can be detected directly, via its elastic scattering off target nuclei. Most current direct detection experiments only measure the energy of the recoiling nuclei. However, directional detection experiments are sensitive to the direction of the nuclear recoil as well. Due to the Sun’s motion with respect to the Galactic rest frame, the directional recoil rate has a dipole feature, peaking around the direction of the Solar motion. This provides a powerful tool for demonstrating the Galactic origin of nuclear recoils and hence unambiguously detecting Dark Matter. Furthermore, the directional recoil distribution depends on the WIMP mass, scattering cross section and local velocity distribution. Therefore, with a large number of recoil events it will be possible to study the physics of Dark Matter in terms of particle and astrophysical properties. We review the potential of directional detectors for detecting and characterizing WIMPs
Supernova Bounds on Majoron-emitting decays of light neutrinos
Neutrino masses arising from the spontaneous violation of ungauged
lepton-number are accompanied by a physical Goldstone boson, generically called
Majoron. In the high-density supernova medium the effects of Majoron-emitting
neutrino decays are important even if they are suppressed in vacuo by small
neutrino masses and/or small off-diagonal couplings. We reconsider the
influence of these decays on the neutrino signal of supernovae in the light of
recent Super-Kamiokande data on solar and atmospheric neutrinos. We find that
majoron-neutrino coupling constants in the range 3\times 10^{-7}\lsim g\lsim
2\times 10^{-5} or g \gsim 3 \times 10^{-4} are excluded by the observation
of SN1987A. Then we discuss the potential of Superkamiokande and the Sudbury
Neutrino Observatory to detect majoron neutrino interactions in the case of a
future galactic supernova. We find that these experiments could probe majoron
neutrino interactions with improved sensitivity.Comment: 28 pages, 5 figure
Doubly charged Higgs from - scattering in the 3-3-1 Model
We studied the production and signatures of doubly charged Higgs bosons in
the process , where is a heavy lepton,
at the International Linear Collider (ILC) and CERN Linear Collider
(CLIC). The intermediate photons are given by the Weizscker-Williams
and laser backscattering distributions. We found that significant signatures
are obtained by bremsstrahlung and backward Comptom scattering of laser. A
clear signal can be obtained for doubly charged Higgs bosons, doubly charged
gauge bosons and heavy leptons
Baryogenesis, Electric Dipole Moments and Dark Matter in the MSSM
We study the implications for electroweak baryogenesis (EWB) within the
minimal supersymmetric Standard Model (MSSM) of present and future searches for
the permanent electric dipole moment (EDM) of the electron, for neutralino dark
matter, and for supersymmetric particles at high energy colliders. We show that
there exist regions of the MSSM parameter space that are consistent with both
present two-loop EDM limits and the relic density and that allow for successful
EWB through resonant chargino and neutralino processes at the electroweak phase
transition. We also show that under certain conditions the lightest neutralino
may be simultaneously responsible for both the baryon asymmetry and relic
density. We give present constraints on chargino/neutralino-induced EWB implied
by the flux of energetic neutrinos from the Sun, the prospective constraints
from future neutrino telescopes and ton-sized direct detection experiments, and
the possible signatures at the Large Hadron Collider and International Linear
Collider.Comment: 32 pages, 10 figures; version to appear on JHE
Neutrino masses through see-saw mechanism in 3-3-1 models
Some years ago it was shown by Ma that in the context of the electroweak
standard model there are, at the tree level, only three ways to generate small
neutrino masses by the see-saw mechanism via one effective dimension-five
operator. Here we extend this approach to 3-3-1 chiral models showing that in
this case there are several dimension-five operators and we also consider their
tree level realization.Comment: RevTex, 7 pages and 4 .eps figures. Version published in Phys. Rev.
D. with a change in the titl
The little flavons
Fermion masses and mixing matrices can be described in terms of spontaneously
broken (global or gauge) flavor symmetries. We propose a little-Higgs inspired
scenario in which an SU(2)xU(1) gauge flavor symmetry is spontaneously (and
completely) broken by the vacuum of the dynamically induced potential for two
scalar doublets (the flavons) which are pseudo-Goldstone bosons remaining after
the spontaneous breaking--at a scale between 10 and 100 TeV--of an approximate
SU(6) global symmetry. The vacuum expectation values of the flavons give rise
to the texture in the fermion mass matrices. We discuss in detail the case of
leptons. Light-neutrino masses arise by means of a see-saw-like mechanism that
takes place at the same scale at which the SU(6) global symmetry is broken. We
show that without any fine tuning of the parameters the experimental values of
the charged-lepton masses,the neutrino square mass differences and the
Pontecorvo-Maki-Nakagawa-Sakata mixing matrix are reproduced.Comment: 13 pages, revTeX4. Version to be published in PR
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