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S. Pastor

Publications and source records attributed to S. Pastor.

46 records · Page 3Linked to original sources
arXiv1998

Neutrino magnetic moments and low-energy solar neutrino-electron scattering experiments

The scattering of solar neutrinos on electrons is sensitive to the neutrino magnetic moments through an interference of electromagnetic and weak amplitudes in the cross section. We show that future low-energy solar neutrino experiments with good angular resolution can be sensitive to the resulting azimuthal asymmetries in event number and should provide useful information on non-standard neutrino properties such as magnetic moments. We compare asymmetries expected at HELLAZ (mainly pp neutrinos) with those at the Kamiokande and Super-Kamiokande experiments (Boron neutrinos), both for the case of Dirac and Majorana neutrinos and discuss the advantages of low energies. Potentially interesting information on the solar magnetic fields may be accessible.

hep-ph↗
arXiv1998

New tests for neutrinos in low-energy solar experiments

We show how future solar neutrino experiments in the low energy region can be used to test novel neutrino properties. Information on the Majorana nature or neutrino magnetic moments can be extracted from the observation of electron anti-neutrinos from the Sun and the measurement of an azimuthal asymmetry in the total number of events, respectively.

hep-ph↗
arXiv1998

Low-energy solar anti-neutrinos

If neutrino conversions within the Sun result in partial polarization of initial solar neutrino fluxes, then a new opportunity arises to observe the anti-ν_e's in future neutrino experiments in the low energy region (such as BOREXINO or HELLAZ) and thus to probe the Majorana nature of the neutrinos. The ν_e -> anti-ν_e conversions may take place for low energy solar neutrinos while being unobservable at the Kamiokande and Super-Kamiokande experiments.

hep-ph↗
arXiv1998

Low-energy Anti-neutrinos from the Sun

We consider the sensitivity of future neutrino experiments in the low energy region, such as BOREXINO or HELLAZ, to a solar electron antineutrino signal. We show that, if neutrino conversions within the Sun result in partial polarization of initial solar neutrino fluxes, then a new opportunity arises to observe the electron antineutrinos and thus to probe the Majorana nature of the neutrinos. This is achieved by comparing the slopes of the energy dependence of the differential neutrino electron scattering cross section for different neutrino conversion scenarios. We also show how the ν_e -> \barν_e conversions may take place for low energy solar neutrinos while being unobservable at the Kamiokande and Super-Kamiokande experiments.

hep-ph↗
arXiv1997

Primordial Nucleosynthesis, Majorons and Heavy Tau Neutrinos

We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in the presence of nu-tau annihilations into Majorons, as expected in a wide class of particle physics models of neutrino mass. We determine the equivalent number of light neutrino species $N_{eq}$ as a function of nu-tau mass and the nu-tau-Majoron coupling $g$. We show that for theoretically plausible $g$ values $\gsim 10^{-4}$ present nucleosynthesis observations can not rule out nu-tau masses in the MeV range. Moreover, these models give $N_{eq} \leq 3$ in the nu-tau mass region 1-10 MeV, for very reasonable values of $g \geq 3 \times 10^{-4}$. The evasion of the cosmological limits brings new interest to the improvement of the present laboratory limit on the nu-tau mass which can be achieved at a tau-charm factory.

hep-ph↗
arXiv1996

An improved cosmological bound on the tau-neutrino mass

We consider the influence of non-equilibrium electronic neutrinos (and anti-neutrinos) on the neutron-to-proton ratio. These neutrinos would come from massive $ν_τ$ annihilations $\bar ν_τν_τ\rightarrow \bar ν_e ν_e$. For sufficiently large $ν_τ$ masses this new effect would strongly enhance the (n/p)-ratio, leading to a very stringent bound on the $ν_τ$ mass, even adopting a rather weak upper bound on the effective number on neutrino species during nucleosynthesis.

hep-ph↗
arXiv1995

Bounds on Neutrino Transition Magnetic Moments in Random Magnetic Fields

We consider the conversions of active to sterile Majorana neutrinos $ν_{a}$ and $ν_{s}$, due to neutrino transition magnetic moments in the presence of random magnetic fields (r.m.f.) generated at the electroweak phase transition. From a simple Schrödinger-type evolution equation, we derive a stringent constraint on the corresponding transition magnetic moments and display it as a function of the domain size and field geometry. For typical parameter choices one gets limits much stronger than usually derived from stellar energy loss considerations. These bounds are consistent with the hypothesis of seeding of galactic magnetic fields by primordial fields surviving past the re-combination epoch. We also obtain a bound on active-sterile neutrino transition magnetic moments from supernova energy loss arguments. For r.m.f. strengths in the range $10^7$ to $10^{12}$ Gauss we obtain limits varying from $μ_{as}^ν \lsim 10^{-13}μ_B$ to $μ_{as}^ν \lsim 10^{-18}μ_B$, again much stronger than in the case without magnetic fields.

hep-ph↗
arXiv1995

Structure Formation with a Decaying Mev Tau Neutrino and a Kev Majoron

We consider the scenario of large scale structure formation with tau neutrino with mass in the MeV range and lifetime of order of years which decays into a massive majoron with KeV mass. The latter are the present-day cold dark matter particles. In contrast to the usual collisionless dark matter, the majorons have a relatively strong self-interaction and the picture of structure formation is rather different from the standard. The decay $J \ra γγ$ leads to the existence of an X-ray line at $E_γ= m_J/2$ which could be detectable. Electron and muon neutrinos are expected to be very light, as required in order to account for the solar neutrino deficit through \ne to \nm oscillations. Supersymmetry with spontaneously broken R parity provides a natural particle physics model for our scenario.

astro-ph↗
arXiv1994

Active Sterile Neutrino Conversions in a Supernova with Random Magnetic Fields

{Large enough random magnetic fields may affect in an important way neutrino conversion rates, even in the case where neutrinos have zero transition magnetic moments. We consider their effect in the case of active to sterile \neu conversions in a supernova and show that for KeV neutrino masses these limits may overcome those derived for the case of zero magnetic field.}

hep-ph↗