arXiv subjects

Luis Bento

Publications and source records attributed to Luis Bento.

At least 19 recordsLinked to original sources

arXiv2006

Fast Neutron - Mirror Neutron Oscillation and Ultra High Energy Cosmic Rays

If there exists the mirror world, a parallel hidden sector of particles with exactly the same microphysics as that of the observable particles, then the primordial nucleosynthesis constraints require that the temperature of the cosmic background of mirror relic photons should be smaller than that of the ordinary relic photons, T'/T < 0.5 or so. On the other hand, the present experimental and astrophysical limits allow a rather fast neutron - mirror neutron oscillation in vacuum, with an oscillation time $τ\sim 1$ s, much smaller than the neutron lifetime. We show that this could provide a very efficient mechanism for transporting ultra high energy protons at large cosmological distances. The mechanism operates as follows: a super-GZK energy proton scatters a relic photon producing a neutron that oscillates into a mirror neutron which then decays into a mirror proton. The latter undergoes a symmetric process, scattering a mirror relic photon and producing back an ordinary nucleon, but only after traveling a distance $(T/T')^{3}$ times larger than ordinary protons. This may relax or completely remove the GZK-cutoff in the cosmic ray spectrum and also explain the correlation between the observed ultra high energy protons and far distant sources as are the BL Lacs.

hep-ph↗

arXiv2006

Neutron - Mirror Neutron Oscillations: How Fast Might They Be?

We discuss the phenomenological implications of the neutron (n) oscillation into the mirror neutron (n'), a hypothetical particle exactly degenerate in mass with the neutron but sterile to normal matter. We show that the present experimental data allow a maximal n-n' oscillation in vacuum with a characteristic time $τ$ much shorter than the neutron lifetime, in fact as small as 1 sec. This phenomenon may manifest in neutron disappearance and regeneration experiments perfectly accessible to present experimental capabilities and may also have interesting astrophysical consequences, in particular for the propagation of ultra high energy cosmic rays.

hep-ph↗

arXiv2005

Neutrino helicity asymmetries in leptogenesis

It is pointed out that the heavy singlet neutrinos characteristic of leptogenesis develop asymmetries in the abundances of the two helicity states as a result of the same mechanism that generates asymmetries in the standard lepton sector. Neutrinos and standard leptons interchange asymmetries in collisions with each other. It is shown that an appropriate quantum number, B-L', combining baryon, lepton and neutrino asymmetries, is not violated as fast as the standard B-L. This suppresses the washout effects relevant for the derivation of the final baryon asymmetry. One presents detailed calculations for the period of neutrino thermal production in the framework of the singlet seesaw mechanism.

hep-ph↗

arXiv2003

Leptogenesis in a prompt decay scenario

Leptogenesis is studied within the seesaw neutrino mass model in a regime where all sterile neutrinos have prompt rather than delayed decays. It is shown that during neutrino thermal production lepton asymmetries are generated in both active lepton and sterile neutrino sectors. The large B-L asymmetry is slowly pumped into the chemically decoupled right-handed quarks and leptons and baryon number sector which later protect B-L from fast L violating processes. The dependence of the final baryon asymmetry on couplings and masses is totally different from the decay scenario. B does not vanish in the limit of degenerate light neutrinos and the observed asymmetry is naturally obtained for a sum of square masses between the atmospheric neutrino mass gap and 0.2 eV^2.

hep-ph↗

arXiv2003

Sphaleron relaxation temperatures

The transition of sphaleron processes from non-equilibrium to thermal equilibrium in the early Universe is examined in detail. The relations between the damping rates and frequencies of the weak and QCD sphaleron degeneracy parameters are determined in general form and the respective relaxation temperatures are calculated in specific scenarios. It is pointed out that the gauge coupling constants running with energy produces strong and weak sphaleron rates closer to each other at very high temperatures and makes them larger in supersymmetric models than in the standard model case.

hep-ph↗

arXiv2001

Blocking Active-Sterile Neutrino Oscillations in the Early Universe with a Majoron Field

We propose a new mechanism to block the active-sterile neutrino oscillations in the Early Universe. We show that a typical consequence of theories where the lepton number is spontaneously broken is the existence of a coherent cosmological Majoron field with a strength proportional to the lepton and baryon numbers of the Universe. This field interacts with leptons and changes the potentials relevant for neutrino oscillations. If the scale of lepton number symmetry breaking is of the order of 1 GeV then a Majoron field and lepton number asymmetry of the order of the baryon asymmetry are strong enough to block the active-sterile neutrino oscillations with the atmospheric neutrino mass gap which otherwise would bring the sterile neutrino into equilibrium at the big bang nucleosynthesis epoch.

hep-ph↗

arXiv2001

Baryogenesis: The Lepton Leaking Mechanism

We propose a baryo- and leptogenesis mechanism in which the B-L asymmetry is produced in the conversion of ordinary leptons into particles of some depleted hidden sector. In particular, we consider the lepton number violating reactions, l Higgs -> l' Higgs', \bar{l'} \bar{Higgs'}, mediated by the heavy Majorana neutrinos N of the seesaw mechanism, where l and Higgs are ordinary lepton and Higgs doublets and l', Higgs' the ``sterile'' leptons and Higgs. This mechanism can operate even if the reheat temperature is smaller than the N Majorana masses, in which case the usual leptogenesis mechanism through N decays is ineffective. In particular, the reheat tempearture can be as low as 10^9 GeV or less.

hep-ph↗

arXiv2001

Leptogenesis via Collisions: Leaking Lepton Number to the Hidden Sector

We propose a lepto-baryogenesis mechanism in which the non-zero B-L of the universe is produced in out-of-equilibrium, lepton number and CP violating scattering processes that convert ordinary particles into particles of some hidden sector. In particular, we consider the processes $l ϕ> l' ϕ', \bar l' \bar phi'$ mediated by the heavy Majorana neutrinos $N$ of the seesaw mechanism, where $l$ and $ϕ$ are ordinary lepton and Higgs doublets and $l'$, $ϕ'$ their hidden counterparts. Such a leptogenesis mechanism is effective even if the reheating temperature is much smaller than the heavy neutrino masses. In particular, it can be as low as $10^{9}$ GeV.

hep-ph↗

arXiv2001

Interaction between gravitational waves and domain walls

We study the gravitational perturbations of thick domain walls. The refraction index and spin properties of the solutions interior to the wall are analyzed in detail. It is shown that the gravitational waves suffer a refraction process by domain walls. The reflection and transmission coefficients are derived in the thin wall limit. In relation to the spin content, it is shown that the ``$\times$'' helicity 2 gravitational wave mode maintains in the domain wall the same polarization state as in vacuum. On the contrary, the ``+'' mode, of pure helicity 2 in vacuum, is contaminated inside the wall with a spin 0 state, as well as with spin 2, helicity 0 and 1 states.

gr-qc↗

arXiv2001

Instabilities in neutrino-plasma density waves

One examines the interaction and possible resonances between supernova neutrinos and electron plasma waves. The neutrino phase space distribution and its boundary regions are analyzed in detail. It is shown that the boundary regions are too wide to produce non-linear resonant effects. The growth or damping rates induced by neutrinos are always proportional to the neutrino flux and $G_{\rm F}^{2}$.

hep-ph↗

arXiv2000

Gravitational instabilities in helicity-1 waves propagating through matter in equilibrium

It is shown that the interaction of helicity-1 waves of gravity and matter in a thin slab configuration produces new types of instabilities. Indeed, a transverse spin-2 helicity-1 mode interacts strongly with the shear motion of matter. This mode is unstable above a critical wavelength which reminds the Jeans wavelength but with the speed of sound interchanged by the speed of light. The two instabilities are of course different. For the case analyzed, a plane parallel configuration, Jeans instability appears through a density wave perturbation, the material collapsing into a set of plane-parallel slabs. On the other hand, the helicity-1 wave instability induces a transverse motion in the fluid that tends to shear in the material along the node of the perturbation.

gr-qc↗

arXiv2000

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 $\barψψ$. 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 $m_ν/300$ GeV.

hep-ph↗

arXiv2000

Neutrino mixing scenarios and AGN

Active galactic nuclei (AGN) have been suggested to be sources of very high energy neutrinos. We consider the possibility of using AGN neutrinos to test neutrino mixings. From the atmospheric, solar and laboratory data on neutrino oscillations we derive the flavour composition of the AGN neutrino flux in different neutrino mixing schemes. We show that most of the schemes considered can be distinguished from each other and the existence of a sterile neutrino can be specially tested. AGN neutrinos can also be used to test those four-neutrino scenarios where solar neutrinos oscillate into an arbitrary mixture of $ν_s$ and $ν_τ$.

hep-ph↗

arXiv1999

Recent Development on Collective Neutrino Interactions

Quantum Field Theory is applied to study an electron plasma under an intense neutrino flux. The dispersion relation of the longitudinal waves is derived and the damping rate is calculated. It is shown that in the case of Supernova emission the neutrinos are not collimated enough to cause plasma instabilities associated to a strong neutrino resonance effect.

hep-ph↗

arXiv1999

Plasma wave instabilities induced by neutrinos

Quantum field theory is applied to study the interaction of an electron plasma with an intense neutrino flux. A connection is established between the field theory results and classical kinetic theory. The dispersion relation and damping rate of the plasma longitudinal waves are derived in the presence of neutrinos. It is shown that Supernova neutrinos are never collimated enough to cause non-linear effects associated with a neutrino resonance. They only induce neutrino Landau damping, linearly proportional to the neutrino flux and $G_{\mathrm{F}}^{2}$.

hep-ph↗

arXiv1999

Classical Nambu-Goldstone fields

It is shown that a true Nambu-Goldstone (NG) boson develops a coherent long-range field whenever the charge associated with it that is carried by the other particles is not conserved in a macroscopic scale. The source of a NG field is the time rate of quantum number violation. If the lepton numbers are spontaneously broken at a scale below 1 TeV, the neutrino oscillation processes generate long-range majoron fields that are strong enough in Supernovae to modify the neutrino flavor dynamics. Two examples are given: NG fields may improve the adiabaticity of $ν_{e}\leftrightarrow ν_{X}$ transitions or cause resonant anti-neutrino oscillations otherwise impossible with solely weak interactions.

hep-ph↗

arXiv1999

Neutrino Oscillations: a source of Goldstone fields and consequences for Supernovae

It is shown that true Nambu-Goldstone (NG) bosons develop coherent fields whenever the associated charges of the matter particles are not conserved in a macroscopic scale. The sources of the NG fields are the time rates of quantum number violation. If the lepton numbers are spontaneously broken at a scale below 1 TeV, the neutrino oscillation processes generate classic NG fields that are strong enough in Supernovae to modify the neutrino flavor dynamics. The oscillation patterns may change in the periods of largest $ν$ fluxes. Two examples are given: 1. the back reaction of a NG field improves the adiabaticity of the $ν_{e}$ resonant conversion; 2. ${\barν_{e}} \leftrightarrow {\barν_μ}$ oscillations may occur even if $ν_{e}$ is the lightest of the neutrinos.

hep-ph↗

arXiv1998

Supernova neutrino oscillations: Adiabaticity improvement by Majoron fields

If the lepton numbers are associated with global symmetries spontaneously broken at a scale below 1 TeV, neutrino oscillations in supernovae produce classic Majoron fields that perturb the neutrino propagation itself and may change the oscillation patterns in the periods of largest $ν$ fluxes. The impact of the Majoron fields on the same transitions as $ν_{e}\to ν_{X}$ that presumably occur in the Sun is studied in the case of the non-adiabatic MSW solution. It is shown how the back reaction of the Majoron fields may improve the adiabaticity of these oscillations in a supernova environment which has implications on the outgoing $ν_{e}$ spectrum.

hep-ph↗