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Francesco Vissani

Publications and source records attributed to Francesco Vissani.

At least 91 records · Page 5Linked to original sources
arXiv2005

Expected neutrino signal from supernova remnant RX J1713.7-3946 and flavor oscillations

We consider the impact of oscillations on 1-200 TeV neutrinos expected from RX J1713.7-3946. After a description of the nature of the source, we obtain a prediction for the neutrino fluxes, based on the intense gamma ray flux first seen by CANGAROO and recently measured by H.E.S.S. experiment. We study the effect of 3 flavor oscillations in detail and consider the impact on the muon flux induced by these high energy neutrinos, potentially observable by a neutrino telescope located in the Northern hemisphere. A detector in the Mediterranean with an effective area of 1 km^2 and unit detection efficiency should be able to see a signal of about 10 muons per year.

astro-ph↗
arXiv2005

Low scale gravity as the source of neutrino masses?

We address the question whether low-scale gravity alone can generate the neutrino mass matrix needed to accommodate the observed phenomenology. In low-scale gravity the neutrino mass matrix in the flavor basis is characterized by one parameter (the gravity scale M_X) and by an exact or approximate flavor blindness (namely, all elements of the mass matrix are of comparable size). Neutrino masses and mixings are consistent with the observational data for certain values of the matrix elements, but only when the spectrum of mass is inverted or degenerate. For the latter type of spectra the parameter M_{ee} probed in double beta experiments and the mass parameter probed by cosmology are close to existing upper limits.

hep-ph↗
arXiv2005

Implications of neutrino data circa 2005

Adopting the 3 neutrino framework, we present an updated determination of the oscillation parameters. We perform a global analysis and develope simple arguments that give essentially the same result. We also discuss determinations of solar neutrino fluxes, capabilities of future experiments, tests of CPT, implications for neutrino-less double-beta decay, beta decay, cosmology.

hep-ph↗
arXiv2004

Probing oscillations into sterile neutrinos with cosmology, astrophysics and experiments

We perform a thorough analysis of oscillation signals generated by one extra sterile neutrino, extending previous analyses done in simple limiting cases and including the effects of established oscillations among active neutrinos. We consider the following probes: solar, atmospheric, reactor and beam neutrinos, Big-Bang Nucleosynthesis (helium-4, deuterium), Cosmic Microwave Background, Large Scale Structure, supernovae, neutrinos from other astrophysical sources. We find no evidence for a sterile neutrino in present data, identify the still allowed regions, and study which future experiments can best probe them: sub-MeV solar experiments, more precise studies of CMB or BBN, future supernova explosions, etc. We discuss how the LSND hint is strongly disfavoured by the constraints of (standard) cosmology.

hep-ph↗
arXiv2004

SN1987A and the properties of neutrino burst

We reanalyze the neutrino events from SN1987A in IMB and Kamiokande-II (KII) detectors, and compare them with the expectations from simple theoretical models of the neutrino emission. In both detectors the angular distributions are peaked in the forward direction, and the average cosines are 2 sigma above the expected values. Furthermore, the average energy in KII is low if compared with the expectations; but, as we show, the assumption that a few (probably one) events at KII have been caused by elastic scattering is not in contrast with the 'standard' picture of the collapse and yields a more satisfactory distributions in angle and (marginally) in energy. The observations give useful information on the astrophysical parameters of the collapse: in our evaluations, the mean energy of electron antineutrinos is =12-16 MeV, the total energy radiated around (2-3)*1.E53 erg, and there is a hint for a relatively large radiation of non-electronic neutrino species. These properties of the neutrino burst are not in disagreement with those suggested by the current theoretical paradigm, but the data leave wide space to non-standard pictures, especially when neutrino oscillations are included.

astro-ph↗
arXiv2004

Probing the nature of the seesaw in renormalizable SO(10)

We study the nature of the see-saw mechanism in the context of renormalizable SO(10) with Higgs fields in the 10-plets and 126-plet representations, paying special attention to the supersymmetric case. We discuss analytically the situation for the second and third generations of fermions ignoring any CP violating phase. It is shown that b-tau unification and large atmospheric mixing angle strongly disfavor the dominance of the type I see-saw.

hep-ph↗
arXiv2003

Neutrinos as astrophysical probes

The aim of these notes is to provide a brief review of the topic of neutrino astronomy and in particular of neutrinos from core collapse supernovae. They are addressed to a curious reader, beginning to work in a multidisciplinary area that involves experimental neutrino physics, astrophysics, nuclear physics and particle physics phenomenology. After an introduction to the methods and goals of neutrinos astronomy, we focus on core collapse supernovae, as (one of) the most promising astrophysical source of neutrinos. The first part is organized almost as a tale, the last part is a bit more technical. We discuss the impact of flavor oscillations on the supernova neutrino signal (=the change of perspective due to recent achievements) and consider one specific example of signal in detail. This shows that effects of oscillations are important, but astrophysical uncertainties should be thought as an essential systematics for a correct interpretation of future experimental data. Three appendices corroborate the text with further details and some basics on flavor oscillations; but no attempt of a complete bibliographical survey is done (in practice, we selected a few references that we believe are useful for a `modern' introduction to the subject. We suggest the use of public databases for papers as SPIRES or NASA/ESO or for experiments as SPIRES or PaNAGIC to get a more complete information).

astro-ph↗
arXiv2003

Neutrino oscillations and signals in beta and 0nu2beta experiments

Assuming Majorana neutrinos, we infer from oscillation data the expected values of the parameters m_{nu_e} and m_{ee} probed by beta and 0nu2beta-decay experiments. If neutrinos have a `normal hierarchy' we get the 90% CL ranges |m_{ee}| = (0.7 - 4.6) meV, and discuss in which cases future experiments can test this possibility. For `inverse hierarchy', we get |m_{ee}| = (12 - 57) meV and m_{ν_e} = (40 - 57) meV. The 0nu2beta data imply that almost degenerate neutrinos are lighter than 1.05 h eV at 90% CL, competitive with the beta-decay bound. We critically reanalyse the data that were recently used to claim an evidence for 0nu2beta, and discuss their implications. Finally, we review the predictions of flavour models for m_{ee} and theta_{13}.

hep-ph↗
arXiv2003

The minimal supersymmetric grand unified theory

We show that the minimal renormalizable supersymmetric SO(10) GUT with the usual three generations of spinors has a Higgs sector consisting only of a "light" 10-dimensional and "heavy" 126, 126-bar and 210 supermultiplets. The theory has only two sets of Yukawa couplings with fifteen real parameters and ten real parameters in the Higgs superpotential. It accounts correctly for all the fermion masses and mixings. The theory predicts at low energies the MSSM with exact R-parity. It is arguably the minimal consistent supersymmetric grand unified theory.

hep-ph↗
arXiv2003

U(e3) from physics above the GUT scale

We consider non-renormalizable 1/M_X interaction terms as a perturbation of the conventional neutrino mass matrix. Particular attention is given to the gravitational interaction with M_X=M_Pl. We find that for the degenerate neutrino mass spectrum, the considered perturbation generates a non-zero U(e3) which is within reach of the high performance neutrino factories and just on the borderline to be of interest for supernova physics. For the hierarchical mass spectrum this effect is small. For 1/M_X interaction terms with M_X about the GUT scale, a detectable U(e3) term is induced for the hierarchical mass spectra also. Numerical estimates are given for all the above mentioned cases and renormalization effects are considered.

hep-ph↗
arXiv2003

Precise quasielastic neutrino/nucleon cross section

Quasielastic antineutrino/proton and neutrino/neutron scatterings can be well approximated by simple formulae, valid around MeV or GeV energies. We obtain a single expression valid in the whole range, and discuss its relevance for studies of supernova neutrinos, which reach intermediate energies.

astro-ph↗
arXiv2003

Mirror model for sterile neutrinos

Sterile neutrinos are studied as subdominant contribution to solar neutrino physics. The mirror-matter neutrinos are considered as sterile neutrinos. We use the symmetric mirror model with gravitational communication between mirror and visible sectors. This communication term provides mixing between visible and mirror neutrinos with the basic scale mu=v^2/M_Pl=5*10^-6 eV, where v=174 GeV is the vacuum expectation value of the standard electroweak group and M_Pl is the Planckian mass. It is demonstrated that each mass eigenstate of active neutrinos splits into two states separated by small Delta m^2. Unsuppressed oscillations between active and sterile neutrinos nu_a --> nu_s occur only in transitions between each of these close pairs (``windows''). These oscillations are characterized by very small Delta m^2 and can suppress the flux and distort spectrum of pp-neutrinos in detectable way. The other observable effect is anomalous seasonal variation of neutrino flux, which appears in LMA solution. The considered subdominant neutrino oscillations nu_a <--> nu_s can reveal itself as big effects in observations of supernova neutrinos and high energy (HE) neutrinos. In the case of HE neutrinos they can provide a very large diffuse flux of active neutrinos unconstrained by the e-m cascade upper limit.

hep-ph↗
arXiv2002

Which solar neutrino data favour the LMA solution?

Assuming neutrino oscillations, global analyses of solar data find that the LOW solution is significantly disfavoured, leaving LMA as the best solution. But the preference for LMA rests on three weak hints: the spectrum of earth matter effects (Super-Kamiokande sees an overall day/night asymmetry only at 1 sigma), the Cl rate (but LMA and LOW predictions are both above the measured value), the Ga rate (newer data decrease towards the LOW predictions both in GNO and SAGE). Only new data will tell us if LMA is the true solution.

hep-ph↗
arXiv2001

A Statistical Approach to Leptonic Mixings and Neutrino Masses

Based on existing data, we argue for a peculiar structure of the neutrino mass matrix, that has a block of relatively large elements--a dominant block. We analyze this ansatz and extract its predictions, assuming that the O(1) coefficients (that are needed to define the model fully) are random variables. Further insights are obtained by postulating that this structure of the mass matrix is due to U(1) selection rules, a la Froggatt and Nielsen. A particularly interesting case emerges, when the angle theta(13) (namely, the mixing U(e3)) is within reach for next generation experiments, and the large mixing angle solution for solar neutrinos is the preferred one.

hep-ph↗
arXiv2001

How Neutrino and Charged Fermion Masses Are Connected Within Minimal Supersymmetric SO(10)

Massive neutrinos are a generic prediction of SO(10), and models of unification cry for supersymmetry. Since we have a rather detailed information on neutrino and charged fermion masses, the real question is: how/whether it is possible to build a SO(10) supersymmetric model, that correctly incorporates fermion masses. We show that a simple construction is possible in the context of a minimal theory. We concentrate on the two heaviest generations, discuss the predictions of the model, and briefly comment on open questions.

hep-ph↗
arXiv2001

Which solar neutrino experiment after KamLAND and Borexino?

We estimate how well we will know the parameters of solar neutrino oscillations after KamLAND and Borexino. The expected error on Delta m^2 is few per-mille in the VO and QVO regions, few per-cent in the LMA region, and around 10% in the LOW region. The expected error on sin^2 2theta is around 5%. KamLAND and Borexino will tell unambiguously which specific new measurement, dedicated to pp solar neutrinos, is able to contribute to the determination of theta and perhaps of Delta m^2. The present data suggest as more likely outcomes: no measurement, or the total pp rate, or its day/night variation.

hep-ph↗