arXiv subjects

Francesco Vissani

Publications and source records attributed to Francesco Vissani.

At least 55 records · Page 3Linked to original sources

arXiv2017

Solar neutrino physics on the beginning of 2017

This writeup is a review of current hot topics on solar neutrinos. It is based on a talk at the conference "Neutrinos: the quest for a new physics scale", held at the CERN on March 2017, where the Organizers entrusted me with a discussion of the provocative question "whether solar neutrino physics is over". Rather than providing a straight (negative) answer, in view of an audience consisting mostly of colleagues working in theoretical particle physics, I deemed it more useful providing a description of what is the current activity of the physicists working in solar neutrinos, leaving the listener free of forming his/her own opinion apropos.

nucl-th↗

arXiv2017

Can BL Lac emission explain the neutrinos above 0.2 PeV?

Multi-messenger astronomy can help to investigate the sources of the high-energy neutrinos observed by the high-energy neutrino telescope IceCube. We consider the hypothesis that the highest energy neutrinos are produced by BL Lacs, arguing that this is not contradicted severely by any known fact. We check the BL Lac hypothesis by searching for correlations between the through-going muon events of IceCube and the BL Lacs of the second catalog of Fermi-LAT (2FHL). We expect 10.2 $\pm$ 2.4 correlated events but we find that just 1 event has a BL Lac as counterpart. We also assess the probability of observing one multiplet from the same source, finding that the present null result is not yet of critical significance. We conclude that the hypothesis that the BL Lacs are the main emitters of the highest-energy neutrinos observed by IceCube is disfavored at 3.7σ. We discuss implications and possible ways out; for example, this could work if the angular resolution was 4°, which is much more than expected.

astro-ph.HE↗

arXiv2017

Neutrinos and γ-rays from the Galactic Center Region After H.E.S.S. Multi-TeV Measurements

The hypothesis of a PeVatron in the Galactic Center, emerged with the recent γ-ray measurements of H.E.S.S., motivates the search for neutrinos from this source. The effect of γ-ray absorption is studied: at the energies currently probed, the known background radiation fields lead to small effects, whereas it is not possible to exclude large effects due to new IR radiation fields near the very Center. Precise upper limits on neutrino fluxes are derived and the underlying hypotheses are discussed. The expected number of events for ANTARES, IceCube and KM3NeT, based on the H.E.S.S. measurements, are calculated. It is shown that km3-class telescopes in the Northern hemisphere have the potential of observing high-energy neutrinos from this important astronomical object and can check the existence of a hadronic PeV galactic accelerator.

astro-ph.HE↗

arXiv2016

On the IceCube spectral anomaly

Recently it was noted that different IceCube datasets are not consistent with the same power law spectrum of the cosmic neutrinos: this is the IceCube spectral anomaly, that suggests that they observe a multicomponent spectrum. In this work, the main possibilities to enhance the description in terms of a single extragalactic neutrino component are examined. The hypothesis of a sizable contribution of Galactic high-energy neutrino events distributed as $E^{-2.7}$ [ApJ 826, 185 (2016)] is critically analyzed and its natural generalization is considered. The stability of the expectations is studied by introducing free parameters, motivated by theoretical considerations and observational facts. The upgraded model here examined has 1)~a Galactic component with different normalization and shape $E^{- 2.4}$; 2)~an extragalactic neutrino spectrum based on new data; 3)~a non-zero prompt component of atmospheric neutrinos. The two key predictions of the model concern the `high-energy starting events' collected from the Southern sky. The Galactic component produces a softer spectrum and a testable angular anisotropy. A second, radically different class of models, where the second component is instead isotropic, plausibly extragalactic and with a relatively soft spectrum, is disfavored instead by existing observations of muon neutrinos from the Northern sky and below few 100 TeV.

astro-ph.HE↗

arXiv2016

Extragalactic plus Galactic model for IceCube neutrino events

The hypothesis that high energy cosmic neutrinos are power law distributed is critically analyzed. We propose a model with two components that explains better the observations. The extragalactic component of the high energy neutrino flux has a canonical $E_ν^{-2}$ spectrum while the galactic component has a $E_ν^{-2.7}$ spectrum; both of them are significant. This model has several implications, that can be tested by IceCube and ANTARES in the next years. Moreover, the existence of a diffuse component close to the Galactic plane and that yields (20-30)\% of IceCube's events, is interesting for the future $\mbox{km}^3$ neutrino telescopes located in the Northern Hemisphere and for gamma ray telescopes aiming at measuring events till few 100 TeV from the Southern sky.

astro-ph.HE↗

arXiv2016

Double pulses and cascades above 2 PeV in IceCube

IceCube collaboration has seen an unexpected population of high energy neutrinos compatible with an astrophysical origin. We consider two categories of events that can help to diagnose cosmic neutrinos: double pulse, that may allow us to clearly discriminate the cosmic component of tau neutrinos; cascades with deposited energy above 2 PeV, including events produced by electron antineutrinos at the Glashow resonance, that can be used to investigate the neutrino production mechanisms. We show that one half of the double pulse signal is due to the neutrinos spectral region already probed by IceCube. By normalizing to HESE data, we find that 10 more years are required to obtain 90% probability to observe a double pulse. The cascades above 2 PeV provide us a sensitive probe of the high energy tail of the neutrino spectrum and are potentially observable, but even in this case, the dependence on type of the source is mild. In fact we find that pp or pγ mechanisms give a difference in the number of cascades above 2 PeV of about 25 % that can be discriminated at 2σ in about 50 years of data taking.

astro-ph.HE↗

arXiv2015

The contribution of light Majorana neutrinos to neutrinoless double beta decay and cosmology

Cosmology is making impressive progress and it is producing stringent bounds on the sum of the neutrino masses Σ, a parameter of great importance for the current laboratory experiments. In this letter, we exploit the potential relevance of the analysis of Palanque-Delabrouille et al. [JCAP 1502, 045 (2015)] to the neutrinoless double beta decay (0νββ) search. This analysis indicates small values for the lightest neutrino mass, since the authors find Σ < 84 meV at 1σ C. L., and provides a 1σ preference for the normal hierarchy. The allowed values for the Majorana effective mass, probed by 0νββ, turn out to be < 75meV at 3σC.L. and lower down to less than 20meV at 1σC.L.. If this indication is confirmed, the impact on the 0νββ experiments will be tremendous since the possibility of detecting a signal will be out of the reach of the next generation of experiments.

hep-ph↗

arXiv2015

The natural parametrization of cosmic neutrino oscillations

The natural parameterization of vacuum oscillations in three neutrino flavors is studied. Compact and exact relations of its three parameters with the ordinary three mixing angles and CP violating phase are obtained. Its usefulness is illustrated by considering various applications: the study of the flavor ratio and of its uncertainties, the comparison of expectations and observations in the flavor triangle, the intensity of the signal due to Glashow resonance. The results in the literature are easily reproduced and in particular the recently obtained agreement of the observations of IceCube with the hypothesis of cosmic neutrino oscillations is confirmed. It is argued that a Gaussian treatment of the errors appropriately describes the effects of the uncertainties on neutrino oscillation parameters.

hep-ph↗

arXiv2015

Neutrino Sources and Properties

In this lecture, prepared for PhD students, basic considerations on neutrino interactions, properties and sites of production are overviewed. The detailed content is as follows: Sect. 1, Weak interactions and neutrinos: Fermi coupling; definition of neutrinos; global numbers. Sect. 2, A list of neutrino sources: Explanatory note and examples (solar pp- and supernova-neutrinos). Sect. 3, Neutrinos oscillations: Basic formalism (Pontecorvo); matter effect (Mikheev, Smirnov, Wolfenstein); status of neutrino masses and mixings. Sect. 4, Modifying the standard model to include neutrinos masses: The fermions of the standard model; one additional operator in the standard model (Weinberg); implications. One summary table and several exercises offer the students occasions to check, consolidate and extend their understanding; the brief reference list includes historical and review papers and some entry points to active research in neutrino physics.

hep-ph↗

arXiv2015

A facility to Search for Hidden Particles at the CERN SPS: the SHiP physics case

This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (Search for Hidden Particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, $τ\to 3μ$ and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the Standard Model and describe interactions between new particles and four different portals - scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the Standard Model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation

hep-ph↗

arXiv2014

Comparative analysis of SN1987A antineutrino fluence

We discuss the electron antineutrino fluence derived from the events detected by Kamiokande-II, IMB and Baksan on February 23, 1987. The data are analysed adopting a new simple and accurate formula for the signal, improving on the previous modeling of the detectors response, considering the possibility of background events. We perform several alternative analyses to quantify the relevance of various descriptions, approximations and biases. In particular, we study the effect of: omitting Baksan data or neglecting the background, using simplified formulae for the signal, modifying the fluence to account for oscillations and pinching, including the measured times and angles of the events, using other descriptions of detector response, etc. We show that most of these effects are small or negligible and argue, by comparing the allowed regions for astrophysical parameters, that the results are stable. We comment on the accordance with theoretical results and on open questions.

astro-ph.HE↗

arXiv2014

New expectations and uncertainties on neutrinoless double beta decay

The hypothesis that the Majorana mass of ordinary neutrinos dominates the rate of neutrinoless double beta decay is investigated. Predictions from neutrino oscillations are updated. Nuclear uncertainties are discussed, evaluating the impact of the quenching of the axial vector coupling constant in the nuclear medium, recently pointed out by Iachello et al. [Phys. Rev. C87, 014315 (2013)]. Also, the sensitivity of present and future experiments is assessed and possible implications of the knowledge on neutrino masses from cosmology are studied. The predictions from neutrino oscillations are compared with the results from cosmology and from neutrinoless double beta decay searches, emphasizing the important role of the measurement errors. The obstacles to an experimental determination of the Majorana phases are pointed out.

hep-ph↗

arXiv2014

La Thuile 2014: Theoretical premises to neutrino round table

This talk, dedicated to the memory of G. Giacomelli, introduced the round table on neutrinos held in February 2014. The topics selected for the discussion are: 1) the neutrinoless double beta decay rate (interpretation in terms of light neutrinos, nuclear uncertainties); 2) the physics in the gigantic water Cherenkov detectors (proton decay, atmospheric neutrinos); 3) the study of neutrino oscillations (mass hierarchy and CP violation; other neutrino states); 4) the neutrino astronomy at low and high energies (solar, supernova, cosmic neutrinos). The importance of an active interplay between theory and experiment is highlighted.

hep-ph↗

arXiv2014

The fraction of muon tracks in cosmic neutrinos

The study of the distintive signatures of the ultra high energy events recently seen by IceCube can allow to single the neutrino origin out. The detection of tau neutrinos would be a clear way to prove that they come from cosmic distances, but at the highest energies currently seen, about 1 PeV, an experimental characterization of tau events is difficult. The study of the fraction of the muon tracks seems more promising. In fact, for any initial composition, because of the occurrence of flavor oscillations and despite their uncertainties, the fraction of muon tracks in the cosmic neutrinos is smaller than the one of atmospheric neutrinos, even hypothesizing an arbitrarily large contribution from charmed mesons. A good understanding of the detection efficiencies and the optimization of the analysis cuts, along with a reasonable increase in the statistics, should provide us with a significant test of the cosmic origin of these events.

astro-ph.HE↗

arXiv2013

Neutrinos from Pion Decay at Rest to Probe the Proton Strangeness in an Underground Lab

The study of the neutral current elastic scattering of neutrinos on protons at lower energies can be used as a compelling probe to improve our knowledge of the strangeness of the proton. We consider a neutrino beam generated from pion decay at rest, as provided by a cyclotron or a spallation neutron source and a 1 kton scintillating detector with a potential similar to the Borexino detector. Despite several backgrounds from solar and radioactive sources it is possible to estimate two optimal energy windows for the analysis, one between 0.65-1.1 MeV and another between 1.73-2.2 MeV. The expected number of neutral current events in these two regions, for an exposure of 1 year, is enough to obtain an error on the strange axial-charge 10 times smaller than available at present.

hep-ph↗

arXiv2013

Counting muons to probe the neutrino mass spectrum

The experimental evidence that θ_{13} is large opens new opportunities to identify the neutrino mass spectrum. We outline a possibility to investigate this issue by means of conventional technology. The ideal setup turns out to be long baseline experiment: the muon neutrino beam, with 10^{20} protons on target, has an average energy of 6 (8) GeV; the neutrinos, after propagating 6000 (8000) km, are observed by a muon detector of 1 Mton and with a muon energy threshold of 2 GeV. The expected number of muon events is about 1000, and the difference between the two neutrino spectra is sizeable, about 30%. This allows the identification of the mass spectrum just counting muon tracks. The signal events are well characterized experimentally by their time and direction of arrival, and 2/3 of them are in a region with little atmospheric neutrino background, namely, between 4 GeV and 10 GeV. The distances from CERN to Baikal Lake and from Fermilab to KM3NET, or ANTARES, fit in the ideal range.

hep-ph↗

arXiv2012

A Critical Appraisal of Some Concepts Used in Neutrino Physics

We examine the value of certain concepts highly regarded in the past decade, that concern neutrino propagation, models for the leptonic mixing, interpretations of neutrinoless double beta dec\ ay and of SN1987A observations. We argue that it would useful to strengthen the role of the discussions among experts of neutrino physics, regarding the hypotheses underlying the theoretical investigations.

hep-ph↗

arXiv2012

Heavy Sterile Neutrinos and Neutrinoless Double Beta Decay

Sterile neutrinos of mass up to a few tens of TeV can saturate the present experimental bound of neutrinoless double beta decay process. Due to the updated nuclear matrix elements, the bound on mass and mixing angle is now improved by one order of magnitude. We have performed a detailed analysis of neutrinoless double beta decay for the minimal Type I seesaw scenario. We have shown that in spite of the naive expectation that the light neutrinos give the dominant contribution, sterile neutrinos can saturate the present experimental bound of neutrinoless double beta decay process. However, in order to be consistent with radiative stability of light neutrino masses, the mass scale of sterile neutrinos should be less than 10 GeV.

hep-ph↗