arXiv subjects

F. Vissani

Publications and source records attributed to F. Vissani.

At least 19 recordsLinked to original sources

arXiv2021

Complementarity between neutrinoless double beta decay and collider searches for heavy neutrinos in composite-fermion models

Composite-fermion models predict excited quarks and leptons with mass scales which can potentially be observed at high-energy colliders like the LHC; the most recent exclusion limits from the CMS and ATLAS Collaborations corner excited-fermion masses and the compositeness scale to the multi-TeV range. At the same time, hypothetical composite Majorana neutrinos would lead to observable effects in neutrinoless double beta decay ($0νββ$) experiments. In this work, we show that the current composite-neutrino exclusion limit $M_N>4.6$ TeV, as extracted from direct searches at the LHC, can indeed be further improved to $M_N>8.8$ TeV by including the bound on the nuclear transition $^{136}$Xe $\to$ $^{136}$Ba $+2e^-$. Looking ahead, the forthcoming HL-LHC will allow probing a larger portion of the parameter-space, nevertheless, it will still benefit from the complementary limit provided by $0 νββ$ future detectors to explore composite-neutrino masses up to $12.6$ TeV.

hep-ph↗

arXiv2021

Discovery probabilities of Majorana neutrinos based on cosmological data

We discuss the impact of the cosmological measurements on the predictions of the Majorana mass of the neutrinos, the parameter probed by neutrinoless double-beta decay experiments. Using a minimal set of assumptions, we quantify the probabilities of discovering neutrinoless double-beta decay and introduce a new graphical representation that could be of interest for the community.

hep-ph↗

arXiv2020

EeV Astrophysical neutrinos from FSRQs?

Flat Spectrum Radio Quasars (FSRQ) are the most powerful blazars in the gamma-ray band. Although they are supposed to be good candidates in producing high energy neutrinos, no secure detection of FSRQs has been obtained up to now, except for a possible case of PKS B1424-418. In this work, we compute the expected flux of high energy neutrinos from FSRQs using standard assumptions for the properties of the radiation fields filling the regions surrounding the central supermassive black hole. We obtain as a result that high energy neutrinos are naturally expected from FSRQs in the sub-EeV-EeV energy range and not at PeV energies. This justifies the non-observation of neutrinos from FSRQs with the present technology, since only neutrinos below 10 PeV have been observed. We found that for a non-negligible range of the parameters the cumulative flux from FSRQs is comparable to or even exceeds the expected cosmogenic neutrino flux. This result is intriguing and highlights the importance to disentangle these point-source emissions from the diffuse cosmogenic background.

astro-ph.HE↗

arXiv2019

The effects of a revised $^7$Be e$^-$-capture rate on solar neutrino fluxes

The electron-capture rate on $^7$Be is the main production channel for $^7$Li in several astrophysical environments. Theoretical evaluations have to account for not only the nuclear interaction, but also the processes in the plasma where $^7$Be ions and electrons interact. In the past decades several estimates were presented, pointing out that the theoretical uncertainty in the rate is in general of few percents. In the framework of fundamental solar physics, we consider here a recent evaluation for the $^7$Be+e$^-$ rate, not used up to now in the estimate of neutrino fluxes. We analysed the effects of the new assumptions on Standard Solar Models (SSMs) and compared the results obtained by adopting the revised $^7$Be+e$^-$ rate to those obtained by the one reported in a widely used compilation of reaction rates (ADE11). We found that new SSMs yield a maximum difference in the efficiency of the $^7$Be channel of about -4\% with respect to what is obtained with the previously adopted rate. This fact affects the production of neutrinos from $^8$B, increasing the relative flux up to a maximum of 2.7\%. Negligible variations are found for the physical and chemical properties of the computed solar models. The agreement with the SNO measurements of the neutral current component of the $^8$B neutrino flux is improved.

astro-ph.SR↗

arXiv2018

Late time supernova neutrino signal and proto-neutron star radius

We discuss the possibility of reconstructing the newly formed proto-neutron star radius from the late time neutrino signal. A black-body emission is assumed for the neutron star cooling phase. We parametrize the neutrino time-integrated fluxes based on simulations of Roberts and Reddy. A likelihood analysis of the inverse-beta decay and elastic scattering events in Hyper-Kamiokande is performed in both three flavor and an effective one flavor scenario. We show that the precision achievable in the radius reconstruction strongly depends on a correlation with the pinching parameter and therefore the corresponding prior. Although this correlation hinders the precise measurement of the newly formed neutron star radius, it could help measure the pinching parameters with good accuracy in view of the current constraints on neutron star radius, or if the neutron star radius is precisely measured.

hep-ph↗

arXiv2016

Neutrinoless double beta decay: 2015 review

The discovery of neutrino masses through the observation of oscillations boosted the importance of neutrinoless double beta decay ($0νββ$). In this paper, we review the main features of this process, underlining its key role both from the experimental and theoretical point of view. In particular, we contextualize the $0νββ$ in the panorama of lepton-number violating processes, also assessing some possible particle physics mechanisms mediating the process. Since the $0νββ$ existence is correlated with neutrino masses, we also review the state-of-art of the theoretical understanding of neutrino masses. In the final part, the status of current $0νββ$ experiments is presented and the prospects for the future hunt for $0νββ$ are discussed. Also, experimental data coming from cosmological surveys are considered and their impact on $0νββ$ expectations is examined.

hep-ph↗

arXiv2015

Testing neutrino decay scenarios with IceCube data

We test the hypothesis of non-radiative neutrinos decay using the latest IceCube data. Namely, we calculate the track-to-shower ratio expected in IceCube for the normal and inverted neutrino mass hierarchy taking into account the uncertainties in neutrino oscillation parameters. We show that the subset of data with energy above 60 TeV actually excludes the possibility of a neutrinos decay at the 1 sigma level of significance for both neutrino mass hierarchies.

hep-ph↗

arXiv2015

Which is the flavor of cosmic neutrinos seen by IceCube?

We analyze the high-energy neutrino events observed by IceCube, aiming to probe the initial flavor of cosmic neutrinos. We study the track-to-shower ratio of the subset with energy above 60 TeV, where the signal is expected to dominate and show that different production mechanisms give rise to different predictions even accounting for the uncertainties due to neutrino oscillations. We include for the first time the passing muons observed by IceCube in the analysis. They corroborate the hypotheses that cosmic neutrinos have been seen and their flavor matches expectations.

astro-ph.HE↗

arXiv2014

Spectrum of Supernova Neutrinos in Ultra-pure Scintillators

There is a great interest in measuring the non-electronic component of neutrinos from core collapse supernovae by observing, for the first time, also neutral-current reactions. In order to assess the physics potential of the ultra-pure scintillators in this respect, we study the entire expected energy spectrum in the Borexino, KamLAND and SNO+ detectors. We examine the various sources of uncertainties in the expectations, and in particular, those due to specific detector features and to the relevant cross sections. We discuss the possibility to identify the different neutrino flavors, and we quantify the effect of confusion, due to other components of the energy spectrum, overlapped with the neutral-current reactions of interest.

astro-ph.SR↗

arXiv2013

The Future of Neutrino Mass Measurements: Terrestrial, Astrophysical, and Cosmological Measurements in the Next Decade. Highlights of the NuMass 2013 Workshop. Milano, Italy, February 4 - 7, 2013

The third Workshop of the NuMass series ("The Future of Neutrino Mass Measurements: Terrestrial, Astrophysical, and Cosmological Measurements in the Next Decade: NuMass 2013") was held at Dipartimento di Fisica "G. Occhialini, University of Milano-Bicocca in Milano, Italy, on 4-7 February 2013. The goal of this international workshop was to review the status and future of direct and indirect neutrino mass measurements in the laboratory as well as from astrophysical and cosmological observations. This paper collects most of the contributions presented during the Workshop.

hep-ex↗

arXiv2011

On the generality of the Cohen and Glashow constraints on the neutrino velocity

We discuss the kinematic limits for the process ν_μ\rightarrow ν_μ+ e^+ + e^- in the assumption that neutrinos are superluminal. We derive our results by assuming that: i) it exists one reference frame in which energy and momentum are conserved; ii) the Hamilton-Jacobi equation v=dE/dp is valid; iii) the present experimental information on the neutrino velocity at different energies are correct. We show that the considered process cannot be avoided unless very peculiar neutrino dispersion laws are assumed.

hep-ph↗

arXiv2011

A step toward CNO solar neutrinos detection in liquid scintillators

The detection of CNO solar neutrinos in ultrapure liquid scintillator detectors is limited by the background produced by Bismuth-210 nuclei that undergo beta-decay to Polonium-210 with a lifetime equal to about 7 days. Polonium-210 nuclei are unstable and decay with a lifetime equal to about 200 days emitting alpha particles that can be also detected. In this letter, we show that the Bi-210 background can be determined by looking at the time evolution of alpha-decay rate of Po-210, provided that alpha particle detection efficiency is stable over the data acquisition period and external sources of Po-210 are negligible. A sufficient accuracy can be obtained in a relatively short time. As an example, if the initial Po-210 event rate is 2000 cpd/100 ton or lower, a Borexino-like detector could start discerning CNO neutrino signal from Bi-210 background in about 1 yr.

hep-ph↗

arXiv2010

What is the issue with SN1987A neutrinos?

What did we learn out of SN1987A neutrino observations? What do we still need for a full understanding? We select important issues debated in the literature on SN1987A. We focus the discussion mostly on the relevance of certain data features; on the role of detailed statistical analyses of the data; on the astrophysics of the neutrino emission process; on the effects of oscillations and of neutrino masses. We attempt to clearly identify those issues that are still open.

hep-ph↗

arXiv2010

Using supernova neutrinos to monitor the collapse, to search for gravity waves and to probe neutrino masses

We discuss the importance of observing supernova neutrinos. By analyzing the SN1987A observations of Kamiokande-II, IMB and Baksan, we show that they provide a 2.5σ support to the standard scenario for the explosion. We discuss in this context the use of neutrinos as trigger for the search of the gravity wave impulsive emission. We derive a bound on the neutrino mass using the SN1987A data and argue, using simulated data, that a future galactic supernova could probe the sub-eV region.

hep-ph↗

arXiv2010

Searching for prompt signatures of nearby core-collapse supernovae by a joint analysis of neutrino and gravitational-wave data

We discuss the science motivations and prospects for a joint analysis of gravitational-wave (GW) and low-energy neutrino data to search for prompt signals from nearby supernovae (SNe). Both gravitational-wave and low-energy neutrinos are expected to be produced in the innermost region of a core-collapse supernova, and a search for coincident signals would probe the processes which power a supernova explosion. It is estimated that the current generation of neutrino and gravitational-wave detectors would be sensitive to Galactic core-collapse supernovae, and would also be able to detect electromagnetically dark SNe. A joint GW-neutrino search would enable improvements to searches by way of lower detection thresholds, larger distance range, better live-time coverage by a network of GW and neutrino detectors, and increased significance of candidate detections. A close collaboration between the GW and neutrino communities for such a search will thus go far toward realizing a much sought-after astrophysics goal of detecting the next nearby supernova.

astro-ph.IM↗

arXiv2009

The likelihood for supernova neutrino analyses

We derive the event-by-event likelihood that allows to extract the complete information contained in the energy, time and direction of supernova neutrinos, and specify it in the case of SN1987A data. We resolve discrepancies in the previous literature, numerically relevant already in the concrete case of SN1987A data.

hep-ph↗

arXiv2009

Neutrinos from Supernovae as a Trigger for Gravitational Wave Search

Exploiting an improved analysis of the electronic antineutrinos signal from the explosion of a galactic core collapse supernova, we show that it is possible to identify within about ten milliseconds the time of the bounce, which is strongly correlated to the time of the maximum amplitude of the gravitational signal. This allows to precisely identify the gravitational wave burst timing.

hep-ph↗

arXiv2008

Improved analysis of SN1987A antineutrino events

We propose a new parameterization of the antineutrino flux from core collapse supernovae, that allows an interpretation of its astrophysical parameters within the Bethe and Wilson scenario for the explosion, and that leads to a reasonable (smooth) behavior of the average energy and of the luminosity curve. We apply it to analyze the events observed by Kamiokande-II, IMB and Baksan detectors in correlation with SN1987A. For the first time, we consider in the same analysis all data characteristics: times, energies and angles of the observed events. We account for the presence of background and evaluate the impact of neutrino oscillations. The hypothesis that the initial luminous phase of emission (accretion) is absent can be rejected at the 2 % significance level. Without the need to impose external priors in the likelihood analysis, the best-fit values of the astrophysical parameters are found to be in remarkable agreement with the expectations of the standard core-collapse scenario; in particular, the electron antineutrino-sphere radius is 16 km, the duration of the accretion phase is found to be 0.55 s, and the initial accreting mass is 0.22 M(sun). Similarly the total energy emitted in neutrinos is 2.2*10^{53} erg, again close to the expectations. The errors on the parameters are evaluated and found to be relatively large, consistently with the limited number of detected events; the two dimensional confidence regions, that demonstrate the main correlations between the parameters, are also given.

astro-ph↗