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Cristina Volpe

Publications and source records attributed to Cristina Volpe.

At least 19 recordsLinked to original sources
arXiv2017

Helicity coherence in binary neutron star mergers and non-linear feedback

Neutrino flavor conversion studies based on astrophysical environments usually implement neutrino mixings, neutrino interactions with matter and neutrino self-interactions. In anisotropic media, the most general mean-field treatment includes neutrino mass contributions as well, that introduce a coupling between neutrinos and antineutrinos termed helicity or spin coherence. We discuss resonance conditions for helicity coherence for Dirac and Majorana neutrinos. We explore the role of these mean-field contributions on flavor evolution in the context of a binary neutron star merger remnant. We find that resonance conditions can be satisfied in neutron star merger scenarios while adiabaticity is not sufficient for efficient flavor conversion. We analyse our numerical findings by discussing general conditions to have multiple MSW-like resonances, in presence of non-linear feedback, in astrophysical environments.

hep-ph↗
arXiv2017

Neutrino Flavor Evolution in Binary Neutron Star Merger Remnants

We study the neutrino flavor evolution in the neutrino-driven wind from a binary neutron star merger remnant consisting of a massive neutron star surrounded by an accretion disk. With the neutrino emission characteristics and the hydrodynamical profile of the remnant consistently extracted from a three-dimensional simulation, we compute the flavor evolution by taking into account neutrino coherent forward scattering off ordinary matter and neutrinos themselves. We employ a "single-trajectory" approach to investigate the dependence of the flavor evolution on the neutrino emission location and angle. We also show that the flavor conversion in the merger remnant can affect the (anti-)neutrino absorption rates on free nucleons and may thus impact the $r$-process nucleosynthesis in the wind. We discuss the sensitivity of such results on the change of neutrino emission characteristics, also from different neutron star merger simulations.

astro-ph.HE↗
arXiv2016

Neutrino Astrophysics

We summarize the progress in neutrino astrophysics and emphasize open issues in our understanding of neutrino flavor conversion in media. We discuss solar neutrinos, core-collapse supernova neutrinos and conclude with ultra-high energy neutrinos.

astro-ph.HE↗
arXiv2016

Theoretical developments in supernova neutrino physics : mass corrections and pairing correlators

We highlight the progress in our understanding of how neutrinos change their flavor in astrophysical environments, in particular effects from the neutrino self-interaction. We emphasize extended descriptions of neutrino propagation in massive stars that are beyond the current one based on the mean-field approximation. The extended equations include, in particular, corrections from (anti)neutrino-(anti)neutrino pairing correlations and from the neutrino mass. We underline open issues and challenges.

astro-ph.HE↗
arXiv2015

Neutrino Quantum Kinetic Equations

Neutrinos propagate in astrophysical and cosmological environments modifying their flavor in intriguing ways. The study of neutrino propagation in media is based on the mean-field, extended mean-field and Boltzmann equations. We summarise salient features of these evolution equations and the methods employed so far to derive them. We emphasize applications to situations of observational interest.

astro-ph.SR↗
arXiv2015

Neutrino astrophysics : recent advances and open issues

We highlight recent advances in neutrino astrophysics, the open issues and the interplay with neutrino properties. We emphasize the important progress in our understanding of neutrino flavor conversion in media. We discuss the case of solar neutrinos, of core-collapse supernova neutrinos and of SN1987A, and of the recently discovered ultra-high energy neutrinos whose origin is to be determined.

astro-ph.SR↗
arXiv2015

Neutrino-antineutrino correlations in dense anisotropic media

We derive the most general evolution equations describing in-medium (anti)neutrino propagation in the mean-field approximation. In particular, we consider various types of neutrino-antineutrino mixing, for both Dirac and Majorana fields, resulting either from nontrivial pair correlations or from helicity coherence due to the nonvanishing neutrino masses. We show that, unless the medium is spatially homogeneous and isotropic, these correlations are sourced by the usual neutrino and antineutrino densities. This may be of importance in astrophysical environments such as core-collapse supernovae.

hep-ph↗
arXiv2014

Recent advances in neutrino astrophysics

Neutrinos are produced by a variety of sources that comprise our Sun, explosive environments such as core-collapse supernovae, the Earth and the Early Universe. The precise origin of the recently discovered ultra-high energy neutrinos is to be determined yet. These weakly interacting particles give us information on their sources, although the neutrino fluxes can be modified when neutrinos traverse an astrophysical environment. Here we highlight recent advances in neutrino astrophysics and emphasise the important progress in our understanding of neutrino flavour conversion in media.

hep-ph↗
arXiv2013

Extended evolution equations for neutrino propagation in astrophysical and cosmological environments

We derive the evolution equations for a system of neutrinos interacting among themselves and with a matter background, based upon the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy. This theoretical framework gives an (unclosed) set of first-order coupled integro-differential equations governing the evolution of the reduced density matrices. By employing the hierarchy, we first rederive the mean-field evolution equations for the neutrino one-body density matrix associated with a system of neutrinos and antineutrinos interacting with matter and with an anisotropic neutrino background. Then, we derive extended evolution equations to determine neutrino flavor conversion beyond the commonly used mean-field approximation. To this aim we include neutrino-antineutrino pairing correlations to the two-body density matrix. The inclusion of these new contributions leads to an extended evolution equation for the normal neutrino density and to an equation for the abnormal one involving the pairing mean-field. We discuss the possible impact of neutrino-antineutrino correlations on neutrino flavor conversion in the astrophysical and cosmological environments, and possibly upon the supernova dynamics. Our results can be easily generalized to an arbitrary number of neutrino families.

hep-ph↗
arXiv2013

Open issues in neutrino astrophysics

Neutrinos of astrophysical origin are messengers produced in stars, in explosive phenomena like core-collapse supernovae, in the accretion disks around black holes, or in the Earth's atmosphere. Their fluxes and spectra encode information on the environments that produce them. Such fluxes are modified in characteristic ways when neutrinos traverse a medium. Here our current understanding of neutrino flavour conversion in media is summarized. The importance of this domain for astrophysical observations is emphasized. Examples are given of the fundamental properties that astrophysical neutrinos have uncovered, or might reveal in the future.

hep-ph↗
arXiv2012

Search for new physics with neutrinos at Radioactive Ion Beam facilities

We propose applications of Radioactive Ion Beam facilities to investigate physics beyond the Standard Model. In particular, we focus on the possible measurement of coherent neutrino-nucleus scattering and on a search for sterile neutrinos, by means of a low energy beta-beam with a Lorentz boost factor $γ\approx 1$. In the considered setup the collected radioactive ions are sent inside a 4$π$ detector. For the first application we provide the number of events associated with neutrino-nucleus coherent scattering, when the detector is filled in with a noble liquid. For the sterile search we consider that the spherical detector is filled in with a liquid scintillator, and that the neutrino detection channel is inverse-beta decay. We provide the exclusion curves for the sterile neutrino mixing parameters, based upon the 3+1 formalism, depending upon the achievable ion intensity. Our results are obtained both from total rates, and including spectral information with binning in energy and in distance. The proposed experiment represents a possible alternative to clarify the current anomalies observed in neutrino experiments.

hep-ph↗
arXiv2011

The neutrino signal at HALO: learning about the primary supernova neutrino fluxes and neutrino properties

Core-collapse supernova neutrinos undergo a variety of phenomena when they travel from the high neutrino density region and large matter densities to the Earth. We perform analytical calculations of the supernova neutrino fluxes including collective effects due to the neutrino-neutrino interactions, the Mikheev-Smirnov-Wolfenstein (MSW) effect due to the neutrino interactions with the background matter and decoherence of the wave packets as they propagate in space. We predict the numbers of one- and two-neutron charged and neutral-current electron-neutrino scattering on lead events. We show that, due to the energy thresholds, the ratios of one- to two-neutron events are sensitive to the pinching parameters of neutrino fluxes at the neutrinosphere, almost independently of the presently unknown neutrino properties. Besides, such events have an interesting sensitivity to the spectral split features that depend upon the presence/absence of energy equipartition among neutrino flavors. Our calculations show that a lead-based observatory like the Helium And Lead Observatory (HALO) has the potential to pin down important characteristics of the neutrino fluxes at the neutrinosphere, and provide us with information on the neutrino transport in the supernova core.

astro-ph.SR↗
arXiv2011

Neutrinos and core-collapse supernovae

We discuss the recent progress in our understanding of neutrino flavour conversion in core-collapse supernovae and focus on the effects coming from the neutrino-neutrino interaction. The latter has been shown to engender new phenomena, modifying significantly the neutrino fluxes and supernova observations. In particular, we make the link between the spectral split and the magnetic resonance phenomenon. Moreover, recent investigations have demonstrated the existence of leptonic CP violation effects on the supernova neutrino fluxes. We summarize these findings.

astro-ph.SR↗
arXiv2011

The neutrino spectral split in core-collapse supernovae: a magnetic resonance phenomenon

A variety of neutrino flavour conversion phenomena occur in core-collapse supernova, due to the large neutrino density close to the neutrinosphere, and the importance of the neutrino-neutrino interaction. Three different regimes have been identified so far, usually called the synchronization, the bipolar oscillations and the spectral split. Using the formalism of polarization vectors, within two-flavours, we focus on the spectral split phenomenon and we show for the first time that the physical mechanism underlying the neutrino spectral split is a magnetic resonance phenomenon. In particular, we show that the precession frequencies fulfill the magnetic resonance conditions. Our numerical calculations show that the neutrino energies and the location at which the resonance takes place in the supernova coincide well with the neutrino energies at which a spectral swap occurs. The corresponding adiabaticity parameters present spikes at the resonance location.

astro-ph.SR↗
arXiv2010

Turbulence effects on supernova neutrinos

Multi-dimensional core-collapse supernova simulations exhibit turbulence of large amplitude and over large scales. As neutrinos pass through the supernova mantle the turbulence is expected to modify their evolution compared to the case where the explosion is free of turbulence. In this paper we study this turbulence effect upon the neutrinos modelling the turbulence expected from multi-dimensional simulations by adding matter density fluctuations to density profiles taken from one-dimensional hydrodynamical simulations. We investigate the impact upon the supernova neutrino transition probabilities as a function of the neutrino mixing angle theta_13 and turbulence amplitude. In the high (H) resonant channel and with large theta_13 values we find that turbulence is effectively two flavor for fluctuation amplitudes <~ 1% and have identified a new effect due to the combination of turbulence and multiple H resonances that leads to a sensitivity to fluctuations amplitudes as small as ~ 0.001%. At small values of theta_13, beyond the range achievable in Earth based experiments, we find that turbulence leads to new flavor transient effects in the channel where the MSW H resonance occurs. Finally, we investigate large amplitude fluctuations which lead to three flavor effects due to broken HL factorization and significant non-resonant transitions and identify two non-resonant turbulence effects, one depending on the theta_13, and the other independent of this angle and due to the low (L) MSW resonance.

hep-ph↗
arXiv2009

Search for CP violation in the lepton sector

One of the major open issues in neutrino physics is the possible existence of CP violation in the neutrino sector. Such an observation would have an important impact in various domains of physics, from high energy physics to cosmology. Its search requires future accelerator neutrino facilities producing intense and pure neutrino beams such as "beta-beams". Here we review the different beta-beam scenarios proposed so far and discuss the present status, with a particular emphasis on the original baseline scenario and its feasibility. Alternative strategies for the CP violation search are to be pursued as well. A possibility is to search for CP violation effects in astrophysical environments. Here we present recent analytical and numerical results obtained in the context of core-collapse supernovae. In particular, we point out the conditions under which there can be CP violating effects in dense media and show numerical results on the supernova (anti-)neutrino fluxes and on the electron fraction, relevant for the r-process nucleosynthesis.

hep-ph↗
arXiv2009

Shockwaves in Supernovae: New Implications on the Diffuse Supernova Neutrino Background

We investigate shock wave effects upon the diffuse supernova neutrino background using dynamic profiles taken from hydrodynamical simulations and calculating the neutrino evolution in three flavors with the S-matrix formalism. We show that the shock wave impact is significant and introduces modifications of the relic fluxes by about $20 \%$ and of the associated event rates at the level of $10-20 \%$. Such an effect is important since it is of the same order as the rate variation introduced when different oscillation scenarios (i.e. hierarchy or $θ_{13}$) are considered. In addition, due to the shock wave, the rates become less sensitive to collective effects, in the inverted hierarchy and when $\sin^2 2 θ_{13}$ is between the Chooz limit and $10^{-5}$. We propose a simplified model to account for shock wave effects in future predictions.

hep-ph↗