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.Comment: 19 pages, 3 figures, minor corrections, references adde

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.Comment: 30 pages, 12 figures, 6 tables, minor correction

Supernova neutrino signal at HALO: Learning about the primary neutrino fluxes

We predict the numbers of one- and two-neutron charged and neutral-current electron-neutrino scattering on lead events including collective effects due to the neutrino-neutrino interactions and the Mikheev-Smirnov-Wolfenstein (MSW) effect due to the neutrino interactions with the background matter. We show that 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

Propagation des neutrinos dans des milieux denses (aspect phénoménologiques et description détaillée)

Cosmic neutrinos provide a natural probe to study both the fundamental properties of neutrinos and the underlying physics of their sources. In this Thesis, we first present new predictions for the expected supernova neutrino signal in Helium And Lead Observatory currently operational at SNOLAB, Canada. Our calculations include the usual MSW effect and also the collective effects due to the neutrino-neutrino interactions. We show that information can be extracted on the precise shape of the primary neutrino energy spectra emitted at neutrinospheres using the one- and two-neutron emission channels in HALO. Then, we focus on the theoretical description of neutrino propagation in dense environments. We use an original approach based on the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy allowing us to reproduce the commonly employed mean-field evolution equations and to go beyond this approximation. Particularly, we derive a new set of equations including pairing type correlations between neutrinos and anti-neutrinos. This is the first time such pairing type correlations have been explicitly considered in a supernova environment. Finally, we introduce simplified methods to study neutrino evolution in astrophysical and cosmological environments. We present a general linearization procedure and apply it both to the derived mean-field equations and to the extended evolution equations including neutrino anti-neutrino pairing correlations. The stationary state corresponding to the extended Hamiltonian is obtained by generalizing the fermionic Bogoliubov-Valatin quasi-particle transformations.Les neutrinos cosmiques fournissent une sonde naturelle pour étudier à la fois les propriétés fondamentales des neutrinos et la physique de leurs sources. Dans cette thèse, nous présentons tout d'abord des nouvelles prédictions du signal neutrino de supernova attendu dans l'observatoire HALO opérationnel a SNOLAB. Nos calculs incluent l'effet MSW et les effets collectifs dus aux interactions neutrino-neutrino. Nos résultats montrent que l'on peut extraire des informations sur la forme précise des spectres d'énergie primaires des neutrinos émis à la neutrino-sphère. Puis, nous nous concentrons sur la description théorique de la propagation des neutrinos dans les milieux. Nous utilisons une approche originale basée sur la hiérarchie Bogolioubov-Born-Green-Kirkwood-Yvon pour dériver les équations, couramment utilisés, d'évolution de neutrinos basées sur le champ moyen et pour aller au-delà de cette approximation. En effet, nous présentons un nouvel ensemble d'équations incluant les corrélations d'appariement entre les neutrinos et les anti-neutrinos. C'est la première fois que de telles corrélations sont prises en compte dans le contexte des supernovae. Finalement, nous introduisons des méthodes simplifiées pour étudier les neutrinos astrophysiques et cosmologiques. Nous présentons une procédure générale de linéarisation et son application à la fois aux équations de champ moyen et aux équations d'évolution étendues, comprenant les correlations des paires neutrino-antineutrino. Les états stationnaires correspondant à l'Hamiltonien étendu sont déterminés en introduisant des transformations généralisées de Bogolioubov-Valatin pour des quasi-particules fermioniques.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF