arXiv subjects

R. Buras

Publications and source records attributed to R. Buras.

23 records · Page 2Linked to original sources

arXiv2002

The Mechanism of Core-Collapse Supernovae and the Ejection of Heavy Elements

We present here the first results of two-dimensional hydrodynamical simulations of the neutrino-heating phase in the collapsed core of a 15 solar mass star, where the neutrino transport is treated with a variable Eddington factor method for solving the Boltzmann transport equation, and the neutrino interactions include nucleon-nucleon bremsstrahlung, nucleon recoils and correlations, and weak-magnetism effects as well as direct interactions between neutrinos of different flavors. With the given input physics (neutrino reactions and nuclear equation of state), our best simulations do not develop strong convection in the neutrino-heating layer behind the shock and do not yield explosions. With about 30% higher neutrino-energy deposition behind the shock, however, an explosion occurs on a timescale of 150 ms after core bounce. It leaves behind a neutron star with an initial baryonic mass of 1.4 solar masses and ejects the N = 50 isotopes of Sr, Y and Zr in amounts consistent with Galactic abundances.

astro-ph↗

arXiv2002

Core-collapse supernova simulations: Variations of the input physics

Spherically symmetric simulations of stellar core collapse and post-bounce evolution are used to test the sensitivity of the supernova dynamics to different variations of the input physics. We consider a state-of-the-art description of the neutrino-nucleon interactions, possible lepton-number changing neutrino reactions in the neutron star, and the potential impact of hydrodynamic mixing behind the supernova shock.

astro-ph↗

arXiv2000

Maximum lepton asymmetry from active-sterile neutrino oscillations in the Early Universe

A large lepton asymmetry could be generated in the Early Universe by oscillations of active to sterile neutrinos with a small mixing angle sin 2 θ< 10^-2. The final order of magnitude of the lepton asymmetry ηis mainly determined by its growth in the last stage of evolution when the MSW resonance dominates the kinetic equations. In this paper we present a simple way of calculating the maximum possible lepton asymmetry which can be created. Our results are in good agreement to previous calculations. Furthermore, we find that the growth of asymmetry does not obey any particular power law. We find that the maximum possible asymmetry at the freeze-out of the n/p ratio at T \sim 1 MeV strongly depends on the mass-squared difference δm^2: the asymmetry is negligible for δm^2 \ll 1 eV^2 and reaches asymptotically large values for δm^2 \ge 50 eV^2.

hep-ph↗

arXiv2000

Lepton asymmetry creation in the Early Universe

Oscillations of active to sterile neutrinos with a small mixing angle sin 2 θ< 10^{-2} could generate a large lepton asymmetry in the Early Universe. The final order of magnitude of the lepton asymmetry ηis mainly determined by its growth in the last stage of evolution, the so called power-law regime. There exist two contradictory results in the literature, η\propto T^{-1} and η\propto T^{-4}, where T is the background medium temperature. In the first case, the lepton asymmetry does not exceed values of 10^{-4} for |δm^2| < 1 eV^2, while in the second case it can become larger than 10^{-1}. In this work we analytically investigate the case η\propto T^{-1}, using a new approach to solve the kinetic equations. We find that the power-law solution η\propto T^{-1} is not self-consistent. Instead, we find the power law η\propto T^{-11/3} to be a good approximation, which leads to a large final asymmetry.

hep-ph↗

arXiv2000

Sterile Neutrinos in Big Bang Nucleosynthesis

We investigate analytically the evolution of the primordial neutrino asymmetry caused by active-sterile neutrino oscillations. In particular, we concentrate on possible chaotic oscillations of the asymmetry. For a certain range of parameters, we find that the asymmetry indeed oscillates, provided we neglect the momentum distribution.

hep-ph↗