Etudes des proprietes des neutrinos dans les contextes ...

tel-00450051, version 1 - 25 Jan 2010
trinos of all flavors are produced in the hot core of the proto-neutron star, which
has a temperature of about 40 MeV, through electron-positron pair annihilation,
electron-nucleon bremsstrahlung,
nucleon-nucleon bremsstrahlung,
plasmon decay
and photo-annihilation
e + + e − → νl + νl, (3.9)
e ± + N → e ± + N + νl + νl, (3.10)
N + N → N + N + νl + νl, (3.11)
γ → νl + νl, (3.12)
γ + e ± → e ± + νl + νl, (3.13)
Electron neutrinos are also produced by the electron capture process in Eq.(3.3),
and electron antineutrinos are produced by positron capture on neutrons. Even
though the neutrinos interact weakly with matter, they are trapped in the SN
core because of the very high matter density. When the matter density is low
enough (of the order of 10 11 g.cm −3 ), neutrinos can exit freely of the mantle of
the proto-neutron star since their mean free path is larger than the radius of the
core. The sphere from which neutrinos stream out freely is called the neutrino
sphere.
The neutrino spheres
The neutrino energy being too low in such environments to create muons and
taus by charged-current, the medium is only composed of protons, neutrons,
and electrons. This implies the existence of different energy dependent neutrino
spheres for different neutrino flavors whose estimated radii are typically between
50 and 100 km. There are roughly three energy-dependent neutrino spheres: one
for νe, one for νe and one for νµ, νµ, ντ, ντ. Indeed, the flavor neutrinos νe and νe
can interact with the medium through both charged-current and neutral-current
weak processes, whereas the neutrinos νµ, νµ, ντ, ντ can interact only through
neutral current weak processes, which are flavor-independent. From now on, in
this chapter, we will denote νµ, νµ, ντ, ντ collectively as νx, as usually done in the
literature. After the shock breakout, each neutrino sphere produces a thermal
flux of the corresponding neutrino flavor. In the next section, we will give a model
of these thermal fluxes.
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