106 research outputs found
Collective neutrino-pair emission due to Cooper pairing of protons in superconducting neutron stars
The neutrino emission due to formation and breaking of Cooper pairs of
protons in superconducting cores of neutron stars is considered with taking
into account the electromagnetic coupling of protons to ambient electrons. It
is shown that collective response of electrons to the proton quantum transition
contributes coherently to the complete interaction with a neutrino field and
enhances the neutrino-pair production. Our calculation shows that the
contribution of the vector weak current to the emissivity of
protons is much larger than that calculated by different authors without taking
into account the plasma effects. Partial contribution of the pairing protons to
the total neutrino radiation from the neutron star core is very sensitive to
the critical temperatures for the proton and neutron pairing. We show domains
of these parameters where the neutrino radiation, caused by a singlet-state
pairing of protons is dominating.Comment: 34 pages, including 9 figure
Bulk viscosity in superfluid neutron star cores. III. Effects of hyperons
Bulk viscosity of neutron star cores containing hyperons is studied taking
into account non-equilibrium weak process .
Rapid growth of the bulk viscosity within the neutron star core associated with
switching on new reactions (modified Urca process, direct Urca process, hyperon
reactions) is analyzed. The suppression of the bulk viscosity by superfluidity
of baryons is considered and found out to be very important.Comment: LaTeX, 9 pages, added reference, version accepted by Astron.
Astrophy
Neutrino Emission from Superfluid Neutron-Star Cores: Various Types of Neutron Pairing
We calculate and provide analytic fits of the factors which describe the
reduction of the neutrino emissivity of modified Urca and nucleon-nucleon
bremsstrahlung processes by superfluidity of neutrons and protons in
neutron-star cores. We consider S pairing of protons and either
S or P pairing of neutrons. We analyze two types of P
pairing: the familiar pairing with zero projection of the total angular
momentum of neutron pairs onto quantization axis, ; and the pairing with
which leads to the gap with nodes at the neutron Fermi surface.
Combining the new data with those available in the literature we fully describe
neutrino emission by nucleons from neutron star cores to be used in simulations
of cooling of superfluid neutron stars.Comment: 14 pages, 6 figures, A&A, accepte
Cooling neutron stars and superfluidity in their interiors
We study the heat capacity and neutrino emission reactions (direct and
modified Urca processes, nucleon-nucleon bremsstrahlung, Cooper pairing of
nucleons) in matter of supranuclear density of the neutron star cores with
superfluid neutrons and protons. Various superfluidity types are analysed
(singlet-state pairing and two types of triplet-state pairing, without and with
nodes of the gap at a nucleon Fermi surface). The results are used for cooling
simulations of isolated neutron stars. Both, the standard cooling and the
cooling enhanced by the direct Urca process, are strongly affected by nucleon
superfluidity. Comparison of cooling theory of isolated neutron stars with
observations of their thermal radiation may give stringent constraints on the
critical temperatures of the neutron and proton superfluidities in the neutron
star cores.Comment: LaTeX, 85 pages, 23 figures, Physics - Uspekhi (accepted
Bulk viscosity in superfluid neutron star cores. I. Direct Urca processes in npe\mu matter
The bulk viscosity of the neutron star matter due to the direct Urca
processes involving nucleons, electrons and muons is studied taking into
account possible superfluidity of nucleons in the neutron star cores. The cases
of singlet-state pairing or triplet-state pairing (without and with nodes of
the superfluid gap at the Fermi surface) of nucleons are considered. It is
shown that the superfluidity may strongly reduce the bulk viscosity. The
practical expressions for the superfluid reduction factors are obtained. For
illustration, the bulk viscosity is calculated for two models of dense matter
composed of neutrons, protons,electrons and muons. The presence of muons
affects the bulk viscosity due to the direct Urca reactions involving electrons
and produces additional comparable contribution due to the direct Urca
reactions involving muons. The results can be useful for studying damping of
vibrations of neutron stars with superfluid cores.Comment: 14 pages, 7 figures, latex, uses aa.cls, to be published in Astronomy
and Astrophysic
Neutrino emission due to Cooper pairing of protons in cooling neutron stars: Collective effects
The process of neutrino-pair radiation due to formation and breaking of
Cooper pairs of protons in superconducting cores of neutron stars is considered
with taking into account of the electromagnetic coupling of protons to ambient
electrons. It is shown that plasma polarization strongly modifies the effective
vector weak current of protons. Collective response of ambient electrons to the
proton quantum transition contributes coherently to the complete interaction
with the neutrino field and enhances the rate of neutrino-pair production by
two orders of magnitude.Comment: 11 pages, 2 figure
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