368 research outputs found
Neutrino Interactions in Octet Baryon Matter
Neutrino processes caused by the neutral current are studied in octet baryon
matter. Previous confusion about the baryonic matrix elements of the neutral
current interaction is excluded, and a correct table for them improved by
consideration of the proton spin problem is presented instead.Comment: 6 page
Occurrence of Hyperon Superfluidity in Neutron Star Cores
Superfluidity of and admixed in neutron star (NS) cores
is investigated realistically for hyperon ()-mixed NS models obtained using
a -matrix-based effective interaction approach. Numerical results for the
equation of state (EOS) with the mixing ratios of the respective components and
the hyperon energy gaps including the temperature dependence are presented.
These are meant to serve as physical inputs for -cooling calculations of
NSs. By paying attention to the uncertainties of the EOS and the
interactions, it is shown that both and are superfluid as
soon as they appear although the magnitude of the critical temperature and the
density region where superfluidity exists depend considerably on the
pairing potential. Considering momentum triangle condition and the occurrence
of superfluidity, it is found that a so-called `` hyperon
cooling\rq\rq~(neutrino-emission from direct Urca process including )
combined with -superfluidity may be able to account for observations of the
colder class of NSs. It is remarked that -hyperons play a decisive
role in the hyperon cooling scenario. Some comments are given regarding the
consequences of the less attractive interaction recently
suggested by the `` NAGARA event\rq\rq~He.Comment: 25 pages, 12figures; final version; will appear in Prog. THeor. Phys.
Vol.115, No.
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
Quark description of the Nambu-Goldstone bosons in the color-flavor locked phase
We investigate the color-singlet order parameters and the quark description
of the Nambu-Goldstone (NG) bosons in the color-flavor locked (CFL) phase. We
put emphasis on the NG boson (phason) called ``H'' associated with the
symmetry breaking. We qualitatively argue the nature of H as
the second sound in the hydrodynamic regime. We articulate, based on a diquark
picture, how the structural change of the condensates and the associated NG
bosons occurs continuously from hadronic to CFL quark matter if the
quark-hadron continuity is realized. We sharpen the qualitative difference
between the flavor octet pions and the singlet phason. We propose a conjecture
that superfluid H matter undergoes a crossover to a superconductor with
tightly-bound diquarks, and then a crossover to superconducting matter with
diquarks dissociated.Comment: 14 pages, 1 table, 1 figure and confusing statements are correcte
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
Confronting Neutron Star Cooling Theories with New Observations
With the successful launch of Chandra and XMM/Newton X-ray space missions
combined with the lower-energy band observations, we are in the position where
careful comparison of neutron star cooling theories with observations will make
it possible to distinguish among various competing theories. For instance, the
latest theoretical and observational developments already exclude both nucleon
and kaon direct URCA cooling. In this way we can now have realistic hope for
determining various important properties, such as the composition, degree of
superfluidity, the equation of state and steller radius. These developments
should help us obtain better insight into the properties of dense matter.Comment: 11 pages, 1 figur
Baryon superfluidity and neutrino emissivity of neutron stars
For neutron stars with hyperon-mixed core, neutrino emissivity is studied
under the equation of state, obtained by introducing repulsive three-body force
universal for all baryons so as to assure the maximum mass compatible with the
observation. By paying attention to the density-dependence of critical
temperatures of baryon superfluids, which reflect the nature of baryon-baryon
interaction and control neutron star cooling, we show what neutrino emission
processes are efficient in the regions with and without hyperon mixing and
remark its implications related to neutron star cooling.Comment: 5pages, 4 figure
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