3,167 research outputs found
Couplings of heavy hadrons with soft pions from QCD sum rules
We estimate the couplings in the Heavy Hadron Chiral Theory (HHCT) lagrangian
from the QCD sum rules in an external axial field. We take into account the
perturbative correction to the meson correlator in the infinite mass limit.
With the perturbative correction and three successive power corrections, the
meson correlator in an axial field becomes one of the best known correlators.
In spite of this, the corresponding sum rule is not very stable. It yields the
result g_1 F^2/(380MeV)^3 = 0.1 - 0.2, where F^2 = f_M^2 m/4 = (380MeV)^3 is
the central value of the heavy meson decay constant with the perturbative
correction. This result is surprisingly low as compared with the constituent
quark model estimate g_1 = 0.75. The sum rules for g_{2,3} following from
nondiagonal Sigma-Sigma and diagonal Lambda-Sigma baryon correlators in an
external axial field suggest g_{2,3} = 0.4 - 0.7, while diagonal Sigma-Sigma
and nondiagonal Lambda-Sigma baryon sum rules have too large uncertainties.Comment: 15 pages, LaTeX2e, 6 ps figures include
Statistical theory of thermal evolution of neutron stars
Thermal evolution of neutron stars is known to depend on the properties of
superdense matter in neutron star cores. We suggest a statistical analysis of
isolated cooling middle-aged neutron stars and old transiently accreting
quasi-stationary neutron stars warmed up by deep crustal heating in low-mass
X-ray binaries. The method is based on simulations of the evolution of stars of
different masses and on averaging the results over respective mass
distributions. This gives theoretical distributions of isolated neutron stars
in the surface temperature--age plane and of accreting stars in the photon
thermal luminosity--mean mass accretion rate plane to be compared with
observations. This approach permits to explore not only superdense matter but
also the mass distributions of isolated and accreting neutron stars. We show
that the observations of these stars can be reasonably well explained by
assuming the presence of the powerful direct Urca process of neutrino emission
in the inner cores of massive stars, introducing a slight broadening of the
direct Urca threshold (for instance, by proton superfluidity), and by tuning
mass distributions of isolated and accreted neutron stars.Comment: 13 pages, 20 figure
Shear viscosity in magnetized neutron star crust
The electron shear viscosity due to Coulomb scattering of degenerate
electrons by atomic nuclei throughout a magnetized neutron star crust is
calculated. The theory is based on the shear viscosity coefficient calculated
neglecting magnetic fields but taking into account gaseous, liquid and solid
states of atomic nuclei, multiphonon scattering processes, and finite sizes of
the nuclei albeit neglecting the effects of electron band structure. The
effects of strong magnetic fields are included in the relaxation time
approximation with the effective electron relaxation time taken from the
field-free theory. The viscosity in a magnetized matter is described by five
shear viscosity coefficients. They are calculated and their dependence on the
magnetic field and other parameters of dense matter is analyzed. Possible
applications and open problems are outlined.Comment: 6 pages, 3 figures, EPL, accepte
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