1,561 research outputs found
Neutrino emission in neutron matter from magnetic moment interactions
Neutrino emission drives neutron star cooling for the first several hundreds
of years after its birth. Given the low energy ( keV) nature of this
process, one expects very few nonstandard particle physics contributions which
could affect this rate. Requiring that any new physics contributions involve
light degrees of freedom, one of the likely candidates which can affect the
cooling process would be a nonzero magnetic moment for the neutrino. To
illustrate, we compute the emission rate for neutrino pair bremsstrahlung in
neutron-neutron scattering through photon-neutrino magnetic moment coupling. We
also present analogous differential rates for neutrino scattering off nucleons
and electrons that determine neutrino opacities in supernovae. Employing
current upper bounds from collider experiments on the tau magnetic moment, we
find that the neutrino emission rate can exceed the rate through neutral
current electroweak interaction by a factor two, signalling the importance of
new particle physics input to a standard calculation of relevance to neutron
star cooling. However, astrophysical bounds on the neutrino magnetic moment
imply smaller effects.Comment: 9 pages, 1 figur
On the Transport Properties of a Quark-Hadron Coulomb Lattice in the Cores of Neutron Stars
Already more that 40 years ago, it has been suggested that because of the
enormous mass densities in the cores of neutron stars, the hadrons in the
centers of neutron stars may undergo a phase transition to deconfined quark
matter. In this picture, neutron stars could contain cores made of pure (up,
down, strange) quark matter which are surrounded by a mixed phase of quarks and
hadrons. More than that, because of the competition between the Coulomb and the
surface energies associated with the positively charged regions of nuclear
matter and negatively charged regions of quark matter, the mixed phase may
develop geometrical structures, similarly to what is expected of the
sub-nuclear liquid-gas phase transition. In this paper we restrict ourselves to
considering the formation of rare phase blobs in the mixed quark-hadron phase.
The influence of rare phase blobs on the thermal and transport properties of
neutron star matter is investigated. The total specific heat, , thermal
conductivity, , and electron-blob Bremsstrahlung neutrino emissivities,
, of quark-hybrid matter are computed and the results
are compared with the associated thermal and transport properties of standard
neutron star matter. Our results show that the contribution of rare phase blobs
to the specific heat is negligibly small. This is different for the neutrino
emissivity from electron-blob Bremsstrahlung scattering, which turns out to be
of the same order of magnitude as the total contributions from other
Bremsstrahlung processes for temperatures below about K.Comment: minor changes, accepted by Phys. Rev.
Magnetars as cooling neutron stars with internal heating
We study thermal structure and evolution of magnetars as cooling neutron
stars with a phenomenological heat source in a spherical internal layer. We
explore the location of this layer as well as the heating rate that could
explain high observable thermal luminosities of magnetars and would be
consistent with the energy budget of neutron stars. We conclude that the heat
source should be located in an outer magnetar's crust, at densities rho < 5e11
g/cm^3, and should have the heat intensity of the order of 1e20 erg/s/cm^3.
Otherwise the heat energy is mainly emitted by neutrinos and cannot warm up the
surface.Comment: 8 pages, 5 figures, submitted to MNRA
On the angular distribution of extensive air showers
Angular distributions of extensive air showers with different number of
charged particles in the range 2.5x10^5--4x10^7 are derived using the
experimental data obtained with the EAS MSU array. Possible approximations of
the obtained distributions with different empiric functions available in
literature, are analysed. It is shown that the exponential function provides
the best approximation of the angular distributions in the sense of the
chi-squared criterion.Comment: 5 pages including 1 figur
Neutral weak currents in nucleon superfluid Fermi liquids: Larkin-Migdal and Leggett approaches
Neutrino emission in processes of breaking and formation of nucleon Cooper
pairs is calculated in the framework of the Larkin-Migdal and the Leggett
approaches to the description of superfluid Fermi liquids at finite
temperatures. We explain peculiarities of both approaches and explicitly
demonstrate that they lead to the same expression for the emissivity in pair
breaking and formation processes.Comment: 24 pages, 3 figure
Unstable Nonradial Oscillations on Helium Burning Neutron Stars
Material accreted onto a neutron star can stably burn in steady state only
when the accretion rate is high (typically super-Eddington) or if a large flux
from the neutron star crust permeates the outer atmosphere. For such situations
we have analyzed the stability of nonradial oscillations, finding one unstable
mode for pure helium accretion. This is a shallow surface wave which resides in
the helium atmosphere above the heavier ashes of the ocean. It is excited by
the increase in the nuclear reaction rate during the oscillations, and it grows
on the timescale of a second. For a slowly rotating star, this mode has a
frequency of approximately 20-30 Hz (for l=1), and we calculate the full
spectrum that a rapidly rotating (>>30 Hz) neutron star would support. The
short period X-ray binary 4U 1820--30 is accreting helium rich material and is
the system most likely to show this unstable mode,especially when it is not
exhibiting X-ray bursts. Our discovery of an unstable mode in a thermally
stable atmosphere shows that nonradial perturbations have a different stability
criterion than the spherically symmetric thermal perturbations that generate
type I X-ray bursts.Comment: Accepted for publication in Astrophysical Journal, 22 pages, 14
figure
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