2,786 research outputs found
The neutrino emission due to plasmon decay and neutrino luminosity of white dwarfs
One of the effective mechanisms of neutrino energy losses in red giants,
presupernovae and in the cores of white dwarfs is the emission of
neutrino-antineutrino pairs in the process of plasmon decay. In this paper, we
numerically calculate the emissivity due to plasmon decay in a wide range of
temperatures (10^7-10^11) K and densities (200-10^14) g cm^-3. Numerical
results are approximated by convenient analytical expressions. We also
calculate and approximate by analytical expressions the neutrino luminosity of
white dwarfs due to plasmon decay, as a function of their mass and internal
temperature. This neutrino luminosity depends on the chemical composition of
white dwarfs only through the parameter mu_e (the net number of baryons per
electron) and is the dominant neutrino luminosity in all white dwarfs at the
neutrino cooling stage.Comment: 19 pages, 3 figures, accepted for publication in MNRA
Randomly Charged Polymers, Random Walks, and Their Extremal Properties
Motivated by an investigation of ground state properties of randomly charged
polymers, we discuss the size distribution of the largest Q-segments (segments
with total charge Q) in such N-mers. Upon mapping the charge sequence to
one--dimensional random walks (RWs), this corresponds to finding the
probability for the largest segment with total displacement Q in an N-step RW
to have length L. Using analytical, exact enumeration, and Monte Carlo methods,
we reveal the complex structure of the probability distribution in the large N
limit. In particular, the size of the longest neutral segment has a
distribution with a square-root singularity at l=L/N=1, an essential
singularity at l=0, and a discontinuous derivative at l=1/2. The behavior near
l=1 is related to a another interesting RW problem which we call the "staircase
problem". We also discuss the generalized problem for d-dimensional RWs.Comment: 33 pages, 19 Postscript figures, RevTe
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