3,402,366 research outputs found
Legendre expansion of the neutrino-antineutrino annihilation kernel: Influence of high order terms
We calculate the Legendre expansion of the rate of the process up to 3rd order extending previous results
of other authors which only consider the 0th and 1st order terms. Using
different closure relations for the moment equations of the radiative transfer
equation we discuss the physical implications of taking into account quadratic
and cubic terms on the energy deposition outside the neutrinosphere in a
simplified model. The main conclusion is that 2nd order is necessary in the
semi-transparent region and gives good results if an appropriate closure
relation is used.Comment: 14 pages, 4 figures. To be published in A&A Supplement Serie
Contractions from to the M-theory superalgebra extended by additional fermionic generators
We study here the generalized Weimar-Woods contractions of the superalgebra
in order to obtain a suitable algebra that could
describe the gauge group of supergravity. The contracted superalgebras
are assumed to be given in terms of fermionic extensions of the M-theory
superalgebra. We show that the only superalgebra of this type obtained by
contraction is the only one for which the three-form of supergravity
cannot be trivialized. Therefore, supergravity cannot be connected in
this way with a contraction of
The dynamic electric polarizability of a particle bound by a double delta potential
In this paper we derive an expression for the dynamic electric polarizability
of a particle bound by a double delta potential for frequencies below and above
the absolute value of the particle's ground state energy. The derived
expression will be used to study some of the fundamental features of the system
and its representation of real systems. In addition we derive a general
expression of the dynamic electric polarizability for a potential of
multi-delta functions.Comment: 11 pages, 5 figure
Comments on a Full Quantization of the Torus
Gotay showed that a representation of the whole Poisson algebra of the torus
given by geometric quantization is irreducible with respect to the most natural
overcomplete set of observables. We study this representation and argue that it
cannot be considered as physically acceptable. In particular, classically
bounded observables are quantized by operators with unbounded spectrum.
Effectively, the latter amounts to lifting the constraints that compactify both
directions in the torus.Comment: 10 pages. New "Discussion" section. References added. To appear in
IJMP
Submm-bright QSOs at z~2: signposts of co-evolution at high z
We have assembled a sample of 5 X-ray and submm-luminous z~2 QSOs which are
therefore both growing their central black holes through accretion and forming
stars copiously at a critical epoch. Hence, they are good laboratories to
investigate the co-evolution of star formation and AGN. We have performed a
preliminary analysis of the AGN and SF contributions to their UV-to-FIR SEDs,
fitting them with simple direct (disk), reprocessed (torus) and star formation
components. All three are required by the data and hence we confirm that these
objects are undergoing strong star formation in their host galaxies at rates
500-2000 Msun/y. Estimates of their covering factors are between about 30 and
90%. In the future, we will assess the dependence of these results on the
particular models used for the components and relate their observed properties
to the intrinsice of the central engine and the SF material, as well as their
relevance for AGN-galaxy coevolution.Comment: 6 pages, 2 figures, contributed talk to "Nuclei of Seyfert galaxies
and QSOs - Central engine & conditions of star formation" November 6-8, 2012.
MPIfR, Bonn, Germany. Po
Physical parameters of GRB 970508 and GRB 971214 from their afterglow synchrotron emission
We have calculated synchrotron spectra of relativistic blast waves, and find
predicted characteristic frequencies that are more than an order of magnitude
different from previous calculations. For the case of an adiabatically
expanding blast wave, which is applicable to observed gamma-ray burst (GRB)
afterglows at late times, we give expressions to infer the physical properties
of the afterglow from the measured spectral features.
We show that enough data exist for GRB970508 to compute unambiguously the
ambient density, n=0.03/cm**3, and the blast wave energy per unit solid angle,
E=3E52 erg/4pi sr. We also compute the energy density in electrons and magnetic
field. We find that they are 12% and 9%, respectively, of the nucleon energy
density and thus confirm for the first time that both are close to but below
equipartition.
For GRB971214, we discuss the break found in its spectrum by Ramaprakash et
al. (1998). It can be interpreted either as the peak frequency or as the
cooling frequency; both interpretations have some problems, but on balance the
break is more likely to be the cooling frequency. Even when we assume this, our
ignorance of the self-absorption frequency and presence or absence of beaming
make it impossible to constrain the physical parameters of GRB971214 very well.Comment: very strongly revised analysis of GRB971214 and discussion, submitted
to ApJ, 11 pages LaTeX, 4 figures, uses emulateapj.sty (included
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