6,931 research outputs found
On the structure of line-driven winds near black holes
A general physical mechanism of the formation of line-driven winds at the
vicinity of strong gravitational field sources is investigated in the frame of
General Relativity. We argue that gravitational redshifting should be taken
into account to model such outflows. The generalization of the Sobolev
approximation in the frame of General Relativity is presented. We consider all
processes in the metric of a nonrotating (Schwarzschild) black hole. The
radiation force that is due to absorbtion of the radiation flux in lines is
derived. It is demonstrated that if gravitational redshifting is taken into
account, the radiation force becomes a function of the local velocity gradient
(as in the standard line-driven wind theory) and the gradient of . We
derive a general relativistic equation of motion describing such flow. A
solution of the equation of motion is obtained and confronted with that
obtained from the Castor, Abbott & Klein (CAK) theory. It is shown that the
proposed mechanism could have an important contribution to the formation of
line-driven outflows from compact objects.Comment: 20 pages, submitted to Ap
Recent Progress in Parton Distributions and Implications for LHC Physics
I outline some of the most recent developments on the global fit to parton
distributions performed by the MRST collaboration.Comment: 6 pages, 7 figures. To appear in proceedings of XIII International
Workshop on Deep Inelastic Scattering, April,27 - May,1, 2005, Madison,
Wisconsin, US
Calculation of High Energy Neutrino-Nucleon Cross Sections and Uncertainties Using the MSTW Parton Distribution Functions and Implications for Future Experiments
We present a new calculation of the cross sections for charged current (CC)
and neutral current (NC) and interactions in the neutrino
energy range GeV using the most recent MSTW parton
distribution functions (PDFs), MSTW 2008. We also present the associated
uncertainties propagated from the PDFs, as well as parametrizations of the
cross section central values, their uncertainty bounds, and the inelasticity
distributions for ease of use in Monte Carlo simulations. For the latter we
only provide parametrizations for energies above GeV. Finally, we assess
the feasibility of future neutrino experiments to constrain the cross
section in the ultra-high energy (UHE) regime using a technique that is
independent of the flux spectrum of incident neutrinos. A significant deviation
from the predicted Standard Model cross sections could be an indication of new
physics, such as extra space-time dimensions, and we present expected
constraints on such models as a function of the number of events observed in a
future subterranean neutrino detector.Comment: 20 pages, 13 figures, 5 tables, published in Phys.Rev.D. This version
fixes a typo in Equation 16 of the publication. Also since version v1, the
following changes are in v2 and also in the published version: tables with cs
values, parametrization of the y distribution at low-y improved, the
discussions on likelihood and also earth absorption are expanded, added a
needed minus sign in Eq. 17 of v
Tidal coupling of a Schwarzschild black hole and circularly orbiting moon
We describe the possibility of using LISA's gravitational-wave observations
to study, with high precision, the response of a massive central body to the
tidal gravitational pull of an orbiting, compact, small-mass object. Motivated
by this application, we use first-order perturbation theory to study tidal
coupling for an idealized case: a massive Schwarzschild black hole, tidally
perturbed by a much less massive moon in a distant, circular orbit. We
investigate the details of how the tidal deformation of the hole gives rise to
an induced quadrupole moment in the hole's external gravitational field at
large radii. In the limit that the moon is static, we find, in Schwarzschild
coordinates and Regge-Wheeler gauge, the surprising result that there is no
induced quadrupole moment. We show that this conclusion is gauge dependent and
that the static, induced quadrupole moment for a black hole is inherently
ambiguous. For the orbiting moon and the central Schwarzschild hole, we find
(in agreement with a recent result of Poisson) a time-varying induced
quadrupole moment that is proportional to the time derivative of the moon's
tidal field. As a partial analog of a result derived long ago by Hartle for a
spinning hole and a stationary distant companion, we show that the orbiting
moon's tidal field induces a tidal bulge on the hole's horizon, and that the
rate of change of the horizon shape leads the perturbing tidal field at the
horizon by a small angle.Comment: 14 pages, 0 figures, submitted to Phys. Rev.
Gravitational wave scintillation by a stellar cluster
The diffraction effects on gravitational waves propagating through a stellar
cluster are analyzed in the relevant approximation of Fresnel diffraction
limit. We find that a gravitational wave scintillation effect - similar to the
radio source scintillation effect - comes out naturally, implying that the
gravitational wave intensity changes in a characteristic way as the observer
moves.Comment: 9 pages, in press in IJMP
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