39,521 research outputs found
iResum: a new paradigm for resumming gravitational wave amplitudes
We introduce a new, resummed, analytical form of the post-Newtonian (PN),
factorized, multipolar amplitude corrections of the
effective-one-body (EOB) gravitational waveform of spinning, nonprecessing,
circularized, coalescing black hole binaries (BBHs). This stems from the
following two-step paradigm: (i) the factorization of the orbital
(spin-independent) terms in ; (ii) the resummation of the residual
spin (or orbital) factors. We find that resumming the residual spin factor by
taking its inverse resummed (iResum) is an efficient way to obtain amplitudes
that are more accurate in the strong-field, fast-velocity regime. The
performance of the method is illustrated on the and waveform
multipoles, both for a test-mass orbiting around a Kerr black hole and for
comparable-mass BBHs. In the first case, the iResum 's are much
closer to the corresponding "exact" functions (obtained solving numerically the
Teukolsky equation) up to the light-ring, than the nonresummed ones, especially
when the black-hole spin is nearly extremal. The iResum paradigm is also more
efficient than including higher post-Newtonian terms (up to 20PN order): the
resummed 5PN information yields per se a rather good numerical/analytical
agreement at the last-stable-orbit, and a well-controlled behavior up to the
light-ring. For comparable mass binaries (including the highest PN-order
information available, 3.5PN), comparing EOB with Numerical Relativity (NR)
data shows that the analytical/numerical fractional disagreement at merger,
without NR-calibration of the EOB waveform, is generically reduced by iResum,
from a of the usual approach to just a few percents. This suggests that
EOBNR waveform models for coalescing BBHs may be improved using iResum
amplitudes.Comment: 6 pages, 7 figures. Improved discussion for the comparable-mass cas
Linear-in-mass-ratio contribution to spin precession and tidal invariants in Schwarzschild spacetime at very high post-Newtonian order
Using black hole perturbation theory and arbitrary-precision computer
algebra, we obtain the post-Newtonian (pN) expansions of the
linear-in-mass-ratio corrections to the spin-precession angle and tidal
invariants for a particle in circular orbit around a Schwarzschild black hole.
We extract coefficients up to 20pN order from numerical results that are
calculated with an accuracy greater than 1 part in . These results
can be used to calibrate parameters in effective-one-body models of compact
binaries, specifically the spin-orbit part of the effective Hamiltonian and the
dynamically significant tidal part of the main radial potential of the
effective metric. Our calculations are performed in a radiation gauge, which is
known to be singular away from the particle. To overcome this irregularity, we
define suitable Detweiler-Whiting singular and regular fields in this gauge,
and we devise a rigorous mode-sum regularization method to compute the
invariants constructed from the regular field
Dynamics of Charged Bulk Viscous Collapsing Cylindrical Source With Heat Flux
In this paper, we have explored the effects of dissipation on the dynamics of
charged bulk viscous collapsing cylindrical source which allows the out follow
of heat flux in the form of radiations. Misner-Sharp formulism has been
implemented to drive the dynamical equation in term of proper time and radial
derivatives. We have investigated the effects of charge and bulk viscosity on
the dynamics of collapsing cylinder. To determine the effects of radial heat
flux, we have formulated the heat transport equations in the context of
Mller-Israel-Stewart theory by assuming that thermodynamics
viscous/heat coupling coefficients can be neglected within some approximations.
In our discussion, we have introduced the viscosity by the standard
(non-casual) thermodynamics approach. The dynamical equations have been coupled
with the heat transport equation equation, the consequences of resulting
coupled heat equation have been analyzed in detail.Comment: 17 Pages, no figur
Roadmap for Logistics Excellence: Need to Break the Unholy Equilibrium
This white paper attempts to provide a roadmap for India to move towards logistics excellence. Apart from raising issues that are currently relevant, it also draws from the issues that were raised in the previous three logistics summits and continue to be relevant today. As a departure from the earlier summits, it was felt that some of the issues could be presented even prior to the summit, to enable discussions and prioritization during the summit. The paper begins with an assessment of the overall performance of logistics in India, followed by a framework of an “unholy equilibrium” that seeks to explain where we are and why, and then provides actor wise action agenda as the roadmap towards logistics excellence.
Raising and Lowering operators of spin-weighted spheroidal harmonics
In this paper we generalize the spin-raising and lowering operators of
spin-weighted spherical harmonics to linear-in- spin-weighted
spheroidal harmonics where is an additional parameter present in the
second order ordinary differential equation governing these harmonics. One can
then generalize these operators to higher powers in . Constructing
these operators required calculating the -, - and -raising and
lowering operators (and various combinations of them) of spin-weighted
spherical harmonics which have been calculated and shown explicitly in this
paper
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