121246958
Electromagnetic absorption cross section of Reissner-Nordström black holes
The absorption cross section of Reissner-Nordstroem black holes for the electromagnetic field is computed numerically for arbitrary frequencies. The numerical results are in excellent agreement with the low- and high-frequency limits, which are obtained with analytical methods. Special emphasis is given to the extreme Reissner-Nordstroem black hole case.
124961099
Absorption of scalar waves by static black holes and analogues
121641075
Electromagnetic absorption cross section of Reissner-Nordström black holes revisited
The absorption cross section of Reissner-Nordstroem black holes for the electromagnetic field is computed numerically for arbitrary frequencies, taking into account the coupling of the electromagnetic and gravitational perturbations. We also compute the conversion coefficients of electromagnetic to gravitational waves by scattering from a Reissner-Nordstroem black hole.
118486572
Scattering by a draining bathtub vortex
We present an analysis of scattering by a fluid-mechanical `black hole analogue', known as the draining bathtub vortex: a two-dimensional flow which possesses both a sonic horizon and an ergoregion. We consider the scattering of a plane wave of fixed frequency impinging upon the vortex. At low frequency, we encounter a modified Aharonov-Bohm effect. At high frequencies, we observe regular `orbiting' oscillations in the scattering length, due to interference between contra-orbiting rays. We present approximate formulae for both effects, and a selection of numerical results obtained by summing partial-wave series. Finally, we examine interference patterns in the vicinity of the vortex, and highlight the prospects for experimental investigation.
119111122
Greybody factors for nonminimally coupled scalar fields in Schwarzschild–de Sitter spacetime
We compute the greybody factors for non-minimally coupled scalar fields in four-dimensional Schwarzschild-de Sitter spacetime. In particular, we demonstrate that the zero-angular-momentum greybody factor generically tends to zero in the zero-frequency limit like frequency squared if there is non-vanishing coupling to the scalar curvature. This is in contrast with the minimally coupled case, where the greybody factor is known to tend to a finite constant. We also study the Hawking radiation for non-minimally coupled massless scalar fields in Schwarzschild-de Sitter spacetime, formulate a sensible notion of a generalized absorption cross section and investigate its properties.
55565544
Absorption of planar massless scalar waves by Kerr black holes
We consider planar massless scalar waves impinging upon a Kerr black hole, for general angles of incidence. We compute the absorption cross section via the partial wave approach, and present a gallery of results. In the low-frequency regime, we show that the cross section approaches the horizon area; in the high-frequency regime, we show that the cross section approaches the geodesic capture cross section. In the aligned case, we extend the complex angular momentum method to obtain a `sinc' approximation, which relates the regular high-frequency oscillations in the cross section to the properties of the polar null orbit. In the non-aligned case, we show, via a semi-analytic approximation, that the reduction in symmetry generates a richer, less regular absorption cross section. We separate the absorption cross section into corotating and counterrotating contributions, showing that the absorption is larger for counterrotating waves, as expected.
99013897
An independent estimate of the triple-Pomeron coupling
Abstract The value of the important triple-Pomeron coupling is estimated by an unorthodox procedure using the known diffractive parton distribution functions. The result is g 3 P ≃ 0.2 g N , where g N is the Pomeron–nucleon coupling. This is in excellent agreement with an independent determination, g 3 P ≃ 0.2 g N , previously obtained by analysing the available data in the triple-Regge region with absorptive effects taken into account.
120230298
Global analysis of HERA and RHIC data with a momentum space dipole model
Within the kt-factorization formalism we show the results on the charged hadron yield for p + p collisions at LHC using the AGBS momentum space dipole scattering amplitude. This model is based on a correspondence between the LO Balitsky-Kovchegov evolution equation and the reaction-diffusion physics and was globally fitted to the DIS HERA data and inclusive hadron production on p + p and d + Au collisions at RHIC. Despite the fact it is a LO calculation, the present LHC data is quite well described.
120006989
Bound states in a strong magnetic field
We expect a strong magnetic field to be produced in the perpendicular direction to the reaction plane, in a noncentral heavy-ion collision . The strength of the magnetic field is estimated to be eB ∼ m2π ∼ 0.02 GeV2 at the RHIC and eB ∼ 15m2π ∼ 0.3 GeV2 at the LHC. We investigate the effects of the magnetic field on B0 and D0 mesons, focusing on the changes of the energy levels and of the mass of the bound states.
53584802
BFKL equation for an integrated gluon density
We show how it is possible to rewrite the BFKL equation for the unintegrated gluon distribution, in terms of integrated gluons, similar to that used in DGLAP. We add to our equation the next-to-leading log terms which provide exact energy-momentum conservation and account for the kinematic constraint in real gluon emission. In this way the equation includes the major part of the higher-order corrections to BFKL evolution. We discuss the possibility to obtain a unified BFKL–DGLAP evolution equation relevant to processes at the LHC where both log$$(1/x)$$(1/x) and log$$Q^2$$Q2 are large simultaneously.
119989152
A–dependence in dilepton rapidity distributions: parton model and dipole approach analysis
We calculate dilepton production cross section at RHIC using the improved parton model and color dipole approach in p–A collisions at backward rapidities. Our results are given as nuclear modification factors. We test three nuclear parton distribution functions: EKS, EPS08 and EPS09; we found no changes in the results. In the color dipole approach, we use GBW, DHJ, and BUW color dipole cross section models; again, no relevant difference is found in the nuclear modification factor, in spite of that DHJ breaks geometric scaling and that the p–p cross sections show relevant differences. The presence of intrinsic transverse momentum in the improved parton model is investigated, showing that nuclear effects are sensitive to this assumption. The color dipole approach lacks this intrinsic k T and thus nuclear effects can discriminate among both analysis. We extend our improved parton model results to forward rapidities and compare with CGC results, obtaining agreement between the models.