118954601
Scattering of sound waves by a canonical acoustic hole
This is a study of a monochromatic planar perturbation impinging upon a canonical acoustic hole. We show that acoustic hole scattering shares key features with black hole scattering. The interference of wave fronts passing in opposite senses around the hole creates regular oscillations in the scattered intensity. We examine this effect by applying a partial wave method to compute the differential scattering cross section for a range of incident wavelengths. We demonstrate the existence of a scattering peak in the backward direction, known as the glory. We show that the glory created by the canonical acoustic hole is approximately 170 times less intense than the glory created by the Schwarzschild black hole, for equivalent horizon-to-wavelength ratios. We hope that direct experimental observations of such effects may be possible in the near future.
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.
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.
124961099
Absorption of scalar waves by static black holes and analogues
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.
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.
38260061
Dipole Scattering Amplitude in Momentum Space: Investigating Fluctuations at HERA
not included in the original Balitsky-JIMWLK hierarchy and obviously missed in its mean field version, the BK equation. The fluctuations have been exhaustively investigated in recent years and their effects in the high energy evolution will be discussed in the next sections of this contribution. What one can antecipate is that they dramatically influence the high energy scattering, at least in the case when the strong coupling constant as is fixed. Among these investigations, one can cite a recent study [6] of the possible implications of the gluon number fluctuations in the measurements of the F2 proton structure function of deep inelastic scattering (DIS) at HERA, through well known models for the dipole-proton cross section in coordinate space [7,8]. The results show that, although they may be present in the DIS measurements, they seem not to strongly influence the evolution at HERA energies. In these proceedings we use the first model for the dipoleproton cross section developed in momentum space [9] with fluctuation effects included to fit the last HERA data. This model has shown to be successful in the description of DIS data, specially with heavy quark (charm) contributions included, by using a mean-field (BK) inspired parametrization for the scattering amplitude, which enters in the expression for the dipole-proton cross section. Some preliminary results are presented and some future expectations on the effects of fluctuations at HERA are discussed.
122917905
DILEPTON PRODUCTION AT BACKWARD RAPIDITIES
119285420
DIS and the effects of fluctuations: a momentum space analysis
Among the dipole models of deep inelastic scattering at small values of the Bjorken variable x, one has been recently proposed which relates the virtual photon–proton cross section to the dipole–proton forward scattering amplitude in momentum space. The latter is parametrized by an expression which interpolates between its behavior at saturation and the travelling wave, ultraviolet, amplitudes predicted by perturbative QCD from the Balitsky–Kovchegov equation. Inspired by recent developments in coordinate space, we use this model to parametrize the structure function of the proton and confront it with HERA data on ep deep inelastic scattering. Both event-by-event and physical amplitudes are considered, the latter being used to investigate the effect of gluon number fluctuations, beyond the mean-field approximation. We conclude that fluctuations are not present in DIS at HERA energies.
120780905
Hadron production at LHC in dipole momentum space
The dipole color approach is the framework that considers the quark-antiquark pair scattering off the target. The rapidity evolution of color dipoles is given by the nonlinear Balitsky-Kovchegov (BK) equation, for which analytical solutions are not yet known. A good way to explore the asymptotic BK solutions is through the traveling wave method of QCD, that uses a correspondence between the BK evolution equation in momentum space and reaction-diffusion physics. Using the traveling wave based AGBS model for the dipole amplitude in momentum space, and within the k{sub t}-factorization formalism, we describe the LHC data on single inclusive hadron yield for p-p collisions.
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.