120762974
Absorption of planar waves in a draining bathtub
We present an analysis of the absorption of acoustic waves by a black hole analogue in (2+1) dimensions generated by a fluid flow in a draining bathtub. We show that the low-frequency absorption length is equal to the acoustic hole circumference and that the high-frequency absorption length is 4 times the ergoregion radius. For intermediate values of the wave frequency, we compute the absorption length numerically and show that our results are in excellent agreement with the low- and high-frequency limits. We analyze the occurrence of superradiance, manifested as negative partial absorption lengths for corotating modes at low frequencies.
124961099
Absorption of scalar waves by static black holes and analogues
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.
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.
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.
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.
119262141
Momentum space saturation model for deep inelastic scattering and single inclusive hadron production
We show how the AGBS model, originally developed for deep inelastic scattering applied to HERA data on the proton structure function, can also describe the RHIC data on single inclusive hadron yield for $d+Au$ and $p+p$ collisions through a new simultaneous fit. The single inclusive hadron production is modeled through the color glass condensate, which uses the quark(and gluon)--condensate amplitudes in momentum space. The AGBS model is also a momentum space model based on the asymptotic solutions of the BK equation, although a different definition of the Fourier transform is used. This aspect is overcome and a description entirely in transverse momentum of both processes arises for the first time. The small difference between the simultaneous fit and the one for HERA data alone suggests that the AGBS model describes very well both kind of processes and thus emerges as a good tool to investigate the inclusive hadron production data. We use this model for predictions at LHC energies, which agree very well with available experimental data.
119249393
Improving the Drell–Yan probe of small x partons at the LHC via a kt cut
We show that the observation of the Drell–Yan production of low-mass lepton-pairs (M≲20 GeV) at high rapidities (Y≳3) at the LHC can make a direct measurement of parton distribution functions (PDFs) in the low x region, x≲10−4. We describe a procedure that greatly reduces the sensitivity of the predictions to the choice of the factorization scale and, in particular, show how, by imposing a cutoff on the transverse momentum of the lepton-pair, the data are able to probe PDFs in the important low scale, low x domain. We include the effects of the Sudakov suppression factor.
119213193
Inclusive hadron and photon production at the LHC in dipole momentum space
Using a momentum space model for the dipole scattering amplitude we present an analysis of the saturation effects at LHC energies, describing the data on proton-proton and proton-lead collisions. The model is based on the asymptotic solutions of the Balitsky-Kovchegov equation, being ideal in the saturation domain where the target wave function has a high occupation number. We also make predictions for the nuclear modification ratios on charged hadron and prompt photon production in the forward region, where the high parton density effects are important.
118485927
Treatment of heavy quarks in QCD
We show that to correctly describe the effects of the heavy-quark mass, mh, in DGLAP evolution, it is necessary to work in the so-called ‘physical’ scheme. In this way, we automatically obtain a smooth transition through the heavy-quark thresholds. Moreover, we show that to obtain NLO accuracy, it is sufficient to account for the heavy-quark mass, mh, just in the LO (one-loop) splitting function. The use of the $\overline{\mathrm{MS}}$ factorization scheme is not appropriate, since at NLO we deal with a mixture of quarks and gluon (that is, the mass of the heavy parton is not well-defined). The formulas for the explicit mh dependence of the splitting functions, and for αs, are presented.
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.