118963556
AharonovBohm effect in a draining bathtub vortex
Abstract We study planar waves in a circulating, draining fluid flow, which: (i) exhibit an analogue of the Aharonov–Bohm (AB) effect in Quantum Mechanics; (ii) obey a Klein–Gordon equation on an ‘effective spacetime’ which resembles the Kerr spacetime of General Relativity; and (iii) may be observed in the laboratory using gravity waves in a shallow basin. We describe a modified AB effect which depends on two dimensionless parameters, associated with the circulation α and draining β rates; we call this the ‘ αβ effect’. We show that the αβ effect is inherently asymmetric even in the low-frequency limit, and that it leads to novel interference patterns which carry the signature of both rotation and absorption.
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
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.
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.
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.
122039764
Running coupling and pomeron loop effects on inclusive and diffractive DIS cross sections
Within the framework of a (1+1)-dimensional model which mimics high-energy QCD, we study the behavior of the cross sections for inclusive and diffractive deep inelastic γ∗h scattering cross sections. We analyze the cases of both fixed and running coupling within the mean-field approximation, in which the evolution of the scattering amplitude is described by the Balitsky–Kovchegov equation, and also through the pomeron loop equations, which include in the evolution the gluon number fluctuations. In the diffractive case, similarly to the inclusive one, suppression of the diffusive scaling, as a consequence of the inclusion of the running of the coupling, is observed.
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.
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.
4827292
Backward dilepton production in color dipole and parton models
The Drell-Yan dilepton production at backward rapidities is studied in proton-nucleus collisions at Relativistic Heavy Ion Collider and LHC energies by comparing two different approaches: the k{sub T} factorization at next-to-leading order with intrinsic transverse momentum and the same process formulated in the target rest frame, i.e., the color dipole approach. Our results are expressed in terms of the ratio between p(d)-A and p-p collisions as a function of transverse momentum and rapidity. Three nuclear parton distribution functions are used: EKS (Eskola, Kolhinen, and Ruuskanen), EPS08, and EPS09 and, in both approaches, dileptons show sensitivity to nuclear effects, specially regarding the intrinsic transverse momentum. Also, there is room to discriminate between formalisms: the color dipole approach lacks soft effects introduced by the intrinsic k{sub T}. Geometric scaling GBW (Golec-Biernat and Wusthoff) and BUW (Boer, Utermann, and Wessels) color dipole cross section models and also a DHJ (Dumitru, Hayashigaki, and Jalilian-Marian) model, which breaks geometric scaling, are used. No change in the ratio between collisions is observed, showing that this observable is not changed by the particular shape of the color dipole cross section. Furthermore, our k{sub T} factorization results are compared with color glass condensate results at forward rapidities: themore » results agree at Relativistic Heavy Ion Collider although disagree at LHC, mainly due to the different behavior of target gluon and quark shadowing.« less
118600889
The LHC can probe small x PDFs; the treatment of the infrared region
First, we show how to reduce the sensitivity of the NLO predictions of the Drell-Yan production of low-mass, lepton-pairs, at high rapidity, to the choice of factorization scale. In this way, observations of this process at the LHC can make direct measurements of parton distribution functions in the low x domain; x ≲10−4. Second, we find an inconsistency in the conventional NLO treatment of the infrared region. We illustrate the problem using the NLO coefficient function of Drell-Yan production.