Anomalous mass dependence of radiative quark energy loss in a finite-size quark-gluon plasma

We demonstrate that for a finite-size quark-gluon plasma the induced gluon radiation from heavy quarks is stronger than that for light quarks when the gluon formation length becomes comparable with (or exceeds) the size of the plasma. The effect is due to oscillations of the light-cone wave function for the in-medium $q\to gq$ transition. The dead cone model by Dokshitzer and Kharzeev neglecting quantum finite-size effects is not valid in this regime. The finite-size effects also enhance the photon emission from heavy quarks.Comment: 8 pages, 3 figure

On the relationship between nonlinear equations integrable by the method of characteristics and equations associated with commuting vector fields

It was shown recently that Frobenius reduction of the matrix fields reveals interesting relations among the nonlinear Partial Differential Equations (PDEs) integrable by the Inverse Spectral Transform Method ($S$-integrable PDEs), linearizable by the Hoph-Cole substitution ($C$-integrable PDEs) and integrable by the method of characteristics ($Ch$-integrable PDEs). However, only two classes of $S$-integrable PDEs have been involved: soliton equations like Korteweg-de Vries, Nonlinear Shr\"odinger, Kadomtsev-Petviashvili and Davey-Stewartson equations, and GL(N,\CC) Self-dual type PDEs, like Yang-Mills equation. In this paper we consider the simple five-dimensional nonlinear PDE from another class of $S$-integrable PDEs, namely, scalar nonlinear PDE which is commutativity condition of the pair of vector fields. We show its origin from the (1+1)-dimensional hierarchy of $Ch$-integrable PDEs after certain composition of Frobenius type and differential reductions imposed on the matrix fields. Matrix generalization of the above scalar nonlinear PDE will be derived as well.Comment: 14 pages, 1 figur

Induced photon emission from quark jets in ultrarelativistic heavy-ion collisions

We study the induced photon bremsstrahlung from a fast quark produced in AA-collisions due to multiple scattering in quark-gluon plasma. For RHIC and LHC conditions the induced photon spectrum is sharply peaked at photon energy close to the initial quark energy. In this region the contribution of the induced radiation to the photon fragmentation function exceeds the ordinary vacuum radiation. Contrary to previous analyses our results show that at RHIC and LHC energies the final-state interaction effects in quark-gluon plasma do not suppress the direct photon production, and even may enhance it at p_{T} about 5-15 GeV.Comment: 11 pages, 4 figure

Classical Strongly Coupled QGP: VII. Energy Loss

We use linear response analysis and the fluctuation-dissipation theorem to derive the energy loss of a heavy quark in the SU(2) classical Coulomb plasma in terms of the $l=1$ monopole and non-static structure factor. The result is valid for all Coulomb couplings $\Gamma=V/K$, the ratio of the mean potential to kinetic energy. We use the Liouville equation in the collisionless limit to assess the SU(2) non-static structure factor. We find the energy loss to be strongly dependent on $\Gamma$. In the liquid phase with $\Gamma\approx 4$, the energy loss is mostly metallic and soundless with neither a Cerenkov nor a Mach cone. Our analytical results compare favorably with the SU(2) molecular dynamics simulations at large momentum and for heavy quark masses.Comment: 18 pages, 15 figures. v2: added references, changed title, replaced figures for Fig. 7, corrected typo

Variation of jet quenching from RHIC to LHC and thermal suppression of QCD coupling constant

We perform a joint jet tomographic analysis of the data on the nuclear modification factor $R_{AA}$ from PHENIX at RHIC and ALICE at LHC. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant. Our results show that the observed slow variation of $R_{AA}$ from RHIC to LHC indicates that the QCD coupling constant is suppressed in the quark-gluon plasma produced at LHC.Comment: 9 pages, 2 figure

Statistical Description of Acoustic Turbulence

We develop expressions for the nonlinear wave damping and frequency correction of a field of random, spatially homogeneous, acoustic waves. The implications for the nature of the equilibrium spectral energy distribution are discussedComment: PRE, Submitted. REVTeX, 16 pages, 3 figures (not included) PS Source of the paper with figures avalable at http://lvov.weizmann.ac.il/onlinelist.htm

Non-linear effects in hopping conduction of single-crystal La_{2}CuO_{4 + \delta}

The unusual non-linear effects in hopping conduction of single-crystal La_{2}CuO_{4 + \delta} with excess oxygen has been observed. The resistance is measured as a function of applied voltage U (10^{-3} V - 25 V) in the temperature range 5 K 0.1 V) the conduction of sample investigated corresponds well to Mott's variable-range hopping (VRH). An unusual conduction behavior is found, however, in low voltage range (approximately below 0.1 V), where the influence of electric field and (or) electron heating effect on VRH ought to be neglected. Here we have observed strong increase in resistance at increasing U at T < 20 K, whereas at T > 20 K the resistance decreases with increasing U. The magnetoresistance of the sample below 20 K has been positive at low voltage and negative at high voltage. The observed non-Ohmic behavior is attributable to inhomogeneity of the sample, and namely, to the enrichment of sample surface with oxygen during the course of the heat treatment of the sample in helium and air atmosphere before measurements. At low enough temperature (below 20 K) the surface layer with increased oxygen concentration is presumed to consist of disconnected superconducting regions (with T_{c} about 20 K) in poor-conducting matrix. The results obtained demonstrate that transport properties of cuprate oxides may be determined in essential degree by structural or stoichimetric inhomogeneities. This should be taken into account at evaluation of "quality" of high-temperature superconductors on the basis of transport properties measurements.Comment: 12 pages, REVTex, 11 Postscript figures, To be published in Fizika Nizkikh Temperatur (published by AIP as Low Temperature Physics

Final state interaction effects in D(e,e′p)D(e,e'p) scattering

We present a systematic study of the final-state interaction (FSI) effects in $D(e,e'p)$ scattering in the CEBAF energy range with particular emphasis on the phenomenon of the angular anisotropy of the missing momentum distribution. We find that FSI effects dominate at missing momentum p_m \gsim 1.5 fm$^{-1}$. FSI effects in the excitation of the $S$-wave state are much stronger than in the excitation of the $D$-wave.Comment: LATEX, 11 pages, 5 figures available from the authors on request, KFA-IKP(TH)-1994-3

Differential reductions of the Kadomtsev-Petviashvili equation and associated higher dimensional nonlinear PDEs

We represent an algorithm allowing one to construct new classes of partially integrable multidimensional nonlinear partial differential equations (PDEs) starting with the special type of solutions to the (1+1)-dimensional hierarchy of nonlinear PDEs linearizable by the matrix Hopf-Cole substitution (the B\"urgers hierarchy). We derive examples of four-dimensional nonlinear matrix PDEs together with they scalar and three-dimensional reductions. Variants of the Kadomtsev-Petviashvili type and Korteweg-de Vries type equations are represented among them. Our algorithm is based on the combination of two Frobenius type reductions and special differential reduction imposed on the matrix fields of integrable PDEs. It is shown that the derived four-dimensional nonlinear PDEs admit arbitrary functions of two variables in their solution spaces which clarifies the integrability degree of these PDEs.Comment: 20 pages, 1 fugur