3,261 research outputs found
Relating the description of gluon production in pA collisions and parton energy loss in AA collisions
We calculate the classical gluon field of a fast projectile passing through a
dense medium. We show that this allows us to calculate both the initial state
gluon production in proton-nucleus collisions and the final state gluon
radiation off a hard parton produced in nucleus-nucleus collisions. This
unified description of these two phenomena makes the relation between the
saturation scale and the transport coefficient more transparent.
Also, we discuss the validity of the eikonal approximation for gluon
propagation inside the nucleus in proton-nucleus collisions at RHIC energy.Comment: 18 pages, 3 figure
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 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
Transverse Spectra of Radiation Processes in Medium
We develop a formalism for evaluation of the transverse momentum dependence
of cross sections of the radiation processes in medium. The analysis is based
on the light-cone path integral approach to the induced radiation. The results
are applicable in both QED and QCD
The role of finite kinematic bounds in the induced gluon emission from fast quarks in a finite size quark-gluon plasma
We study the influence of finite kinematic boundaries on the induced gluon
radiation from a fast quark in a finite size quark-gluon plasma. The
calculations are carried out for fixed and running coupling constant. We find
that for running coupling constant the kinematic correction to the radiative
energy loss is small for quark energy larger than about 5 GeV. Our results
differ both analytically and numerically from that obtained by the GLV group
[6]. The effect of the kinematic cut-offs is considerably smaller than reported
in [6].Comment: 11 pages, 4 figure
Radiative parton energy loss and jet quenching in high-energy heavy-ion collisions
We study within the light-cone path integral approach [3] the effect of the
induced gluon radiation on high-p_{T} hadrons in high-energy heavy-ion
collisions. The induced gluon spectrum is represented in a new form which is
convenient for numerical simulations. For the first time, computations are
performed with a realistic parametrization of the dipole cross section. The
results are in reasonable agreement with suppression of high-p_{T} hadrons in
Au+Au collisions at \sqrt{s}=200 GeV observed at RHIC.Comment: 12 pages, 3 epsi figures. Typos correcte
Collinear Photon Emission from the Quark-Gluon Plasma: The Light-Cone Path Integral Formulation
We give a simple physical derivation of the photon emission rate from the
weakly coupled quark-gluon plasma connected with the collinear processes and . The analysis is based on the light-cone
path integral approach to the induced radiation. Our results agree with that by
Arnold, Moore and Yaffe obtained using the real-time thermal perturbation
theory. It is demonstrated that the solution of the AMY integral equation is
nothing but the time-integrated Green's function of the light-cone path
integral approach written in the momentum representation.Comment: 12 pages, 2 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 (-integrable PDEs),
linearizable by the
Hoph-Cole substitution (-integrable PDEs) and integrable by the method of
characteristics (-integrable PDEs). However, only two classes of
-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 -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 -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
Elastic energy loss and longitudinal straggling of a hard jet
The elastic energy loss encountered by jets produced in deep-inelastic
scattering (DIS) off a large nucleus is studied in the collinear limit. In
close analogy to the case of (non-radiative) transverse momentum broadening,
which is dependent on the medium transport coefficient , a class of
medium enhanced higher twist operators which contribute to the non-radiative
loss of the forward light-cone momentum of the jet () are identified and
the leading correction in the limit of asymptotically high is isolated.
Based on these operator products, a new transport coefficient is
motivated which quantifies the energy loss per unit length encountered by the
hard jet. These operator products are then computed, explicitly, in the case of
a similar hard jet traversing a deconfined quark-gluon-plasma (QGP) in the
hard-thermal-loop (HTL) approximation. This is followed by an evaluation of
sub-leading contributions which are suppressed by the light-cone momentum
, which yields the longitudinal "straggling" i.e., a slight change in
light cone momentum due to the Brownian propagation through a medium with a
fluctuating color field.Comment: 5 pages, 1 figure, Revtex
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
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