10,881 research outputs found
Hydrogen-like Atoms from Ultrarelativistic Nuclear Collisions
The number of hydrogen-like atoms produced when heavy nuclei collide is
estimated for central collisions at the Relativistic Heavy Ion Collider using
the sudden approximation of Baym et al. As first suggested by Schwartz, a
simultaneous measurement of the hydrogen and hadron spectra will allow an
inference of the electron or muon spectra at low momentum where a direct
experimental measurement is not feasible.Comment: 6 pages, 4 figure
Friction in inflaton equations of motion
The possibility of a friction term in the equation of motion for a scalar
field is investigated in non-equilibrium field theory. The results obtained
differ greatly from existing estimates based on linear response theory, and
suggest that dissipation is not well represented by a term of the form
.Comment: 4 pages, 2 figures, RevTex4. An obscurity in the original version has
been clarifie
Radiative and Collisional Jet Energy Loss in a Quark-Gluon Plasma
We calculate radiative and collisional energy loss of hard partons traversing
the quark-gluon plasma created at RHIC and compare the respective size of these
contributions. We employ the AMY formalism for radiative energy loss and
include additionally energy loss by elastic collisions. Our treatment of both
processes is complete at leading order in the coupling, and accounts for the
probabilistic nature of jet energy loss. We find that a solution of the
Fokker-Planck equation for the probability density distributions of partons is
necessary for a complete calculation of the nuclear modification factor
for pion production in heavy ion collisions. It is found that the
magnitude of is sensitive to the inclusion of both collisional and
radiative energy loss, while the average energy is less affected by the
addition of collisional contributions. We present a calculation of for
at RHIC, combining our energy loss formalism with a relativistic
(3+1)-dimensional hydrodynamic description of the thermalized medium.Comment: 4 pages, 4 figures, contributed to Quark Matter 2008, Jaipur, Indi
Dissipation in equations of motion of scalar fields
The methods of non-equilibrium quantum field theory are used to investigate
the possibility of representing dissipation in the equation of motion for the
expectation value of a scalar field by a friction term, such as is commonly
included in phenomenological inflaton equations of motion. A sequence of
approximations is exhibited which reduces the non-equilibrium theory to a set
of local evolution equations. However, the adiabatic solution to these
evolution equations which is needed to obtain a local equation of motion for
the expectation value is not well defined; nor, therefore, is the friction
coefficient. Thus, a non-equilibrium treatment is essential, even for a system
that remains close to thermal equilibrium, and the formalism developed here
provides one means of achieving this numerically.Comment: 17 pages, 5 figure
Color conductivity and ladder summation in hot QCD
The color conductivity is computed at leading logarithmic order using a Kubo
formula. We show how to sum an infinite series of planar ladder diagrams,
assuming some approximations based on the dominance of soft scattering
processes between hard particles in the plasma. The result agrees with the one
obtained previously from a kinetical approach.Comment: 15 pages, 4 figures. Explanations enlarged, two figures and some refs
added, typos corrected. Final version to be published in Phys.Rev.
Particle yield fluctuations and chemical non-equilibrium at RHIC
We study charge fluctuations within the statistical hadronization model.
Considering both the particle yield ratios and the charge fluctuations we show
that it is possible to differentiate between chemical equilibrium and
non-equilibrium freeze-out conditions. As an example of the procedure we show
quantitatively how the relative yield ratio together with the
normalized net charge fluctuation v(Q)=\ave{\Delta Q^2}/\ave{\Nch} constrain
the chemical conditions at freeze-out. We also discuss the influence of the
limited detector acceptance on fluctuation measurements, and show how this can
be accounted for within a quantitative analysis.Comment: Accepted for publication by Physical Review
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