999 research outputs found
Behavior of logarithmic branch cuts in the self-energy of gluons at finite temperature
We give a simple argument for the cancellation of the log(-k^2) terms (k is
the gluon momentum) between the zero-temperature and the temperature-dependent
parts of the thermal self-energy.Comment: 4 page
Gauge Independence of Limiting Cases of One-Loop Electron Dispersion Relation in High-Temperature QED
Assuming high temperature and taking subleading temperature dependence into
account, gauge dependence of one-loop electron dispersion relation is
investigated in massless QED at zero chemical potential. The analysis is
carried out using a general linear covariant gauge. The equation governing the
gauge dependence of the dispersion relation is obtained and used to prove that
the dispersion relation is gauge independent in the limiting case of momenta
much larger than . It is also shown that the effective mass is not
influenced by the leading temperature dependence of the gauge dependent part of
the effective self-energy. As a result the effective mass, which is of order
, does not receive a correction of order from one loop, independent
of the gauge parameter.Comment: Revised and enlarged version, 14 pages, Revte
The Boltzmann Equation in Scalar Field Theory
We derive the classical transport equation, in scalar field theory with a
V(phi) interaction, from the equation of motion for the quantum field. We
obtain a very simple, but iterative, expression for the effective action which
generates all the n-point Green functions in the high-temperature limit. An
explicit closed form is given in the static case.Comment: 10 pages, using RevTeX (corrected TeX misprints
Light-front Schwinger Model at Finite Temperature
We study the light-front Schwinger model at finite temperature following the
recent proposal in \cite{alves}. We show that the calculations are carried out
efficiently by working with the full propagator for the fermion, which also
avoids subtleties that arise with light-front regularizations. We demonstrate
this with the calculation of the zero temperature anomaly. We show that
temperature dependent corrections to the anomaly vanish, consistent with the
results from the calculations in the conventional quantization. The gauge
self-energy is seen to have the expected non-analytic behavior at finite
temperature, but does not quite coincide with the conventional results.
However, the two structures are exactly the same on-shell. We show that
temperature does not modify the bound state equations and that the fermion
condensate has the same behavior at finite temperature as that obtained in the
conventional quantization.Comment: 10 pages, one figure, version to be published in Phys. Rev.
Thermal quark production in ultra-relativistic nuclear collisions
We calculate thermal production of u, d, s, c and b quarks in
ultra-relativistic heavy ion collisions. The following processes are taken into
account: thermal gluon decay (g to ibar i), gluon fusion (g g to ibar i), and
quark-antiquark annihilation (jbar j to ibar i), where i and j represent quark
species. We use the thermal quark masses, ,
in all the rates. At small mass (), the production is largely
dominated by the thermal gluon decay channel. We obtain numerical and analytic
solutions of one-dimensional hydrodynamic expansion of an initially pure glue
plasma. Our results show that even in a quite optimistic scenario, all quarks
are far from chemical equilibrium throughout the expansion. Thermal production
of light quarks (u, d and s) is nearly independent of species. Heavy quark (c
and b) production is quite independent of the transition temperature and could
serve as a very good probe of the initial temperature. Thermal quark production
measurements could also be used to determine the gluon damping rate, or
equivalently the magnetic mass.Comment: 14 pages (latex) plus 6 figures (uuencoded postscript files);
CERN-TH.7038/9
Energy and pressure densities of a hot quark-gluon plasma
We calculate the energy and hydrostatic pressure densities of a hot
quark-gluon plasma in thermal equilibrium through diagrammatic analyses of the
statistical average, , of the
energy-momentum-tensor operator . To leading order at high
temperature, the energy density of the long wave length modes is consistently
extracted by applying the hard-thermal-loop resummation scheme to the
operator-inserted no-leg thermal amplitudes .
We find that, for the long wave length gluons, the energy density, being
positive, is tremendously enhanced as compared to the noninteracting case,
while, for the quarks, no noticeable deviation from the noninteracting case is
found.Comment: 33 pages. Figures are not include
Vehicle/engine integration
VEHICLE/ENGINE Integration Issues are explored for orbit transfer vehicles (OTV's). The impact of space basing and aeroassist on VEHICLE/ENGINE integration is discussed. The AOTV structure and thermal protection subsystem weights were scaled as the vehicle length and surface was changed. It is concluded that for increased allowable payload lengths in a ground-based system, lower length-to-diameter (L/D) is as important as higher mixture ration (MR) in the range of mid L/D ATOV's. Scenario validity, geometry constraints, throttle levels, reliability, and servicing are discussed in the context of engine design and engine/vehicle integration
The graviton self-energy in thermal quantum gravity
We show generally that in thermal gravity, the one-particle irreducible
2-point function depends on the choice of the basic graviton fields. We derive
the relevant properties of a physical graviton self-energy, which is
independent of the parametrization of the graviton field. An explicit
expression for the graviton self-energy at high-temperature is given to
one-loop order.Comment: 13 pages, 2 figure
Thermal matter and radiation in a gravitational field
We study the one-loop contributions of matter and radiation to the
gravitational polarization tensor at finite temperatures. Using the
analytically continued imaginary-time formalism, the contribution of matter is
explicitly given to next-to-leading () order. We obtain an exact form for
the contribution of radiation fields, expressed in terms of generalized Riemann
zeta functions. A general expression is derived for the physical polarization
tensor, which is independent of the parametrization of graviton fields. We
investigate the effective thermal masses associated with the normal modes of
the corresponding graviton self-energy.Comment: 32 pages, IFUSP/P-107
Strength and conditioning practices of Brazilian Olympic sprint and jump coaches
Olympic coaches are likely to have adequate knowledge and implement effective training programs. This study aimed to describe and critically examine the strength and conditioning practices adopted by Brazilian Olympic sprint and jump coaches. Nineteen Olympic coaches (age: 50.2 ± 10.8 years; professional experience: 25.9 ± 13.1 years) completed a survey consisting of eight sections: 1) background information; 2) strength-power development; 3) speed training; 4) plyometrics; 5) flexibility training; 6) physical testing; 7) technology use; and 8) programming. It was noticed that coaches prioritized the development of explosiveness, power, and sprinting speed in their training programs, given the specific requirements of sprint and jump events. Nevertheless, unexpectedly, we observed: (1) large variations in the number of repetitions performed per set during resistance training in the off-season period, (2) a higher volume of resistance training prescribed during the competitive period (compared to other sports), and (3) infrequent use of traditional periodization models. These findings are probably related to the complex characteristics of modern competitive sports (e.g., congested competitive schedule) and the individual needs of sprinters and jumpers. Identification of training practices commonly used by leading track and field coaches may help practitioners and sport scientists create more effective research projects and training programs
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