29,560 research outputs found
Hard thermal loops in the real-time formalism
We present a systematic discussion of Braaten and Pisarski's hard thermal
loop (HTL) effective theory within the framework of the real-time
(Schwinger-Keldysh) formalism. As is well known, the standard imaginary-time
HTL amplitudes for hot gauge theory express the polarization of a medium made
out of nonabelian charged point-particles; we show that the complete real-time
HTL theory includes, in addition, a second set of amplitudes which account for
Gaussian fluctuations in the charge distributions, but nothing else. We give a
concise set of graphical rules which generate both set of functions, and
discuss its relation to classical plasma physics.Comment: 14 pages, 6 figure
Perturbative and Nonperturbative Kolmogorov Turbulence in a Gluon Plasma
In numerical simulations of nonabelian plasma instabilities in the hard-loop
approximation, a turbulent spectrum has been observed that is characterized by
a phase-space density of particles with exponent , which is larger than expected from relativistic
scatterings. Using the approach of Zakharov, L'vov and Falkovich, we analyse
possible Kolmogorov coefficients for relativistic -particle
processes, which give at most perturbatively for an energy cascade.
We discuss nonperturbative scenarios which lead to larger values. As an extreme
limit we find the result generically in an inherently nonperturbative
effective field theory situation, which coincides with results obtained by
Berges et al.\ in large- scalar field theory. If we instead assume that
scaling behavior is determined by Schwinger-Dyson resummations such that the
different scaling of bare and dressed vertices matters, we find that
intermediate values are possible. We present one simple scenario which would
single out .Comment: published versio
A transport coefficient: the electrical conductivity
I describe the lattice determination of the electrical conductivity of the
quark gluon plasma. Since this is the first extraction of a transport
coefficient with a degree of control over errors, I next use this to make
estimates of other transport related quantities using simple kinetic theory
formulae. The resulting estimates are applied to fluctuations, ultra-soft
photon spectra and the viscosity. Dimming of ultra-soft photons is exponential
in the mean free path, and hence is a very sensitive probe of transport.Comment: Talk given in ICPAQGP 2005, SINP, Kolkat
Uranium(III) coordination chemistry and oxidation in a flexible small-cavity macrocycle
U(III) complexes of the conformationally flexible, small-cavity macrocycle trans-calix[2]benzene[2]pyrrolide (L)2–, [U(L)X] (X = O-2,6-tBu2C6H3, N(SiMe3)2), have been synthesized from [U(L)BH4] and structurally characterized. These complexes show binding of the U(III) center in the bis(arene) pocket of the macrocycle, which flexes to accommodate the increase in the steric bulk of X, resulting in long U–X bonds to the ancillary ligands. Oxidation to the cationic U(IV) complex [U(L)X][B(C6F5)4] (X = BH4) results in ligand rearrangement to bind the smaller, harder cation in the bis(pyrrolide) pocket, in a conformation that has not been previously observed for (L)2–, with X located between the two ligand arene rings
Empirical Emission Functions for LPM Suppression of Photon Emission from Quark-Gluon Plasma
The LPM suppression of photon emission rates from the quark gluon plasma have
been studied at different physical conditions of the plasma given by
temperature and chemical potentials.The integral equation for the transverse
vector function (f(p_t)) consisting of multiple scattering effects is solved
for the parameter set {p,k,kappa,T}, for bremsstrahlung and AWS processes. The
peak positions of these distributions depend only on the dynamical variable
x=(T/kappa)|1/p-1/(p+k)|. Integration over these distributions multiplied by
x^2 factor also depends on this variable x,leading to a unique global emission
function g(x) for all parameters. Empirical fits to this dimensionless emission
function, g(x), are obtained. The photon emission rate calculations with LPM
suppression effects reduce to one dimensional integrals involving folding over
the empirical g(x) function with appropriate distribution functions and the
kinematic factors. Using this approach, the suppression factors for both
bremsstrahlung and AWS have been estimated for various chemical potentials and
compared with the variational method
Looking for CP Violation in W Production and Decay
We describe CP violating observables in resonant and plus one
jet production at the Tevatron. We present simple examples of CP violating
effective operators, consistent with the symmetries of the Standard Model,
which would give rise to these observables. We find that CP violating effects
coming from new physics at the scale could in principle be observable at
the Tevatron with decays.Comment: 15 pgs with standard LATEX, 7 ps figures embedded with eps
Predicting the outcome of renal transplantation
ObjectiveRenal transplantation has dramatically improved the survival rate of hemodialysis patients. However, with a growing proportion of marginal organs and improved immunosuppression, it is necessary to verify that the established allocation system, mostly based on human leukocyte antigen matching, still meets today's needs. The authors turn to machine-learning techniques to predict, from donor-recipient data, the estimated glomerular filtration rate (eGFR) of the recipient 1 year after transplantation.DesignThe patient's eGFR was predicted using donor-recipient characteristics available at the time of transplantation. Donors' data were obtained from Eurotransplant's database, while recipients' details were retrieved from Charite Campus Virchow-Klinikum's database. A total of 707 renal transplantations from cadaveric donors were included.MeasurementsTwo separate datasets were created, taking features with <10% missing values for one and <50% missing values for the other. Four established regressors were run on both datasets, with and without feature selection.ResultsThe authors obtained a Pearson correlation coefficient between predicted and real eGFR (COR) of 0.48. The best model for the dataset was a Gaussian support vector machine with recursive feature elimination on the more inclusive dataset. All results are available at http://transplant.molgen.mpg.de/.LimitationsFor now, missing values in the data must be predicted and filled in. The performance is not as high as hoped, but the dataset seems to be the main cause.ConclusionsPredicting the outcome is possible with the dataset at hand (COR=0.48). Valuable features include age and creatinine levels of the donor, as well as sex and weight of the recipient
Transport coefficients in high temperature gauge theories: (II) Beyond leading log
Results are presented of a full leading-order evaluation of the shear
viscosity, flavor diffusion constants, and electrical conductivity in high
temperature QCD and QED. The presence of Coulomb logarithms associated with
gauge interactions imply that the leading-order results for transport
coefficients may themselves be expanded in an infinite series in powers of
1/log(1/g); the utility of this expansion is also examined. A
next-to-leading-log approximation is found to approximate the full
leading-order result quite well as long as the Debye mass is less than the
temperature.Comment: 38 pages, 6 figure
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