Peter Arnold

Transport coefficients in high temperature gauge theories (I): leading-log results

Leading-log results are derived for the shear viscosity, electrical conductivity and flavor diffusion constants in both abelian and non-abelian high temperature gauge theories with various matter field content.

Transport coefficients in high temperature gauge theories, 2. 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 i n 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.

Photon and gluon emission in relativistic plasmas

We recently derived, using diagrammatic methods, the leading-order hard photon emission rate in ultra-relativistic plasmas. This requires a correct treatment of multiple scattering effects which limit the coherence length of emitted radiation (the Landau-Pomeranchuk-Migdal effect). In this paper, we provide a more physical derivation of this result, and extend the treatment to the case of gluon radiation.

Photon emission from quark gluon plasma: Complete leading order results

Wecomputethephotonemissionrateofanequilibrated,hotQCDplasmaat zero chemical potential, to leading order in both fiEM and the QCD coupling gs(T). This requires inclusion of near-collinear bremsstrahlung and inelastic pair annihilation contri- butions, andcorrect incorporation of Landau-Pomeranchuk-Migdal suppressionefiects for these processes. Analogous resultsfor aQED plasmaare also included.

Photon Emission from Ultrarelativistic Plasmas

The emission rate of photons from a hot, weakly coupled ultrarelativistic plasma is analyzed. Leading-log results, reflecting the sensitivity of the emission rate to scattering events with momentum transfers from gT to T, have previously been obtained. But a complete leading-order treatment requires including collinearly enhanced, inelastic processes such as bremsstrahlung. These inelastic processes receive O(1) modifications from multiple scattering during the photon emission process, which limits the coherence length of the emitted radiation (the Landau-Pomeranchuk-Migdal effect). We perform a diagrammatic analysis to identify, and sum, all leading-order contributions. We find that the leading-order photon emission rate is not sensitive to non-perturbative g2T scale dynamics. We derive an integral equation for the photon emission rate which is very similar to the result of Migdal in his original discussion of the LPM effect. The accurate solution of this integral equation for specific theories of interest will be reported in a companion paper.

Bulk viscosity of high-temperature QCD

We compute the bulk viscosity {zeta} of high-temperature QCD to leading order in powers of the running coupling {alpha}{sub s}(T). We find that it is negligible compared to shear viscosity {eta} for any {alpha}{sub s} that might reasonably be considered small. The physics of bulk viscosity in QCD is a bit different than in scalar {phi}{sup 4} theory. In particular, unlike in scalar theory, we find that an old, crude estimate of {zeta}{approx_equal}15((1/3)-v{sub s}{sup 2}){sup 2}{eta} gives the correct order of magnitude, where v{sub s} is the speed of sound. We also find that leading-log expansions of our result for {zeta} are not accurate except at very small coupling.

Serotonergic modulation of hyperpolarization‐activated current in acutely isolated rat dorsal root ganglion neurons

1 The effect of serotonin (5‐HT) on the hyperpolarization‐activated cation current (IH) was studied in small‐, medium‐ and large‐diameter acutely isolated rat dorsal root ganglion (DRG) cells, including cells categorized as type 1, 2, 3 and 4 based on membrane properties. 5‐HT increased IH in 91 % of medium‐diameter DRG cells (including type 4) and in 67 % of large‐diameter DRG cells, but not other DRG cell types. 2 The increase of IH by 5‐HT was antagonized by spiperone but not cyanopindolol, and was mimicked by 5‐carboxyamidotryptamine, but not (+)‐8‐hydroxydipropylaminotetralin (8‐OH‐DPAT) or cyanopindolol. These data suggested the involvement of 5‐HT7 receptors, which were shown to be expressed by medium‐diameter DRG cells using RT‐PCR analysis. 3 5‐HT shifted the conductance‐voltage relationship of IH by +6 mV without changing peak conductance. The effects of 5‐HT on IH were mimicked and occluded by forskolin, but not by inactive 1,9‐dideoxy forskolin. 4 At holding potentials negative to ‐50 mV, 5‐HT increased steady‐state inward current and instantaneous membrane conductance (fast current). The 5‐HT‐induced inward current and fast current were blocked by Cs+ but not Ba2+ and reversed at ‐23 mV, consistent with the properties of tonically activated IH. 5 In medium‐diameter neurons recorded from in the current clamp mode, 5‐HT depolarized the resting membrane potential, decreased input resistance and facilitated action potential generation by anode‐break excitation. 6 The above data suggest that in distinct subpopulations of DRG neurons, 5‐HT increases cAMP levels via activation of 5‐HT7 receptors, which shifts the voltage dependence of IH to more depolarized potentials and increases neuronal excitability.

BEC transition temperature of a dilute homogeneous imperfect Bose gas.

The leading-order effect of interactions on a homogeneous Bose gas is theoretically predicted to shift the critical temperature by an amount DeltaT(c) approximately equal to ca(sc)n(1/3)T(0) from the ideal gas result T(0), where a(sc) is the scattering length, n is the density, and c is a pure number. There have been several different theoretical estimates for c. We claim to settle the issue by measuring the numerical coefficient in a lattice simulation of O(2) straight phi(4) field theory in three dimensions-an effective theory which, as observed previously in the literature, can be systematically matched to the dilute Bose gas problem to reproduce nonuniversal quantities such as the critical temperature. We find c = 1.32+/-0.02.

Evaluation of resorbable barriers for preventing surgical adhesions

OBJECTIVE To evaluate the ability of collagen film, collagen gel, sodium hyaluronate/carboxymethylcellulose film, and fibrin glue to prevent adhesion formation. DESIGN Randomized trial using a rat model of a standardized abdominal wound and cecal wound. SETTING University research laboratory. ANIMAL(S) Sprague-Dawley female rats. INTERVENTION(S) Resorbable barriers or no barrier (controls) were placed between an abdominal wall wound (1 cm x 2 cm) and a similarly sized cecal wound. MAIN OUTCOME MEASURE(S) Adhesion formation between wounds was assessed and quantitated 7 days after surgery. RESULT(S) Without treatment, 34 of 35 untreated rats (97%) developed adhesions. Treatment with collagen gel (3 of 33 rats), collagen film (3 of 10 rats), or sodium hyaluronate/carboxymethylcellulose film (2 of 10 rats) significantly reduced the incidence of adhesion formation. Treatment with fibrin sealant resulted in 9 of 10 animals having adherent wounds 7 days after surgery. CONCLUSION(S) Resorbable barriers of collagen gel, collagen films and sodium hyaluronate/carboxymethylcellulose film were effective in significantly reducing adhesion formation. Fibrin sealant at 7 days had an incidence of adhesion formation similar to that in untreated control animals.

Fate of non-Abelian plasma instabilities in 3 + 1 dimensions

Plasma instabilities can play a fundamental role in plasma equilibration. There are similarities and differences between plasma instabilities in Abelian and non-Abelian gauge theories. In particular, it has been an open question whether non-Abelian self-interactions are the limiting factor in the growth of non-Abelian plasma instabilities. We study this problem with 3+1 dimensional numerical simulations. We find that non-Abelian plasma instabilities behave very differently from Abelian ones once they grow to be nonperturbatively large, in contrast with earlier results of 1+1 dimensional simulations. In particular, they grow more slowly at late times, with linear rather than exponential dependence of magnetic energy on time.