1,164 research outputs found
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 to ,
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 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.Comment: 50 pages, 20 figures. Added references and minor rewordings:
published versio
Pressure of Hot QCD at Large N_f
We compute the pressure and entropy of hot QCD in the limit of large number
of fermions, N_f >> N_c ~ 1, to next to leading order in N_f. At this order the
calculation can be done exactly, up to ambiguities due to the presence of a
Landau pole in the theory; the ambiguities are O(T^8/\Lambda^4_{Landau}) and
remain negligible long after the perturbative series (in g^2 N_f) has broken
down. Our results can be used to test several proposed resummation schemes for
the pressure of full QCD.Comment: 16 pages including 4 figures. Short enough for you to read. Numerical
results corrected after an error was found by Andreas Ipp and Anton Rebha
Effective Kinetic Theory for High Temperature Gauge Theories
Quasiparticle dynamics in relativistic plasmas associated with hot,
weakly-coupled gauge theories (such as QCD at asymptotically high temperature
) can be described by an effective kinetic theory, valid on sufficiently
large time and distance scales. The appropriate Boltzmann equations depend on
effective scattering rates for various types of collisions that can occur in
the plasma. The resulting effective kinetic theory may be used to evaluate
observables which are dominantly sensitive to the dynamics of typical
ultrarelativistic excitations. This includes transport coefficients
(viscosities and diffusion constants) and energy loss rates. We show how to
formulate effective Boltzmann equations which will be adequate to compute such
observables to leading order in the running coupling of high-temperature
gauge theories [and all orders in ]. As previously proposed
in the literature, a leading-order treatment requires including both
particle scattering processes as well as effective ``'' collinear
splitting processes in the Boltzmann equations. The latter account for nearly
collinear bremsstrahlung and pair production/annihilation processes which take
place in the presence of fluctuations in the background gauge field. Our
effective kinetic theory is applicable not only to near-equilibrium systems
(relevant for the calculation of transport coefficients), but also to highly
non-equilibrium situations, provided some simple conditions on distribution
functions are satisfied.Comment: 40 pages, new subsection on soft gauge field instabilities adde
Isolation of cationic and neutral (allenylidene)(carbene) and bis(allenylidene)gold complexes.
The one-electron reduction of a cationic (allenylidene)[cyclic(alkyl) (amino)carbene]gold(i) complex leads to the corresponding neutral, paramagnetic, formally gold(0) complex. DFT calculations reveal that the spin density of this highly robust coinage metal complex is mainly located on the allenylidene fragment, with only 1.8 and 3.1% on the gold center and the CAAC ligand, respectively. In addition, the first homoleptic bis(allenylidene)gold(i) complex has been prepared and fully characterized
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Inhibition of a viral enzyme by a small-molecule dimer disruptor.
We identified small-molecule dimer disruptors that inhibit an essential dimeric protease of human Kaposi's sarcoma-associated herpesvirus (KSHV) by screening an alpha-helical mimetic library. Next, we synthesized a second generation of low-micromolar inhibitors with improved potency and solubility. Complementary methods including size exclusion chromatography and 1H-13C HSQC titration using selectively labeled 13C-Met samples revealed that monomeric protease is enriched in the presence of inhibitor. 1H-15N HSQC titration studies mapped the inhibitor binding site to the dimer interface, and mutagenesis studies targeting this region were consistent with a mechanism where inhibitor binding prevents dimerization through the conformational selection of a dynamic intermediate. These results validate the interface of herpesvirus proteases and other similar oligomeric interactions as suitable targets for the development of small-molecule inhibitors
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