464 research outputs found
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
A way to estimate the heavy quark thermalization rate from the lattice
The thermalization rate of a heavy quark is related to its momentum diffusion
coefficient. Starting from a Kubo relation and using the framework of the heavy
quark effective theory, we argue that in the large-mass limit the momentum
diffusion coefficient can be defined through a certain Euclidean correlation
function, involving color-electric fields along a Polyakov loop. Furthermore,
carrying out a perturbative computation, we demonstrate that the spectral
function corresponding to this correlator is relatively flat at small
frequencies. Therefore, unlike in the case of several other transport
coefficients, for which the narrowness of the transport peak makes analytic
continuation from Euclidean lattice data susceptible to severe systematic
uncertainties, it appears that the determination of the heavy quark
thermalization rate could be relatively well under control.Comment: 17 pages. v2: clarifications and references added, published versio
Integrated and independent evolution of heteromorphic sperm types
Sperm are a simple cell type with few components, yet they exhibit tremendous between-species morphological variation in those components thought to reflect selection in different fertilization environments. However, within a species, sperm components are expected to be selected to be functionally integrated for optimal fertilization of eggs. Here, we take advantage of within-species variation in sperm form and function to test whether sperm components are functionally and genetically integrated both within and between sperm morphologies using a quantitative genetics approach. Drosophila pseudoobscura males produce two sperm types with different functions but which positively interact together in the same fertilization environment; the long eusperm fertilizes eggs and the short parasperm appear to protect eusperm from a hostile female reproductive tract. Our analysis found that all sperm traits were heritable, but short sperm components exhibited evolvabilities 10 times that of long sperm components. Genetic correlations indicated functional integration within, but not between, sperm morphs. These results suggest that sperm, despite sharing a common developmental process, can become developmentally and functionally non-integrated, evolving into separate modules with the potential for rapid and independent responses to selection
Enhanced thermal production of hard dileptons by processes
In the framework of the Hard Thermal Loop effective theory, we calculate the
two-loop contributions to hard lepton pair production in a quark-gluon plasma.
We show that the result is free of any infrared and collinear singularity. We
also recover the known fact that perturbation theory leads to integrable
singularities at the location of the threshold for . It
appears that the process calculated here significantly enhances the rate of low
mass hard dileptons.Comment: 32 latex pages, 14 postscript figure
Can invasions occur without change? A comparison of G-matrices and selection in the peach-potato aphid, Myzus persicae
Most evolutionary research on biological invasions has focused on changes seen between the native and invaded range for a particular species. However, it is likely that species that live in human-modified habitats in their native range might have evolved specific adaptations to those environments, which increase the likelihood of establishment and spread in similar human-altered environments. From a quantitative genetic perspective, this hypothesis suggests that both native and introduced populations should reside at or near the same adaptive peak. Therefore, we should observe no overall changes in the G (genetic varianceâcovariance) matrices between native and introduced ranges, and stabilizing selection on fitness-related traits in all populations. We tested these predictions comparing three populations of the worldwide pest Myzus persicae from the Middle East (native range) and the UK and Chile (separately introduced ranges). In general, our results provide mixed support for this idea, but further comparisons of other species are needed. In particular, we found that there has been some limited evolution in the studied traits, with the Middle East population differing from the UK and Chilean populations. This was reflected in the structure of the G-matrices, in which Chile differed from both UK and Middle East populations. Furthermore, the amount of genetic variation was massively reduced in Chile in comparison with UK and Middle East populations. Finally, we found no detectable selection on any trait in the three populations, but clones from the introduced ranges started to reproduce later, were smaller, had smaller offspring, and had lower reproductive fitness than clones from the native range
Construction of Field Algebras with Quantum Symmetry from Local Observables
It has been discussed earlier that ( weak quasi-) quantum groups allow for
conventional interpretation as internal symmetries in local quantum theory.
From general arguments and explicit examples their consistency with (braid-)
statistics and locality was established. This work addresses to the
reconstruction of quantum symmetries and algebras of field operators. For every
algebra \A of observables satisfying certain standard assumptions, an
appropriate quantum symmetry is found. Field operators are obtained which act
on a positive definite Hilbert space of states and transform covariantly under
the quantum symmetry. As a substitute for Bose/Fermi (anti-) commutation
relations, these fields are demonstrated to obey local braid relation.Comment: 50 pages, HUTMP 93-B33
Energy Budget of Cosmological First-order Phase Transitions
The study of the hydrodynamics of bubble growth in first-order phase
transitions is very relevant for electroweak baryogenesis, as the baryon
asymmetry depends sensitively on the bubble wall velocity, and also for
predicting the size of the gravity wave signal resulting from bubble
collisions, which depends on both the bubble wall velocity and the plasma fluid
velocity. We perform such study in different bubble expansion regimes, namely
deflagrations, detonations, hybrids (steady states) and runaway solutions
(accelerating wall), without relying on a specific particle physics model. We
compute the efficiency of the transfer of vacuum energy to the bubble wall and
the plasma in all regimes. We clarify the condition determining the runaway
regime and stress that in most models of strong first-order phase transitions
this will modify expectations for the gravity wave signal. Indeed, in this
case, most of the kinetic energy is concentrated in the wall and almost no
turbulent fluid motions are expected since the surrounding fluid is kept mostly
at rest.Comment: 36 pages, 14 figure
In situ measurement of fluid flow from cold seeps at active continental margins
In situ measurement of fluid flow rates from active margins is an important parameter in evaluating dissolved mass fluxes and global geochemical balances as well as tectonic dewatering during developments of accretionary prisms. We have constructed and deployed various devices that allow for the direct measurement of this parameter. An open bottom barrel with an exhaust port at the top and equipped with a mechanical flowmeter was initially used to measure flow rates in the Cascadia accretionary margin during an Alvin dive program in 1988. Sequentially activated water bottles inside the barrel sampled the increase of venting methane in the enclosed body of water. Subsequently, a thermistor flowmeter was developed to measure flow velocities from cold seeps. It can be used to measure velocities between 0.01 and 50 cm sâ1, with a response time of 200 ms. It was deployed again by the submersible Alvin in visits to the Cascadia margin seeps (1990) and in conjunction with sequentially activated water bottles inside the barrel. We report the values for the flow rates based on the thermistor flowmeter and estimated from methane flux calculations. These results are then compared with the first measurement at Cascadia margin employing the mechanical flowmeter. The similarity between water flow and methane expulsion rates over more than one order of magnitude at these sites suggests that the mass fluxes obtained by our in situ devices may be reasonably realistic values for accretionary margins. These values also indicate an enormous variability in the rates of fluid expulsion within the same accretionary prism.
Finally, during a cruise to the active margin off Peru, another version of the same instrument was deployed via a TV-controlled frame within an acoustic transponder net from a surface ship, the R.V. Sonne. The venting rates obtained with the thermistor flowmeter used in this configuration yielded a value of 4411 mâ2 dayâ1 at an active seep on the Peru slope. The ability for deployment of deep-sea instruments capable of measuring fluid flow rates and dissolved mass fluxes from conventional research vessels will allow easier access to these seep sites and a more widespread collection of the data needed to evaluate geochemical processes resulting from venting at cold seeps on a global basis. Comparison of the in situ flow rates from steady-state compactive dewatering models differ by more than 4 orders of magnitude. This implies that only a small area of the margin is venting and that there must be recharge zones associated with venting at convergent margin
Classical BV theories on manifolds with boundary
In this paper we extend the classical BV framework to gauge theories on
spacetime manifolds with boundary. In particular, we connect the BV
construction in the bulk with the BFV construction on the boundary and we
develop its extension to strata of higher codimension in the case of manifolds
with corners. We present several examples including electrodynamics, Yang-Mills
theory and topological field theories coming from the AKSZ construction, in
particular, the Chern-Simons theory, the theory, and the Poisson sigma
model. This paper is the first step towards developing the perturbative
quantization of such theories on manifolds with boundary in a way consistent
with gluing.Comment: The second version has many typos corrected, references added. Some
typos are probably still there, in particular, signs in examples. In the
third version more typoes are corrected and the exposition is slightly
change
Atomic Dark Matter
We propose that dark matter is dominantly comprised of atomic bound states.
We build a simple model and map the parameter space that results in the early
universe formation of hydrogen-like dark atoms. We find that atomic dark matter
has interesting implications for cosmology as well as direct detection:
Protohalo formation can be suppressed below for weak scale dark matter due to Ion-Radiation interactions in the
dark sector. Moreover, weak-scale dark atoms can accommodate hyperfine
splittings of order 100 \kev, consistent with the inelastic dark matter
interpretation of the DAMA data while naturally evading direct detection
bounds.Comment: 17 pages, 3 figure
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