314 research outputs found
Matching pre-equilibrium dynamics and viscous hydrodynamics
We demonstrate how to match pre-equilibrium dynamics of a 0+1 dimensional
quark gluon plasma to 2nd-order viscous hydrodynamical evolution. The matching
allows us to specify the initial values of the energy density and shear tensor
at the initial time of hydrodynamical evolution as a function of the lifetime
of the pre-equilibrium period. We compare two models for the pre-equilibrium
quark-gluon plasma, longitudinal free streaming and collisionally-broadened
longitudinal expansion, and present analytic formulas which can be used to fix
the necessary components of the energy-momentum tensor. The resulting dynamical
models can be used to assess the effect of pre-equilibrium dynamics on
quark-gluon plasma observables. Additionally, we investigate the dependence of
entropy production on pre-equilibrium dynamics and discuss the limitations of
the standard definitions of the non-equilibrium entropy.Comment: 24 pages, 5 figures,v2: minor modifications and updated references.
Accepted for publication in Phys. Rev.
Thermalization and the chromo-Weibel instability
Despite the apparent success of ideal hydrodynamics in describing the
elliptic flow data which have been produced at Brookhaven National Lab's
Relativistic Heavy Ion Collider, one lingering question remains: is the use of
ideal hydrodynamics at times t < 1 fm/c justified? In order to justify its use
a method for rapidly producing isotropic thermal matter at RHIC energies is
required. One of the chief obstacles to early isotropization/thermalization is
the rapid longitudinal expansion of the matter during the earliest times after
the initial nuclear impact. As a result of this expansion the parton
distribution functions become locally anisotropic in momentum space. In
contrast to locally isotropic plasmas anisotropic plasmas have a spectrum of
soft unstable modes which are characterized by exponential growth of transverse
chromo-magnetic/-electric fields at short times. This instability is the QCD
analogue of the Weibel instability of QED. Parametrically the chromo-Weibel
instability provides the fastest method for generation of soft background
fields and dominates the short-time dynamics of the system.Comment: 8 pages, 4 figures, Invited plenary talk given at the 19th
International Conference on Ultrarelativistic Nucleus-Nucleus Collisions:
Quark Matter 2006 (QM 2006), Shanghai, China, 14-20 Nov 200
Ultraviolet avalanche in anisotropic non-Abelian plasmas
We present solutions of coupled particle-field evolution in classical U(1)
and SU(2) gauge theories in real time on three-dimensional lattices. For
strongly anisotropic particle momentum distributions, we find qualitatively
different behavior for the two theories when the field strength is high enough
that non-Abelian self-interactions matter for SU(2). It appears that the energy
drained by a Weibel-like plasma instability from the particles does not build
up exponentially in transverse magnetic fields but instead returns,
isotropically, to the hard scale via a rapid avalanche into the ultraviolet.Comment: 22 pages, 10 figures; v3: small textual changes; updated to
correspond with version to appear in publicatio
Three-loop Phi-derivable Approximation in QED
In this paper we examine Phi-derivable approximations in QED. General
theorems tell us that the gauge dependence of the n-loop Phi-derivable
approximation shows up at order g^(2n) where g is the coupling constant. We
consider the gauge dependence of the two-loop Phi-derivable approximation to
the Debye mass and show that it is of order e^4 as expected. We solve the
three-loop Phi-derivable approximation in QED by expanding sum-integrals in
powers of e^2 and m/T, where m is the Debye mass which satisfies a variational
gap equation. The results for the pressure and the Debye mass are accurate to
order e^5.Comment: 10 pages, 5 figures. v2: typos corrected and references adde
An X-ray Mini-survey of Nearby Edge-on Starburst Galaxies II. The Question of Metal Abundance
(abbreviated) We have undertaken an X-ray survey of a far-infrared flux
limited sample of seven nearby edge-on starburst galaxies. Here, we examine the
two X-ray-brightest sample members NGC 253 and M 82 in a self-consistent
manner, taking account of the spatial distribution of the X-ray emission in
choosing our spectral models. There is significant X-ray absorption in the disk
of NGC 253. When this is accounted for we find that multi-temperature thermal
plasma models with significant underlying soft X-ray absorption are more
consistent with the imaging data than single-temperature models with highly
subsolar abundances or models with minimal absorption and non-equilibrium
thermal ionization conditions. Our models do not require absolute abundances
that are inconsistent with solar values or unusually supersolar ratios of the
alpha-burning elements with respect to Fe (as claimed previously). We conclude
that with current data, the technique of measuring abundances in starburst
galaxies via X-ray spectral modeling is highly uncertain.
Based on the point-like nature of much of the X-ray emission in the PSPC
hard-band image of NGC 253, we suggest that a significant fraction of the
``extended'' X-ray emission in the 3-10 keV band seen along the disk of the
galaxy with ASCA and BeppoSAX (Cappi et al.) is comprised of discrete sources
in the disk, as opposed to purely diffuse, hot gas. This could explain the low
Fe abundances of ~1/4 solar derived for pure thermal models.Comment: (accepted for publication in the Astrophysical Journal
Necrobiome framework for bridging decomposition ecology of autotrophically and heterotrophically derived organic matter
Decomposition contributes to global ecosystem function by contributing to nutrient recycling, energy flow, and limiting biomass accumulation. The decomposer organisms influencing this process form diverse, complex, and highly dynamic communities that often specialize on different plant or animal resources. Despite performing the same net role, there is a need to conceptually synthesize information on the structure and function of decomposer communities across the spectrum of dead plant and animal resources. A lack of synthesis has limited cross-disciplinary learning and research in important areas of ecosystem and community ecology. Here we expound on the “necrobiome” concept and develop a framework describing the decomposer communities and their interactions associated with plant and animal resource types within multiple ecosystems.We outline the biotic structure and ecological functions of the necrobiome, along with how the necrobiome fits into a broader landscape and ecosystem context. The expanded necrobiome model provides a set of perspectives on decomposer communities across resource types, and conceptually unifies plant and animal decomposer communities into the same framework, while acknowledging key differences in processes and mechanisms. This framework is intended to raise awareness among researchers, and advance the construction of explicit, mechanistic hypotheses that further our understanding of decomposer community contributions to biodiversity, the structure and function of ecosystems, global nutrient recycling and energy flow
NECROBIOME FRAMEWORK FOR BRIDGING DECOMPOSITION ECOLOGY OF AUTOTROPHICALLY AND HETEROTROPHICALLY DERIVED ORGANIC MATTER
Life arises from death through species that decompose dead biomass or necromass. This paper provides a synthesis of the species responsible for dead plant and animal decomposition and describes a conceptual perspective—the “necrobiome”— that defines the diverse and complex communities that interact to recycle necromass. The concept brings unification to the previously disparate fields of plant and animal decomposition by discussing the universal processes occurring across all forms of necromass. It highlights the factors that make each form of dead biomass different in a way that defines how unique necrobiomes drive decomposition and ultimately shape ecosystem structure and function
Screened Perturbation Theory to Three Loops
The thermal physics of a massless scalar field with a phi^4 interaction is
studied within screened perturbation theory (SPT). In this method the
perturbative expansion is reorganized by adding and subtracting a mass term in
the lagrangian. We consider several different mass prescriptions that
generalize the one-loop gap equation to two-loop order. We calculate the
pressure and entropy to three-loop order and the screening mass to two-loop
order. In contrast to the weak-coupling expansion, the SPT-improved
approximations appear to converge even for rather large values of the coupling
constant.Comment: 30 pages, 10 figure
Hard-Loop Effective Action for Anisotropic Plasmas
We generalize the hard-thermal-loop effective action of the equilibrium
quark-gluon plasma to a non-equilibrium system which is space-time homogeneous
but for which the parton momentum distribution is anisotropic. We show that the
manifestly gauge-invariant Braaten-Pisarski form of the effective action can be
straightforwardly generalized and we verify that it then generates all n-point
functions following from collisionless gauge-covariant transport theory for a
homogeneous anisotropic plasma. On the other hand, the Taylor-Wong form of the
hard-thermal-loop effective action has a more complicated generalization to the
anisotropic case. Already in the simplest case of anisotropic distribution
functions, it involves an additional term that is gauge invariant by itself,
but nontrivial also in the static limit.Comment: 12 pages. Version 3: typo in (15) corrected, note added discussing
metric conventions use
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