290 research outputs found
The dynamics of cosmological perturbations in thermal theory
Using a recent thermal-field-theory approach to cosmological perturbations,
the exact solutions that were found for collisionless ultrarelativistic matter
are generalized to include the effects from weak self-interactions in a
model through order . This includes the effects
of a resummation of thermal masses and associated nonlocal gravitational
vertices, thus going far beyond classical kinetic theory. Explicit solutions
for all the scalar, vector, and tensor modes are obtained for a
radiation-dominated Einstein-de Sitter model containing a weakly interacting
scalar plasma with or without the admixture of an independent component of
perfect radiation fluid.Comment: 32 pages, REVTEX, 13 postscript figures included by epsf.st
Topological-charge anomalies in supersymmetric theories with domain walls
Domain walls in 1+2 dimensions are studied to clarify some general features
of topological-charge anomalies in supersymmetric theories, by extensive use of
a superfield supercurrent. For domain walls quantum modifications of the
supercharge algebra arise not only from the short-distance anomaly but also
from another source of long-distance origin, induced spin in the domain-wall
background, and the latter dominates in the sum. A close look into the
supersymmetric trace identity, which naturally accommodates the central-charge
anomaly and its superpartners, shows an interesting consequence of the
improvement of the supercurrent: Via an improvement the anomaly in the central
charge can be transferred from induced spin in the fermion sector to an induced
potential in the boson sector. This fact reveals a dual character, both
fermionic and bosonic, of the central-charge anomaly, which reflects the
underlying supersymmetry. The one-loop superfield effective action is also
constructed to verify the anomaly and BPS saturation of the domain-wall
spectrum.Comment: 8 pages, Revte
Boundary Terms in Supergravity and Supersymmetry
We begin with the simplest possible introduction to supergravity. Then we
discuss its spin 3/2 stress tensor; these results are new. Next, we discuss
boundary conditions on fields and boundary actions for N=1 supergravity.
Finally, we discuss new boundary contributions to the mass and central charge
of monopoles in N=4 super Yang-Mills theory. All models are in 3+1 dimensions.Comment: 15 pages. Talk given by P. van Nieuwenhuizen at the
Einstein-celebration gravitational conference at Puri (India) in December
200
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
Central charge and renormalization in supersymmetric theories with vortices
Some quantum features of vortices in supersymmetric theories in 1+2
dimensions are studied in a manifestly supersymmetric setting of the superfield
formalism. A close examination of the supercurrent that accommodates the
central charge and super-Poincare charges in a supermultiplet reveals that
there is no genuine quantum anomaly in the supertrace identity and in the
supercharge algebra, with the central-charge operator given by the bare
Fayet-Iliopoulos term alone. The central charge and the vortex spectrum undergo
renormalization on taking the expectation value of the central-charge operator.
It is shown that the vortex spectrum is exactly determined at one loop while
the spectrum of the elementary excitations receives higher-order corrections.Comment: 9 pages, revte
Polyakov loop and spin correlators on finite lattices A study beyond the mass gap
We derive an analytic expression for point-to-point correlation functions of
the Polyakov loop based on the transfer matrix formalism. For the Ising
model we show that the results deduced from point-point spin correlators are
coinciding with those from zero momentum correlators. We investigate the
contributions from eigenvalues of the transfer matrix beyond the mass gap and
discuss the limitations and possibilities of such an analysis. The finite size
behaviour of the obtained Ising model matrix elements is examined. The
point-to-point correlator formula is then applied to Polyakov loop data in
finite temperature gauge theory. The leading matrix element shows all
expected scaling properties. Just above the critical point we find a Debye
screening mass , independent of the volume.Comment: 13 pages and 8 figures, late
Thermodynamics and phase diagram of anisotropic Chern-Simons deformed gauge theories
We consider 3+1-dimensional gauge theories at finite temperature and a finite
density of charges which couple to a 2+1-dimensional Chern-Simons operator,
giving rise to a theta-term with constant spatial gradient of theta. The
strong-coupling limit of thermal N=4 super-Yang-Mills theory with this kind of
anisotropic deformation has been used in the context of the AdS/CFT
correspondence as a model for strongly coupled anisotropic quark-gluon plasma.
In this paper we work out the thermodynamics and the (nontrivial) phase diagram
in the limit of vanishing gauge coupling and compare with the corresponding
strong-coupling results.Comment: 23 pages, 7 figures, v2: low temperature expansion corrected,
references added, some discussion expande
Optimal Renormalization-Group Improvement of R(s) via the Method of Characteristics
We discuss the application of the method of characteristics to the
renormalization-group equation for the perturbative QCD series within the
electron-positron annihilation cross-section. We demonstrate how one such
renormalization-group improvement of this series is equivalent to a closed-form
summation of the first four towers of renormalization-group accessible
logarithms to all orders of perturbation theory
The entropy of the QCD plasma
Self-consistent approximations in terms of fully dressed propagators provide
a simple expression for the entropy of an ultrarelativistic plasma, which
isolates the contribution of the elementary excitations as a leading
contribution. Further approximations, whose validity is checked on a soluble
model involving a scalar field, allow us to calculate the entropy of the QCD
plasma. We obtain an accurate description of lattice data for purely gluonic
QCD, down to temperatures of about twice the transition temperature.Comment: 12 pages, 3 figures, REVTEX (minor modifications
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