172 research outputs found
Ultraviolet asymptotics of scalar and pseudoscalar correlators in hot Yang-Mills theory
Inspired by recent lattice measurements, we determine the short-distance (a
> omega >> pi T) asymptotics
of scalar (trace anomaly) and pseudoscalar (topological charge density)
correlators at 2-loop order in hot Yang-Mills theory. The results are expressed
in the form of an Operator Product Expansion. We confirm and refine the
determination of a number of Wilson coefficients; however some discrepancies
with recent literature are detected as well, and employing the correct values
might help, on the qualitative level, to understand some of the features
observed in the lattice measurements. On the other hand, the Wilson
coefficients show slow convergence and it appears uncertain whether this
approach can lead to quantitative comparisons with lattice data. Nevertheless,
as we outline, our general results might serve as theoretical starting points
for a number of perhaps phenomenologically more successful lines of
investigation.Comment: 27 pages. v2: minor improvements, published versio
Notes on Operator Equations of Supercurrent Multiplets and the Anomaly Puzzle in Supersymmetric Field Theories
Recently, Komargodski and Seiberg have proposed a new type of supercurrent
multiplet which contains the energy-momentum tensor and the supersymmetry
current consistently. In this paper we study quantum properties of the
supercurrent in renormalizable field theories. We point out that the new
supercurrent gives a quite simple resolution to the classic problem, called the
anomaly puzzle, that the Adler-Bardeen theorem applied to an R-symmetry current
is inconsistent with all order corrections to functions. We propose an
operator equation for the supercurrent in all orders of perturbation theory,
and then perform several consistency checks of the equation. The operator
equation we propose is consisitent with the one proposed by Shifman and
Vainshtein, if we take some care in interpreting the meaning of non-conserved
currents.Comment: 28 pages; v2:clarifications and references added, some minor change
Accretion Disc Theory: From the Standard Model Until Advection
Accretion disc theory was first developed as a theory with the local heat
balance, where the whole energy produced by a viscous heating was emitted to
the sides of the disc. One of the most important new invention of this theory
was a phenomenological treatment of the turbulent viscosity, known as ''alpha''
prescription, when the (r) component of the stress tensor was
approximated by ( P) with a unknown constant . This
prescription played the role in the accretion disc theory as well important as
the mixing-length theory of convection for stellar evolution. Sources of
turbulence in the accretion disc are discussed, including nonlinear
hydrodynamical turbulence, convection and magnetic field role. In parallel to
the optically thick geometrically thin accretion disc models, a new branch of
the optically thin accretion disc models was discovered, with a larger
thickness for the same total luminosity. The choice between these solutions
should be done of the base of a stability analysis. The ideas underlying the
necessity to include advection into the accretion disc theory are presented and
first models with advection are reviewed. The present status of the solution
for a low-luminous optically thin accretion disc model with advection is
discussed and the limits for an advection dominated accretion flows (ADAF)
imposed by the presence of magnetic field are analysed.Comment: Roceeding of the Int. Workshop "Observational Evidence for Black
Holes in the Universe". Calcutta, 11-17 January 1998. Kluwer Acad. Pu
Finite-Temperature Fractional D2-Branes and the Deconfinement Transition in 2+1 Dimensions
The supergravity dual to N regular and M fractional D2-branes on the cone
over \mathbb{CP}^3 has a naked singularity in the infrared. One can resolve
this singularity and obtain a regular fractional D2-brane solution dual to a
confining 2+1 dimensional N = 1 supersymmetric field theory. The confining
vacuum of this theory is described by the solution of Cvetic, Gibbons, Lu and
Pope. In this paper, we explore the alternative possibility for resolving the
singularity - the creation of a regular horizon. The black-hole solution we
find corresponds to the deconfined phase of this dual gauge theory in three
dimensions. This solution is derived in perturbation theory in the number of
fractional branes. We argue that there is a first-order deconfinement
transition. Connections to Chern--Simons matter theories, the ABJM proposal and
fractional M2-branes are presented.Comment: v3: analytic solutions are expose
The Shapes of Cooperatively Rearranging Regions in Glass Forming Liquids
The shapes of cooperatively rearranging regions in glassy liquids change from
being compact at low temperatures to fractal or ``stringy'' as the dynamical
crossover temperature from activated to collisional transport is approached
from below. We present a quantitative microscopic treatment of this change of
morphology within the framework of the random first order transition theory of
glasses. We predict a correlation of the ratio of the dynamical crossover
temperature to the laboratory glass transition temperature, and the heat
capacity discontinuity at the glass transition, Delta C_p. The predicted
correlation agrees with experimental results for the 21 materials compiled by
Novikov and Sokolov.Comment: 9 pages, 6 figure
Theory of disk accretion onto supermassive black holes
Accretion onto supermassive black holes produces both the dramatic phenomena
associated with active galactic nuclei and the underwhelming displays seen in
the Galactic Center and most other nearby galaxies. I review selected aspects
of the current theoretical understanding of black hole accretion, emphasizing
the role of magnetohydrodynamic turbulence and gravitational instabilities in
driving the actual accretion and the importance of the efficacy of cooling in
determining the structure and observational appearance of the accretion flow.
Ongoing investigations into the dynamics of the plunging region, the origin of
variability in the accretion process, and the evolution of warped, twisted, or
eccentric disks are summarized.Comment: Mostly introductory review, to appear in "Supermassive black holes in
the distant Universe", ed. A.J. Barger, Kluwer Academic Publishers, in pres
Quantum Symmetries and Marginal Deformations
We study the symmetries of the N=1 exactly marginal deformations of N=4 Super
Yang-Mills theory. For generic values of the parameters, these deformations are
known to break the SU(3) part of the R-symmetry group down to a discrete
subgroup. However, a closer look from the perspective of quantum groups reveals
that the Lagrangian is in fact invariant under a certain Hopf algebra which is
a non-standard quantum deformation of the algebra of functions on SU(3). Our
discussion is motivated by the desire to better understand why these theories
have significant differences from N=4 SYM regarding the planar integrability
(or rather lack thereof) of the spin chains encoding their spectrum. However,
our construction works at the level of the classical Lagrangian, without
relying on the language of spin chains. Our approach might eventually provide a
better understanding of the finiteness properties of these theories as well as
help in the construction of their AdS/CFT duals.Comment: 1+40 pages. v2: minor clarifications and references added. v3: Added
an appendix, fixed minor typo
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