214 research outputs found
Chiral symmetry restoration, eigenvalue density of Dirac operator and axial U(1) anomaly at finite temperature
We reconsider constraints on the eigenvalue density of the Dirac operator in
the chiral symmetric phase of 2 flavor QCD at finite temperature. To avoid
possible ultra-violet(UV) divergences, we work on a lattice, employing the
overlap Dirac operator, which ensures the exact "chiral" symmetry at finite
lattice spacings. Studying multi-point correlation functions in various
channels and taking their thermodynamical limit (and then taking the chiral
limit), we obtain stronger constraints than those found in the previous
studies: both the eigenvalue density at the origin and its first and second
derivatives vanish in the chiral limit of 2 flavor QCD. In addition we show
that the axial U(1) anomaly becomes invisible in susceptibilities of scalar and
pseudo scalar mesons, suggesting that the 2nd order chiral phase transition
with the O(4) scaling is not realized in 2 flavor QCD. Possible lattice
artifacts when non-chiral lattice Dirac operator is employed are briefly
discussed.Comment: 39 pages, 1 figure(2 eps files), a version published in PR
Nonequilibrium steady state thermodynamics and fluctuations for stochastic systems
We use the work done on and the heat removed from a system to maintain it in
a nonequilibrium steady state for a thermodynamic-like description of such a
system as well as of its fluctuations. Based on a generalized Onsager-Machlup
theory for nonequilibrium steady states we indicate two ambiguities, not
present in an equilibrium state, in defining such work and heat: one due to a
non-uniqueness of time-reversal procedures and another due to multiple
possibilities to separate heat into work and an energy difference in
nonequilibrium steady states. As a consequence, for such systems, the work and
heat satisfy multiple versions of the first and second laws of thermodynamics
as well as of their fluctuation theorems. Unique laws and relations appear only
to be obtainable for concretely defined systems, using physical arguments to
choose the relevant physical quantities. This is illustrated on a number of
systems, including a Brownian particle in an electric field, a driven torsion
pendulum, electric circuits and an energy transfer driven by a temperature
difference.Comment: 39 pages, 3 figur
Boundary condition independence of molecular dynamics simulations of planar elongational flow
The simulation of liquid systems in a nonequilibrium steady state under planar elongational flow (PEF) for indefinite time is possible only with the use of the so-called Kraynik-Reinelt (KR) periodic boundary conditions (PBCs) on the simulation cell. These conditions admit a vast range of implementation parameters, which regulate how the unit lattice is deformed under elongation and periodically remapped onto itself. Clearly, nonequilibrium properties of homogeneous systems in a steady state have to be independent of the boundary conditions imposed on the unit cell. In order to confirm the independence of measurable properties of a system under PEF from the particular set of periodic boundary conditions, we compute the Lyapunov spectra, apply the conjugate pairing rule, and carefully analyze the so-called unpaired exponents for an atomic fluid of various sizes and state points. We further compute the elongational viscosity for various implementations of boundary conditions. All our results confirm the independence from KR PBCs for the dynamics of phase-space trajectories and for the transport coefficients
Onsager-Machlup theory for nonequilibrium steady states and fluctuation theorems
A generalization of the Onsager-Machlup theory from equilibrium to
nonequilibrium steady states and its connection with recent fluctuation
theorems are discussed for a dragged particle restricted by a harmonic
potential in a heat reservoir. Using a functional integral approach, the
probability functional for a path is expressed in terms of a Lagrangian
function from which an entropy production rate and dissipation functions are
introduced, and nonequilibrium thermodynamic relations like the energy
conservation law and the second law of thermodynamics are derived. Using this
Lagrangian function we establish two nonequilibrium detailed balance relations,
which not only lead to a fluctuation theorem for work but also to one related
to energy loss by friction. In addition, we carried out the functional
integrals for heat explicitly, leading to the extended fluctuation theorem for
heat. We also present a simple argument for this extended fluctuation theorem
in the long time limit.Comment: 20 pages, 2 figure
Predictions and recent results in susy on the lattice
In this brief review, I summarize the current theoretical knowledge in
supersymmetry on the lattice, with special emphasis on recent results in the
framework of N=1 supersymmetric Yang Mills theory, Wess-Zumino model and
Yang-Mills theory with extended supersymmetries.Comment: 15 pages. Invited brief review for Modern Physics Letters A. Minor
change
Super Yang-Mills on the lattice with domain wall fermions
The dynamical N=1, SU(2) Super Yang-Mills theory is studied on the lattice
using a new lattice fermion regulator, domain wall fermions. This formulation
even at non-zero lattice spacing does not require fine-tuning, has improved
chiral properties and can produce topological zero-mode phenomena. Numerical
simulations of the full theory on lattices with the topology of a torus
indicate the formation of a gluino condensate which is sustained at the chiral
limit. The condensate is non-zero even for small volume and small supersymmetry
breaking mass where zero mode effects due to gauge fields with fractional
topological charge appear to play a role.Comment: LaTeX, 35 pages, 11 eps figures. A few changes in sec. 5.3, figure 11
added. To appear in Phys. Rev.
Fluctuations of the total entropy production in stochastic systems
Fluctuations of the excess heat in an out of equilibrium steady state are
experimentally investigated in two stochastic systems : an electric circuit
with an imposed mean current and a harmonic oscillator driven out of
equilibrium by a periodic torque. In these two linear systems, we study excess
heat that represents the difference between the dissipated heat out of
equilibrium and the dissipated heat at equilibrium. Fluctuation theorem holds
for the excess heat in the two experimental systems for all observation times
and for all fluctuation magnitudes.Comment: 6
Critical Review of Theoretical Models for Anomalous Effects (Cold Fusion) in Deuterated Metals
We briefly summarize the reported anomalous effects in deuterated metals at
ambient temperature, commonly known as "Cold Fusion" (CF), with an emphasis on
important experiments as well as the theoretical basis for the opposition to
interpreting them as cold fusion. Then we critically examine more than 25
theoretical models for CF, including unusual nuclear and exotic chemical
hypotheses. We conclude that they do not explain the data.Comment: 51 pages, 4 Figure
Scapinin, the Protein Phosphatase 1 Binding Protein, Enhances Cell Spreading and Motility by Interacting with the Actin Cytoskeleton
Copyright (c) 2009 Sagara et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Scapinin, also named phactr3, is an actin and protein phosphatase 1 (PP1) binding protein, which is expressed in the adult brain and some tumor cells. At present, the role(s) of scapinin in the brain and tumors are poorly understood. We show that the RPEL-repeat domain of scapinin, which is responsible for its direct interaction with actin, inhibits actin polymerization in vitro. Next, we established a Hela cell line, where scapinin expression was induced by tetracycline. In these cells, expression of scapinin stimulated cell spreading and motility. Scapinin was colocalized with actin at the edge of spreading cells. To explore the roles of the RPEL-repeat and PP1-binding domains, we expressed wild-type and mutant scapinins as fusion proteins with green fluorescence protein (GFP) in Cos7 cells. Expression of GFP-scapinin (wild type) also stimulated cell spreading, but mutation in the RPEL-repeat domain abolished both the actin binding and the cell spreading activity. PP1-binding deficient mutants strongly induced cell retraction. Long and branched cytoplasmic processes were developed during the cell retraction. These results suggest that scapinin enhances cell spreading and motility through direct interaction with actin and that PP1 plays a regulatory role in scapinin-induced morphological changes.ArticlePLOS ONE. 4(1):e4247 (2009)journal articl
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
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