161 research outputs found
The Thermal Renormalization Group for Fermions, Universality, and the Chiral Phase-Transition
We formulate the thermal renormalization group, an implementation of the
Wilsonian RG in the real-time (CTP) formulation of finite temperature field
theory, for fermionic fields. Using a model with scalar and fermionic degrees
of freedom which should describe the two-flavor chiral phase-transition, we
discuss the mechanism behind fermion decoupling and universality at second
order transitions. It turns out that an effective mass-like term in the fermion
propagator which is due to thermal fluctuations and does not break chiral
symmetry is necessary for fermion decoupling to work. This situation is in
contrast to the high-temperature limit, where the dominance of scalar over
fermionic degrees of freedom is due to the different behavior of the
distribution functions. The mass-like contribution is the leading thermal
effect in the fermionic sector and is missed if a derivative expansion of the
fermionic propagator is performed. We also discuss results on the
phase-transition of the model considered where we find good agreement with
results from other methods.Comment: References added, minor typos correcte
Heisenberg frustrated magnets: a nonperturbative approach
Frustrated magnets are a notorious example where the usual perturbative
methods are in conflict. Using a nonperturbative Wilson-like approach, we get a
coherent picture of the physics of Heisenberg frustrated magnets everywhere
between and . We recover all known perturbative results in a single
framework and find the transition to be weakly first order in . We compute
effective exponents in good agreement with numerical and experimental data.Comment: 5 pages, Revtex, technical details available at
http://www.lpthe.jussieu.fr/~tissie
Flow Equations without Mean Field Ambiguity
We compare different methods used for non-perturbative calculations in
strongly interacting fermionic systems. Mean field theory often shows a basic
ambiguity related to the possibility to perform Fierz transformations. The
results may then depend strongly on an unphysical parameter which reflects the
choice of the mean field, thus limiting the reliability. This ambiguity is
absent for Schwinger-Dyson equations or fermionic renormalization group
equations. Also renormalization group equations in a partially bosonized
setting can overcome the Fierz ambiguity if the truncation is chosen
appropriately. This is reassuring since the partially bosonized renormalization
group approach constitutes a very promising basis for the explicit treatment of
condensates and spontaneous symmetry breaking even for situations where the
bosonic correlation length is large.Comment: New version to match the one published in PRD. New title (former
title: Solving Mean Field Ambiguity by Flow Equations), added section IX and
appendix B. More explanations in the introduction and conclusions. 16 pages,
6 figures and 3 tables uses revtex
A non perturbative approach of the principal chiral model between two and four dimensions
We investigate the principal chiral model between two and four dimensions by
means of a non perturbative Wilson-like renormalization group equation. We are
thus able to follow the evolution of the effective coupling constants within
this whole range of dimensions without having recourse to any kind of small
parameter expansion. This allows us to identify its three dimensional critical
physics and to solve the long-standing discrepancy between the different
perturbative approaches that characterizes the class of models to which the
principal chiral model belongs.Comment: 5 pages, 1 figure, Revte
On the Mass Spectrum of the SU(2) Higgs Model in 2+1 Dimensions
We calculate the masses of the low-lying states with quantum numbers
in the Higgs and confinement regions of the
three-dimensional SU(2) Higgs model, which plays an important r\^ole in the
description of the thermodynamic properties of the standard model at finite
temperatures. We extract the masses from correlation functions of
gauge-invariant operators which are calculated by means of a lattice Monte
Carlo simulation. The projection properties of our lattice operators onto the
lowest states are greatly improved by the use of smearing techniques. We also
consider cross correlations between various operators with the same quantum
numbers. From these the mass eigenstates are determined by means of a
variational calculation. In the symmetric phase, we find that some of the
ground state masses are about 30\% lighter than those reported from previous
simulations. We also obtain the masses of the first few excited states in the
symmetric phase. Remarkable among these is the occurrence of a state
composed almost entirely of gauge degrees of freedom. The mass of this state,
as well as that of its first excitations, is nearly identical to the
corresponding glueball states in three-dimensional SU(2) pure gauge theory,
indicating an approximate decoupling of the pure gauge sector from the Higgs
sector of the model. We perform a detailed study of finite size effects and
extrapolate the lattice mass spectrum to the continuum.Comment: 30 pages LATEX, uses epsf.st
The PERK Inhibitor GSK2606414 Enhances Reovirus Infection in Head and Neck Squamous Cell Carcinoma via an ATF4-Dependent Mechanism.
Reovirus type 3 Dearing (reovirus) is a tumor-selective oncolytic virus currently under evaluation in clinical trials. Here, we report that the therapeutic efficacy of reovirus in head and neck squamous cell cancer can be enhanced by targeting the unfolded protein response (UPR) kinase, protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK). PERK inhibition by GSK2606414 increased reovirus efficacy in both 2D and 3D models in vitro, while perturbing the normal host cell response to reovirus-induced endoplasmic reticulum (ER) stress. UPR reporter constructs were used for live-cell 3D spheroid imaging. Profiling of eIF2a-ATF4, IRE1a-XBP1, and ATF6 pathway activity revealed a context-dependent increase in eIF2a-ATF4 signaling due to GSK2606414. GSK2606414 blocked eIF2a-ATF4 signaling because of the canonical ER stress agent thapsigargin. In the context of reovirus infection, GSK2606414 induced eIF2a-ATF4 signaling. Knockdown of eIF2a kinases PERK, GCN2, and PKR revealed eIF2a-ATF4 reporter activity was dependent on either PERK or GCN2. Knockdown of ATF4 abrogated the GSK2606414-induced increase in reovirus protein levels, confirming eIF2a-ATF signaling as key to the observed phenotype. Our work identifies a novel approach to enhance the efficacy and replication of reovirus in a therapeutic setting
Two-Loop Effective Potential of O(N)-Symmetric Scalar QED in 4-epsilon Dimensions
The effective potential of scalar QED is computed analytically up to two
loops in the Landau gauge. The result is given in 4-epsilon dimensions using
minimal subtraction and epsilon-expansions. In three dimensions, our
calculation is intended to help throw light on unsolved problems of the
superconducting phase transition, where critical exponents and the position of
the tricritical point have not yet found a satisfactory explanation within the
renormalization group approach.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper (including all PS fonts) at
http://www.physik.fu-berlin.de/~kleinert/32
Critical Phenomena with Linked Cluster Expansions in a Finite Volume
Linked cluster expansions are generalized from an infinite to a finite
volume. They are performed to 20th order in the expansion parameter to approach
the critical region from the symmetric phase. A new criterion is proposed to
distinguish 1st from 2nd order transitions within a finite size scaling
analysis. The criterion applies also to other methods for investigating the
phase structure such as Monte Carlo simulations. Our computational tools are
illustrated at the example of scalar O(N) models with four and six-point
couplings for and in three dimensions. It is shown how to localize
the tricritical line in these models. We indicate some further applications of
our methods to the electroweak transition as well as to models for
superconductivity.Comment: 36 pages, latex2e, 7 eps figures included, uuencoded, gzipped and
tarred tex file hdth9607.te
Masses and Phase Structure in the Ginzburg-Landau Model
We study numerically the phase structure of the Ginzburg-Landau model, with
particular emphasis on mass measurements. There is no local gauge invariant
order parameter, but we find that there is a phase transition characterized by
a vanishing photon mass. For type I superconductors the transition is of 1st
order. For type II 1st order is excluded by susceptibility analysis, but the
photon correlation length suggests 2nd order critical behaviour with \nu ~ 1/2.
The scalar mass, in contrast, does not show clear critical behaviour in the
type II regime for V \to \infty, contrary to the conventional picture.Comment: 16 pages, 6 figures. More data gathered, allowing more definite
conclusion
Deconfinement transition in three-dimensional compact U(1) gauge theories coupled to matter fields
It is shown that permanent confinement in three-dimensional compact U(1)
gauge theory can be destroyed by matter fields in a deconfinement transition.
This is a consequence of a non-trivial infrared fixed point caused by matter,
and an anomalous scaling dimension of the gauge field. This leads to a
logarithmic interaction between the defects of the gauge-fields, which form a
gas of magnetic monopoles. In the presence of logarithmic interactions, the
original electric charges are unconfined. The confined phase which is permanent
in the absence of matter fields is reached at a critical electric charge, where
the interaction between magnetic charges is screened by a pair unbinding
transition in a Kosterlitz-Thouless type of phase-transition.Comment: RevTex4, 4 pages, no figures; version accepted for publication in PR
- …