1,725 research outputs found
Exact Flow Equations and the U(1)-Problem
The effective action of a SU(N)-gauge theory coupled to fermions is evaluated
at a large infrared cut-off scale k within the path integral approach. The
gauge field measure includes topologically non-trivial configurations
(instantons). Due to the explicit infrared regularisation there are no gauge
field zero modes. The Dirac operator of instanton configurations shows a zero
mode even after the infrared regularisation, which leads to U_A(1)-violating
terms in the effective action. These terms are calculated in the limit of large
scales k.Comment: 22 pages, latex, no figures, with stylistic changes and some
arguments streamlined, typos corrected, References added, to appear in Phys.
Rev.
Effective Average Action in N=1 Super-Yang-Mills Theory
For N=1 Super-Yang-Mills theory we generalize the effective average action
Gamma_k in a manifest supersymmetric way using the superspace formalism. The
exact evolution equation for Gamma_k is derived and, introducing as an
application a simple truncation, the standard one-loop beta-function of N=1 SYM
theory is obtained.Comment: 17 pages, LaTeX, some remarks added, misprints corrected, to appear
in Phys. Rev.
The beta functions of a scalar theory coupled to gravity
We study a scalar field theory coupled to gravity on a flat background, below
Planck's energy. Einstein's theory is treated as an effective field theory.
Within the context of Wilson's renormalization group, we compute gravitational
corrections to the beta functions and the anomalous dimension of the scalar
field, taking into account threshold effects.Comment: 13 pages, plainTe
Various Super Yang-Mills Theories with Exact Supersymmetry on the Lattice
We continue to construct lattice super Yang-Mills theories along the line
discussed in the previous papers \cite{sugino, sugino2}. In our construction of
theories in four dimensions, the problem of degenerate vacua
seen in \cite{sugino} is resolved by extending some fields and soaking up
would-be zero-modes in the continuum limit, while in the weak coupling
expansion some surplus modes appear both in bosonic and fermionic sectors
reflecting the exact supersymmetry. A slight modification to the models is made
such that all the surplus modes are eliminated in two- and three-dimensional
models obtained by dimensional reduction thereof. models in
three dimensions need fine-tuning of three and one parameters respectively to
obtain the desired continuum theories, while two-dimensional models with do not require any fine-tuning.Comment: 28 pages, no figure, LaTeX, JHEP style; (v2) published version to
JHEP; (v3) argument on the vacuum degeneracy revised, 34 page
Deconstruction and other approaches to supersymmetric lattice field theories
This report contains both a review of recent approaches to supersymmetric
lattice field theories and some new results on the deconstruction approach. The
essential reason for the complex phase problem of the fermion determinant is
shown to be derivative interactions that are not present in the continuum.
These irrelevant operators violate the self-conjugacy of the fermion action
that is present in the continuum. It is explained why this complex phase
problem does not disappear in the continuum limit. The fermion determinant
suppression of various branches of the classical moduli space is explored, and
found to be supportive of previous claims regarding the continuum limit.Comment: 70 page
Wess-Zumino model with exact supersymmetry on the lattice
A lattice formulation of the four dimensional Wess-Zumino model that uses
Ginsparg-Wilson fermions and keeps exact supersymmetry is presented. The
supersymmetry transformation that leaves invariant the action at finite lattice
spacing is determined by performing an iterative procedure in the coupling
constant. The closure of the algebra, generated by this transformation is also
showed.Comment: 13 pages. Few references added. New appendix on Ward identity added.
Version to be published in JHE
Lattice formulation of super Yang-Mills theory
We construct a lattice action for super Yang-Mills theory in
four dimensions which is local, gauge invariant, free of spectrum doubling and
possesses a single exact supersymmetry. Our construction starts from the
observation that the fermions of the continuum theory can be mapped into the
component fields of a single real anticommuting Kahler-Dirac field. The
original supersymmetry algebra then implies the existence of a nilpotent scalar
supercharge and a corresponding set of bosonic superpartners. Using this
field content we write down a -exact action and show that, with an
appropriate change of variables, it reduces to a well-known twist of super Yang-Mills theory due to Marcus. Using the discretization
prescription developed in an earlier paper on the theory in two
dimensions we are able to translate this geometrical action to the lattice.Comment: 15 pages. 1 reference correcte
Effective Action for the Quark-Meson Model
The scale dependence of an effective average action for mesons and quarks is
described by a nonperturbative flow equation. The running couplings lead to
spontaneous chiral symmetry breaking. We argue that for strong Yukawa coupling
between quarks and mesons the low momentum physics is essentially determined by
infrared fixed points. This allows us to establish relations between various
parameters related to the meson potential. The results for and
\VEV{\olpsi\psi} are not very sensitive to the poorly known details of the
quark--meson effective action at scales where the mesonic bound states form.
For realistic constituent quark masses we find around 100\MeV.Comment: 56 pages (including 10 figures and 1 table), uses epsf.st
Gluon Condensation in Nonperturbative Flow Equations
We employ nonperturbative flow equations for an investigation of the
effective action in Yang-Mills theories. We compute the effective action
for constant color magnetic fields and examine Savvidy's
conjecture of an unstable perturbative vacuum. Our results indicate that the
absolute minimum of occurs for B=0. Gluon condensation is described
by a nonvanishing expectation value of the regularized composite operator
which agrees with phenomenological estimates.Comment: 64 pages, late
Space-Time Supersymmetry of Extended Fermionic Strings in Dimensions
The fermionic string theory is revisited in light of its recently
proposed equivalence to the non-compact fermionic string model. The
issues of space-time Lorentz covariance and supersymmetry for the BRST
quantized strings living in uncompactified dimensions are
discussed. The equivalent local quantum supersymmetric field theory appears to
be the most transparent way to represent the space-time symmetries of the
extended fermionic strings and their interactions. Our considerations support
the Siegel's ideas about the presence of Lorentz symmetry as well as
at least one self-dual space-time supersymmetry in the theory of the
fermionic strings, though we do not have a compelling reason to argue about the
necessity of the {\it maximal} space-time supersymmetry. The world-sheet
arguments about the absence of all string massive modes in the physical
spectrum, and the vanishing of all string-loop amplitudes in the Polyakov
approach, are given on the basis of general consistency of the theory.Comment: 29 pages, LaTeX, ITP-UH-1/9
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