172 research outputs found
Chiral Lattice Gauge Theories Via Mirror-Fermion Decoupling: A Mission (im)Possible?
This is a review of the status and outstanding issues in attempts to
construct chiral lattice gauge theories by decoupling the mirror fermions from
a vectorlike theory. In the first half, we explain why studying nonperturbative
chiral gauge dynamics may be of interest, enumerate the problems that a lattice
formulation of chiral gauge theories must overcome, and briefly review our
current knowledge. We then discuss the motivation and idea of mirror-fermion
decoupling and illustrate the desired features of the decoupling dynamics by a
simple solvable toy model. The role of exact chiral symmetries and matching of
't Hooft anomalies on the lattice is also explained. The second, more
technical, half of the article is devoted to a discussion of the known and
unknown features of mirror-decoupling dynamics formulated with Ginsparg-Wilson
fermions. We end by pointing out possible directions for future studies.Comment: 53 pp; 6 figs; added table of contents, references, fixed typo
Continuity, Deconfinement, and (Super) Yang-Mills Theory
We study the phase diagram of SU(2) Yang-Mills theory with one adjoint Weyl
fermion on R^3xS^1 as a function of the fermion mass m and the compactification
scale L. This theory reduces to thermal pure gauge theory as m->infinity and to
circle-compactified (non-thermal) supersymmetric gluodynamics in the limit
m->0. In the m-L plane, there is a line of center symmetry changing phase
transitions. In the limit m->infinity, this transition takes place at
L_c=1/T_c, where T_c is the critical temperature of the deconfinement
transition in pure Yang-Mills theory. We show that near m=0, the critical
compactification scale L_c can be computed using semi-classical methods and
that the transition is of second order. This suggests that the deconfining
phase transition in pure Yang-Mills theory is continuously connected to a
transition that can be studied at weak coupling. The center symmetry changing
phase transition arises from the competition of perturbative contributions and
monopole-instantons that destabilize the center, and topological molecules
(neutral bions) that stabilize the center. The contribution of molecules can be
computed using supersymmetry in the limit m=0, and via the
Bogomolnyi--Zinn-Justin (BZJ) prescription in the non-supersymmetric gauge
theory. Finally, we also give a detailed discussion of an issue that has not
received proper attention in the context of N=1 theories---the non-cancellation
of nonzero-mode determinants around supersymmetric BPS and KK
monopole-instanton backgrounds on R^3xS^1. We explain why the non-cancellation
is required for consistency with holomorphy and supersymmetry and perform an
explicit calculation of the one-loop determinant ratio.Comment: A discussion of the non-cancellation of the nonzero mode determinants
around supersymmetric monopole-instantons in N=1 SYM on R^3xS^1 is added,
including an explicit calculation. The non-cancellation is, in fact, required
by supersymmetry and holomorphy in order for the affine-Toda superpotential
to be reproduced. References have also been adde
New Mechanisms of Dynamical Supersymmetry Breaking and Direct Gauge Mediation
We construct supersymmetric gauge theories with new mechanisms of dynamical
supersymmetry breaking. The models have flat directions at the classical level,
and different mechanisms lift these flat directions in different regions of the
classical moduli space. In one branch of the moduli space, supersymmetry is
broken by confinement in a novel manner. The models contain only dimensionless
couplings and have large groups of unbroken global symmetries, making them
potentially interesting for model-building. As an illustrative application, we
couple the standard model gauge group to a model with an SU(5) global symmetry,
resulting in a model with composite messengers and a non-minimal spectrum of
superpartner masses.Comment: 18 pages, LaTeX2e, no figures. Minor corrections; version to be
published in Phys. Rev.
Varieties of vacua in classical supersymmetric gauge theories
We give a simple description of the classical moduli space of vacua for
supersymmetric gauge theories with or without a superpotential. The key
ingredient in our analysis is the observation that the lagrangian is invariant
under the action of the complexified gauge group \Gc. From this point of view
the usual -flatness conditions are an artifact of Wess--Zumino gauge. By
using a gauge that preserves \Gc invariance we show that every constant
matter field configuration that extremizes the superpotential is \Gc
gauge-equivalent (in a sense that we make precise) to a unique classical
vacuum. This result is used to prove that in the absence of a superpotential
the classical moduli space is the algebraic variety described by the set of all
holomorphic gauge-invariant polynomials. When a superpotential is present, we
show that the classical moduli space is a variety defined by imposing
additional relations on the holomorphic polynomials. Many of these points are
already contained in the existing literature. The main contribution of the
present work is that we give a careful and self-contained treatment of limit
points and singularities.Comment: 14 pages, LaTeX (uses revtex.sty
Flavor in Supersymmetry with an Extended R-symmetry
We propose a new solution to the supersymmetric flavor problem without
flavor-blind mediation. Our proposal is to enforce a continuous or a suitably
large discrete R-symmetry on weak scale supersymmetry, so that Majorana gaugino
masses, trilinear A-terms, and the mu-term are forbidden. We find that
replacing the MSSM with an R-symmetric supersymmetric model allows order one
flavor-violating soft masses, even for squarks of order a few hundred GeV. The
minimal R-symmetric supersymmetric model contains Dirac gaugino masses and
R-symmetric Higgsino masses with no left-right mixing in the squark or slepton
sector. Dirac gaugino masses of order a few TeV with vanishing A-terms solve
most flavor problems, while the R-symmetric Higgs sector becomes important at
large tan(beta). epsilon_K can be accommodated if CP is preserved in the SUSY
breaking sector, or if there is a moderate flavor degeneracy, which can arise
naturally. epsilon'/epsilon, as well as neutron and electron EDMs are easily
within experimental bounds. The most striking phenomenological distinction of
this model is the order one flavor violation in the squark and slepton sector,
while the Dirac gaugino masses tend to be significantly heavier than the
corresponding squark and slepton masses.Comment: 15 pages, REVTEX4, 9 figure files, typos fixed, refs added, published
versio
Next-to-Minimal Supersymmetric Standard Model with the Gauge Mediation of Supersymmetry Breaking
We study the Next-to-Minimal Supersymmetric Standard Model (NMSSM) as the
simplest candidate solution to the -problem in the context of the gauge
mediation of supersymmetry breaking (GMSB). We first review various proposals
to solve the -problem in models with the GMSB. We find none of them
entirely satisfactory and point out that many of the scenarios still lack
quantitative studies, and motivate the NMSSM as the simplest possible solution.
We then study the situation in the Minimal Supersymmetric Standard Model (MSSM)
with the GMSB and find that an order 10% cancellation is necessary between the
-parameter and the soft SUSY-breaking parameters to correctly reproduce
. Unfortunately, the NMSSM does not to give a phenomenologically viable
solution to the -problem. We present quantitative arguments which apply
both for the low-energy and high-energy GMSB and prove that the NMSSM does not
work for either case. Possible modifications to the NMSSM are then discussed.
The NMSSM with additional vector-like quarks works phenomenologically, but
requires an order a few percent cancellation among parameters. We point out
that this cancellation has the same origin as the cancellation required in the
MSSM.Comment: 36 pages, LaTeX, epsf.sty, 5 figures, references added, comments on
some other papers based on our misundestanding corrected, none of our results
change
Gauge/Anomaly Syzygy and Generalized Brane World Models of Supersymmetry Breaking
In theories in which SUSY is broken on a brane separated from the MSSM matter
fields, supersymmetry breaking is naturally mediated in a variety of ways.
Absent other light fields in the theory, gravity will mediate supersymmetry
breaking through the conformal anomaly. If gauge fields propagate in the extra
dimension they, too, can mediate supersymmetry breaking effects. The presence
of gauge fields in the bulk motivates us to consider the effects of new
messenger fields with holomorphic and non-holomorphic couplings to the
supersymmetry breaking sector. These can lead to contributions to the soft
masses of MSSM fields which dramatically alter the features of brane world
scenarios of supersymmetry breaking. In particular, they can solve the negative
slepton mass squared problem of anomaly mediation and change the predictions of
gaugino mediation.Comment: 4 pages, RevTe
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