150 research outputs found

### Strongly coupled 't Hooft model on the lattice

A lattice strong coupling calculation of the spectrum and chiral condensate
of the 't Hooft model is presented. The agreement with the results of the
continuum theory is strikingly good even at the fourth order in the strong
coupling expansion.Comment: LATTICE99(Spin Models), talk presented by F. Berruto, 3 pages, LaTex,
espcrc2.st

### Calculation of the neutron electric dipole moment with two dynamical flavors of domain wall fermions

We present a study of the neutron electric dipole moment ($\vec d_N$) within
the framework of lattice QCD with two flavors of dynamical lig ht quarks. The
dipole moment is sensitive to the topological structure of the gaug e fields,
and accuracy can only be achieved by using dynamical, or sea quark, calc
ulations. However, the topological charge evolves slowly in these calculations,
le ading to a relatively large uncertainty in $\vec d_N$. It is shown, using
quenched configurations, that a better sampling of the charge d istribution
reduces this problem, but because the CP even part of the fermion determinant
is absent, both the topological charge dis tribution and $\vec d_N$ are
pathological in the chiral limit. We discuss the statistical and systematic
uncertainties arising from the topological charge distr ibution and unphysical
size of the quark mass in our calculations and prospects fo r eliminating them.
Our calculations employ the RBC collaboration two flavor domain wall fermion
and DBW2 gauge action lattices with inverse lattice spacing $a^{-1}\approx$ 1.7
GeV, physical volume $V\approx (2$ fm)$^3$, and light quark mass roughly equal
to the strange quark mass ($m_{sea}=0.03$ and 0.04). We determine a value of
the electric dipole moment that is zero withi n (statistical) errors, $|\vec
d_N| = -0.04(20)$ e-$\theta$-fm at the smaller sea quark mass. Satisfactory
results for the magnetic and electric form factors of the proton and neutron
are also obtained and presented.Comment: 46 pages. Changed one author addres

### Low-lying meson spectrum of large $N_C$ strongly coupled lattice QCD

We compute the low energy mass spectrum of lattice QCD in the large $N_C$
limit. Expanding around a gauge-invariant ground state, which spontaneously
breaks the discrete chiral symmetry, we derive an improved strong-coupling
expansion and evaluate, for any value of $N_C$, the masses of the low-lying
states in the unflavored meson spectrum. We then take the 't Hooft limit by
rescaling $g^2 N_C\to g^2$; the 't Hooft limit is smooth and no arbitrary
parameters are needed. We find, already at the fourth order of the strong
coupling perturbation theory, a very good agreement between the results of our
lattice computation and the known continuum values.Comment: 43 pages, 1 figure. Minor corrections. One reference added in section

### Lattice Gauge Theories and the Heisenberg Antiferromagnetic Chain

We study the strongly coupled 2-flavor lattice Schwinger model and the
SU(2)-color QCD_2. The strong coupling limit, even with its inherent
nonuniversality, makes accurate predictions of the spectrum of the continuum
models and provides an intuitive picture of the gauge theory vacuum. The
massive excitations of the gauge model are computable in terms of spin-spin
correlators of the quantum Heisenberg antiferromagnetic spin-1/2 chain.Comment: Proceedings LATTICE99 (spin models), 3 page

### On the Doubling Phenomenon in Lattice Chern-Simons Theories

We analyse the pure Chern-Simons theory on an Euclidean infinite lattice. We
point out that, as a consequence of its symmetries, the Chern-Simons theory
does not have an integrable kernel. Due to the linearity of the action in the
derivatives, the situation is very similar to the one arising in the lattice
formulation of fermionic theories. Doubling of bosonic degrees of freedom is
removed by adding a Maxwell term with a mechanism similar to the one proposed
by Wilson for fermionic models.Comment: Lattice 2000, 4 pages, Late

### Strongly coupled N=1 SYM theory on the lattice

We propose a strong coupling expansion as a possible tool to obtain
qualitative and quantitative informations about N=1 SYM theory. We point out
the existence of a mapping between strongly coupled lattice N=1 SYM theory and
a generalized SO(4) antiferromagnetic spin system.Comment: Lattice2002(spin), 3 pages, no figure

### The Chiral Condensate of Strongly Coupled QCD in the 't Hooft Limit

Using the recently proposed generalization to an arbitrary number of colors
of the strong coupling approach to lattice gauge
theories\cite{Grignani:2003uv}, we compute the chiral condensate of massless
QCD in the 't Hooft limit.Comment: 12 pages, revtex

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