32,960 research outputs found
Numerical Exploration of the RI/MOM Scheme Gauge Dependence
The gauge dependence of some fermion bilinear RI/MOM renormalization
constants is studied by comparing data which have been gauge-fixed in two
different realizations of the Landau gauge and in a generic covariant gauge.
The very good agreement between the various sets of results and the theory
indicates that the numerical uncertainty induced by the lattice gauge-fixing
procedure is below the statistical errors of our data sample which is of the
order of (1-1.5)%.Comment: 3 pages, 2 figures, Lattice2002(theoretical
Glauber dynamics for the quantum Ising model in a transverse field on a regular tree
Motivated by a recent use of Glauber dynamics for Monte-Carlo simulations of
path integral representation of quantum spin models [Krzakala, Rosso,
Semerjian, and Zamponi, Phys. Rev. B (2008)], we analyse a natural Glauber
dynamics for the quantum Ising model with a transverse field on a finite graph
. We establish strict monotonicity properties of the equilibrium
distribution and we extend (and improve) the censoring inequality of Peres and
Winkler to the quantum setting. Then we consider the case when is a regular
-ary tree and prove the same fast mixing results established in [Martinelli,
Sinclair, and Weitz, Comm. Math. Phys. (2004)] for the classical Ising model.
Our main tool is an inductive relation between conditional marginals (known as
the "cavity equation") together with sharp bounds on the operator norm of the
derivative at the stable fixed point. It is here that the main difference
between the quantum and the classical case appear, as the cavity equation is
formulated here in an infinite dimensional vector space, whereas in the
classical case marginals belong to a one-dimensional space
Comparison of Swendsen-Wang and Heat-Bath Dynamics
We prove that the spectral gap of the Swendsen-Wang process for the Potts
model on graphs with bounded degree is bounded from below by some constant
times the spectral gap of any single-spin dynamics. This implies rapid mixing
of the Swendsen-Wang process for the two-dimensional Potts model at all
temperatures above the critical one, as well as rapid mixing at the critical
temperature for the Ising model. After this we introduce a modified version of
the Swendsen-Wang algorithm for planar graphs and prove rapid mixing for the
two-dimensional Potts models at all non-critical temperatures.Comment: 22 pages, 1 figur
A High-Statistics Lattice Calculation of and in the meson
We present a high-statistics lattice calculation of the kinetic energy
of the heavy quark inside the -meson and of the
chromo-magnetic term , related to the -- mass splitting,
performed in the HQET. Our results have been obtained from a numerical
simulation based on 600 gauge field configurations generated at , on
a lattice volume and using, for the meson correlators, the
results obtained with the SW-Clover improved lattice action for the
light quarks. For the kinetic energy we found ~GeV, which
is interesting for phenomenological applications. We also find GeV, corresponding to GeV, which is about one half of the experimental value. The origin
of the discrepancy with the experimental number needs to be clarified.Comment: 26 pages, latex, 5 figure
Small firms, borrowing constraints, and reputation
This paper presents a simple model relating firm age with firm size and access to credit markets. Lending to new firms is risky because lenders have had no time to accumulate observations about them. As a result, interest rates are high and loans are small for entering firms. As firms need credit to operate, credit markets impose a limit on the scale of operation of new firms. Reputation building by the firms allows markets to overcome these difficulties over time. Large firms face lower interest rates than small firms, and credit markets fluctuations are shown to have different effects on firms of different size
Hadronic Weak Interactions of Light Quarks
In this review, three subjects are discussed: a phenomenological application
of lattice predictions to -- mixing in Super Symmetry; a
discussion of the non-perturbative renormalization methods for four-fermion
operators and a new approach to extract weak matrix elements in effective
theories denoted as OPE without OPE (operator product expansion without
operator product expansion)Comment: 14 pages - 1 figur
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