496 research outputs found
A solvable twisted one-plaquette model
We solve a hot twisted Eguchi-Kawai model with only timelike plaquettes in
the deconfined phase, by computing the quadratic quantum fluctuations around
the classical vacuum. The solution of the model has some novel features: the
eigenvalues of the time-like link variable are separated in L bunches, if L is
the number of links of the original lattice in the time direction, and each
bunch obeys a Wigner semicircular distribution of eigenvalues. This solution
becomes unstable at a critical value of the coupling constant, where it is
argued that a condensation of classical solutions takes place. This can be
inferred by comparison with the heat-kernel model in the hamiltonian limit, and
the related Douglas-Kazakov phase transition in QCD2. As a byproduct of our
solution, we can reproduce the dependence of the coupling constant from the
parameter describing the asymmetry of the lattice, in agreement with previous
results by Karsch.Comment: Minor corrections; final version to appear on IJMPA. 22 pages, Latex,
2 (small) figures included with eps
Analytic results in 2+1-dimensional Finite Temperature LGT
In a 2+1-dimensional pure LGT at finite temperature the critical coupling for
the deconfinement transition scales as , where
is the number of links in the ``time-like'' direction of the symmetric
lattice. We study the effective action for the Polyakov loop obtained by
neglecting the space-like plaquettes, and we are able to compute analytically
in this context the coefficient for any SU(N) gauge group; the value of
is instead obtained from the effective action by means of (improved) mean
field techniques. Both coefficients have already been calculated in the large N
limit in a previous paper. The results are in very good agreement with the
existing Monte Carlo simulations. This fact supports the conjecture that, in
the 2+1-dimensional theory, space-like plaquettes have little influence on the
dynamics of the Polyakov loops in the deconfined phase.Comment: 15 pages, Latex, 2 figures included with eps
Finite Temperature Lattice QCD in the Large N Limit
Our aim is to give a self-contained review of recent advances in the analytic
description of the deconfinement transition and determination of the
deconfinement temperature in lattice QCD at large N. We also include some new
results, as for instance in the comparison of the analytic results with
Montecarlo simulations. We first review the general set-up of finite
temperature lattice gauge theories, using asymmetric lattices, and develop a
consistent perturbative expansion in the coupling of the space-like
plaquettes. We study in detail the effective models for the Polyakov loop
obtained, in the zeroth order approximation in , both from the Wilson
action (symmetric lattice) and from the heat kernel action (completely
asymmetric lattice). The distinctive feature of the heat kernel model is its
relation with two-dimensional QCD on a cylinder; the Wilson model, on the other
hand, can be exactly reduced to a twisted one-plaquette model via a procedure
of the Eguchi-Kawai type. In the weak coupling regime both models can be
related to exactly solvable Kazakov-Migdal matrix models. The instability of
the weak coupling solution is due in both cases to a condensation of
instantons; in the heat kernel case, it is directly related to the
Douglas-Kazakov transition of QCD2. A detailed analysis of these results
provides rather accurate predictions of the deconfinement temperature. In spite
of the zeroth order approximation they are in good agreement with the
Montecarlo simulations in 2+1 dimensions, while in 3+1 dimensions they only
agree with the Montecarlo results away from the continuum limit.Comment: 66 pages, plain Latex, figures included by eps
Two dimensional QCD is a one dimensional Kazakov-Migdal model
We calculate the partition functions of QCD in two dimensions on a cylinder
and on a torus in the gauge by integrating explicitly
over the non zero modes of the Fourier expansion in the periodic time variable.
The result is a one dimensional Kazakov-Migdal matrix model with eigenvalues on
a circle rather than on a line. We prove that our result coincides with the
standard expansion in representations of the gauge group. This involves a non
trivial modular transformation from an expansion in exponentials of to
one in exponentials of . Finally we argue that the states of the
or partition function can be interpreted as a gas of N free fermions,
and the grand canonical partition function of such ensemble is given explicitly
as an infinite product.Comment: DFTT 15/93, 17 pages, Latex (Besides minor changes and comments added
we note that for U(N) odd and even N have to be treated separately
Effective actions for finite temperature Lattice Gauge Theories
We consider a lattice gauge theory at finite temperature in (+1)
dimensions with the Wilson action and different couplings and
for timelike and spacelike plaquettes. By using the character
expansion and Schwinger-Dyson type equations we construct, order by order in
, an effective action for the Polyakov loops which is exact to all
orders in . As an example we construct the first non-trivial order in
for the (3+1) dimensional SU(2) model and use this effective action
to extract the deconfinement temperature of the model.Comment: Talk presented at LATTICE96(finite temperature
Push, don't nudge: behavioral spillovers and policy instruments
Policy interventions are generally evaluated for their direct effectiveness. Little is known about their ability to persist over time and spill across contexts. These latter aspects can reinforce or offset the direct impacts depending on the policy instrument choice. Through an online experiment with 1,486 subjects, we compare four widely used policy instruments in terms of their ability to enforce a norm of fairness in the Dictator Game, and to persist over time (i.e., to a subsequent untreated Dictator Game) or spill over to a norm of cooperation (i.e., to a subsequent Prisoner's Dilemma). As specific policy interventions, we employed two instances of nudges: defaults and social information; and two instances of push measures: rebates and a minimum donation rule. Our results show that (i) rebates, the minimum donation rule and social information have a positive direct effect on fairness, although the effect of social information is only marginally significant, and that (ii) the effect of rebates and the minimum donation rule persists in the second game, but only within the same game type. These findings demonstrate that, within our specific design, push measures are more effective than nudges in promoting fairness
On the Low-Energy Effective Action of N=2 Supersymmetric Yang-Mills Theory
We investigate the perturbative part of Seiberg's low-energy effective action
of N=2 supersymmetric Yang-Mills theory in Wess-Zumino gauge in the
conventional effective field theory technique. Using the method of constant
field approximation and restricting the effective action with at most two
derivatives and not more than four-fermion couplings, we show some features of
the low-energy effective action given by Seiberg based on anomaly and
non-perturbative -function arguments.Comment: 27 pages, RevTex, no figure
Exact Ward-Takahashi identity for the lattice N=1 Wess-Zumino model
The lattice Wess-Zumino model written in terms of the Ginsparg-Wilson
relation is invariant under a generalized supersymmetry transformation which is
determined by an iterative procedure in the coupling constant. By studying the
associated Ward-Takahashi identity up to order we show that this lattice
supersymmetry automatically leads to restoration of continuum supersymmetry
without fine tuning. In particular, the scalar and fermion renormalization wave
functions coincide.Comment: 6 pages, 5 figures, Talk given at QG05, Cala Gonone, Sardinia, Italy.
12-16 September 200
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