10,614 research outputs found
Isospin susceptibility in the O() sigma-model in the delta-regime
We compute the isospin susceptibility in an effective O() scalar field
theory (in dimensions), to third order in chiral perturbation theory
(PT) in the delta--regime using the quantum mechanical rotator picture.
This is done in the presence of an additional coupling, involving a parameter
, describing the effect of a small explicit symmetry breaking term (quark
mass). For the chiral limit we demonstrate consistency with our
previous PT computations of the finite-volume mass gap and isospin
susceptibility. For the massive case by computing the leading mass effect in
the susceptibility using PT with dimensional regularization, we determine
the PT expansion for to third order. The behavior of the shape
coefficients for long tube geometry obtained here might be of broader interest.
The susceptibility calculated from the rotator approximation differs from the
PT result in terms vanishing like for .
We show that this deviation can be described by a correction to the rotator
spectrum proportional to the square of the quadratic Casimir invariant.Comment: 34 page
Locality and exponential error reduction in numerical lattice gauge theory
In non-abelian gauge theories without matter fields, expectation values of
large Wilson loops and loop correlation functions are difficult to compute
through numerical simulation, because the signal-to-noise ratio is very rapidly
decaying for increasing loop sizes. Using a multilevel scheme that exploits the
locality of the theory, we show that the statistical errors in such
calculations can be exponentially reduced. We explicitly demonstrate this in
the SU(3) theory, for the case of the Polyakov loop correlation function, where
the efficiency of the simulation is improved by many orders of magnitude when
the area bounded by the loops exceeds 1 fm^2.Comment: Plain TeX source, 18 pages, figures include
One-loop renormalization factors and mixing coeffecients of bilinear quark operators for improved gluon and quark actions
We calculate one-loop renormalization factors and mixing coefficients of
bilinear quark operators for a class of gluon actions with six-link loops and
O(a)-improved quark action. The calculation is carried out by evaluating
on-shell Green's functions of quarks and gluons in the standard perturbation
theory. We find a general trend that finite parts of one-loop coefficients are
reduced approximately by a factor two for the renormalization-group improved
gluon actions compared with the case of the standard plaquette gluon action.Comment: LATTICE98(improvement), 3 page
Square Symanzik action to one-loop order
We present the one-loop coefficients for an alternative Symanzik improved
lattice action with gauge groups SU(2) or SU(3).Comment: 3 pages, latex, 1 table, no figure
Bethe--Salpeter wave functions in integrable models
We investigate some properties of Bethe--Salpeter wave functions in
integrable models. In particular we illustrate the application of the operator
product expansion in determining the short distance behavior. The energy
dependence of the potentials obtained from such wave functions is studied, and
further we discuss the (limited) phenomenological significance of zero--energy
potentials.Comment: LaTeX, 38 pages, 9 figure
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