19 research outputs found
Meson-meson scattering in the massive Schwinger model: a status report
We discuss the possibility of extracting phase shifts from finite volume energies for meson-meson scattering, where the mesons are fermion-antifermion bound states of the massive Schwinger model with SU(2) flavour symmetry. The existence of analytical strong coupling predictions for the mass spectrum and for the scattering phases makes it possible to test the reliability of numerical results
Temporal team semantics revisited
In this paper, we study a novel approach to asynchronous hyperproperties by reconsidering the foundations of temporal team semantics. We consider three logics: , and , which are obtained by adding quantification over so-called time evaluation functions controlling the asynchronous progress of traces. We then relate synchronous to our new logics and show how it can be embedded into them. We show that the model checking problem for with Boolean disjunctions is highly undecidable by encoding recurrent computations of non-deterministic 2-counter machines. Finally, we present a translation from to Alternating Asynchronous Büchi Automata and obtain decidability results for the path checking problem as well as restricted variants of the model checking and satisfiability problems
Mass spectrum and elastic scattering in the massive SU(2)_f Schwinger model on the lattice
We calculate numerically scattering phases for elastic meson-meson scattering
processes in the strongly coupled massive Schwinger-model with an SU(2) flavour
symmetry. These calculations are based on Luescher's method in which finite
size effects in two-particle energies are exploited. The results from
Monte-Carlo simulations with staggered fermions for the lightest meson ("pion")
are in good agreement with the analytical strong-coupling prediction.
Furthermore, the mass spectrum of low-lying mesonic states is investigated
numerically. We find a surprisingly rich spectrum in the mass region [m_\pi,4
m_\pi].Comment: 43 pages, 15 figures, LaTeX, uses feynmf.st
Interaction effects in the spectrum of the three-dimensional Ising model
The two-point correlation functions of statistical models show in general
both poles and cuts in momentum space. The former correspond to the spectrum of
massive excitations of the model, while the latter originate from interaction
effects, namely creation and annihilation of virtual pairs of excitations. We
discuss the effect of such interactions on the long distance behavior of
correlation functions in configuration space, focusing on certain time-slice
operators which are commonly used to extract the spectrum. For the 3D Ising
model in the scaling region of the broken-symmetry phase, a one-loop
calculation shows that the interaction effects on time-slice correlations is
non negligible for distances up to a few times the correlation length, and
should therefore be taken into account when analysing Monte Carlo data.Comment: 10 pages, LaTeX file + 1 ps figure, uses axodraw.st
Five-loop renormalization-group expansions for the three-dimensional n-vector cubic model and critical exponents for impure Ising systems
The renormalization-group (RG) functions for the three-dimensional n-vector
cubic model are calculated in the five-loop approximation. High-precision
numerical estimates for the asymptotic critical exponents of the
three-dimensional impure Ising systems are extracted from the five-loop RG
series by means of the Pade-Borel-Leroy resummation under n = 0. These
exponents are found to be: \gamma = 1.325 +/- 0.003, \eta = 0.025 +/- 0.01, \nu
= 0.671 +/- 0.005, \alpha = - 0.0125 +/- 0.008, \beta = 0.344 +/- 0.006. For
the correction-to-scaling exponent, the less accurate estimate \omega = 0.32
+/- 0.06 is obtained.Comment: 11 pages, LaTeX, no figures, published versio
Three-loop critical exponents, amplitude functions, and amplitude ratios from variational perturbation theory
We use variational perturbation theory to calculate various universal
amplitude ratios above and below T_c in minimally subtracted phi^4-theory with
N components in three dimensions. In order to best exhibit the method as a
powerful alternative to Borel resummation techniques, we consider only to two-
and three-loops expressions where our results are analytic expressions. For the
critical exponents, we also extend existing analytic expressions for two loops
to three loops.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper (including all PS fonts) at
http://www.physik.fu-berlin.de/~kleinert/kleiner_re318/preprint.htm
25th-order high-temperature expansion results for three-dimensional Ising-like systems on the simple cubic lattice
25th-order high-temperature series are computed for a general
nearest-neighbor three-dimensional Ising model with arbitrary potential on the
simple cubic lattice. In particular, we consider three improved potentials
characterized by suppressed leading scaling corrections. Critical exponents are
extracted from high-temperature series specialized to improved potentials,
obtaining , , ,
, , . Moreover, biased
analyses of the 25th-order series of the standard Ising model provide the
estimate for the exponent associated with the leading scaling
corrections. By the same technique, we study the small-magnetization expansion
of the Helmholtz free energy. The results are then applied to the construction
of parametric representations of the critical equation of state, using a
systematic approach based on a global stationarity condition. Accurate
estimates of several universal amplitude ratios are also presented.Comment: 40 pages, 15 figure
Extension to order of the high-temperature expansions for the spin-1/2 Ising model on the simple-cubic and the body-centered-cubic lattices
Using a renormalized linked-cluster-expansion method, we have extended to
order the high-temperature series for the susceptibility
and the second-moment correlation length of the spin-1/2 Ising models on
the sc and the bcc lattices. A study of these expansions yields updated direct
estimates of universal parameters, such as exponents and amplitude ratios,
which characterize the critical behavior of and . Our best
estimates for the inverse critical temperatures are
and . For the
susceptibility exponent we get and for the correlation
length exponent we get .
The ratio of the critical amplitudes of above and below the critical
temperature is estimated to be . The analogous ratio for
is estimated to be . For the correction-to-scaling
amplitude ratio we obtain .Comment: Misprints corrected, 8 pages, latex, no figure
Improved high-temperature expansion and critical equation of state of three-dimensional Ising-like systems
High-temperature series are computed for a generalized Ising model with
arbitrary potential. Two specific ``improved'' potentials (suppressing leading
scaling corrections) are selected by Monte Carlo computation. Critical
exponents are extracted from high-temperature series specialized to improved
potentials, achieving high accuracy; our best estimates are:
, , , ,
. By the same technique, the coefficients of the small-field
expansion for the effective potential (Helmholtz free energy) are computed.
These results are applied to the construction of parametric representations of
the critical equation of state. A systematic approximation scheme, based on a
global stationarity condition, is introduced (the lowest-order approximation
reproduces the linear parametric model). This scheme is used for an accurate
determination of universal ratios of amplitudes. A comparison with other
theoretical and experimental determinations of universal quantities is
presented.Comment: 65 pages, 1 figure, revtex. New Monte Carlo data by Hasenbusch
enabled us to improve the determination of the critical exponents and of the
equation of state. The discussion of several topics was improved and the
bibliography was update
A cross-sectional survey of the knowledge, attitudes and practices regarding tuberculosis among general practitioners working in municipalities with and without asylum centres in eastern Norway
TB survey among Norwegian GPs survey questionnaire NOR: The survey questionnaire in Norwegian. (PDF 208 kb