1,259 research outputs found
Lattice energy-momentum tensor with Symanzik improved actions
We define the energy-momentum tensor on lattice for the and
for the nonlinear -model Symanzik tree-improved actions, using Ward
identities or an explicit matching procedure. The resulting operators give the
correct one loop scale anomaly, and in the case of the sigma model they can
have applications in Monte Carlo simulations.Comment: Self extracting archive fil
General duality for abelian-group-valued statistical-mechanics models
We introduce a general class of statistical-mechanics models, taking values
in an abelian group, which includes examples of both spin and gauge models,
both ordered and disordered. The model is described by a set of ``variables''
and a set of ``interactions''. A Gibbs factor is associated to each variable
and to each interaction. We introduce a duality transformation for systems in
this class. The duality exchanges the abelian group with its dual, the Gibbs
factors with their Fourier transforms, and the interactions with the variables.
High (low) couplings in the interaction terms are mapped into low (high)
couplings in the one-body terms. The idea is that our class of systems extends
the one for which the classical procedure 'a la Kramers and Wannier holds, up
to include randomness into the pattern of interaction. We introduce and study
some physical examples: a random Gaussian Model, a random Potts-like model, and
a random variant of discrete scalar QED. We shortly describe the consequence of
duality for each example.Comment: 26 pages, 2 Postscript figure
Grassmann Integral Representation for Spanning Hyperforests
Given a hypergraph G, we introduce a Grassmann algebra over the vertex set,
and show that a class of Grassmann integrals permits an expansion in terms of
spanning hyperforests. Special cases provide the generating functions for
rooted and unrooted spanning (hyper)forests and spanning (hyper)trees. All
these results are generalizations of Kirchhoff's matrix-tree theorem.
Furthermore, we show that the class of integrals describing unrooted spanning
(hyper)forests is induced by a theory with an underlying OSP(1|2)
supersymmetry.Comment: 50 pages, it uses some latex macros. Accepted for publication on J.
Phys.
A General Limitation on Monte Carlo Algorithms of Metropolis Type
We prove that for any Monte Carlo algorithm of Metropolis type, the
autocorrelation time of a suitable ``energy''-like observable is bounded below
by a multiple of the corresponding ``specific heat''. This bound does not
depend on whether the proposed moves are local or non-local; it depends only on
the distance between the desired probability distribution and the
probability distribution for which the proposal matrix satisfies
detailed balance. We show, with several examples, that this result is
particularly powerful when applied to non-local algorithms.Comment: 8 pages, LaTeX plus subeqnarray.sty (included at end),
NYU-TH-93/07/01, IFUP-TH33/9
Numerical Evidence for Spontaneously Broken Replica Symmetry in 3D Spin Glasses
By numerical simulations of the Ising spin glass we find evidence that
spontaneous replica symmetry breaking theory and not the droplet model
describes with good accuracy the equilibrium behavior of the system.Comment: PHYSREV format, 2 .ps figures added with figure command in uufiles
forma
Strong Earthquakes in North-Western Africa in the Second Half of the 17th Century, AD: A Critical Reappraisal of the Historical Evidence
The recent seismological literature recorded three strong earthquakes in Algeria, Libya and Tunisia between 1656 and 1694 AD. The historical evidence for these derives from European sources only (gazettes, journalistic pamphlets, missionary literature). Considering the kind of sources involved, their likely biases and the geographical distances that divided their places of production from the places
that they spoke about, it is possible that some of these accounts could be less than
reliable, and therefore have little use as materials from which to assess earthquake
parameters. To answer these doubts, we have retrieved, cross-checked and critically
analysed the original historical sources quoted in previous compilations and studies
Livelihood implications of in situ conservation strategies of wild fruit tree species in Uzbekistan
Throughout 2006 and 2011, Bioversity International has been promoting the conservation and use of plant genetic diversity in Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan under the auspices of the United Nations Environment Programme (UNEP) and Global Environment Facility (GEF).After 2013, an impact assessment study was carried out to examine whether the tangible
benefits of the Bioversity International project were transferred at the household level, with
specific emphasis on Uzbekistan, selected for the country relevance in terms of household characteristics and area covered by the project.In particular, the assessment focused on the effects of the interventions in the activity areas involving the enhancement of use and consumption of target fruits, as well as of their marketing value, to improve household food security and wellbeing
The 1561 Earthquake(s) in Southern Italy: New Insights into a Complex Seismic Sequence
In the summer of 1561, a strong seismic sequence struck southern Italy, then the Spanish-ruled
Kingdom of Naples. Both the Italian seismological tradition and the latest catalogues locate it in
the Vallo di Diano (Diano Valley), a low-seismicity intermontane basin 100 km south-east of
Naples. We explore the hypothesis that current perception of the 1561 earthquake is distorted by
the nature of the historical dataset from which its parameters have been assessed, and which mostly
derive from a single—albeit very detailed—primary source. We present and discuss several previously
unconsidered original accounts. Our results cast doubts on the traditional interpretation of
the earthquake, which could have been either one Vallo di Diano mainshock or several strong
earthquakes within a time/space window compact enough for contemporary viewers to perceive
them as one. Unquestionably, there is much more to the 1561 earthquake(s) than previously
appeared. We hope that this groundbreaking effort will rekindle the interest of the seismological
community in this seismic episode, our knowledge of which is still far from complete
Two and three loops computations of renormalization constants for lattice QCD
Renormalization constants can be computed by means of Numerical Stochastic
Perturbation Theory to two/three loops in lattice perturbation theory, both in
the quenched approximation and in the full (unquenched) theory. As a case of
study we report on the computation of renormalization constants of the
propagator for Wilson fermions. We present our unquenched (N_f=2) computations
and compare the results with non perturbative determinations.Comment: Lattice2004(improv), 3 pages, 4 figure
O(N) and RP^{N-1} Models in Two Dimensions
I provide evidence that the 2D model for is equivalent
to the -invariant non-linear -model in the continuum limit. To
this end, I mainly study particular versions of the models, to be called
constraint models. I prove that the constraint and models are
equivalent for sufficiently weak coupling. Numerical results for their
step-scaling function of the running coupling are
presented. The data confirm that the constraint model is in the samei
universality class as the model with standard action. I show that the
differences in the finite size scaling curves of i and models
observed by Caracciolo et al. can be explained as a boundary effect. It is
concluded, in contrast to Caracciolo et al., that and models
share a unique universality class.Comment: 14 pages (latex) + 1 figure (Postscript) ,uuencode
- …