147,339 research outputs found

### Symmetry Principles for String Theory

The gauge symmetries that underlie string theory arise from inner
automorphisms of the algebra of observables of the associated conformal field
theory. In this way it is possible to study broken and unbroken symmetries on
the same footing, and exhibit an infinite-dimensional supersymmetry algebra
that includes space-time diffeomorphisms and an infinite number of
spontaneously broken level-mixing symmetries. We review progress in this area,
culminating in the identification of a weighted tensor algebra as a subalgebra
of the full symmetry. We also briefly describe outstanding problems. Talk
presented at the Gursey memorial conference, Istanbul, Turkey, June, 1994.Comment: 5 pages, Plain TeX, no figure

### Comment: Bayesian Checking of the Second Levels of Hierarchical Models

We discuss the methods of Evans and Moshonov [Bayesian Analysis 1 (2006)
893--914, Bayesian Statistics and Its Applications (2007) 145--159] concerning
checking for prior-data conflict and their relevance to the method proposed in
this paper. [arXiv:0802.0743]Comment: Published in at http://dx.doi.org/10.1214/07-STS235C the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org

### Spacetime Supersymmetry in a nontrivial NS-NS Superstring Background

In this paper we consider superstring propagation in a nontrivial NS-NS
background. We deform the world sheet stress tensor and supercurrent with an
infinitesimal B_{\mu\nu} field. We construct the gauge-covariant super-Poincare
generators in this background and show that the B_{\mu\nu} field spontaneously
breaks spacetime supersymmetry. We find that the gauge-covariant spacetime
momenta cease to commute with each other and with the spacetime supercharges.
We construct a set of "magnetic" super-Poincare generators that are conserved
for constant field strength H_{\mu\nu\lambda}, and show that these generators
obey a "magnetic" extension of the ordinary supersymmetry algebra.Comment: 13 pages, Latex. Published versio

### Optimal properties of some Bayesian inferences

Relative surprise regions are shown to minimize, among Bayesian credible
regions, the prior probability of covering a false value from the prior. Such
regions are also shown to be unbiased in the sense that the prior probability
of covering a false value is bounded above by the prior probability of covering
the true value. Relative surprise regions are shown to maximize both the Bayes
factor in favor of the region containing the true value and the relative belief
ratio, among all credible regions with the same posterior content. Relative
surprise regions emerge naturally when we consider equivalence classes of
credible regions generated via reparameterizations.Comment: Published in at http://dx.doi.org/10.1214/07-EJS126 the Electronic
Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of
Mathematical Statistics (http://www.imstat.org

### Second cohomology groups and finite covers

For D an infinite set, k>1 and W the set of k-sets from D, there is a natural
closed permutation group G_k which is a non-split extension of \mathbb{Z}_2^W
by \Sym(D). We classify the closed subgroups of G_k which project onto
\Sym(D)$. The question arises in model theory as a problem about finite covers,
but here we formulate and solve it in algebraic terms.Comment: Typos corrected; change of title to 'Second cohomology groups and
finite covers of infinite symmetric groups' in published versio

### Phase Transitions in one-dimensional nonequilibrium systems

The phenomenon of phase transitions in one-dimensional systems is discussed.
Equilibrium systems are reviewed and some properties of an energy function
which may allow phase transitions and phase ordering in one dimension are
identified. We then give an overview of the one-dimensional phase transitions
which we have been studied in nonequilibrium systems. A particularly simple
model, the zero-range process, for which the steady state is know exactly as a
product measure, is discussed in some detail. Generalisations of the model, for
which a product measure still holds, are also discussed. We analyse in detail a
condensation phase transition in the model and show how conditions under which
it may occur may be related to the existence of an effective long-range energy
function. Although the zero-range process is not well known within the physics
community, several nonequilibrium models have been proposed that are examples
of a zero-range process, or closely related to it, and we review these
applications here.Comment: latex, 28 pages, review article; references update

### Bose-Einstein Condensation In Disordered Exclusion Models and Relation to Traffic Flow

A disordered version of the one dimensional asymmetric exclusion model where
the particle hopping rates are quenched random variables is studied. The steady
state is solved exactly by use of a matrix product. It is shown how the
phenomenon of Bose condensation whereby a finite fraction of the empty sites
are condensed in front of the slowest particle may occur. Above a critical
density of particles a phase transition occurs out of the low density phase
(Bose condensate) to a high density phase. An exponent describing the decrease
of the steady state velocity as the density of particles goes above the
critical value is calculated analytically and shown to depend on the
distribution of hopping rates. The relation to traffic flow models is
discussed.Comment: 7 pages, Late

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