16,567 research outputs found
Probabilistic abductive logic programming using Dirichlet priors
Probabilistic programming is an area of research that aims to develop general inference algorithms for probabilistic models expressed as probabilistic programs whose execution corresponds to inferring the parameters of those models. In this paper, we introduce a probabilistic programming language (PPL) based on abductive logic programming for performing inference in probabilistic models involving categorical distributions with Dirichlet priors. We encode these models as abductive logic programs enriched with probabilistic definitions and queries, and show how to execute and compile them to boolean formulas. Using the latter, we perform generalized inference using one of two proposed Markov Chain Monte Carlo (MCMC) sampling algorithms: an adaptation of uncollapsed Gibbs sampling from related work and a novel collapsed Gibbs sampling (CGS). We show that CGS converges faster than the uncollapsed version on a latent Dirichlet allocation (LDA) task using synthetic data. On similar data, we compare our PPL with LDA-specific algorithms and other PPLs. We find that all methods, except one, perform similarly and that the more expressive the PPL, the slower it is. We illustrate applications of our PPL on real data in two variants of LDA models (Seed and Cluster LDA), and in the repeated insertion model (RIM). In the latter, our PPL yields similar conclusions to inference with EM for Mallows models
On Schwinger Pair Creation in Gravity and in Closed Superstring Theory
We investigate the Schwinger pair creation process in the context of
gravitational models with the back reaction of the electric field included in
the geometry. The background is also an exact solution of type II superstring
theory, where the electric field arises by Kaluza-Klein reduction. We obtain a
closed formula for the pair creation rate that incorporates the gravitational
back reaction. At weak fields it has the same structure as the general
Schwinger formula, albeit pairs are produced by a combination of Schwinger and
Unruh effect, the latter due to the presence of a Rindler horizon. In four
spacetime dimensions, the rate becomes constant at strong electric fields. For
states with mass of Kaluza-Klein origin, the rate has a power-like dependence
in the electric field, rather than the familiar (non-perturbative) exponential
dependence. We also reproduce the same formula from the string partition
function for winding string states. Finally, we comment on the generalization
to excited string states.Comment: 21 page
Bounds for the relative n-th nilpotency degree in compact groups
The line of investigation of the present paper goes back to a classical work
of W. H. Gustafson of the 1973, in which it is described the probability that
two randomly chosen group elements commute. In the same work, he gave some
bounds for this kind of probability, providing information on the group
structure. We have recently obtained some generalizations of his results for
finite groups. Here we improve them in the context of the compact groups.Comment: 9 pages; to appear in Asian-European Journal of Mathematics with
several improvement
Classical resolution of singularities in dilaton cosmologies
For models of dilaton-gravity with a possible exponential potential, such as
the tensor-scalar sector of IIA supergravity, we show how cosmological
solutions correspond to trajectories in a 2D Milne space (parametrized by the
dilaton and the scale factor). Cosmological singularities correspond to points
at which a trajectory meets the Milne horizon, but the trajectories can be
smoothly continued through the horizon to an instanton solution of the
Euclidean theory. We find some exact cosmology/instanton solutions that lift to
black holes in one higher dimension. For one such solution, the singularities
of a big crunch to big bang transition mediated by an instanton phase lift to
the black hole and cosmological horizons of de Sitter Schwarzschild spacetimes.Comment: 24 pages, 2 figure
"The Fed's Real Reaction Function: Monetary Policy, Inflation, Unemployment, Inequality-and Presidential Politics"
Using a VAR model of the American economy from 1984 to 2003, we find that, contrary to official claims, the Federal Reserve does not target inflation or react to "inflation signals." Rather, the Fed reacts to the very "real" signal sent by unemployment, in a way that suggests that a baseless fear of full employment is a principal force behind monetary policy. Tests of variations in the workings of a Taylor Rule, using dummy variable regressions, on data going back to 1969 suggest that after 1983 the Federal Reserve largely ceased reacting to inflation or high unemployment, but continued to react when unemployment fell "too low." Further, we find that monetary policy (measured by the yield curve) has significant causal impact on pay inequality-a domain where the Fed refuses responsibility. Finally, we test whether Federal Reserve policy has exhibited a pattern of partisan bias in presidential election years, with results that suggest the presence of such bias, after controlling for the effects of inflation and unemployment.
Dilaton Gravity with a Non-minmally Coupled Scalar Field
We discuss the two-dimensional dilaton gravity with a scalar field as the
source matter. The coupling between the gravity and the scalar, massless, field
is presented in an unusual form. We work out two examples of these couplings
and solutions with black-hole behaviour are discussed and compared with those
found in the literature
Hawking Radiation in the Dilaton Gravity with a Non-Minimally Coupled Scalar Field
We discuss the two-dimensional dilaton gravity with a scalar field as the
source matter where the coupling with the gravity is given, besides the minimal
one, through an external field. This coupling generalizes the conformal anomaly
in the same way as those found in recent literature, but with a diferent
motivation. The modification to the Hawking radiation is calculated explicity
and shows an additional term that introduces a dependence on the (effective)
mass of the black-hole.Comment: 13 pages, latex file, no figures, to be published in IJM
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