228 research outputs found
Schwarz-Sen duality made fully local
Duality symmetric electromagnetic action a la Schwarz-Sen is shown to appear
naturally in a chain of equivalent actions which interchange equations of
motion with Bianchi identities. Full symmetry of the electromagnetic stress
tensor is exploited by generalizing this duality symmetric action to allow for
a space-time dependent mixing angle between electric and magnetic fields. The
rotated fields are shown to satisfy Maxwell-like equations which involve the
mixing angle as a parameter, and a generalized gauge invariance of the new
action is established.Comment: 10 pages, no figures, one reference adde
Auxiliary-variable Exact Hamiltonian Monte Carlo Samplers for Binary Distributions
We present a new approach to sample from generic binary distributions, based
on an exact Hamiltonian Monte Carlo algorithm applied to a piecewise continuous
augmentation of the binary distribution of interest. An extension of this idea
to distributions over mixtures of binary and possibly-truncated Gaussian or
exponential variables allows us to sample from posteriors of linear and probit
regression models with spike-and-slab priors and truncated parameters. We
illustrate the advantages of these algorithms in several examples in which they
outperform the Metropolis or Gibbs samplers.Comment: 11 pages, 4 figures. Proceedings of the 27th Annual Conference Neural
Information Processing Systems (NIPS), 201
FZZ Algebra
The duality between the Sine-Liouville conformal field theory and the two
dimensional black hole is revisited by considering the two possible
Sine-Liouville dressings together. We show that this choice is consistent with
the structure of correlation functions, and that the OPE of the two dressings
yields the black hole deformation operator. As an application of this approach,
we investigate the role of higher winding perturbations in the context of c=1
strings, where we argue that they are related to higher-spin discrete states
that generalize the 2d black hole operator.Comment: 23 pages, JHEP style. v2: small modifications to better clarify some
of the argument
Unitarity of supersymmetric SL(2,R)/U(1) and no-ghost theorem for fermionic strings in AdS(3) x N
The unitarity of the NS supersymmetric coset SL(2,R)/U(1) is studied for the
discrete representations. The results are applied to the proof of the no-ghost
theorem for fermionic strings in AdS(3) x N in the NS sector. A no-ghost
theorem is proved for states in flowed discrete representations.Comment: LaTeX in JHEP style, 16 pages, typos correcte
Bayesian spike inference from calcium imaging data
We present efficient Bayesian methods for extracting neuronal spiking
information from calcium imaging data. The goal of our methods is to sample
from the posterior distribution of spike trains and model parameters (baseline
concentration, spike amplitude etc) given noisy calcium imaging data. We
present discrete time algorithms where we sample the existence of a spike at
each time bin using Gibbs methods, as well as continuous time algorithms where
we sample over the number of spikes and their locations at an arbitrary
resolution using Metropolis-Hastings methods for point processes. We provide
Rao-Blackwellized extensions that (i) marginalize over several model parameters
and (ii) provide smooth estimates of the marginal spike posterior distribution
in continuous time. Our methods serve as complements to standard point
estimates and allow for quantification of uncertainty in estimating the
underlying spike train and model parameters
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