The stability of Killing-Cauchy horizons in colliding plane wave space-times

It is confirmed rigorously that the Killing-Cauchy horizons, which sometimes occur in space-times representing the collision and subsequent interaction of plane gravitational waves in a Minkowski background, are unstable with respect to bounded perturbations of the initial waves, at least for the case in which the initial waves have constant aligned polarizations.Comment: 8 pages. To appear in Gen. Rel. Gra

Attention controls multisensory perception via two distinct mechanisms at different levels of the cortical hierarchy

To form a percept of the multisensory world, the brain needs to integrate signals from common sources weighted by their reliabilities and segregate those from independent sources. Previously, we have shown that anterior parietal cortices combine sensory signals into representations that take into account the signals’ causal structure (i.e., common versus independent sources) and their sensory reliabilities as predicted by Bayesian causal inference. The current study asks to what extent and how attentional mechanisms can actively control how sensory signals are combined for perceptual inference. In a pre- and postcueing paradigm, we presented observers with audiovisual signals at variable spatial disparities. Observers were precued to attend to auditory or visual modalities prior to stimulus presentation and postcued to report their perceived auditory or visual location. Combining psychophysics, functional magnetic resonance imaging (fMRI), and Bayesian modelling, we demonstrate that the brain moulds multisensory inference via two distinct mechanisms. Prestimulus attention to vision enhances the reliability and influence of visual inputs on spatial representations in visual and posterior parietal cortices. Poststimulus report determines how parietal cortices flexibly combine sensory estimates into spatial representations consistent with Bayesian causal inference. Our results show that distinct neural mechanisms control how signals are combined for perceptual inference at different levels of the cortical hierarchy

On the critical slowing down exponents of mode coupling theory

A method is provided to compute the parameter exponent $\lambda$ yielding the dynamic exponents of critical slowing down in mode coupling theory. It is independent from the dynamic approach and based on the formulation of an effective static field theory. Expressions of $\lambda$ in terms of third order coefficients of the action expansion or, equivalently, in term of six point cumulants are provided. Applications are reported to a number of mean-field models: with hard and soft variables and both fully-connected and dilute interactions. Comparisons with existing results for Potts glass model, ROM, hard and soft-spin Sherrington-Kirkpatrick and p-spin models are presented.Comment: 4 pages, 1 figur

Neutrino current in a gravitational plane wave collision background

The behaviour of a massless Dirac field on a general spacetime background representing two colliding gravitational plane waves is discussed in the Newman-Penrose formalism. The geometrical properties of the neutrino current are analysed and explicit results are given for the special Ferrari-Ibanez solution.Comment: 17 pages, 6 Postscript figures, accepted by International Journal of Modern Physics

A prospective clinical cohort study analyzing single-unit implant crowns after three years of loading: introduction of a novel Functional Implant Prosthodontic Score (FIPS)

Objectives The aim of this prospective clinical cohort study was to validate implant crowns with a novel Functional Implant Prosthodontic Score (FIPS). Material and methods Twenty patients were restored with cement-retained crowns on soft tissue level implants (Institut Straumann AG, Basel, Switzerland) in posterior sites and annually followed-up for 3 years. FIPS was applied for the objective outcome assessment including clinical and radiographic examinations. Five variables were defined for evaluation, resulting in a maximum score of 10 per implant restoration. The patients' level of satisfaction was recorded and correlated with FIPS. Results All implants and connected crowns revealed survival rates of 100% without any biological or technical complications after three years of loading. The mean total FIPS score was 7.8 ± 1.5, ranging from 6 to 10. The variable “bone” revealed the highest scores (2 ± 0; range: 2–2), followed by “occlusion” (1.9 ± 0.1; range: 1–2). Mean scores for “design” (1.2 ± 0.6; range: 0–2), “mucosa” (1.3 ± 0.7; range: 0–2), and “interproximal” (1.4 ± 0.4; range: 1–2) were more challenging to satisfy. The patients expressed a high level of functional satisfaction (84.1 ± 9.5; range: 68–100). A significant correlation was found between FIPS and the subjective patients' perception with a coefficient of 0.88 (P < 0.0001). Conclusions The findings of the clinical trial indicated the potential of FIPS as an objective and reliable instrument in assessing implant success. FIPS can be considered as a supportive tool to validate a satisfactory outcome as perceived by patients, to identify possible failure risks, and to compare follow-up observations

Colliding Axion-Dilaton Plane Waves from Black Holes

The colliding plane wave metric discovered by Ferrari and Iba\~{n}ez to be locally isometric to the interior of a Schwarzschild black hole is extended to the case of general axion-dilaton black holes. Because the transformation maps either black hole horizon to the focal plane of the colliding waves, this entire class of colliding plane wave spacetimes only suffers from the formation of spacetime singularities in the limits where the inner horizon itself is singular, which occur in the Schwarzschild and dilaton black hole limits. The supersymmetric limit corresponding to the extreme axion-dilaton black hole yields the Bertotti-Robinson metric with the axion and dilaton fields flowing to fixed constant values. The maximal analytic extension of this metric across the Cauchy horizon yields a spacetime in which two sandwich waves in a cylindrical universe collide to produce a semi-infinite chain of Reissner-Nordstrom-like wormholes. The focussing of particle and string geodesics in this spacetime is explored.Comment: 19 pages, 6 figure

Glueball operators and the microscopic approach to N=1 gauge theories

We explain how to generalize Nekrasov's microscopic approach to N=2 gauge theories to the N=1 case, focusing on the typical example of the U(N) theory with one adjoint chiral multiplet X and an arbitrary polynomial tree-level superpotential Tr W(X). We provide a detailed analysis of the generalized glueball operators and a non-perturbative discussion of the Dijkgraaf-Vafa matrix model and of the generalized Konishi anomaly equations. We compute in particular the non-trivial quantum corrections to the Virasoro operators and algebra that generate these equations. We have performed explicit calculations up to two instantons, that involve the next-to-leading order corrections in Nekrasov's Omega-background.Comment: 38 pages, 1 figure and 1 appendix included; v2: typos and the list of references corrected, version to appear in JHE

Using the past to estimate sensory uncertainty

To form a more reliable percept of the environment, the brain needs to estimate its own sensory uncertainty. Current theories of perceptual inference assume that the brain computes sensory uncertainty instantaneously and independently for each stimulus. We evaluated this assumption in four psychophysical experiments, in which human observers localized auditory signals that were presented synchronously with spatially disparate visual signals. Critically, the visual noise changed dynamically over time continuously or with intermittent jumps. Our results show that observers integrate audiovisual inputs weighted by sensory uncertainty estimates that combine information from past and current signals consistent with an optimal Bayesian learner that can be approximated by exponential discounting. Our results challenge leading models of perceptual inference where sensory uncertainty estimates depend only on the current stimulus. They demonstrate that the brain capitalizes on the temporal dynamics of the external world and estimates sensory uncertainty by combining past experiences with new incoming sensory signals