Self-dual Einstein Spaces, Heavenly Metrics and Twistors

Four-dimensional quaternion-Kahler metrics, or equivalently self-dual Einstein spaces M, are known to be encoded locally into one real function h subject to Przanowski's Heavenly equation. We elucidate the relation between this description and the usual twistor description for quaternion-Kahler spaces. In particular, we show that the same space M can be described by infinitely many different solutions h, associated to different complex (local) submanifolds on the twistor space, and therefore to different (local) integrable complex structures on M. We also study quaternion-Kahler deformations of M and, in the special case where M has a Killing vector field, show that the corresponding variations of h are related to eigenmodes of the conformal Laplacian on M. We exemplify our findings on the four-sphere S^4, the hyperbolic plane H^4 and on the "universal hypermultiplet", i.e. the hypermultiplet moduli space in type IIA string compactified on a rigid Calabi-Yau threefold.Comment: 44 pages, 1 figure; misprints correcte

Candida albicans colonization and dissemination from the murine gastrointestinal tract : the influence of morphology and Th17 immunity

This article is protected by copyright. All rights reserved. This work was supported by the Wellcome Trust (086558, 080088, 102705), a Wellcome Trust Strategic Award (097377) and a studentship from the University of Aberdeen. D.K. was supported by grant 5R01AI083344 from the National Institute of Allergy and Infectious Diseases and by a Voelcker Young Investigator Award from the Max and Minnie Tomerlin Voelcker Fund.Peer reviewedPublisher PD

Integrability and explicit solutions in some Bianchi cosmological dynamical systems

The Einstein field equations for several cosmological models reduce to polynomial systems of ordinary differential equations. In this paper we shall concentrate our attention to the spatially homogeneous diagonal G_2 cosmologies. By using Darboux's theory in order to study ordinary differential equations in the complex projective plane CP^2 we solve the Bianchi V models totally. Moreover, we carry out a study of Bianchi VI models and first integrals are given in particular cases

Fungal Chitin Dampens Inflammation through IL-10 Induction Mediated by NOD2 and TLR9 Activation

Funding: JW and NARG thank the Wellcome Trust (080088, 086827, 075470), The Wellcome Trust Strategic Award in Medical Mycology and Fungal Immunology (097377) and the European Union ALLFUN (FP7/2007 2013, HEALTH-2010-260338) for funding. MGN was supported by a Vici grant of the Netherlands Organisation for Scientific Research. AJPB and DMM were funded by STRIFE, ERC-2009-AdG-249793 and AJPB additionally by FINSysB, PITN-GA-2008-214004 and the BBSRC [BB/F00513X/1]. MDL was supported by the MRC (MR/J008230/1). GDB and SV were funded by the Wellcome Trust (086558) and TB and MK were funded by the Deutsche Forschungsgemeinschaft (Bi 696/3-1; Bi 696/5-2; Bi 696/10-1). MS was supported by the Deutsche Forschungsgemeinschaft (Sch 897/1-3) and the National Institute of Dental and Craniofacial Research (R01 DE017514-01). TDK and RKSM were funded by the National Institute of Health (AR056296, AI101935) and the American Lebanese Syrian Associated Charities (ALSAC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Ricci Collineations of the Bianchi Type II, VIII, and IX Space-times

Ricci and contracted Ricci collineations of the Bianchi type II, VIII, and IX space-times, associated with the vector fields of the form (i) one component of $\xi^a(x^b)$ is different from zero and (ii) two components of $\xi^a(x^b)$ are different from zero, for $a,b=1,2,3,4$, are presented. In subcase (i.b), which is $\xi^a= (0,\xi^2(x^a),0,0)$, some known solutions are found, and in subcase (i.d), which is $\xi^a =(0,0,0,\xi^4(x^a))$, choosing $S(t)=const.\times R(t)$, the Bianchi type II, VIII, and IX space-times is reduced to the Robertson-Walker metric.Comment: 12 Pages, LaTeX, 1 Table, no figure

Self-similar Bianchi type VIII and IX models

It is shown that in transitively self-similar spatially homogeneous tilted perfect fluid models the symmetry vector is not normal to the surfaces of spatial homogeneity. A direct consequence of this result is that there are no self-similar Bianchi VIII and IX tilted perfect fluid models. Furthermore the most general Bianchi VIII and IX spacetime which admit a four dimensional group of homotheties is given.Comment: 5 pages, Latex; One reference and minor clarifications added. To appear in General Relativity and Gravitatio

Variational dynamics in open spacetimes

We study the effect of non-vanishing surface terms at spatial infinity on the dynamics of a scalar field in an open FLRW spacetime. Starting from the path-integral formulation of quantum field theory we argue that classical physics is described by field configurations which extremize the action functional in the space of field configurations for which the variation of the action is well defined. Since these field configurations are not required to vanish outside a bounded domain, there is generally a non-vanishing contribution of a surface term to the variation of the action. We then investigate whether this surface term has an effect on the dynamics of the action-extremizing field configurations. This question appears to be surprisingly nontrivial in the case of the open FLRW geometry, since surface terms tend to grow as fast as volume terms in the infinite volume limit. We find that surface terms can be important for the dynamics of the field at a classical and at a quantum level, when there are supercurvature perturbations.Comment: 21 pages, Latex, no figure

Asymptotic Behaviour of Inhomogeneous String Cosmologies

The asymptotic behaviour at late times of inhomogeneous axion-dilaton cosmologies is investigated. The space-times considered here admit two abelian space-like Killing vectors. These space-times evolve towards an anisotropic universe containing gravitational radiation. Furthermore, a peeling-off behaviour of the Weyl tensor and the antisymmetric tensor field strength is found. The relation to the pre-big-bang scenario is briefly discussed.Comment: 15 pages, Late

Homogeneous Plane-wave Spacetimes and their Stability

We consider the stability of spatially homogeneous plane-wave spacetimes. We carry out a full analysis for plane-wave spacetimes in (4+1) dimensions, and find there are two cases to consider; what we call non-exceptional and exceptional. In the non-exceptional case the plane waves are stable to (spatially homogeneous) vacuum perturbations as well as a restricted set of matter perturbations. In the exceptional case we always find an instability. Also we consider the Milne universe in arbitrary dimensions and find it is also stable provided the strong energy condition is satisfied. This implies that there exists an open set of stable plane-wave solutions in arbitrary dimensions.Comment: 15 pages, no figures; minor changes, new references, to appear in CQ

Anisotropic stresses in inhomogeneous universes

Anisotropic stress contributions to the gravitational field can arise from magnetic fields, collisionless relativistic particles, hydrodynamic shear viscosity, gravitational waves, skew axion fields in low-energy string cosmologies, or topological defects. We investigate the effects of such stresses on cosmological evolution, and in particular on the dissipation of shear anisotropy. We generalize some previous results that were given for homogeneous anisotropic universes, by including small inhomogeneity in the universe. This generalization is facilitated by a covariant approach. We find that anisotropic stress dominates the evolution of shear, slowing its decay. The effect is strongest in radiation-dominated universes, where there is slow logarithmic decay of shear.Comment: 7 pages Revte