Moduli Spaces of Abelian Vortices on Kahler Manifolds

We consider the self-dual vortex equations on a positive line bundle L --> M over a compact Kaehler manifold of arbitrary dimension. When M is simply connected, the moduli space of vortex solutions is a projective space. When M is an abelian variety, the moduli space is the projectivization of the Fourier-Mukai transform of L. We extend this description of the moduli space to the abelian GLSM, i.e. to vortex equations with a torus gauge group acting linearly on a complex vector space. After establishing the Hitchin-Kobayashi correspondence appropriate for the general abelian GLSM, we give explicit descriptions of the vortex moduli space in the case where the manifold M is simply connected or is an abelian variety. In these examples we compute the Kaehler class of the natural L^2-metric on the moduli space. In the simplest cases we compute the volume and total scalar curvature of the muduli space. Finally, we note that for abelian GLSM the vortex moduli space is a compactification of the space of holomorphic maps from M to toric targets, just as in the usual case of M being a Riemann surface. This leads to various natural conjectures, for instance explicit formulae for the volume of the space of maps CP^m --> CP^n.Comment: v2: 48 pages; significant changes; description of the vortex moduli spaces of the GLSM extended to allow general values of the parameters, beyond the generic values of v

A constructive mean field analysis of multi population neural networks with random synaptic weights and stochastic inputs

We deal with the problem of bridging the gap between two scales in neuronal modeling. At the first (microscopic) scale, neurons are considered individually and their behavior described by stochastic differential equations that govern the time variations of their membrane potentials. They are coupled by synaptic connections acting on their resulting activity, a nonlinear function of their membrane potential. At the second (mesoscopic) scale, interacting populations of neurons are described individually by similar equations. The equations describing the dynamical and the stationary mean field behaviors are considered as functional equations on a set of stochastic processes. Using this new point of view allows us to prove that these equations are well-posed on any finite time interval and to provide a constructive method for effectively computing their unique solution. This method is proved to converge to the unique solution and we characterize its complexity and convergence rate. We also provide partial results for the stationary problem on infinite time intervals. These results shed some new light on such neural mass models as the one of Jansen and Rit \cite{jansen-rit:95}: their dynamics appears as a coarse approximation of the much richer dynamics that emerges from our analysis. Our numerical experiments confirm that the framework we propose and the numerical methods we derive from it provide a new and powerful tool for the exploration of neural behaviors at different scales.Comment: 55 pages, 4 figures, to appear in "Frontiers in Neuroscience

Conformal Toda theory with a boundary

We investigate sl(n) conformal Toda theory with maximally symmetric boundaries. There are two types of maximally symmetric boundary conditions, due to the existence of an order two automorphism of the W(n>2) algebra. In one of the two cases, we find that there exist D-branes of all possible dimensions 0 =< d =< n-1, which correspond to partly degenerate representations of the W(n) algebra. We perform classical and conformal bootstrap analyses of such D-branes, and relate these two approaches by using the semi-classical light asymptotic limit. In particular we determine the bulk one-point functions. We observe remarkably severe divergences in the annulus partition functions, and attribute their origin to the existence of infinite multiplicities in the fusion of representations of the W(n>2) algebra. We also comment on the issue of the existence of a boundary action, using the calculus of constrained functional forms, and derive the generating function of the B"acklund transformation for sl(3) Toda classical mechanics, using the minisuperspace limit of the bulk one-point function.Comment: 42 pages; version 4: added clarifications in section 2.2 and footnotes 1 and

Qualitative properties of solutions for an integral system related to the Hardy-Sobolev inequality

This article carries out a qualitative analysis on a system of integral equations of the Hardy--Sobolev type. Namely, results concerning Liouville type properties and the fast and slow decay rates of positive solutions for the system are established. For a bounded and decaying positive solution, it is shown that it either decays with the slow rates or the fast rates depending on its integrability. Particularly, a criterion for distinguishing integrable solutions from other bounded and decaying solutions in terms of their asymptotic behavior is provided. Moreover, related results on the optimal integrability, boundedness, radial symmetry and monotonicity of positive integrable solutions are also established. As a result of the equivalence between the integral system and a system of poly-harmonic equations under appropriate conditions, the results translate over to the corresponding poly-harmonic system. Hence, several classical results on semilinear elliptic systems are recovered and further generalized.Comment: 33 pages, final author versio

New tools for classifying Hamiltonian circle actions with isolated fixed points

For every compact almost complex manifold (M,J) equipped with a J-preserving circle action with isolated fixed points, a simple algebraic identity involving the first Chern class is derived. This enables us to construct an algorithm to obtain linear relations among the isotropy weights at the fixed points. Suppose that M is symplectic and the action is Hamiltonian. If the manifold satisfies an extra "positivity condition" this algorithm determines a family of vector spaces which contain the admissible lattices of weights. When the number of fixed points is minimal, this positivity condition is necessarily satisfied whenever dim(M)< 8, and, when dim(M)=8, whenever the S^1-action extends to an effective Hamiltonian T^2-action, or none of the isotropy weights is 1. Moreover there are no known examples with a minimal number of fixed points contradicting this condition, and their existence is related to interesting questions regarding fake projective spaces [Y]. We run the algorithm for dim(M)< 10, quickly obtaining all the possible families of isotropy weights. In particular, we simplify the proofs of Ahara and Tolman for dim(M)=6 [Ah,T1] and, when dim(M)=8, we prove that the equivariant cohomology ring, Chern classes and isotropy weights agree with the ones of C P^4 with the standard S^1-action (thus proving the symplectic Petrie conjecture [T1] in this setting).Comment: 59 Pages; 16 Figures; Please find accompanying software at page http://www.math.ist.utl.pt/~lgodin/MinimalActions.htm