arXiv subjects

M. Bertola

Publications and source records attributed to M. Bertola.

42 records · Page 3Linked to original sources

arXiv2002

Differential systems for biorthogonal polynomials appearing in 2-matrix models and the associated Riemann-Hilbert problem

We consider biorthogonal polynomials that arise in the study of a generalization of two--matrix Hermitian models with two polynomial potentials V_1(x), V_2(y) of any degree, with arbitrary complex coefficients. Finite consecutive subsequences of biorthogonal polynomials (`windows'), of lengths equal to the degrees of the potentials, satisfy systems of ODE's with polynomial coefficients as well as PDE's (deformation equations) with respect to the coefficients of the potentials and recursion relations connecting consecutive windows. A compatible sequence of fundamental systems of solutions is constructed for these equations. The (Stokes) sectorial asymptotics of these fundamental systems are derived through saddle-point integration and the Riemann-Hilbert problem characterizing the differential equations is deduced.

nlin.SI↗

arXiv2002

Rigidification of pseudo-Riemannian Manifolds by an Elliptic Equation

We study the solvability of the equation for the smooth function F, H=-k F g, on a geodesically complete pseudo-Riemannian manifold (M,g), H being the covariant Hessian of F. A similar equation was considered by Obata and Gallot in the Riemannian case for positive values of the constant k; the result was that the manifold must be the canonical sphere. In this generalized setting we obtain a range of possibilities, depending on the sign of k, the signature of the metric and the value of a certain first integral of the equation: the manifold is shown to be of constant sectional curvature or a warped product with suitable factors depending on the cases.

math.DG↗

arXiv2001

Duality of spectral curves arising in two-matrix models

The two matrix model is considered, with measure given by the exponential of a sum of polynomials in two different variables. It is shown how to derive a sequence of pairs of ``dual'' finite size systems of ODEs for the corresponding biorthonormal polynomials. An inverse theorem is proved showing how to reconstruct such measures from pairs of semi-infinite finite band matrices defining the recursion relations and satisfying the string equation. A proof is given in the $N\to \infty$ limit that the dual systems obtained share the same spectral curve.

nlin.SI↗

arXiv2001

Duality, Biorthogonal Polynomials and Multi-Matrix Models

The statistical distribution of eigenvalues of pairs of coupled random matrices can be expressed in terms of integral kernels having a generalized Christoffel--Darboux form constructed from sequences of biorthogonal polynomials. For measures involving exponentials of a pair of polynomials V_1, V_2 in two different variables, these kernels may be expressed in terms of finite dimensional ``windows'' spanned by finite subsequences having length equal to the degree of one or the other of the polynomials V_1, V_2. The vectors formed by such subsequences satisfy "dual pairs" of first order systems of linear differential equations with polynomial coefficients, having rank equal to one of the degrees of V_1 or V_2 and degree equal to the other. They also satisfy recursion relations connecting the consecutive windows, and deformation equations, determining how they change under variations in the coefficients of the polynomials V_1 and V_2. Viewed as overdetermined systems of linear difference-differential-deformation equations, these are shown to be compatible, and hence to admit simultaneous fundamental systems of solutions. The main result is the demonstration of a spectral duality property; namely, that the spectral curves defined by the characteristic equations of the pair of matrices defining the dual differential systems are equal upon interchange of eigenvalue and polynomial parameters.

nlin.SI↗

arXiv2000

Decomposing Quantum Fields on Branes

We provide a method to decompose the two-point function of a quantum field on a warped manifold in terms of fields living on a lower-dimensional manifold. We discuss explicit applications to Minkowski, de Sitter and anti-de Sitter quantum field theories. This decomposition presents a remarkable analogy with the holography principle, in the sense that physics in d+1 dimensions may be encoded into the physics in one dimension less. Moreover in a context a la Randall--Sundrum, the method outlined here allows a mechanism of generation of mass-spectra in the 3-brane (or more generally a d-1-brane).

hep-th↗

arXiv2000

AdS/CFT correspondence for n-point functions

We provide a new general setting for scalar interacting fields on the covering of a d+1-dimensional AdS spacetime. The formalism is used at first to construct a one-paramater family of field theories, each living on a corresponding spacetime submanifold of AdS, which is a cylinder $R\times S_{d-1}$. We then introduce a limiting procedure which directly produces Luescher-Mack CFT's on the covering of the AdS asymptotic cone. Our AdS/CFT correspondence is generally valid for interacting fields, and is illustrated by a complete treatment of two-point functions, the case of Klein-Gordon fields appearing as particularly simple in our context. We also show how the Minkowskian representation of these boundary CFT's can be directly generated by an alternative limiting procedure involving Minkowskian theories in horocyclic sections (nowadays called (d-1)-branes, 3-branes for AdS_5). These theories are restrictions to the brane of the ambient AdS field theory considered. This provides a more general correspondence between the AdS field theory and a Poincare' invariant QFT on the brane, satisfying all the Wightman axioms. The case of two-point functions is again studied in detail from this viewpoint as well as the CFT limit on the boundary.

hep-th↗