Mathematical Physics Laboratory

Centre de recherches math´┐Żatiques

Atelier sur les matrices aléatoires, déformations isomonodromiques et problèmes de Riemann-Hilbert
Working Seminar on Random Matrices, Isomonodromic Deformations and Riemann-Hilbert Problems

automne/Fall 2005 - hiver/Winter 2006

CRM, UdeM, Pavillon André Aisenstadt, 2920, ch. de la Tour, rm. 4336


Time/Date/Heure: Thursday/jeudi, Oct. 6, le 6 oct. 2005 at/à 14:00 (CRM)
Title/titre: "Frobenius manifolds -> KdV and KP tau-functions -> matrix models"
Speaker/Conférencier: Leonid Chekhov (Steklov Institute, Moscow, Concordia and CRM)

I'll attempt to cover some recent papers by several groups, mainly following Dubrovin's description of the subject. The general aim (not attained as yet) is to establish exact relations between (generalized) matrix model integrals (starting with just the usual Hermitian one-matrix model) in the 1/N-expansion pattern (not restricting to just the planar contribution) and the related hierarchies of integrable equations (especially, in the case of multicut solutions).


Time/Date/Heure: Thursday/jeudi, Oct. 13, le 13 oct. 2005 at/à 15:00 (CRM)
Title/titre: "Frobenius manifolds -> KdV and KP tau-functions -> matrix models II"
Speaker/Conférencier: Leonid Chekhov (Steklov Institute, Moscow, Concordia and CRM)

This is a continuation of the topic begun in the previous week's seminar: moduli spaces of punctured Riemann spheres, relations to tau functions and matrix integrals. The results of Kontsevich and Witten.


Time/Date/Heure: Thursday/jeudi, Oct. 20, le 20 oct. 2005 at/à 15:00 (CRM)
Title/titre: "Moduli spaces of algebraic curves and Strebel differentials"
Speaker/Conférencier: Andrew McIntyre (Concordia, CRM)

An introduction to the topic of moduli spaces and Strebel differentials, with examples.


Time/Date/Heure: Thursday/jeudi, Oct. 27, le 27 oct. 2005 at/à 15:00 (CRM)
Title/titre: "Moduli spaces of algebraic curves and Strebel differentials II."
Speaker/Conférencier: Andrew McIntyre (Concordia, CRM)

We continue the introduction to the topic of moduli spaces and Strebel differentials, with examples.


Time/Date/Heure: Thursday/jeudi, Nov. 3, le 3 nov. 2005 at/à 15:00 (CRM)
Title/titre: "Coordinates on Teichmuller spaces"
Speaker/Conférencier: Andrew McIntyre (Concordia, CRM)

We review in some detail the coordinatization of Teichmuller spaces of marked algebraic curves of higher genus.



Time/Date/Heure: Thursday/jeudi, Nov. 10, le 10 nov. 2005 at/à 15:00 (CRM)
Title/titre: "Hermitian 1-matrix model: Multicut solutions, geometry, and asymptotic expansion in 1/N. Part I."
Speaker/Conférencier: Leonid Chekhov (Steklov Inst., Moscow, Concordia and CRM)

We show that the general (multicut, domain-walls) solutions of the Hermitian 1-matrix model are Whitham tau-functions in the leading order of 1/N-expansion . We develop the technique for solving the loop equation (master equation governing the model) in the 1/N-expansion pattern; this technique is a (very) special form of (Feynmann) diagrammatic technique well-suited for calculating the one- and higher-point resolvents. We demonstrate how to get the free energy from the answer for the 1-point resolvent in full generality. We discuss the momentum technique and why it may be helpful when finding the integrable system tau-functions.


Time/Date/Heure: Thursday/jeudi, Nov. 17, le 17 nov. 2005 at/à 15:00 (CRM)
Title/titre: "Hermitian 1-matrix model: Multicut solutions, geometry, and asymptotic expansion in 1/N. Part II."
Speaker/Conférencier: Leonid Chekhov (Steklov Inst., Moscow, Concordia and CRM)

Continuation of Part I.


Time/Date/Heure: Thursday/jeudi, Nov. 24, le 24 nov. 2005 at/à 15:00 (CRM)
Title/titre: "Hermitian 1-matrix model: Multicut solutions, geometry, and asymptotic expansion in 1/N. Part III - Solution of the loop equations."
Speaker/Conférencier: Leonid Chekhov (Steklov Inst., Moscow, Concordia and CRM)

Continuation of Part II.


Time/Date/Heure: Thursday/jeudi, Dec. 1, le 1 déc. 2005 at/à 15:00 (CRM)
Title/titre: "Free fermion constructions of determinantal correlation functions. Part I."
Speaker/Conférencier: John Harnad (Concordia and CRM)

Many (perhaps all) known identities involving determinants and integrals can be interpreted as special cases of Wick's theorem for free Fermions.
In this talk, I will show how a number of such results follow, and how the expression of correlation functions involving products and quotients of characteristic polynomials of random matrices may be deduced either using "direct methods", which are based on the Cauchy-Binet identity and partial fraction decompositions of symmetric rational functions (both special instances of the above), or by realizing the corresponding matrix integrals as vacuum state expectation values of products of opertors constructed from free fermion creation and annihilation operrators.
This approach makes clear why these integrals may all be interpreted as KP or 2-Toda tau functions.


Time/Date/Heure: Thursday/jeudi, Dec. 8, le 8 déc. 2005 at/à 15:00 (CRM)
Title/titre: "Commuting difference operators and applications to the asymptotics of orthogonal polynomials"
Speaker/Conférencier: Marco Bertola (Concordia and CRM)

In this informal (hopefully informative) talk I will try to present a result by Krichever and Novikov about the classification of commuting difference operators, in a particular case (for sake of simplicity) relevant to orthogonal polynomials. The problem can be easily formulated as: classify all pairs of infinite matrices P,Q where Q is symmetric and tridiagonal (a Jacobi matrix) and P is antisymmetric, under the condition that they commute [P,Q]=0 (plus some technical requirements). The reconstruction can be achieved explicitly in terms of Theta functions on a hyperelliptic curve. This "exercise" has interesting and potentially far-reaching applications in the study of the (formal) asymptotics of orthogonal polynomials (in particular also semiclassical ones). This last is part of an ongoing research project and may not be completely detailed: in particular it applies to a much wider setting, including but not limited to biorthogonal polynomials for the two-matrix model. I plan to give the essentials of the tools


N.B. This is a double session - the last one for 2005. This working seminar series will resume in January.

Time/Date/Heure: Thursday/jeudi, Dec. 15, le 15 déc. 2005 at/à 14:00 (CRM)
Title/titre: "Orthogonal polynomials and spinors on Riemann surfaces"
Speaker/Conférencier: Marco Bertola (Concordia and CRM)

As a follow-up to last week's talk, I will show how spinors and Szego kernels appear quite naturally in the (formal) asymptotics of (bi)orthogonal polynomials, reproducing formulae obtained by Deift et al for the (strong) asymptotics of orthogonal polynomials.

Time/Date/Heure: Thursday/jeudi, Dec. 15, le 15 déc. 2005 at/à 15:00 (CRM)
Title/titre: "Free fermion constructions of determinantal correlation functions. `Part II."
Speaker/Conférencier: John Harnad (Concordia and CRM)

This is a continuation of the talk of Dec. 1 (see abstract above).
All the relevant quantities necessary to demonstrate such determinantal identities will be expressed as fermionic VOV's; including: Vandermonde determinants, Schur functions, partition functions; determinantal correlation functions; biothogonal polynomials, Christoffel Darboux kernels, and second type (Hilbert transform) solutions.


For further information: bertola@CRM.UMontreal.CA