Stability, hyperbolicity, and zero localization of functions
December 5 to December 9, 2011
at the
American Institute of Mathematics,
Palo Alto, California
organized by
Petter Branden,
George Csordas,
Olga Holtz,
and Mikhail Tyaglov
Original Announcement
This workshop will be devoted to the emerging theory
of stability and hyperbolicity of functions. These notions are well known
in the univariate setting, where stability means that all zeros lie in the lefthalf
plane and hyperbolicity means that all zeros are real. The multivariate generalizations
go back to 1950s and are being actively explored now. Among recent applications
of multivariate stability and hyperbolicity are the proof of Johnson's conjectures on
mixed determinants, new proofs of van der Waerden and SchrijverValiant type
conjectures, and the resolution of several conjectures on negative dependence in
discrete probability theory.
Hyperbolic and stable multivariate polynomials arise surprisingly often in matrixtheoretic
and combinatorial applications. For example, three major conjectures  Lieb's "permanentontop" (POT) conjecture in matrix theory/combinatorics, the
BessisMoussaVillani (BMV) conjecture in quantum statistical mechanics, and
Mason's conjecture in combinatorics can all be reformulated by means of real
stable polynomials.
Another important class of examples is provided by analytic number theory, where
the Riemann Zeta function and other Lfunctions are conjectured to have nontrivial
zeros on the line Re z =1/2. This can be restated as the hyperbolicity of the Riemann
Xi function (or other associated functions).
The aim of the workshop is both to contribute to the general theory of stability and
hyperbolicity as well as to find ways of applying this theory to concrete problems
of algebra, analysis, combinatorics, and mathematical physics.
Some of the main open problems that the workshop will focus on are the following.

The BessisMoussaVillani (BMV) conjecture originally arose in the theory of quantum mechanical system. It states that tr (exp(AtB)) is the Laplace transform of a positive measure for any two positive definite matrices A and B. It can be restated as a conjecture about the positivity of all coefficients of specific polynomials. We plan to investigate the zero distribution of these polynomials.
 The Mason conjecture states the ultralog concavity of the fvector of a matroid or, equivalently, of the sequence of coefficient of the socalled independent set polynomial of that matroid. We plan to consider the graphical case of Mason's conjecture using a variety of newly developed techniques.
 LeeYang problems of statistical mechanics and multivariate stability/hyperbolicity: Phase transitions in statistical mechanics can be determined and analyzed using the corresponding partition functions. We would like to understand a general theoretical framework for stability and hyperbolicity of partition functions in statistical mechanics (Ising, Potts, and other models).
 PólyaSchur problems: classification of linear (or nonlinear) preservers of polynomials and entire functions in one or several variables with prescribed zero sets.
Material from the workshop
A list of participants.
The workshop schedule.
A report on the workshop activities.
A list of open problems.
Papers arising from the workshop: