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Time: 19.03.2024, Wednesday, 4:00 pm

Place: Zoom only

Lecturer: Vesselin Petkov (Université Bordeaux)

Title: Dynamical zeta function for billiard flow

Abstract: We will present briefly the connection between Riemann zeta function, Ruellle zeta function and dynamical zeta function. The last one is related to the billiard flow for the union D \subset R^d of a finite collection of pairwise disjoint strictly convex compact obstacles. Let \mu_j \in C, \Im \mu_j > 0 be the resonances of the Laplacian in the exterior of D with Neumann or Dirichlet boundary condition on \partial D. For d odd, u(t) = \sum_j e^{i |t| \mu_j} is a distribution in \mathcal{D}'(R \setminus \{0\}) and the Laplace transforms of the leading singularities of u(t) yield the dynamical zeta functions \eta_{\mathrm N}(s),\: \eta_{\mathrm D}(s) for Neumann and Dirichlet boundary conditions, respectively. These zeta functions play a crucial role in the analysis of the distribution of the resonances. In this talk we discuss two results. (1) Under a non-eclipse condition, we show that \eta_{\mathrm N} and \eta_\mathrm D admit a <em>meromorphic continuation</em> in the whole complex plane with simple poles and integer residues. (2) In the case when the boundary \partial D is real analytic, we prove that the function \eta_\mathrm{D} cannot be entire and the modified Lax Phillips conjecture (MLPC) holds. This conjecture introduced in 1990 says that there exists of a strip \{z \in C: \: 0 < \Im z \leqslant\alpha\} containing an infinite number of resonances \mu_j for the Dirichlet problem. The above results are obtained in a joint work with Yann Chaubet.

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