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Singularities of the scattering kernel related to trapping rays. (English) Zbl 1197.35183
Bove, Antonio (ed.) et al., Advances in phase space analysis of partial differential equations. In Honor of Ferruccio Colombini’s 60th birthday. Selected papers based on the workshop, Siena, Italy, October 2007. Boston, MA: Birkhäuser (ISBN 978-0-8176-4860-2/hbk; 978-0-8176-4861-9/ebook). Progress in Nonlinear Differential Equations and Their Applications 78, 235-251 (2009).
Summary: An obstacle $$K\subset \mathbb R^n$$, $$n\geq 3$$, $$n$$ odd, is called trapping if there exists at least one generalized bicharacteristic $$\gamma(t)$$ of the wave equation staying in a neighborhood of $$K$$ for all $$t\geq 0$$. We examine the singularities of the scattering kernel $$s(t,\theta,\omega)$$ defined as the Fourier transform of tlie scattering amplitude $$a(\lambda,\theta,\omega)$$ related to the Dirichlet problem for the wave equation in $$\Omega=\mathbb R^n\setminus K$$. We prove that if $$K$$ is trapping and $$\gamma(t)$$ is nondegenerate, then there exist reflecting $$(\omega_m,\theta_m)$$-rays $$\delta_m$$, $$m\in\mathbb N$$, with sojourn times $$T_m\to +\infty$$ as $$m\to\infty$$, so that $$-T)_m\in \text{sing\, supp}\,s(t,\theta_m,\omega_m)$$, $$\forall m\in\mathbb N$$. We apply this property to study the behavior of the scattering amplitude in $$\mathbb C$$.
For the entire collection see [Zbl 1187.35004].

##### MSC:
 35P25 Scattering theory for PDEs 47A40 Scattering theory of linear operators 35L05 Wave equation
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