ISGC 251203 talk by Prof. Ignacy Sawicki - CEICO скачать в хорошем качестве

ISGC 251203 talk by Prof. Ignacy Sawicki - CEICO

Title: Causality and Stability from Acoustic Geometry Abstract: Scalar-tensor theories with derivative interactions form backgrounds which spontaneously break Lorentz invariance (e.g. cosmology during inflation or the dark energy era). The dynamics of small scalar fluctuations on general anisotropic backgrounds -- phonons -- can be described as geodesic motion in an effective "acoustic" space time, with the acoustic metric providing the relativistic description of general media. This acoustic metric and its inverse give the dispersion relation, rays and phase velocities and construct two dual sound cones. I will discuss how to read off true instabilities -- ghosts and gradient instabilities -- from the invariant properties of the acoustic metric, but also discuss false instabilities that may appear for some observers, relating this to Cherenkov radiation and the ill-posedness of the Cauchy problem. I will show that the geometric discussion of the sound cones is equivalent to the usual Hamiltonian description for an energy related to a conserved acoustic energy-momentum tensor for the fluctuations, distinct from the usual space-time one. Based on: https://arxiv.org/abs/2412.21169. Speaker: Ignacy Sawicki - CEICO, Institute of Physics of the Czech Academy of Sciences, Czech Republic Date and Time: December 3rd, 2025 - 12pm GMT