Tails of Instability and Decay: a Hydrodynamic Perspective

In the context of quantum field theory (QFT), unstable particles are associated with complex-valued poles two-body scattering matrices in unphysical sheet rapidity space. The Breit-Wigner formula relates this pole to mass and life-time particle, observed events. paper, we uncover new, dynamical signatures excitations show that they have a strong effect on non-equilibrium properties QFT. Focusing 1+1D integrable model, using Generalized Hydrodynamics, study formation decay by analysing release hot matter into low-temperature environment. We observe tails emitted nonlinear waves, sharp contrast situation without excitations. also new phenomenon which wave stable population may persist for long times. expect these presence large degree universality. Our shows out-of-equilibrium dynamics many-body systems can be strongly affected not only spectrum, but finite life-times.