On the Dynamics of Non-Relativistic Flavor-Mixed Particles

TL;DR

This paper studies the complex dynamics of non-relativistic flavor-mixed particles, revealing how collisions can alter their mass states and lead to phenomena like quantum evaporation, with implications for dark matter and cosmic neutrinos.

Contribution

It introduces a theoretical and numerical analysis of mass eigenstate conversions during particle collisions, highlighting their impact on flavor composition and energy, and discusses novel effects like quantum evaporation.

Findings

Mass eigenstate conversions can be large even with negligible elastic scattering.

Conversions are efficient when eigenstates are spatially separated, suppressed when overlapping.

Quantum evaporation allows particles to escape gravitational wells without extra energy.

Abstract

Evolution of a system of interacting non-relativistic quantum flavor-mixed particles is considered both theoretically and numerically. It was shown that collisions of mixed particles not only scatter them elastically, but can also change their mass eigenstates thus affecting particles' flavor composition and kinetic energy. The mass eigenstate conversions and elastic scattering are related but different processes, hence the conversion $S$-matrix elements can be arbitrarily large even when the elastic scattering $S$-matrix elements vanish. The conversions are efficient when the mass eigenstates are well-separated in space but suppressed if their wave-packets overlap; the suppression is most severe for mass-degenerate eigenstates in flat space-time. The mass eigenstate conversions can lead to an interesting process, called `quantum evaporation,' in which mixed particles, initially confined deep inside a gravitational potential well and scattering only off each other, can escape from it without extra energy supply leaving nothing behind inside the potential at $t\to \infty$. Implications for the cosmic neutrino background and the two-component dark matter model are discussed and a prediction for the direct detection dark matter experiments is made.