Caustics, cold flows, and annual modulation

TL;DR

This paper explores how dark matter caustics and cold flows influence annual modulation signals in direct detection experiments, suggesting that even small density enhancements from caustics can be detectable and serve as probes of dark matter structures.

Contribution

It introduces the potential detectability of dark matter caustics through annual modulation signals, emphasizing the role of cold flows and phase analysis in understanding local dark matter velocity distributions.

Findings

Caustic flows can produce detectable annual modulation signals.

Small density enhancements from caustics may still be observable.

The phase of modulation at low energies is not a direct indicator of particle mass.

Abstract

We discuss the formation of dark matter caustics, and their possible detection by future dark matter experiments. The annual modulation expected in the recoil rate measured by a dark matter detector is discussed. We consider the example of dark matter particles with a Maxwell-Boltzmann velocity distribution modified by a cold stream due to a nearby caustic. It is shown that the effect of the caustic flow is potentially detectable, even when the density enhancement due to the caustic is small. This makes the annual modulation effect an excellent probe of inner caustics. We also show that the phase of the annual modulation at low recoil energies does not constrain the particle mass unless the velocity distribution of particles in the solar neighborhood is known.