Speaker
Description
Theoretical studies of direct detection of dark matter (DM) conventionally assume the standard halo model (SHM) and an isotropic target response. However, studies of the structure of the Milky Way halo on one hand, and of sub-GeV DM on the other hand, motivate a broader program where anisotropies in both the DM velocity distribution, and in the material response, must be accounted for. Unlike in the conventional case, where the SHM velocity distribution and an isotropic target response lend themselves largely to an analytical solution of the DM event rate integrals, in the general case one is left with a multidimensional integral which must be tackled numerically. Traditionally, naive multidimensional Monte Carlo integration is used, but is inefficient, and proves insufficient for large parameter-space scans and for the study of daily modulation effects due to target anisotropies.
We propose a novel approach for solving the DM event rate integrals, based on harmonic expansions of the velocity distribution and target response [1]. Specifically, we employ a basis of 3D Zernike polynomials to write a rapidly convergent expansion of the DM velocity distribution. The mathematical properties of this basis enable writing down a simple sum expression for the directional DM scattering rate in terms of the coefficients of the expansion. This leads to new insights about modulation effects in the direct detection event rates, and a new algorithm for their efficient computation, generalizable to both nucleon and electron scattering, enabling computation of event rates for arbitrary velocity distributions and material responses up to a thousand times faster than optimized numerical integration methods.
Based on this approach, we introduce ZebraDM, a C++ library for blazingly fast computation of DM direct detection event rates in a wide variety of scenarios.
[1] S. Sassi et al., PRD 112, 043003 (2025), arXiv:2504.19714.
| Main Contribution topic | Direct detection |
|---|---|
| Secondary contribution topic | Theory / Phenomenology |