Effective theory for light portal dark matter detection

A

bstract

We develop a general framework for the calculation of direct-detection signals from light-portal dark matter, incorporating a consistent treatment of finite momentum transfer. In this framework, dark matter interacts with Standard Model matter through a light mediator, which simultaneously serves as the force carrier for dark matter self-interactions, potentially with a distinct coupling strength. We systematically construct the corresponding effective theory relevant to the detection of this class of dark matter. Our analysis focuses on light (semi)relativistic dark matter, which may be produced through cosmic-ray boosting and can be probed in high-threshold experiments such as large-volume neutrino detectors. In this context, the nucleon matrix elements of the effective operators at finite momentum transfer are required and have become available through recent advances in lattice QCD and related nonperturbative methods. The relativistic Fermi gas model is used to translate the nucleon-level description to the nuclear level, thereby incorporating nuclear effects relevant to experiments with heavy targets. To demonstrate the utility of the framework, we present ultraviolet-complete examples featuring spin-1 and spin-2 portal dark matter. For these models, we compute the differential cross sections with respect to momentum transfer, using parameter choices that address the so-called “core-cusp” problem in astrophysical observations via dark matter self-interactionss.