Energy Dependence of Direct Detection Cross Section for Asymmetric Mirror Dark Matter

TL;DR

The paper addresses how an asymmetric mirror DM model with a light mirror photon portal yields momentum-dependent direct-detection signals. It develops a general operator analysis for DM–nucleon scattering through kinetic mixing, derives explicit $d\sigma/dE_r$ expressions that depend on $|\mathbf{q}|$ and $m_{\gamma'}$, and applies them to neutral mirror neutron DM and charged mirror baryons. For neutral DM the cross section includes a magnetic-dipole and charge-radius contribution, yielding $\mathcal{M}_{nr}$ with $|\mathbf{q}|^2$ and $|\mathbf{q}\times\mathbf{P}|^2$ structures and a low-$E_r$ enhancement, while charged DM yields a conventional SI cross section; parameter choices can accommodate CoGeNT and, with caveats, DAMA. The framework offers distinctive, testable predictions for direct detection and helps discriminate ADM from canonical WIMPs with upcoming detectors.

Abstract

In a recent paper, four of the present authors proposed a class of dark matter models where generalized parity symmetry leads to equality of dark matter abundance with baryon asymmetry of the Universe and predicts dark matter mass to be around 5 GeV. In this note we explore how this model can be tested in direct search experiments. In particular, we point out that if the dark matter happens to be the mirror neutron, the direct detection cross section has the unique feature that it increases at low recoil energy unlike the case of conventional WIMPs. It is also interesting to note that the predicted spin-dependent scattering could make significant contribution to the total direct detection rate, especially for light nucleus. With this scenario, one could explain recent DAMA and CoGeNT results.

Figures (4)

• Figure 1: The kinematics of scattering: $|{\bf q}|^2 = 2 \mu^2 v^2 (1-\cos\theta)$, $|{\bf P}|^2 = 2 \mu^2 v^2 (1+\cos\theta)$ and ${\bf q}\cdot {\bf P} = 0$ in the CM frame.
• Figure 2: These two graphs display the spectral and angular distribution of SI (blue solid line) and SD (red dashed line) differential cross sections. The dot-dashed blue (SI) and red (SD) lines represent the special cases when $m_{\gamma^\prime}=0$, while the black thin solid line stands for the conventional SI (SD) interactions. We have chosen dark matter mass to be 5 GeV, $c_2=0$ and used an arbitrary scale in making the above plots.
• Figure 3: The event rate spectral for $^{73}Ge$ target detector with 5 GeV mirror neutron as the DM. In the left graph, we show the SI and SD contributions separately. In the right panel, we show a fit for the CoGeNT data with different $c_2$ values. The dashed line represents the Gaussian peaks from the L-shell background component.
• Figure 4: The event rate spectral for DAMA and a fit for the annual modulation amplitude $A(E)$.