Constraints on Fermionic Dark Matter Absorption from Radiochemical Solar-Neutrino Measurements

TL;DR

The paper addresses fermionic dark matter absorption by recasting time-integrated radiochemical solar-neutrino measurements as rate meters for non-negative capture-like contributions. It builds a Bayesian likelihood combining chlorine and gallium production rates with priors on solar fluxes, oscillations, cross sections, and explicit solar-metallicity systematics, adopting a pep-normalized operator mapping to report limits in terms of the charged-current parameter $y = \frac{m_χ^2}{4\piΛ^4}$. The results provide 90% upper limits on additive DM-induced rates and on $y(m_χ)$, with thresholds at $m_χ \sim 0.233$ MeV (Ga) and $0.814$ MeV (Cl); at $m_χ \approx 1$ MeV, $y_{90}$ reaches (GS98) $\sim 4.88\times 10^{-49}$ cm$^2$ and (AGSS09met) $\sim 7.08\times 10^{-49}$ cm$^2$. These radiochemical bounds complement xenon-based searches and collider limits, offering a robust, two-target, rate-based constraint with minimal reliance on spectral reconstruction or EFT extrapolations.

Abstract

We reinterpret classic radiochemical solar-neutrino measurements as ``rate meters'' for additional, non-negative capture-like contributions induced by fermionic dark matter absorption. Using the chlorine and gallium production-rate data, we build a Bayesian likelihood that accounts for the dominant uncertainties in the solar-neutrino capture-rate prediction (solar fluxes, oscillation parameters, and capture cross sections). Solar-model metallicity systematics are made explicit by presenting results for both the B16--GS98 and B16--AGSS09met solar-model realizations. From the 1D marginalized posteriors of the joint $(R_{χ,\mathrm{Cl}},R_{χ,\mathrm{Ga}})$ analysis, we obtain 90\% upper limits on additional capture-like rate contributions, dominated by chlorine: $R_{χ,\mathrm{Cl},90}\simeq 0.388~\mathrm{SNU}$ (B16--GS98) and $0.588~\mathrm{SNU}$ (B16--AGSS09met). In the charged-current V--A benchmark, we map these constraints onto upper bounds on $y\equiv m_χ^2/(4πΛ^4)$ for $m_χ$ above the ${}^{71}$Ga and ${}^{37}$Cl capture thresholds, using a pep-normalized operator mapping anchored to solar-neutrino capture inputs, where $m_χ$ is the dark matter mass and $Λ$ is the effective scale suppressing the charged-current operator. At $m_χ\simeq 1~\mathrm{MeV}$, we find $y_{90}\simeq 4.88\times 10^{-49}~\mathrm{cm}^2$ (B16--GS98) and $7.08\times 10^{-49}~\mathrm{cm}^2$ (B16--AGSS09met). These radiochemical bounds are complementary to xenon-based absorption searches and collider interpretations by probing distinct nuclear targets with minimal reliance on spectral reconstruction.

Figures (2)

• Figure 1: Posterior constraints on independent additive DM-induced rates $(R_{\chi,\mathrm{Cl}}^{\mathrm{(free)}},R_{\chi,\mathrm{Ga}}^{\mathrm{(free)}})$ for the two B16 SSM realizations. The central panel shows 68% (inner, solid) and 90% (outer, dashed) credible-region contours in the $(R_{\chi,\mathrm{Cl}}^{\mathrm{(free)}},R_{\chi,\mathrm{Ga}}^{\mathrm{(free)}})$ plane, while the top and right panels show the corresponding 1D marginalized posteriors. Vertical (horizontal) dotted lines indicate the one-sided 90% credible upper limits on $R_{\chi,\mathrm{Cl}}$ ($R_{\chi,\mathrm{Ga}}$).
• Figure 2: Main 90% credible upper limits on charged-current fermionic DM absorption, shown as a bound on $y = m_\chi^2/(4\pi\Lambda^4)$ as a function of the DM mass. Curves correspond to our baseline "pep-normalized" operator mapping, in which the effective nuclear response is calibrated to tabulated pep $\nu_e$ capture cross sections for each target. Results are shown for the two B16 SSM realizations (B16--GS98 and B16--AGSS09met), which bracket the dominant metallicity-driven flux systematic. For context we overlay representative external constraints, including the EXO-200 absorption limit EXO-200:2022adi and the collider/decay bounds as compiled in Refs. Dror:2020FDM_PRLDror:2020FDM_JHEP.