Dark Matter Induced Nucleon Decay Through the Neutron Portal

TL;DR

This paper investigates dark matter-induced nucleon decays mediated by the dimension-7 neutron portal operator, connecting visible and dark sectors within asymmetric dark matter frameworks. It reinterprets Super-Kamiokande searches for $n \to \pi^0 \nu$ and $p \to \pi^+ \nu$ to bound the operator scale $\Lambda$, finding lower limits of $\mathcal{O}(1~\mathrm{TeV})$ for GeV-scale DM; cross sections employ lattice QCD and LCSR form factors and velocity-averaged rates are computed using a truncated Maxwellian DM distribution. The authors detail IND cross sections, efficiency mappings to SK analyses, and a likelihood framework that accounts for backgrounds and systematics, projecting Hyper-Kamiokande reach under reduced uncertainties. They conclude that current SK data constrain the neutron portal operator, while Hyper-K entails only modest gains without substantial reductions in pion-nucleus interaction uncertainties, highlighting the need for dedicated analyses to fully harness future facilities.

Abstract

The neutron portal operator provides a theoretically motivated connection between the visible and dark sectors and features in several well-studied asymmetric dark matter models. This operator leads to dark matter induced nucleon decays that mimic the experimental signature of "ordinary" nucleon decays. In this work, we reinterpret Super-Kamiokande nucleon decay searches for $n \rightarrow π^0 ν$ and $p \rightarrow π^+ ν$ to constrain dark matter induced nucleon decays. For GeV-scale dark matter, we obtain lower bounds of $\mathcal{O}(1~\rm{TeV})$ on the scale of the effective neutron portal operator. We also discuss the prospects for future searches at Hyper-Kamiokande and highlight the importance of a dedicated experimental analysis with reduced systematic uncertainties.

Figures (5)

• Figure 1: Momentum transfer, $q^2$, as a function of the mass splitting, $\Delta m$, for the neutron-$\Phi$ IND process. The upper shaded region represents the range of $q^2$ for which lattice QCD Aoki:2017puj form factors are used, the lower corresponds to LCSR Haisch:2021hvj.
• Figure 2: Velocity-averaged cross sections for the neutron-DM IND processes as a function of the DM mass splitting. The mass of the initial state DM is set to $1~\rm{GeV}$ and a benchmark value of $\Lambda = 1~\rm{TeV}$ is used. The discontinuities occur at the transition between lattice and LCSR form factors.
• Figure 3: Bounds on the scale of the dimension-$7$ neutron portal operator at $95\%$ CL from nucleon-$\Phi$ (top) and nucleon-$\Psi$ (bottom) IND. The solid curves use existing data from Super-K, while the dashed curves show projections for Hyper-K assuming a $50\%$ improvement of the systematics. In each plot, the incoming DM particle (either $\Phi$ or $\Psi$) is assumed to comprise $100\%$ of the galactic DM. The small lighter shaded regions represent the uncertainty due to the matrix element form factors. The hatched region shows where the direct proton decay constraints apply for a DM mass of $0.5~\rm{GeV}$ (blue curves).
• Figure 4: IND constraints on the EFT scale $\Lambda$ in Hylogenesis models (95% CL), which satisfy the additional mass requirement $m_\Phi = 5m_p - m_\Psi$ with $m_\Psi = \{1.7, 2.9\}~\rm{GeV}$. These are shown for the nucleon-$\Phi$ (red) and nucleon-$\Psi$ (blue) IND processes.
• Figure 5: Upper bounds on the IND velocity-averaged cross sections from Super-K (solid) and projected bounds for Hyper-K (dashed). The top (bottom) row is for neutron-DM (proton-DM) IND processes and the left (right) column is for the nucleon-$\Phi$ (nucleon-$\Psi$) process. The hatched region shows where the direct proton decay constraints apply for a DM mass of $0.5~\rm{GeV}$ (blue curves).