Constraints on New Neutrino Interactions via Light Abelian Vector Bosons

TL;DR

This work analyzes a light Abelian vector boson $V$ with mass from the Stuckelberg mechanism that couples to SM neutrinos and charged leptons via a $V$-A current with strength $g_\nu$. The authors derive stringent bounds on $g_\nu$ from $Z$ and $W$ decays, kaon decays, and low-energy $\nu$–$e$ scattering, treating $V$ as an effective theory up to $\Lambda_{UV}\sim 500$ GeV. They obtain $g_\nu \lesssim 0.03$ from $Z$ decays, $g_\nu \lesssim 2\times 10^{-3}$ from $W$ decays, and $g_\nu \lesssim {\rm a~few}\times 10^{-4}$ from kaon decays, with strong Be-7 solar-neutrino scattering constraints that scale roughly as $g_\nu \propto m_V$ for $m_V \gtrsim 1$ MeV. These results place tight constraints on neutrinophilic dark matter models and illustrate that, for sterile neutrinos to evade these bounds, substantial model-building or UV completions are required.

Abstract

We calculate new constraints on extra neutrino interactions via light Abelian vector bosons, where the boson mass arises from Stuckelberg mechanism. We use the requirement that $Z$, $W$, and kaon decays, as well as electron-neutrino scattering, are not altered by the new interactions beyond what is allowed by experimental uncertainties. These constraints are strong and apply to neutrinophilic dark matter, where interactions of neutrinos and dark matter via a new gauge boson are important. In particular, we show that models where neutrino interactions are needed to solve the small-scale structure problems in the $Λ$CDM cosmology are constrained.

Figures (4)

• Figure 1: Constraints on hidden neutrino interactions. If $V$ couples only to neutral active leptons, then only our constraint from $Z$ decay applies. If $V$ couples equally also to charged leptons, all of our constraints apply. The hatched region shows the parameter space of mediator mass and coupling that solves the missing satellites problem of $\Lambda$CDM Aarssen:2012fx. These constraints are valid for $\Lambda_{UV} \sim$ 500 GeV. See text for details.
• Figure 2: Feynman diagram for $Z$-boson decay to neutrinos where a $V$ is radiated from the final state antineutrino. We also take into account another diagram where the $V$ is radiated from the final state neutrino.
• Figure 3: Feynman diagram for $K^- (\bar{u}s)$ decay to a muon where a $V$ is radiated from the final state antineutrino. We also take into account another diagram where the $V$ is also radiated from the muon. The hadronic matrix element $\langle 0| \overline{u} \gamma ^{\alpha} (1-\gamma _5) s|K^- \rangle = f_K\, p_K ^\alpha$ is denoted by the shaded circle.
• Figure 4: Muon spectra from kaon decay for the standard 2-body decay $K^- \rightarrow \mu^- \, \overline{\nu}_\mu$ (solid blue) measured in Ambrosino:2005fw along with the hypothetical 3-body decay $K^- \rightarrow \mu^- \, \overline{\nu}_\mu \, V$ (dashed red) with $g_\nu=10^{-2}$ and $m_V=0.5\,{\rm MeV}$. The shaded region shows the search region of Ref. Pang:1989ut, where no excess events were found. From this we derive an upper bound on the 3-body differential decay rate that is $\sim$10$^4$ times lower than the dashed red line.