$νΛ$MDM: A Model for Sterile Neutrino and Dark Matter Reconciles Cosmological and Neutrino Oscillation Data after BICEP2

TL;DR

The paper introduces a renormalizable UV-complete model, νΛMDM, featuring a dark $U(1)_X$ gauge symmetry broken near the MeV scale to mediate dark matter self-interactions and connect with sterile neutrinos. This framework yields a DM candidate with $M_{\ ext{cut}}$ set by late kinetic decoupling and a transfer cross section that addresses cusp–core and missing satellites problems, while four light sterile neutrinos contribute to $\Delta N_{\mathrm{eff}}$ and HDM mass in a way that aligns cosmological data with neutrino oscillation results at $1\sigma$. By combining $3+2$ neutrino mixing and dark-sector thermal histories, the model can also alleviate the Planck–BICEP2 tension without invoking a running spectral index. The authors outline concrete observational tests, including direct and indirect detection signals and neutrino oscillation probes, enabling empirical scrutiny of the scenario. Overall, νΛMDM offers a cohesive, testable path to unify dark matter phenomenology with sterile neutrino physics and early-universe constraints.

Abstract

We propose a ultraviolet complete theory for cold dark matter(CDM) and sterile neutrino that can accommodate both cosmological data and neutrino oscillation experiments at $1σ$ level. A new $U(1)_X$ dark gauge symmetry is introduced, and is assumed to be broken at $\sim \mathcal{O}$(MeV) scale. Such a light mediator for DM's self-scattering and scattering-off sterile neutrinos can resolve three controversies for cold DM on small cosmological scales, cusp vs. core, too-big-to-fail and missing satellites problems. We can also accommodate $\sim$ eV scale sterile neutrinos as the hot dark matter(HDM) and can fit some neutrino anomalies from neutrino oscillation experiments within $1σ$. Finally the right amount of HDM can make a sizable contribution to dark radiation, and also helps to reconcile the tension between the data on the tensor-to-scalar ratio reported by Planck and BICEP2 Collaborations.

Figures (3)

• Figure 1: Feynman diagrams for (a)$\chi \bar{\chi}$ and (b)$\chi \nu_s$ scattering where $i\neq j$ for $\nu_i$'s Majorana nature, $\bar{\nu}_i\gamma^\mu\nu_i=0$.
• Figure 2: $\sigma_T/m_\chi$ as function of relative velocity for $m_\chi=1\mathrm{TeV},m_X=4\mathrm{MeV}$ and $g_X=0.5$.
• Figure 3: The allowed range for $\Delta N_\textrm{eff}$ and $\sum m_{\nu_s}$. The blue(solid) and purple(dashed) contours Hamann:2013iba correspend to the $1\sigma$ and $2\sigma$ for the cosmological data with the best fit point $\Delta N_\textrm{eff}=0.61\pm 0.30,\; m^{\textrm{eff}}_{\textrm{hdm}}=(0.47\pm 0.13)\textrm{ eV}$. The region between two red vertical lines can be achieved in our model. And the horizontal dotted line marks the centre value for $\sum m_{\nu_s}$ from the global fit for neutrino oscillation data in $3+2$ scenario globalfitnu. We use $m_t\simeq 173$GeV and $T_c$ is the confinement-deconfinement transition between quarks and hadrons. See the text for detail.