[Paper Review] Reducing cosmological small scale structure via a large dark matter-neutrino interaction: constraints and consequences

Bridget Bertoni, Seyda Ipek+2 more|arXiv (Cornell University)|Dec 9, 2014

Dark Matter and Cosmic Phenomena53 references11 citations

TL;DR

This paper proposes a renormalizable model with a sterile neutrino mixing predominantly with the tau neutrino to mediate strong dark matter-neutrino interactions, suppressing small-scale structure formation. By keeping dark matter in kinetic equilibrium with the plasma down to ~10 MeV, it sets a cutoff mass of $10^7$–$10^9~M_\odot$ for dark matter halos, resolving the missing satellites problem with a 50–100 MeV dark matter candidate and a 100 MeV sterile neutrino with significant $\tau$-neutrino component.

ABSTRACT

Cold dark matter explains a wide range of data on cosmological scales. However, there has been a steady accumulation of evidence for discrepancies between simulations and observations at scales smaller than galaxy clusters. Solutions to these small scale structure problems may indicate that simulations need to improve how they include feedback from baryonic matter, or may imply that dark matter properties differ from the standard cold, noninteracting scenario. One promising way to affect structure formation on small scales is a relatively strong coupling of dark matter to neutrinos. We construct an experimentally viable, simple, renormalizable, model with new interactions between neutrinos and dark matter. We show that addressing the small scale structure problems requires dark matter with a mass that is tens of MeV, and a present-day density determined by an initial particle-antiparticle asymmetry in the dark sector. Generating a sufficiently large dark matter-neutrino coupling requires a new heavy neutrino with a mass around 100 MeV. The heavy neutrino is mostly sterile but has a substantial $τ$ neutrino component, while the three nearly massless neutrinos are partly sterile. We provide the first discussion of how such dark matter-neutrino interactions affect neutrino (especially $τ$ neutrino) phenomenology. This model can be tested by future astrophysical, particle physics, and neutrino oscillation data. A feature in the neutrino energy spectrum and flavor content from a future nearby supernova would provide strong evidence of neutrino-dark matter interactions. Promising signatures include anomalous matter effects in neutrino oscillations due to nonstandard interactions and a component of the $τ$ neutrino with mass around 100 MeV.

Motivation & Objective

• To address the missing satellites problem in the cold dark matter paradigm by suppressing small-scale structure formation.
• To construct a renormalizable, experimentally viable model with strong dark matter-neutrino interactions that remain consistent with cosmological and particle physics constraints.
• To identify observable signatures of such interactions in astrophysical and particle physics experiments, particularly involving tau neutrinos and sterile neutrinos.
• To explore the phenomenological consequences of a heavy, mostly sterile neutrino with a significant $\tau$-neutrino component in the context of nonstandard neutrino interactions.

Proposed method

• Introduces a renormalizable theory with a new heavy sterile neutrino that mixes with active neutrinos, enabling strong dark matter-neutrino scattering.
• Uses kinetic decoupling temperature $T_d \sim \Lambda (m_\chi / M_{\rm Pl})^{1/4}$ to determine the scale of structure suppression, linking $T_d$ to the cutoff halo mass $M_{\rm cutoff} \sim 10^8 M_\odot (\rm keV / T_d)^3$.
• Imposes a large mixing $|U_{\tau 4}|^2 \sim 0.1$ to achieve sufficient scattering cross-section, requiring a sterile neutrino with mass ~100 MeV and a dark matter candidate of ~50–100 MeV.
• Analyzes the impact of the heavy sterile neutrino on neutrino oscillation phenomenology, including anomalous matter effects and nonstandard interactions in short-baseline experiments.
• Evaluates the potential for detecting the model via future supernova neutrino signals, particularly distortions in the energy spectrum and flavor content.
• Assesses lepton-flavor-violating processes such as $\tau \to \mu\gamma$, $\mu \to e\gamma$, and $\mu \to e$ conversion, enhanced by the large sterile neutrino mass.

Experimental results

Research questions

• RQ1 Can strong dark matter-neutrino interactions suppress small-scale structure formation to resolve the missing satellites problem?
• RQ2 What are the required properties of a sterile neutrino and dark matter candidate to achieve the necessary scattering cross-section in a renormalizable model?
• RQ3 How do such interactions alter neutrino oscillation phenomenology, particularly in short-baseline experiments?
• RQ4 What observable signatures could arise from a heavy, mostly sterile neutrino with a significant $\tau$-neutrino component?
• RQ5 Can future supernova neutrino observations detect imprints of dark matter-neutrino scattering?

Key findings

• A cutoff halo mass of $10^7$–$10^9~M_\odot$ is achieved when dark matter remains in kinetic equilibrium down to a decoupling temperature of ~10 MeV, consistent with resolving the missing satellites problem.
• The model requires a dark matter candidate with a mass of tens of MeV and a sterile neutrino with a mass of ~100 MeV, mixing predominantly with the $\tau$ neutrino via $|U_{\tau 4}|^2 \sim 0.1$.
• The sterile neutrino is mostly sterile but contains a substantial $\tau$-neutrino component, leading to a detectable signal in $\nu_\mu \to \nu_\tau$ oscillation experiments like MINSIS.
• Future observations of a nearby supernova could reveal distortions in the neutrino energy spectrum and flavor content due to scattering with dark matter, providing strong evidence for the model.
• The model predicts enhanced rates for lepton-flavor-violating processes such as $\tau \to \mu\gamma$ and $\mu \to e\gamma$, with sensitivity expected to improve significantly in upcoming experiments.
• Nonstandard matter effects in neutrino oscillations due to the heavy sterile neutrino component could be probed in short-baseline experiments, offering a direct test of the model.