[Paper Review] First numerical study of Neutrino-Dark Matter Mixed Damping

J. Stadler, Céline Bœhm+1 more|arXiv (Cornell University)|Mar 1, 2019

Dark Matter and Cosmic Phenomena32 references4 citations

TL;DR

This paper presents the first numerical study of neutrino-dark matter mixed damping, a hybrid effect between collisional damping and free-streaming arising from weak interactions between dark matter and neutrinos. It develops a self-consistent framework to model this damping across different regimes, offering critical insights for interpreting small-scale matter power spectrum anomalies beyond ΛCDM.

ABSTRACT

Mixed Damping is a physical effect that occurs when two fluids have interactions with each other but the particles in one fluid are already free-steaming. As such, it is a cross between collisional damping and free-streaming and has never been studied numerically. Mixed damping is particularly relevant in the context of dark matter-neutrino weak interactions and therefore should not be neglected. Here, we provide an accurate, self-consistent, description of the dark matter-neutrino interactions, which accounts for the different damping regimes. This work is critical to characterise the dark matter microphysics and will be extremely important if measurements of the matter power spectrum at small-scales indicate a departure from the $\Lambda$CDM predictions.

Motivation & Objective

• To investigate mixed damping as a novel physical mechanism in dark matter-neutrino interactions.
• To develop a self-consistent numerical framework for modeling mixed damping across different cosmological regimes.
• To assess the impact of neutrino-dark matter interactions on small-scale matter power spectrum, especially in light of potential deviations from ΛCDM.
• To provide a foundation for interpreting future high-precision cosmological data on small-scale structure.

Proposed method

• Formulate a kinetic theory approach to describe dark matter and neutrino interactions with proper treatment of weak scattering cross-sections.
• Implement a numerical solver for the coupled Boltzmann equations governing the evolution of dark matter and neutrino distribution functions.
• Incorporate both collisional damping and free-streaming effects in a unified framework to capture mixed damping dynamics.
• Account for the transition between different damping regimes based on interaction rate and free-streaming timescales.
• Validate the model against known limits, such as pure collisional damping and pure free-streaming, to ensure consistency.

Experimental results

Research questions

• RQ1 How does mixed damping modify the small-scale matter power spectrum compared to pure free-streaming or collisional damping?
• RQ2 What is the quantitative impact of weakly interacting dark matter on neutrino damping in the early universe?
• RQ3 How do different interaction strengths between dark matter and neutrinos affect the damping scale and transfer function?
• RQ4 In what cosmological regimes is mixed damping most significant for structure formation?

Key findings

• Mixed damping provides a new, previously unaccounted-for mechanism that can suppress small-scale power in the matter power spectrum.
• The model shows that weakly interacting dark matter can significantly alter neutrino damping behavior, especially at intermediate redshifts.
• The transition between collisional and free-streaming regimes is sensitive to the dark matter-neutrino interaction cross-section and velocity.
• The framework enables accurate prediction of transfer functions in scenarios with non-minimal dark matter-neutrino couplings.