Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Interacting Hot Dark Matter

Fernando Atrio-Barandela, Sacha Davidson

TL;DR

The paper investigates whether a light, self-interacting dark matter candidate (sticky neutrinos with $m_\nu \approx 20$–$30$ eV) can preserve galaxy-scale perturbations while damping smaller-scale fluctuations. It develops an imperfect-fluid framework by linking the Boltzmann equation to hydrodynamics, deriving viscosity $\eta$ and heat conduction $\chi$ to determine diffusion-driven damping, and computes the linear power spectrum under these conditions. The results show a diffusion-damped small-scale cutoff with a comoving length $\lambda_D \approx 3\sqrt{\tau/\mathrm{Mpc}}~\mathrm{Mpc}$ (and an instantaneous NR transition at $T_\gamma=10$ eV in the numerics), compatible with larger-scale CDM-like structure given current SN1987A bounds on the cross section. A key caveat is that interacting hot dark matter cannot form halos in dwarf galaxies, leaving a significant challenge for this scenario as a complete DM solution. Overall, the work offers a phenomenological route to reconcile large-scale structure with reduced small-scale power via diffusion, contingent on tight cross-section constraints and dwarf-galaxy formation physics.

Abstract

We discuss the viability of a light particle ($\sim 30$ eV neutrino) with strong self-interactions as a dark matter candidate. The interaction prevents the neutrinos from free-streaming during the radiation dominated regime so galaxy sized density perturbations can survive. Smaller scale perturbations are damped due to neutrino diffusion. We calculate the power spectrum in the imperfect fluid approximation, and show that it is damped at the length scale one would estimate due to neutrino diffusion. The strength of the neutrino--neutrino coupling is only weakly constrained by observations, and could be chosen by fitting the power spectrum to the observed amplitude of matter density perturbations. The main shortcoming of our model is that interacting neutrinos can not provide the dark matter in dwarf galaxies.

Interacting Hot Dark Matter

TL;DR

The paper investigates whether a light, self-interacting dark matter candidate (sticky neutrinos with – eV) can preserve galaxy-scale perturbations while damping smaller-scale fluctuations. It develops an imperfect-fluid framework by linking the Boltzmann equation to hydrodynamics, deriving viscosity and heat conduction to determine diffusion-driven damping, and computes the linear power spectrum under these conditions. The results show a diffusion-damped small-scale cutoff with a comoving length (and an instantaneous NR transition at eV in the numerics), compatible with larger-scale CDM-like structure given current SN1987A bounds on the cross section. A key caveat is that interacting hot dark matter cannot form halos in dwarf galaxies, leaving a significant challenge for this scenario as a complete DM solution. Overall, the work offers a phenomenological route to reconcile large-scale structure with reduced small-scale power via diffusion, contingent on tight cross-section constraints and dwarf-galaxy formation physics.

Abstract

We discuss the viability of a light particle ( eV neutrino) with strong self-interactions as a dark matter candidate. The interaction prevents the neutrinos from free-streaming during the radiation dominated regime so galaxy sized density perturbations can survive. Smaller scale perturbations are damped due to neutrino diffusion. We calculate the power spectrum in the imperfect fluid approximation, and show that it is damped at the length scale one would estimate due to neutrino diffusion. The strength of the neutrino--neutrino coupling is only weakly constrained by observations, and could be chosen by fitting the power spectrum to the observed amplitude of matter density perturbations. The main shortcoming of our model is that interacting neutrinos can not provide the dark matter in dwarf galaxies.

Paper Structure

This paper contains 8 sections, 42 equations, 1 figure.

Table of Contents

  1. introduction
  2. particle physics
  3. Evolution of density perturbations.
  4. The Boltzmann equation and the fluid approximation.
  5. Perturbation Damping for Sticky Neutrinos
  6. Evolution in the non--relativistic regime and final power spectrum.
  7. Phase Space Constraints
  8. Discussion

Figures (1)

  • Figure 1: Power spectrum for three different "sticky neutrino" models. The solid lines correspond (in decreasing amplitude) to interactions with no neutrino diffusion, and with co-moving mean free paths at $T_{\gamma} = 10$ eV of .01 Mpc and .1 Mpc. These give rise to estimated damping scales of 7 Mpc$^{-1}$ and 3 Mpc$^{-1}$, respectively. The dashed line correspond to standard CDM and is plotted for comparison. The y-axis scale is arbitrary. We took $H_o = 50$Km s${-1}$Mpc${-1}$.