Constraining Dark Matter-Neutrino Interactions using the CMB and Large-Scale Structure

TL;DR

Addresses whether dark matter–neutrino elastic scattering leaves detectable imprints on the CMB and large-scale structure. It modifies the Boltzmann equations to include a DM–neutrino coupling and analyzes Planck CMB data alongside the Lyman-α forest to bound the cross section for constant and $T^2$ scaling. The results show that the Lyman-α forest provides the strongest constraints, with $\sigma_{ m DM- u}\lesssim 10^{-33}(m_{ m DM}/ m GeV) m ext{cm}^2$ (constant) and $\sigma_{ m DM- u,0}\\lesssim 10^{-45}(m_{ m DM}/ m GeV) m ext{cm}^2$ (T^2), tightening previous limits and linking DM–neutrino interactions to MeV-scale DM scenarios that impact $N_{ m eff}$ and $H_0$. The study demonstrates how the Universe’s matter distribution serves as a robust probe of invisible interactions beyond gravity, with implications for beyond-Standard-Model physics and early-Universe cosmology.

Abstract

We present a new study on the elastic scattering cross section of dark matter (DM) and neutrinos using the latest cosmological data from Planck and large-scale structure experiments. We find that the strongest constraints are set by the Lyman-alpha forest, giving sigma_{DM-neutrino} < 10^{-33} (m_DM/GeV) cm^2 if the cross section is constant and a present-day value of sigma_{DM-neutrino} < 10^{-45} (m_DM/GeV) cm^2 if it scales as the temperature squared. These are the most robust limits on DM-neutrino interactions to date, demonstrating that one can use the distribution of matter in the Universe to probe dark ("invisible") interactions. Additionally, we show that scenarios involving thermal MeV DM and a constant elastic scattering cross section naturally predict (i) a cut-off in the matter power spectrum at the Lyman-alpha scale, (ii) N_eff ~ 3.5 +/- 0.4, (iii) H_0 ~ 71 +/- 3 km/s/Mpc and (iv) the possible generation of neutrino masses.

Figures (5)

• Figure 1: The effect of DM--neutrino interactions on the $TT$ (top), $EE$ (middle) and $BB$ (bottom) components of the angular power spectrum, where $u \equiv \left[{\sigma_{\rm{DM}-\nu}}/{\sigma_{\mathrm{Th}}} \right] \left[{m_{\rm{DM}}}/{100~\rm{GeV}} \right]^{- 1}$ (such that $u = 0$ corresponds to no coupling). We take $\sigma_{\rm{DM}-\nu}$ to be constant and use the ' Planck + WP' best-fit parameters from Ref. Ade:2013zuv. The data points in the $BB$ spectrum are recent measurements from the SPTpol experiment Austermann:2012ga, where the three datasets correspond to $({\hat{\rm{E}}}^{150}{\hat{\phi}}^{\rm{CIB}}) \times {\hat{\rm{B}}}^{150}$, $({\hat{\rm{E}}}^{95}{\hat{\phi}}^{\rm{CIB}}) \times {\hat{\rm{B}}}^{150}$ and $({\hat{\rm{E}}}^{150}{\hat{\phi}}^{\rm{CIB}}) \times {\hat{\rm{B}}}_{\chi}^{150}$ respectively in Ref. Hanson:2013hsb. The new coupling enhances the peaks in the $TT$ and $EE$ spectra, while significantly damping the $B$-modes.
• Figure 2: The impact of DM--neutrino interactions on the matter power spectrum, where $u \equiv \left[{\sigma_{\rm{DM}-\nu}}/{\sigma_{\mathrm{Th}}} \right] \left[{m_{\rm{DM}}}/{100~\rm{GeV}} \right]^{- 1}$ (such that $u = 0$ corresponds to no coupling). We take $\sigma_{\rm{DM}-\nu}$ to be constant and use the ' Planck + WP' best-fit parameters from Ref. Ade:2013zuv. The solid grey curve represents the most recent constraint on warm DM models from the Lyman-$\alpha$ forest Viel:2013fqw. The new coupling produces (power-law) damped oscillations, reducing the number of small-scale structures with respect to vanilla $\Lambda$CDM Boehm:2001hm.
• Figure 3: Triangle plot showing the one and two-dimensional posterior distributions of the cosmological parameters set by Planck for a constant cross section, with $u$ and $N_{\rm eff}$ as free parameters. The contours correspond to 68% and 95% CL.
• Figure 4: Triangle plot showing the one and two-dimensional posterior distributions of the cosmological parameters set by Planck for a temperature-dependent cross section, with $u$ and $N_{\rm eff}$ as free parameters. The contours correspond to 68% and 95% CL.
• Figure 5: Triangle plot showing the one and two-dimensional posterior distributions of the cosmological parameters set by Planck for a constant cross section, where we impose the maximum allowed value obtained in Sec. \ref{['subsec:lss']}, i.e. $\sigma_{\rm{DM}-\nu} \simeq 10^{-33} \left(m_{\rm{DM}}/\rm{GeV}\right) \ \rm{cm^2}$. The contours correspond to 68% and 95% CL.