Using the CMB angular power spectrum to study Dark Matter-photon interactions

Abstract

In this paper, we explore the impact of Dark Matter-photon interactions on the CMB angular power spectrum. Using the one-year data release of the Planck satellite, we derive an upper bound on the Dark Matter-photon elastic scattering cross section of σ DM−γ ≤ 8×10 −31 (m DM /GeV) cm 2 (68% CL) if the cross section is constant and a present-day value of σ DM−γ ≤ 6 × 10 −40 (m DM /GeV) cm 2 (68% CL) if it scales as the temperature squared. For such a limiting cross section, both the B-modes and the T T angular power spectrum are suppressed with respect to ΛCDM predictions for 500 and 3000 respectively, indicating that forthcoming data from CMB polarisation experiments and Planck could help to constrain and characterise the physics of the dark sector. This essentially initiates a new type of dark matter search that is independent of whether dark matter is annihilating, decaying or asymmetric. Thus, any CMB experiment with the ability to measure the temperature and/or polarisation power spectra at high should be able to investigate the potential interactions of dark matter and contribute to our fundamental understanding of its nature.

Using the Milky Way satellites to study interactions between cold dark matter and radiation

“…A definitive calculation would include the full impact of these effects, in particular, supernovae feedback and photoionization heating of the interstellar medium, but this is deferred to a future paper. A similar paucity of subhaloes is seen in the bottom-right panel, in which the DM-photon interaction strength is just allowed by CMB constraints (Wilkinson et al 2013). This model underestimates the number of MW satellites.…”

“…The subhalo population is significantly smaller for this model compared to CDM. However, the suppression of subhaloes in γCDM is too strong if we consider σDM−γ = 10 −7 σ Th (mDM/GeV) (bottom-right panel), which just satisfies the limit from the CMB (Wilkinson et al 2013). Therefore, by adjusting the magnitude of the scattering cross section, not only is there scope to solve the MW satellite problem, but we can also place a more stringent constraint on the γCDM interaction strength.…”

“…where θ is the velocity dispersion, k is the wavenumber, ψ is the (DM-dominated) gravitational potential, H is the expansion rate of the Universe, δ is the density contrast and σ is the anisotropic stress potential 2 (Wilkinson et al 2013). …”

“…The consequences of DM interactions with radiation have been computed in the linear regime (Boehm et al 2002;Sigurdson et al 2004;Wilkinson et al 2013Wilkinson et al , 2014. The γCDM matter power spectrum is damped relative to that of CDM beyond a scale that depends on the interaction cross section.…”

“…For γCDM, the comparison with cosmic microwave background (CMB) data from Planck (Ade et al 2013) gives a constraint on the (constant) elastic scattering cross section of σDM−γ 10 −6 σ Th (mDM/GeV), where σ Th is the Thomson cross section and mDM is the DM mass (Wilkinson et al 2013). However, this linear approach breaks down once the fluctuations become large, preventing one from studying the effects of weak interactions on DM haloes and in particular, on small-scale objects.…”