Implications of baryon-dark matter interaction on IGM temperature and tSZ effect with magnetic field

Abstract: We show that the combined effect of cosmic magnetic field and a possible non-standard interaction between baryons and dark matter has interesting consequences on the thermal Sunyaev$-$Zel${'}$dovich (tSZ) effect depending on the temperature and the ionization state of the intergalactic medium. The drag force between the baryons and dark matter due to the relative velocity between them, and their temperature difference results in heat transfer between these two species. At the same time the ambipolar diffusion and the decaying magnetic turbulence tends to heat up the baryons. This interplay of these two processes give rise to different evolution histories of the thermal and ionization state of the universe and hence influences the CMB spectrum at small scales through the tSZ effect. In this work, we have computed the evolution of the temperature, ionization fraction and the y-parameter of the CMB for different strengths of the magnetic field and the interaction cross-section. We note that an interaction cross-section of $\sigma_0=10^{-42}$ m$^{2}$ (with a magnetic field strength of $3.0$ nG) reduces the y-parameter by an order of magnitude as compared to the case with similar strength of magnetic field but where there is no such interaction between the baryons and dark matter.