The Experiment to Detect the Global Epoch of reionization Signature (EDGES) collaboration has reported an excess absorption dip in the 21 cm signal during cosmic dawn era. The stronger than expected 21 absorption signal indicates that gas was much cooler than the standard cosmological prediction. The observed 21-cm signal can be explained by decreasing the gas temperature via baryon-DM interaction. In this work, we study the temperature evolution of the gas and Dark Matter (DM) in the presence of magnetic fields. The magnetic heating via ambipolar diffusion and the turbulent decay increases both the gas and DM temperature at low redshift and this heating is more in the favour of baryons compared to DM. In the presence of strong magnetic field, a large baryon-DM interaction cross section is required to balance magnetic heating to explain the EDGES signal as compared to weak magnetic field. We also study the brightness temperature during the cosmic dawn era and put constraint on the strength of the magnetic field for a particular mass and baryon-DM cross section.

We study the constraints on primordial magnetic fields (PMFs) in the light of the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) low-band observation and Absolute Radiometer for Cosmology, Astrophysics and Diffuse Emission (ARCADE 2). ARCADE 2 observation detected extra-galactic excess radio radiation in the frequency range 3–90 GHz. The enhancement in the radio radiation is also supported by the first station of the Long Wavelength Array (LWA1) in the frequency range 40–80 MHz. The presence of early radiation excess over the cosmic microwave background can not be completely ruled out, and it may explain the EDGES anomaly. In the presence of decaying PMFs, 21 cm differential brightness temperature can modify due to the heating of the gas by decaying magnetic fields, and we can constraint the magnetic fields. For excess radiation fraction ($$A_r$$ A r ) to be LWA1 limit, we show that the upper bound on the present-day magnetic field strength, $$B_0$$ B 0 , on the scale of 1 Mpc is $$\lesssim 3.7$$ ≲ 3.7  nG for spectral index $$n_B=-2.99$$ n B = - 2.99 . While for $$n_B=-1$$ n B = - 1 , we get $$B_0\lesssim 1.1\times 10^{-3}$$ B 0 ≲ 1.1 × 10 - 3  nG. We also discuss the effects of first stars on IGM gas evolution and the allowed value of $$B_0$$ B 0 . For $$A_r$$ A r to be LWA1 limit, we get the upper constraint on magnetic field to be $$B_0(n_B=-2.99)\lesssim 4.9\times 10^{-1}$$ B 0 ( n B = - 2.99 ) ≲ 4.9 × 10 - 1  nG and $$B_0(n_B=-1)\lesssim 3.7\times 10^{-5}$$ B 0 ( n B = - 1 ) ≲ 3.7 × 10 - 5  nG. By decreasing excess radiation fraction below the LWA1 limit, we get a more stringent bound on $$B_0$$ B 0 .

The effective theory of large-scale structure formation based on $$\Lambda $$ΛCDM paradigm predicts finite dissipative effects in the resulting fluid equations. In this work, we study how viscous effect that could arise if one includes self-interaction among the dark-matter particles combines with the effective theory. It is shown that these two possible sources of dissipation can operate together in a cosmic fluid and the interplay between them can play an important role in determining dynamics of the cosmic fluid. In particular, we demonstrate that the viscosity coefficient due to self-interaction is added inversely with the viscosity calculated using effective theory of $$\Lambda $$ΛCDM model. Thus the larger viscosity has less significant contribution in the effective viscosity. Using the known bounds on $$\sigma /m$$σ/m for self-interacting darkmatter, where $$\sigma $$σ and m are the cross-section and mass of the dark-matter particles respectively, we discuss role of the effective viscosity in various cosmological scenarios.