Axion-Photon conversion in magnetized universe: Impact on the global 21 cm signal

The reported anomalous global 21 cm signal [Formula: see text] from the cosmic dawn era by Experiment to Detect the Global Epoch of Reionization Signature (EDGES) could hint toward new physics beyond the Standard Model. The resonant conversion of the axion-like particles (ALPs) into photons in the presence of primordial magnetic fields (PMFs) could be a viable solution. However, the strength of the PMFs can change over the time as they can decay by ambipolar diffusion and turbulent decay. Consequently, PMFs can dissipate their energy into the intergalactic medium (IGM), which can alter the global 21 cm signal. We simultaneously consider both magnetic heating of IGM and resonant conversion of ALPs to derive physically motivated upper bounds on the coupling strength [Formula: see text] and magnetic field strength [Formula: see text]. Our findings report that, for [Formula: see text], [Formula: see text] is required to recover standard [Formula: see text], while a deeper absorption of [Formula: see text] [Formula: see text]mK pushes the upper bound to [Formula: see text].