Abstract : We have shown that in presence of a cosmic magnetic field the bounds on baryon dark matter cross-section ( \hat { \sigma } ) , dark-matter mass ( m _ { d } ) and values of the magnetic field ( B _ { 0 } ) can strongly influence each other .
This requires to rework the bounds on \hat { \sigma } , m _ { d } and B _ { 0 } which can explain the observed absorption signal by EDGES collaboration .
The upper limit on the magnetic field strength can modify in presence of baryon-dark matter interaction cross-section .
In the presence of a strong magnetic field , a large baryon-dark matter interaction cross-section is required to balance magnetic heating of gas to explain the EDGES signal as compared to a weak magnetic field .
Subsequently , the strong magnetic-fields can even erase the 21 cm signal–this gives an upper bound on the strength of magnetic-fields , dark-matter mass and baryon-dark matter cross-section .
In the special case when \hat { \sigma } =0 , one can recover the bound on magnetic field strength calculated in ( 1 ) .
In this work we find that the allowed range of the primordial magnetic field can increase by three orders of magnitude in comparison with ( 1 ) .
We get upper bound on the magnetic field strength : 3.48 \times 10 ^ { -6 } G for the dark matter mass \lesssim 10 ^ { -2 } GeV .