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: 3.48times 10^{-6} G for the dark matter mass lesssim 10^{-2} GeV.
Highlights
During the cosmic dawn era, the gas temperature is lower than the cosmic microwave background (CMB) temperature hyperfine transitions in the neutral hydrogen atoms produce 21 cm absorption spectra
dark matter (DM) temperature grows due to the drag term in Eq (15) and it can be seen in Fig. 1, temperature of DM for B0 = 10−5 G is larger compared to B0 = 10−6 G
It could erase the observed 21 cm absorption signal, one can calculate the upper bound on the magnetic field
Summary
During the cosmic dawn era, the gas temperature is lower than the CMB temperature hyperfine transitions in the neutral hydrogen atoms produce 21 cm absorption spectra. By the constraint on gas temperature during redshift 15 z 20 (EDGES result), they put a constraint on the upper limit of the PMFs strength: B 10−10 Gauss at the length-scale of 1 Mpc. If one invokes cooling of gas beyond the standard scenario in the presence of baryon dark matter interaction, discussed above, this bound on the strength of PMFs It is to be noted that, we are interested only in the magnetic heating of the gas in the presence of DM-baryon interaction due to the effective cooling of IGM by DM The origin of these PMFs fields could be due to some high energy process in the very early universe [43,44,45,46,47]. Xc and xα are the collisional and Lyα coupling respectively [48], xc
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