Abstract

Analysis of EDGES data shows an absorption signal of the redshifted 21-cm line of atomic hydrogen at z ∼ 17 which is stronger than expected from the standard ΛCDM model. The absorption signal interpreted as brightness temperature T21 of the 21-cm line gives an amplitude of -{500}_{-500}^{+200} mK at 99% C.L. which is a 3.8σ deviation from what the standard ΛCDM cosmology gives. We present a particle physics model for the baryon cooling where a fraction of the dark matter resides in the hidden sector with a U(1) gauge symmetry and a Stueckelberg mechanism operates mixing the visible and the hidden sectors with the hidden sector consisting of dark Dirac fermions and dark photons. The Stueckelberg mass mixing mechanism automatically generates a millicharge for the hidden sector dark fermions providing a theoretical basis for using millicharged dark matter to produce the desired cooling of baryons seen by EDGES by scattering from millicharged dark matter. We compute the relic density of the millicharged dark matter by solving a set of coupled equations for the dark fermion and dark photon yields and for the temperature ratio of the hidden sector and the visible sector heat baths. For the analysis of baryon cooling, we analyze the evolution equations for the temperatures of baryons and millicharged dark matter as a function of the redshift. We exhibit regions of the parameter space which allow consistency with the EDGES data. We note that the Stueckelberg mechanism arises naturally in strings and the existence of a millicharge would point to its string origin.

Highlights

  • Ν = 1420/(1 + z) MHz, where z is the redshift

  • The absorption signal interpreted as brightness temperature T21 of the 21-cm line gives an amplitude of −500+−250000 mK at 99% C.L. which is a 3.8σ deviation from what the standard ΛCDM cosmology gives

  • We present a particle physics model for the baryon cooling where a fraction of the dark matter resides in the hidden sector with a U(1) gauge symmetry and a Stueckelberg mechanism operates mixing the visible and the hidden sectors with the hidden sector consisting of dark Dirac fermions and dark photons

Read more

Summary

A particle physics model for EDGES

We extend the Standard Model (SM) gauge group by an extra U(1)X under which the SM is neutral. The setup of eq (2.1)–(2.3) guarantees the existence of a massless mode (the photon) when canonical diagonalization of the full Lagrangian of eq (2.1) is carried out In this analysis we are interested in millicharge couplings Lm arising from the inclusion of the kinetic and Stueckelberg mass mixing between the visible sector and the hidden sector. In the absence of the Stueckelberg couplings only the Aγμ term in eq (2.7) will exist, and the Z boson coupling in eq (2.7) will be absent, and all of the couplings of eq (2.10) and of eq (A.3) will disappear In this case it would not be possible to carry out a two-temperature evolution of the visible and hidden sectors nor obtain a consistent cosmology discussed . The existence of millicharged particles was predicted in the Stueckelberg extension of the standard model with mass mixing in [34]

Temperature evolution at early times
The brightness temperature of the 21-cm line
Conclusion
Further details of the analysis
A Model details
Findings
B Cross-sections for dark matter relic density calculation
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call