On the possible enhancement of the global 21-cm signal at reionization from the decay of cosmic string cusps

We consider cosmic string cusp annihilations as a possible source of enhancement to the global background radiation temperature in 21-cm photons at reionization. A soft photon spectrum is induced via the Bremsstrahlung and Synchrotron emission of electrons borne out of QCD jets formed off the cusp. The maximal energy density background comes from synchrotron induced photons with a string tension of G mu similar to 10(-18). In this instance, the radiation background at reionization is heated up by 5.10(-3) K. We find that the depth of the absorption trough (delta T-b) in 21-cm at reionization is altered by one part in 10(4) from the strings, requiring high precision measurements to be detectable. This mechanism cannot explain the delta T-b observed by the EDGES experiment.