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

Abstract

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 Gµ ∼ 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 (δT 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 δT b observed by the EDGES experiment.

Constraints on superconducting cosmic strings from the global 21-cm signal before reionization

“…If we demand that the distribution of superconducting string loops does not produce an absorption feature larger in amplitude than has been observed, the parameter space of strings must be constrained to yield R ≤ 1. From (22), (23) and (24) we see that a significant parameter space of high tension and high current superconducting cosmic strings is ruled out.…”

“…A radio excess could possibly explain this signal. In an earlier paper [22], we studied the contribution of electromagnetic radiation from cusp decays of non-superconducting strings to the radio excess and found it to be much too small to effect observations. Superconducting strings, on the other hand, produce much more electromagnetic radiation.…”

“…In a recent paper[22] we studied the radio excess produced by the cusp decay of non-superconducting strings, but we found that the predicted radio spectrum is too low in amplitude to yield constraints on the cosmic string parameter space.…”

Ionization from cosmic strings at cosmic dawn

“…We will be interested in the values of Gµ which give the largest flux. Hence, as discussed in [26], both gravitational radiation and cusp annihilation are important decay mechanisms for the relevant values of Gµ. Therefore, in order to obtain an accurate description of the cusp annihilation spectrum when Gµ ∼ 10 −18 , we will use P = P g + P c .…”

“…The strength of emission depends on both the flux of the charged particles produced by cusp radiation and on the density of the surrounding medium. According to [26,27], the spectrum of photons emitted via Bremsstrahlung per unit time per unit frequency for a cusp at a given time is given by…”