Cosmic Rays from Cosmic Strings with Condensates

TL;DR

This paper investigates how cosmic strings with scalar condensates can produce ultra-high-energy cosmic rays through cusp emissions, aligning with observations for specific string scales, and constrains lighter strings based on cosmic ray excesses.

Contribution

It demonstrates that cosmic strings with bosonic condensates can generate observable ultra-high-energy cosmic rays, constraining their properties and parameter space.

Findings

High-energy cosmic ray flux matches observations for string scale ~10^{13} GeV.

Lighter strings produce excess cosmic rays, conflicting with observations.

Heavier strings (~10^{15} GeV) are constrained by gravitational signatures.

Abstract

We re-visit the production of cosmic rays by cusps on cosmic strings. If a scalar field (``Higgs'') has a linear interaction with the string world-sheet, such as would occur if there is a bosonic condensate on the string, cusps on string loops emit narrow beams of very high energy Higgses which then decay to give a flux of ultra high energy cosmic rays. The ultra-high energy flux and the gamma to proton ratio agree with observations if the string scale is $\sim 10^{13}$ GeV. The diffuse gamma ray and proton fluxes are well below current bounds. Strings that are {\it lighter} and have linear interactions with scalars produce an excess of direct and diffuse cosmic rays and are ruled out by observations, while heavier strings ($\sim 10^{15}$ GeV) are constrained by their gravitational signatures. This leaves a narrow window of parameter space for the existence of cosmic strings with bosonic condensates.