Dark photon dark matter from a network of cosmic strings

We study the production of ultralight dark photons from a network of near-global, Abelian-Higgs cosmic strings. We find that dark photons produced in this way are nonrelativistic today and can make up all of the dark matter for dark photon masses as small as $m_A\sim 10^{-22}\mathrm{eV}$.

Figure 1

The profile functions for a near-global, Abelian-Higgs cosmic string solution with winding number $w=1$ and $m_A^{-1}=100m_{\rho }^{-1}$.

Figure 2

The relic abundance of dark photon dark matter, given by Eq. (24), matches the observed dark matter relic abundance along the red lines labeled “${\mathrm{\Omega }}_A{h}^2\simeq 0.12$” for an interesting region of parameter space where the dark photon’s mass is sub-electron-volts and the scale of symmetry breaking is somewhat below the scale of grand unification. The two red lines serve to quantify the uncertainty in our calculation associated with evolution of the string network.