The price for monopole dark matter

by Giacomo Ferrante (Université Libre de Bruxelles)

Thursday Dec 3, 2026, 12:00 PM → 2:00 PM Europe/Madrid

C7b/058 - Seminar (IFAE Main Building C7b)

 

The magnetic monopole of a dark sector represents a compelling dark matter candidate, as its stability naturally follows from the non-trivial topology of the vacuum. I will explain how the abundance of ’t Hooft-Polyakov monopoles is computed for second-order and first-order thermal phase transitions, identifying the regions of parameter space where their relic density matches that of dark matter. However, a dark sector featuring monopoles necessarily contains stable, electrically charged massive gauge bosons. I will show that their abundance always greatly exceeds the monopole one, regardless of the nature of the phase transition, thus concluding that dark monopoles cannot constitute a sizeable fraction of dark matter in the minimal model. I will then present an extension of the model, featuring a light dark fermion, which lets the gauge bosons decay. This opens up a window where dark matter is composed of monopoles with masses of about 10^8 GeV or larger. The price to pay is dark radiation: the model predicts a sizeable ΔN_eff close to present-day bounds and within the reach of upcoming CMB experiments.