Magnetic Monopoles in Cosmic Magnetic Fields: Acceleration and Constraints

Magnetic monopoles are intriguing hypothetical particles and inevitable pre- dictions of theories of Grand Unification. They should be produced during phase transitions in the early universe, but also mechanisms like the Schwinger eect in strong magnetic fields could contribute to the monopole number density. In this thesis, we demonstrate the importance of the studies on the physics of magnetic monopoles in cosmic environments. In particular, we show how understanding the interplay between the monopoles and cosmic magnetic fields is crucial for the search of monopoles of astrophysical origin. We provide a comprehensive analysis of the acceleration of magnetic monopoles in intergalactic magnetic fields and galactic magnetic fields. We demonstrate that monopoles with intermediate to low masses can be accelerated to relativistic velocities. This can significantly aect direct and indirect searches for magnetic monopoles. Concerning indirect searches, we show that the Parker bounds on the survival of galactic magnetic fields are modified in the presence of intergalactic fields. We also find that a cosmic population of monopoles can produce significant backreaction on the intergalactic fields. In the case of direct searches, experimental constraints on the monopole flux are often expressed in terms of the monopole velocity. From the study of the monopole acceleration, we obtain a speed-mass-abundance relation for the monopoles that might be detected by the terrestrial detectors. With this relation, we revisit for the first time the current bounds on the monopole flux from terrestrial experiments in terms of the monopole mass, providing a recipe for future works. We also show that by improving their constraints such experiments will soon be sensible to values of the monopole flux where the monopole velocity is influenced by the physics of magnetic fields in intergalactic voids. We also present a comprehensive study of Parker-type bounds on magnetic monopoles with arbitrarily magnetic charges, including minicharged monopoles and magnetic black holes. In particular, we provide new bounds on the cosmic abundance of magnetic monopoles based on the survival of primordial magnetic fields during the reheating and radiation-dominated epochs. The new bounds can be stronger than the conventional Parker bound from galactic magnetic fields, as well as bounds from direct searches. We find that monopoles with dierent magnetic charges are best constrained by dierent astrophysical systems: while monopoles with a Dirac charge are tightly constrained by seed galactic magnetic fields, minicharged monopoles are strongly constrained by primordial magnetic fields, and magnetic black holes by the density of dark matter. We also assess the viability of the various types of monopoles as dark matter, by studying whether they can cluster with galaxies hosting magnetic fields. Finally, we apply our primordial bounds to monopoles produced by the primordial magnetic fields themselves through the Schwinger effect and derive additional conditions for the survival of the primordial fields.