Abstract
Magnetic monopoles may be produced by the Schwinger effect in the strong magnetic fields of peripheral heavy-ion collisions. We review the form of the electromagnetic fields in such collisions and calculate from first principles the cross section for monopole pair production. Using the worldline instanton method, we work to all orders in the magnetic charge, and hence are not hampered by the breakdown of perturbation theory. Our result depends on the spacetime inhomogeneity through a single dimensionless parameter, the Keldysh parameter, which is independent of collision energy for a given monopole mass. For realistic heavy-ion collisions, the computational cost of the calculation becomes prohibitive and the finite size of the monopoles needs to be taken into account, and therefore our current results are not applicable to them. Nonetheless, our results show that the spacetime dependence enhances the production cross section and would therefore lead to stronger monopole mass bounds than in the constant-field case.
Highlights
Magnetic monopoles, hypothetical particles with a single magnetic pole, are present in generic classes of theories beyond the Standard Model, and their existence would explain the quantization of electric charge [1,2,3]
We review the form of the electromagnetic fields in such collisions and calculate from first principles the cross section for monopole pair production
Our results hold for collision and monopole parameters such that the worldline instanton curvature is large compared to the size of the monopole—this removes the possibility of applying our results directly to real heavy-ion collisions at the Large Hadron Collider (LHC)
Summary
Hypothetical particles with a single magnetic pole, are present in generic classes of theories beyond the Standard Model, and their existence would explain the quantization of electric charge [1,2,3]. In heavy-ion collisions, none of these arguments for exponential suppression apply This is because the fundamental process of magnetic monopole pair production does not proceed from a hard initial state with a small number of d.o.f. Instead, pair production proceeds by the quantummechanical decay of a classically occupied electromagnetic field, the Schwinger mechanism [46,47,48,49,50]. A reliable computation of the production cross section for magnetic monopoles in these collisions is of high experimental and theoretical interest If this can be achieved, at particle colliders such as the LHC, it will be possible to confirm or rule out the existence of magnetic monopoles with masses in a certain, computable range.
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