EXCITED DYONIC STATES OF MONOPOLES AND ASTRONOMICAL BOUNDS ON AN AXION-PHOTON-DARK PHOTON INTERACTION

Abstract

The study of beyond the standard model physics can largely be broken into twocategories: theoretical and phenomenological. In the former, we study theories in depth to better understand their implications while in the latter, we hold models of our physical world to scrutiny against experimental evidence. Both are crucial to understanding physics beyond the standard model. To reflect this dichotomy, this thesis is broken into two acts, one covering theoretic research and the other discussing progress made on the phenomenological front. Chapter 2, comprising the entirety of Act 1 of this thesis, concerns the theory of magnetic monopoles. In the mid-1970’s t’Hooft and Polyakov discovered magnetic monopoles exist as generic solutions in spontaneously broken gauge theories. Since then much progress has been made in understanding these monopoles, most notably by Callan who argued that the fermion vacuum is non-trivial around the core of the magnetic monopole. These non-trivial vacuua can be interpreted as bound states of fermions with fractional fermion number. In this work, we explicitly compute these fermion bound states in an SU (2) gauge theory coupled to Nf fermions. We demonstrate there are two unique ways to grant mass to the fermions in the SU (2) theory which, after symmetry breaking, give the same UEM (1) theory of fermions. Despite this low energy equivalence, we show that the two theories exhibit very different physics at low energy scales around a magnetic monopole. We show that there may exist stable excited dyonic states with differing charges and energies between the two theories. We find the ground states can also differ in energy and charge between the two theories. We demonstrate the monopole can inherit a mass correction and charge distribution that depends on the topological θ angle even if one of the fermions is massless. This effect is present in one of the theories and is completely absent in the other. Finally, we discuss the implications of these effects on the SU (5) GUT monopole. Act two, comprising of chapters 3 and 4, focuses on the phenomoenological side of beyond the standard model physics. In these chapters, we consider two highly motivated beyond the standard model particles, the axion, φ, and the dark photon AD which are coupled to the standard model photon via a coupling φF ̃FD. In some models, this coupling can provide the leading order coupling between our sector and the dark sector containing the axion and dark photon. In chapter 2, we demonstrate the effect this coupling has on the Cosmic Microwave Background (CMB) in the scenario where either the axion or the dark photon constitutes dark matter. Depending on which we choose to be dark matter, we show that this interaction leads to the conversion of the CMB photons into the other dark sector particle, leading to a distortion in the CMB spectrum. We present the details of these unique distortion signatures and the resulting constraints on the φF ̃FD coupling. In particular, we find that for a wide range of masses, the constraints from this effect are stronger than on the more widely studied axion-photon-photon coupling. We also demonstrate that CMB distortions of this type can a exhibit unique, non-thermal frequency profile which could be detected by future experiments. In chapter 3, we consider the astrophysical effects of the φF ̃FD coupling, in particular, its effect on supernova cooling rates. We show that the bound on this interaction due to supernova cooling exhibits two unusual features. If there is a large mass difference between the axion and dark photon, we show both production and scattering become suppressed and the bounds from bulk (volume) emission and trapped (area) emission both weaken exponentially. We show that these bounds do not intersect leading to a larger area of excluded parameter space than may have otherwise been expected. The other unusual feature occurs because the longitudinal modes of light dark photons couple more weakly than their transverse modes. As a consequence, the longitudinal modes can still cause excessive cooling even if the transverse modes are trapped. Thus, the supernova constraints for massive dark photons look like two independent supernova bounds super-imposed on top of each other. We also briefly consider the effect of this interaction on white dwarf cooling and Big Bang Nucleosynthesis.