Effective Operators and Long-Range Forces for Dark Matter

Abstract

As successful as the Standard Model has proven to be, many unknowns cloud our understanding of the Universe; in particular, the nature of as much as 80% of matter remains mysterious, and the search for dark matter (DM) is one of the main areas of research in particle physics. In this thesis, we consider two approaches
to help solve the DM problem. First, we consider axion-like particles and show how the addition of shift symmetry-breaking operators affects the phenomenology of the QCD axion. In particular, we show that potentials resulting from the exchange of a pair of virtual axions acquire a different scaling as we include some higher-order operators. We demonstrate how this result affects the sensitivity of searches for
new long-range forces. Later, we study a shift-symmetry preserving, Z2 invariant dimension-6 interaction term between an axion and the Higgs field. We compare constraints from Higgs-boson and meson decays, bounds from atomic spectroscopy searching for fifth forces, and astrophysical observables. In the other approach, we study the Stodolsky effect, a spin-dependent shift in the energy of a fermion sitting in a bath of neutrinos. We generalise this effect to DM candidates and give expressions for the induced energy shifts, considering all effective operators up to dimension-6. We consider two experimental setups, a torsion balance and a SQUID magnetometer, to place constraints on the parameter space for these candidates.