Abstract
Parity solutions to the strong CP problem are a compelling alternative to approaches based on Peccei-Quinn symmetry, particularly given the expected violation of global symmetries in a theory of quantum gravity. The most natural of these solutions break parity at a low scale, giving rise to a host of experimentally accessible signals. We assess the status of the simplest parity-based solution in light of LHC data and flavor constraints, highlighting the prospects for near-future tests at colliders, tabletop experiments, and gravitational wave observatories. The origin of parity breaking and associated gravitational effects play crucial roles, providing new avenues for discovery through EDMs and gravity waves. These experimental opportunities underline the promise of generalized parity, rather than Peccei-Quinn symmetry, as a robust and testable solution to the strong CP problem.
Highlights
Where θq is the argument of the determinant of the quark mass matrix, and θs the coefficient of the GGoperator
The single most pressing issue for phenomenology is to establish a lower bound on the amount of global symmetry violation that must be present in the IR
In the remainder of this section we study the effect of Planck-suppressed higher dimensional operators (HDOs) on parity solutions to the strong CP problem
Summary
We introduce the main features of symmetry-based solutions to the strong CP problem based on parity. In 2.1 we review the basic idea, as first introduced in [4,5,6]. We focus on the scalar potential in 2.2, with an emphasis on the implications for fine-tuning of the weak scale that arise as a result of the breaking of parity. In 2.3 we discuss how the scale of additional colored particles can be decoupled from the parity-breaking scale, in turn minimizing the level of fine-tuning
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