Parity nonconservation induced by spacetime geometry

TL;DR

This paper explores how spacetime geometry can induce parity nonconservation through a new fermion interaction, providing experimental bounds and suggesting the potential for observable effects beyond the Standard Model.

Contribution

It introduces a novel geometrical interaction involving fermions and spacetime torsion, with calculable effects on parity violation and experimental bounds on its coupling constants.

Findings

The interaction can produce measurable parity nonconservation effects.

Coupling constants are constrained to be within an order of magnitude of weak interactions.

The effect persists even in flat spacetime, independent of curvature.

Abstract

The interaction of fermion spin with spacetime can be non-universal, leading to a new interaction beyond the Standard Model, independent of gravitation. Fermions generate spacetime torsion, which can be integrated out in favor of a four-fermion interaction in a torsion-free background. This is a current-current interaction which involves all fermions and generically has different coupling constants for different chiralities and species of fermions. It does not vanish when curvature goes to zero, so accelerator experiments should be able to see its effect. We calculate the contribution of this geometrical interaction to parity nonconservation in $e^-e^-$ and $e^-D$ scattering and compare with known observations. This provides an estimate of an upper bound on the coupling constants, suggesting that the strength of the ``new physics'' can be as large as only one order of magnitude smaller than that of weak interactions.