Phenomenological Implications of Very Special Relativity

TL;DR

This paper explores the phenomenological consequences of Very Special Relativity (VSR), a Lorentz-violating theory with a preferred space-time direction, analyzing its effects on particle masses, experiments, and decay processes to establish potential tests and limits.

Contribution

It provides a detailed analysis of VSR's implications on fundamental fermion masses, experimental signals, and decay angular distributions, proposing new methods to test VSR effects.

Findings

VSR predicts unique signals in torsion pendulum and clock experiments.

Decay product angular distributions are affected by VSR, showing sidereal time dependence.

Limits on VSR parameters can be derived from experimental data if no signals are observed.

Abstract

We discuss several phenomenological implications of Very Special Relativity (VSR). It is assumed that there is a small violation of Lorentz invariance and the true symmetry group of nature is a subgroup called SIM(2). This symmetry group postulates the existence of a fundamental or preferred direction in space-time. We study its implications by using an effective action which violates Lorentz invariance but respects VSR. We find that the problem of finding the masses of fundamental fermions is in general intractable in the presence of VSR term. The problem can be solved only in special cases which we pursue in this paper. We next determine the signal of VSR in torsion pendulum experiment as well as clock comparison experiment. We find that VSR predicts a signal which is different from other Lorentz violating theories and hence a dedicated data analysis is needed in order to impose reliable limits. Assuming that signal is absent in data we determine the limits that can be imposed on the VSR parameters. We also study the implications of VSR in particle decay experiments taking the charged pion and kaon decay as an example. The effective interaction between the charged pion and the final state leptons is related to the fundamental VSR mass terms through a loop calculation. We also predict a shift in the angular dependence of the decay products due to VSR. In particular we find that these no longer display azimuthal symmetry with respect to the momentum of the pion. Furthermore the azimuthal and polar angle distributions show time dependence with a period of a sidereal day. This time dependence provides us with a novel method to test VSR in future experiments.