Left-Right Symmetry at LHC

TL;DR

This paper reevaluates the constraints on Left-Right symmetry breaking scale in a minimal gauge theory, analyzing different symmetry definitions and their implications for collider phenomenology and CP violation.

Contribution

It provides a comprehensive numerical analysis of quark mixing matrices without common assumptions, and compares the bounds on right-handed gauge boson masses for parity and charge conjugation symmetries.

Findings

Lower bound on M_WR can be slightly reduced when defining symmetry as parity.

Charge conjugation symmetry yields more robust bounds on M_WR.

Both gauge bosons could be detectable at the LHC with distinctive lepton number violating signals.

Abstract

We revisit the issue of the limit on the scale of Left-Right symmetry breaking. We focus on the minimal SU(2)_L x SU(2)_R x U(1)_B-L gauge theory with the seesaw mechanism and discuss the two possibilities of defining Left-Right symmetry as parity or charge conjugation. In the commonly adopted case of parity, we perform a complete numerical study of the quark mass matrices and the associated left and right mixing matrices without any assumptions usually made in the literature about the ratio of vacuum expectation values. We find that the usual lower limit on the mass of the right-handed gauge boson from the K mass difference, M_WR>2.5TeV, is subject to a possible small reduction due to the difference between right and left Cabibbo angles. In the case of charge conjugation the limit on M_WR is somewhat more robust. However, the more severe bounds from CP-violating observables are absent in this case. In fact, the free phases can also resolve the present mild discrepancy between the Standard Model and CP-violation in the $B$-sector. Thus, even in the minimal case, both charged and neutral gauge bosons may be accessible at the Large Hadron Collider with spectacular signatures of lepton number violation.