Bounds on Gauge Bosons Coupled to Non-conserved Currents

TL;DR

This paper establishes new experimental bounds on gauge bosons coupled to non-conserved currents, highlighting the exponential growth of emission rates in certain theories and deriving constraints from LHC data that surpass cosmological limits.

Contribution

It introduces novel bounds on Stueckelberg gauge bosons with non-conserved currents, emphasizing the exponential growth of emission rates and providing the strongest collider constraints for low masses.

Findings

LHC mono-lepton + missing energy bounds surpass cosmological limits for sub-keV masses.

Exponential growth of emission rates occurs in Stueckelberg theories due to longitudinal gauge boson emission.

Perturbativity constraints at the LHC provide additional, though more uncertain, bounds.

Abstract

We discuss new bounds on vectors coupled to currents whose non-conservation is due to mass terms, such as $U(1)_{L_\mu - L_\tau}$. Due to the emission of many final state longitudinally polarized gauge bosons, inclusive rates grow exponentially fast in energy, leading to constraints that are only logarithmically dependent on the symmetry breaking mass term. This exponential growth is unique to Stueckelberg theories and reverts back to polynomial growth at energies above the mass of the radial mode. We present bounds coming from the high transverse mass tail of mono-lepton+missing transverse energy events at the LHC, which beat out cosmological bounds to place the strongest limit on Stueckelberg $U(1)_{L_\mu - L_\tau}$ models for most masses below a keV. We also discuss a stronger, but much more uncertain, bound coming from the validity of perturbation theory at the LHC.