Long-Lived, Colour-Triplet Scalars from Unnaturalness

TL;DR

This paper investigates long-lived colour-triplet scalars predicted by unnatural composite Higgs models, analyzing their collider signatures, current experimental bounds, and future discovery prospects at hadron colliders.

Contribution

It provides the first detailed collider phenomenology study of colour-triplet scalars in split composite Higgs models, including current limits and future discovery potential.

Findings

Existing LHC searches exclude triplet masses below 845 GeV.

Future 13 TeV LHC runs can discover triplet scalars up to 1.4 TeV.

Displaced-vertex searches can reach up to 1.8 TeV.

Abstract

Long-lived, colour-triplet scalars are a generic prediction of unnatural, or split, composite Higgs models where the spontaneous global-symmetry breaking scale $f \gtrsim 10$ TeV and an unbroken $SU(5)$ symmetry is preserved. Since the triplet scalars are pseudo Nambu-Goldstone bosons they are split from the much heavier composite-sector resonances and are the lightest exotic, coloured states. This makes them ideal to search for at colliders. Due to discrete symmetries the triplet scalar decays via a dimension-six term and given the large suppression scale $f$ is often metastable. We show that existing searches for collider-stable R-hadrons from Run-I at the LHC forbid a triplet scalar mass below 845 GeV, whereas with $300\,\mathrm{fb}^{-1}$ at 13 TeV triplet scalar masses up to 1.4 TeV can be discovered. For shorter lifetimes displaced-vertex searches provide a discovery reach of up to 1.8 TeV. In addition we present exclusion and discovery reaches of future hadron colliders as well as indirect limits that arise from modifications of the Higgs couplings.