On long-lived electroweak-singlet coloured scalars

TL;DR

This paper explores long-lived electroweak singlet scalars charged under colour SU(3) near a TeV mass, analyzing their decay channels, stability, and potential bound states relevant for LHC searches.

Contribution

It identifies which colour representations of these scalars can decay or remain stable, highlighting the unique properties of octets and decuplets in forming bound states.

Findings

Only octet scalars can decay into multi-jet final states.

Other representations form stable, fractionally charged colour singlets.

Decuplets can form electrically neutral bound states.

Abstract

There has been much recent interest in long-lived massive particles at the LHC, understood as those with lifetimes between tens of micrometers and several meters. In this context we consider the possibility of long-lived electroweak singlet scalars charged under colour $\mathrm{SU}(3)$ with masses near a TeV. The shortest lifetime of interest is already longer than typical hadronisation scales. These exotic new particles would therefore appear as colour singlet bound states of the new scalars with quarks and gluons and it is their colour charge that prevents them from decaying. In particular we consider colour representations consistent with maintaining asymptotic freedom, those with dimensionality $d_R \leq 15$. We find that only the octets can decay, and they do so into multi-jet final states through the two-gluon channel. The other representations are stable and form fractionally charged colour singlets, with the decuplet being the only one that can form electrically neutral colour singlets.