Composite GUTs: models and expectations at the LHC

TL;DR

This paper explores composite grand unified theories where the Higgs boson is a Nambu-Goldstone boson, proposing models that achieve gauge unification and electroweak symmetry breaking with distinctive collider signatures, as alternatives to supersymmetric GUTs.

Contribution

It constructs minimal composite GUT models with a simple global symmetry group, demonstrating gauge unification, electroweak symmetry breaking, and distinctive collider signatures, offering an alternative to supersymmetric GUTs.

Findings

Achieves gauge coupling unification with composite sectors.

Realizes electroweak symmetry breaking with little fine-tuning.

Predicts distinctive collider signatures involving top and bottom quarks.

Abstract

We investigate grand unified theories (GUTs) in scenarios where electroweak (EW) symmetry breaking is triggered by a light composite Higgs, arising as a Nambu-Goldstone boson from a strongly interacting sector. The evolution of the standard model (SM) gauge couplings can be predicted at leading order, if the global symmetry of the composite sector is a simple group G that contains the SM gauge group. It was noticed that, if the right-handed top quark is also composite, precision gauge unification can be achieved. We build minimal consistent models for a composite sector with these properties, thus demonstrating how composite GUTs may represent an alternative to supersymmetric GUTs. Taking into account the new contributions to the EW precision parameters, we compute the Higgs effective potential and prove that it realizes consistently EW symmetry breaking with little fine-tuning. The G group structure and the requirement of proton stability determine the nature of the light composite states accompanying the Higgs and the top quark: a coloured triplet scalar and several vector-like fermions with exotic quantum numbers. We analyse the signatures of these composite partners at hadron colliders: distinctive final states contain multiple top and bottom quarks, either alone or accompanied by a heavy stable charged particle, or by missing transverse energy.