Composite GUTs: models and expectations at the LHC

TL;DR

This work shows that a four-dimensional composite-Higgs framework with a simple global symmetry containing the SM gauge group can realize precision gauge coupling unification at leading order once the right-handed top is fully composite. Using an SO(11)/SO(10) coset, the authors derive a minimal, anomaly-free spectrum that includes a light coloured triplet $T$ and vector-like fermions, while maintaining custodial symmetry and a controlled electroweak-like potential for EWSB with $\xi\equiv v^2/f^2\sim 0.1$. They analyze two explicit realizations for the top partners, examine EWPT constraints, and compute the NGB effective potential to classify viable parameter regions, predicting TeV-scale exotics accessible at the LHC. The collider phenomenology features distinctive final states with multiple top/bottom quarks and possible stable or long-lived states, offering concrete signatures to test the composite GUT scenario and its unification mechanism. Overall, the paper presents a self-consistent, highly predictive alternative to supersymmetric GUTs, linking GUT-scale unification to TeV-scale composite dynamics with tangible experimental consequences.

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.

Figures (9)

• Figure 1: Diagrammatic representation of the leading-order contribution from the strong sector to the SM gauge coupling running, parametrized in Eq. (\ref{['strongrun']}).
• Figure 2: Example of sub-leading diagrams contributing to the differential running of the SM gauge couplings, on the left with a loop of elementary gauge bosons, and on the right with a loop of elementary fermions.
• Figure 3: The bounds on $\sqrt{\xi}\equiv v/f$ coming from the EWPTs in case (1), as a function of the ratio $\lambda_{b'}/g_\rho$. The solid (dashed) lines correspond to $g_\rho=8$ (4), while the left (right) panel corresponds to a physical Higgs mass $m_h=117$ GeV ($300$ GeV). The green horizontal lines give the 95% C.L. upper bound from the $\widehat{S}$ parameter, the region between the two orange curved lines corresponds to the 95% C.L. allowed range for the $\widehat{T}$ parameter, and finally the blue straight rising lines represent the $2\sigma$ upper bound from $\delta g_{b_L}$.
• Figure 4: The bounds on $\sqrt{\xi}\equiv v/f$ coming from the EWPTs in case (2), as a function of the coupling difference $\delta\lambda_l/g_\rho\equiv |\lambda_{l^c}-\lambda_{l'}|/g_\rho$. The solid (dashed) lines correspond to $g_\rho=8$ (4), while the left (right) panel corresponds to a physical Higgs mass $m_h=117$ GeV ($300$ GeV). The green horizontal lines give the 95% C.L. upper bound from the $\widehat{S}$ parameter, while the two orange curved lines correspond to the 95% C.L. lower and upper values of the $\widehat{T}$ parameter (the allowed region lies between the two lines). There is no relevant constraint from $\delta g_{b_L}$ in this case.
• Figure 5: Leading order contribution in the number of gauge spurions and loops to the effective potential for the NGBs.