Simple and Realistic Composite Higgs Models in Flat Extra Dimensions

TL;DR

The authors construct three flat-space gauge-Higgs unification/composite-Higgs models with large boundary kinetic terms to reconcile electroweak symmetry breaking with precision constraints. They demonstrate that flat extra dimensions can replicate the phenomenology of warped GHU models, producing a light Higgs and TeV-scale fermion resonances while simplifying model-building and parameter counts. The FBKT$_{10}$, FBKT$_{5}$, and MCHM$_{5}$ realizations, analyzed via holographic methods, show viable regions with $s_\alpha$ in the range $\sim$0.2–0.3 and Higgs masses up to about a few hundred GeV, with distinctive fermionic spectra and moderate tuning. Overall, the work predicts accessible new fermionic states and potential deviations in Higgs and top couplings, guiding future collider searches for composite-Higgs/GHU scenarios in flat space.

Abstract

We construct new composite Higgs/gauge-Higgs unification (GHU) models in flat space that overcome all the difficulties found in the past in attempting to construct models of this sort. The key ingredient is the introduction of large boundary kinetic terms for gauge (and fermion) fields. We focus our analysis on the electroweak symmetry breaking pattern and the electroweak precision tests and show how both are compatible with each other. Our models can be seen as effective TeV descriptions of analogue warped models. We point out that, as far as electroweak TeV scale physics is concerned, one can rely on simple and more flexible flat space models rather than considering their unavoidably more complicated warped space counterparts. The generic collider signatures of our models are essentially undistinguishable from those expected from composite Higgs/warped GHU models, namely a light Higgs, colored fermion resonances below the TeV scale and sizable deviations to the Higgs and top coupling.

Figures (9)

• Figure 1: Scatter plot of points obtained from a scan over the parameter space of the FBKT$_{10}$ model. Small red dots represent points which don't pass EWPT at $99\%$C.L., square blue dots represent points which pass EWPT at $99\%$C.L. but not at $90\%$ C.L., and star shape green dots represent points which pass EWPT at $90\%$C.L.. The region below the LEP bound ($m_H < 114\ {\rm GeV}$) is shaded.
• Figure 2: Higgs mass $m_H$ versus the mass of the first KK resonances (before EWSB) for the points of the FBKT$_{10}$ model with $m_H>114\ {\rm GeV}$ and $\alpha\in[0.16,0.23]$ .
• Figure 3: Scatter plot of points in the FBKT$_{10}$ model with $m_H > 114\ {\rm GeV}$ and projected on the $T_{NP}$-$S_{NP}$ plane. We have set $M_{H,eff} = 120\ {\rm GeV}$. Small red dots represent points which don't pass EWPT at $99\%$ C.L., square blue dots represent points which pass EWPT at $99\%$C.L. but not at $90\%$ C.L., and star shape green dots represent points which pass EWPT at $90\%$ C.L.. The big and small ellipses correspond to $99\%$ and $90\%$ C.L. respectively.
• Figure 4: Scatter plot of points obtained from a scan over the parameter space of the FBKT$_5$ model. Small red dots represent points which don't pass EWPT at $99\%$C.L., square blue dots represent points which pass EWPT at $99\%$C.L. but not at $90\%$C.L., and star shape green dots represent points which pass EWPT at $90\%$C.L.. The region below the LEP bound ($m_H < 114\ {\rm GeV}$) is shaded.
• Figure 5: Higgs mass $m_H$ versus the mass of the first KK resonances (before EWSB) for the points of the FBKT$_{5}$ model with $m_H>114\ {\rm GeV}$ and $\alpha\in[0.16,0.22]$.