Electroweak spin-1 resonances in Composite Higgs models

TL;DR

This work analyzes electroweak spin-1 resonances predicted by Composite Higgs models with custodial symmetry, focusing on three symmetric cosets that yield two neutral and one charged resonances capable of mixing with SM vector bosons. By employing a hidden local symmetry framework and CCWZ construction, the authors map the parameter space to physically meaningful quantities, study four benchmark coupling scenarios, and compute decay and production patterns including decays into pNGBs and HV/WW channels. They confront the model with LHC data using full recasts and UFO-based simulations, deriving 95% CL exclusions in the mass–coupling plane. The key finding is that, despite stringent DY constraints, masses as low as around $1.5$ TeV remain viable in scenarios with sizable decays to pNGBs and strong vector–pNGB couplings, highlighting rich collider phenomenology and guiding future searches for these resonances.

Abstract

Composite Higgs models predict the existence of various bound states. Among these are spin-1 resonances. We investigate models containing $\text{SU(2)}_L\times \text{SU(2)}_R$ as part of the unbroken subgroup in the new strong sector. These models predict that there are two neutral and one charged spin-1 resonances mixing sizably with the SM vector bosons. As a consequence, these can be singly produced in Drell-Yan processes at the LHC. We explore their rich LHC phenomenology and show that there are still viable scenarios consistent with existing LHC data where the masses of these states can be as low as about 1.5 TeV.

Figures (19)

• Figure 1: Contour lines for the masses of $V^+_{1\mu}$, $V^0_{1\mu}$ and $V^0_{2\mu}$ in the $M_V$-$\Tilde{g}$ plane, where $M_V$ is given by \ref{['eq:mass-parameter']}. The results look nearly identical for each coset $\mathrm{SU}(4)/\mathrm{Sp}(4)$, $\mathrm{SU}(5)/\mathrm{SO}(5)$ and $\mathrm{SU}(4)\times \mathrm{SU}(4)/\mathrm{SU}(4)$.
• Figure 2: Partial decay widths of selected spin-1 resonances for the $\mathrm{SU}(5) / \mathrm{SO}(5)$ coset. The solid lines of the pNGB, $W^+ W^-$, $HZ$, $W^+Z$ and $H W^+$ channels correspond to a scenario with $g_{V\pi\pi}=4$, while the corresponding dashed lines correspond to $g_{V\pi\pi}=0$. For the top quark channels, the solid lines correspond to $g_t = 1$ and the dashed lines to SM-like couplings. We have set $M_V=3000$ GeV and $M_\pi=700$ GeV. These also represent the partial widths for the $\mathrm{SU}(4)/\mathrm{Sp}(4)$ coset for which the black lines (additional pNGB channels) are absent.
• Figure 3: Partial decay widths of selected spin-1 resonances for the $\mathrm{SU}(4) \times \mathrm{SU}(4)/\mathrm{SU}(4)$ coset. The solid lines of the pNGB, $W^+ W^-$, $HZ$, $W^+Z$ and $H W^+$ channels correspond to a scenario with $g_{V\pi\pi}=4$, while the dashed lines correspond to $g_{V\pi\pi}=0$. For the top quark channels, the solid lines correspond to $g_t = 1$ and the dashed lines to SM-like couplings. We have set $M_V=3000$ GeV and $M_\pi=450$ GeV.
• Figure 4: Drell-Yan production of heavy vectors. The left panel shows typical Feynman diagrams. The right panel shows the production cross sections at $\sqrt s = 13$ TeV of the heavy vector states in the $\mathrm{SU}(5)/\mathrm{SO}(5)$ coset in the $M_V$-$\tilde{g}$-plane assuming a small $g_{V\pi\pi}$ coupling and (nearly) SM-like couplings to the top-quarks.
• Figure 5: Bounds on the single production of heavy vectors in the $\mathrm{SU}(5)/\mathrm{SO}(5)$ coset for a pNGB mass of 700 GeV. In the scenarios, "SM $t$" means the couplings of the $\mathcal{V}^0/ \mathcal{V}^\pm$ to $tt/tb$ are equal to the quark couplings to $Z/W^\pm$, whereas for "PC $t$" these couplings are set to 1. For the pNGB, "weak" and "strong $\pi$" refers to couplings $g_{V\pi\pi}=0$ and $g_{V\pi\pi}=4$, respectively. In (a)-(d) the upper limits on the cross sections are taken from direct searches ATLAS:2019erbATLAS:2020lksATLAS:2019lsyATLAS:2023ibb. In (e) we distinguish further between fermiophobic and fermiophilic decay of the pNGBs. The bounds are derived from recasts of ATLAS:2018nud and ATLAS:2021twpATLAS:2021fbtCMS:2019zmdCMS:2017abv, respectively. The bounds in (f) are derived from recasts of CMS:2017moiCMS:2019xjfMrowietz:2020ztqCMS:2019xudConte:2021xttCMS:2019iusATLAS:2020wzfATLAS:2022nrpATLAS:2021jgwCMS:2022ubqATLAS:2019zciATLAS:2019rob. The regions with small $\tilde{g} \lesssim 2$ are not entirely reliable for scenarios with strong $\pi$ since the resonances are no longer narrow.