Constraints on Loryons in a Two Higgs Doublet Model

TL;DR

This work investigates scalar Loryons—BSM states whose masses receive a substantial fraction from electroweak symmetry breaking—within a custodially symmetric two-Higgs-doublet model. By examining unitarity bounds, the HEFT SMEFT regime, electroweak precision tests, and Higgs decay observables across selected representations ([1,1]_0, [1,1]_1, [1,3]_0/[3,1]_0, and [2,2]_0), the authors map the viable parameter space under a benchmark 2HDM spectrum near alignment. They find neutral singlets can remain viable up to around 700 GeV for moderate mass-fraction f_φ, while representations with charged states are heavily constrained, especially as f_φ increases, largely due to h→γγ constraints. The analysis highlights how non-decoupling scalar sectors in extended Higgs frameworks tightly restring Loryon viability, suggesting future precision Higgs measurements and direct searches could decisively test these scenarios.

Abstract

We consider Loryons, particles beyond the Standard Model that receive a significant fraction of their masses from electroweak symmetry breaking, in the context of a two Higgs doublet model. Using scalar Loryons in the the $[1,1]$, $[1,3]$ (as well as the equivalent $[3,1]$) and the $[2,2]$ representations of the custodial $SU(2)_L \times SU(2)_R$ global symmetry as benchmarks, we study the constraints on the Loryon parameter space, focusing on unitarity, Higgs decay observables, and the absence of Loryon vacuum expectation values. We find that while neutral singlet Loryons remain viable for masses up to 700 GeV, representations containing charged scalars are severely constrained by LHC data, particularly as the fraction of mass generated by symmetry breaking increases.

Figures (8)

• Figure 1: The values of the three eigenvalues of the $[a_0]$ matrix as a function of to the center-of-frame energy $\sqrt s$, shown for $f_\phi = 1$ and Loryon mass $m_V = 425~\text{GeV}$.
• Figure 2: The dominant one-loop vacuum polarization diagram contributing to the oblique parameter $S$. The external neutral gauge bosons, $W^3$ and $B$, mix via a loop of scalar Loryon mass eigenstates $\varphi_i$ and $\varphi_j$.
• Figure 3: The allowed parameter space for the $[1,1]_X$ Loryon, taking into account constraints from perturbative unitarity and Higgs decay measurements, for fixed fraction $f_\phi=0.5$ and different values of $(\cos(\beta-\alpha),\tan\beta)$ as indicated at the bottom of each panel. The part of the parameter space outside the colored region is ruled out by unitarity bounds and the dark-shaded region is ruled out by the $\kappa_\gamma$ bound. The white region is unphysical as ($m_\phi^2 < 0$) there. Inside the allowed region, the color gradient from blue to red represents the physical mass of the Loryon.
• Figure 4: Similar to Figure \ref{['fig:LR11Yf05']}, but with the mass fraction fixed to $f_{\phi}=0.6$.
• Figure 5: Constraints for the $[2,2]_0$ Loryon representation in the alignment limit ($\cos(\beta-\alpha)=0$) with $\tan\beta=1$ and fixed mass fractions $f_{0}=f_{1}=0.5$. The left panel varies the singlet couplings $(C_{+}^{0},C_{-}^{0})$ with fixed triplet couplings $(C_{+}^{1},C_{-}^{1})=(5,5)$; as the singlet is neutral, the excluded regions are determined solely by perturbative unitarity (gray) and mass positivity (white, where $m^2 < 0$). The right panel varies the triplet couplings $(C_{+}^{1},C_{-}^{1})$ with fixed singlet couplings $(C_{+}^{0},C_{-}^{0})=(5,5)$; here, the black region indicates additional parameter space excluded by Higgs diphoton decays ($\kappa_\gamma$) due to the charged components of the triplet. The color gradient from blue to red represents the physical Loryon mass within the allowed region.