Next Generation Higgs Bosons: Theory, Constraints and Discovery Prospects at the Large Hadron Collider

TL;DR

The paper investigates the viability and collider phenomenology of next-generation Higgs bosons motivated by string-inspired scenarios. It develops a formalism for multiple Higgs doublets, addressing tree-level FCNC suppression via symmetry-driven couplings and examining both supersymmetric and Standard Model extensions. A key result is that the lightest CP-even Higgs mass can be raised in SUSY 2HGM through inter-doublet mixing, albeit at the cost of perturbativity scales, with the top Yukawa coupling potentially hitting a Landau pole at relatively low energies. The authors analyze experimental/precision constraints (meson mixing, b→sγ, LEP2) and propose a promising LHC discovery channel, pp→Ah→Zh→Zbb bb, yielding a distinctive 4b+2l final state and demonstrating viable prospects for detecting next-generation Higgs sectors. Overall, the work highlights how extra Higgs generations can be consistent with current data and offers concrete strategies for LHC searches that probe high-scale physics themes.

Abstract

Particle physics model building within the context of string theory suggests that further copies of the Higgs boson sector may be expected. Concerns regarding tree-level flavor changing neutral currents are easiest to allay if little or no couplings of next generation Higgs bosons are allowed to Standard Model fermions. We detail the resulting general Higgs potential and mass spectroscopy in both a Standard Model extension and a supersymmetric extension. We present the important experimental constraints from meson-meson mixing, loop-induced $b\to sγ$ decays and LEP2 direct production limits. We investigate the energy range of valid perturbation theory of these ideas. In the supersymmetric context we present a class of examples that marginally aids the fine-tuning problem for parameter space where the lightest Higgs boson mass is greater than the Standard Model limit of 114 GeV. Finally, we study collider physics signatures generic to next generation Higgs bosons, with special emphasis on $Ah\to hhZ\to 4b+2l$ signal events, and describe the capability of discovery at the Large Hadron Collider.

Figures (12)

• Figure 1: Flavor changing neutral current contributions to $B_d^0-\bar{B}_d^0$ mixing from (a) Higgs exchange diagrams in an arbitrary 2HDM (there are also $t$-channel diagrams that we have not shown here), and (b) SM gauge contributions. Note that the SM diagrams are one-loop whereas the competing Higgs exchange is tree-level. Experiment is consistent with SM results, which implies severe constraints on the Higgs flavor-changing neutral current couplings $\xi_{ij}^F\ll 1$.
• Figure 2: Contours of the upper bound on the mass of the lightest Higgs (in $M_Z$ units) in the SUSY 2HGM taking $\cos 2 \beta_2=-1$. We have also shown contours of equal $\Lambda_{SC}$ (in GeV), the energy scale at which the top Yukawa coupling $\lambda_t$ becomes larger than $4\pi$. Details about the calculation of $\Lambda_{SC}$ appear in section \ref{['secRG']}.
• Figure 3: Parameter space for massive and massless photon in a type I 2HDM with potential A.
• Figure 4: Parameter space for the different patterns of EWSB in the type I 2HDM with potential B.
• Figure 5: The solid lines show contours of constant $r$, the fractional deviation of the type I 2HDM value of the $b\rightarrow s\gamma$ width from the SM value. The dashed lines are the boundaries of the region in the $m_{H^+}$-$\tan \omega$ plane excluded by constraints from the $b\rightarrow s\gamma$ branching rate at two standard deviations. As one can see from eq. (\ref{['eq:bsgamma']}) there are two different ways of satisfying the constraint: (1) if $\tan \omega$ is small the type I 2HDM width is close to the SM value, or (2) $\tan^2 \omega$ can be tuned to a higher value so that $\left|\sum_{i=c,t}\lambda_i C_{7i}(m_b) \right|$ in eq. (\ref{['eq:bsgamma']}) is close to the SM value ($C_{7i}\simeq -C_{7i}^{SM}$). Thus there are two disconnected allowed regions in Fig. \ref{['bsgamma']}. The star shows our choice of $m_{H^+}$ and $\tan \omega$ that we use for collider simulations later.