Higgs Yukawa coupling constraints on a benchmark one-loop radiative mass model for the bottom, charm and tau

TL;DR

Addresses how Higgs Yukawa coupling measurements constrain radiative fermion mass models. Constructs a benchmark where $m_t$ is generated at tree level while $m_b$, $m_c$, $m_ au$, and $m_{ u_ au}$ arise at one loop, suppressed by $1/(16\pi^2)$, with a viable dark matter candidate in the spectrum. Derives the one-loop effective Yukawas $y_f^{\text{eff}}$ and analyzes current and projected constraints from Higgs decays, electroweak precision tests, and rare top decays, showing viable parameter space but that future data will push the new-physics scale higher. Demonstrates a dark matter candidate compatible with the observed relic density and discusses extensions to all three SM generations as well as axion possibilities.

Abstract

Measurements of Higgs boson Yukawa couplings to Standard Model (SM) fermions constrain radiative mass models for those species. Such models, motivated by the observed fermion mass hierarchy, act as foils for the SM tree-level mechanism: we cannot claim to have verified the standard mechanism if other possibilities also fit the data well. We construct a benchmark model which generates the top mass at tree level, and the bottom, charm, tau, and tau Dirac neutrino masses at one-loop level. Current theoretical and experimental constraints on the model, including from Higgs decays, demonstrate it possesses viable regions of parameter space. We show that future improvements to measurements will not be able to rule out the model, only increase the scale of new physics required, illustrating how difficult it will be to verify the SM fermion mass generation mechanism with great precision. As a bonus, a dark matter candidate is shown to be capable of reproducing the correct relic density within the permitted parameter space.

Figures (4)

• Figure 1: Mass generation (left) and effective Yukawa coupling (right) diagrams for $f=\tau,\nu_\tau,b,c$ at one loop after EWSB. For $\tau$ and $\nu_\tau$ the virtual fermion $\alpha$ is $\psi$, while $\alpha = \chi$ for $b$ and $c$.
• Figure 2: Theoretical and current $2\sigma$ experimental constraints on the model for two benchmark slices of parameter space. Shaded regions are excluded, except for the case of $\Delta > 100$ where they are disfavoured.
• Figure 3: Projected $2\sigma$ experimental sensitivities when $m_\phi^2 = m_\eta^2$ and $m_\psi^2 = m_\chi^2 = m_2^2$. Plots shown are the sensitivities for $T$ (top left), $\mu_\tau$ (top right), $\mu_b$ (bottom left), and $\mu_c$ (bottom right). Values for $\Delta T$ taken from STfuture and for $\Delta\kappa_\tau, \Delta\kappa_b, \Delta\kappa_c$ from collider_future. Shaded regions correspond to the same constraints as in Figure \ref{['fig:constraints']}.
• Figure 4: Exclusion plot with $\psi^{up}$ as a dark matter candidate. Blue dots are points for which the observed relic density is reproduced, given a set value for $m_\psi$.