Interpreting the current Higgs excesses at the LHC in the 2HD+a framework

Abstract

There are several excesses of events in current LHC data, yet not exceeding the level of significance which would make them to be considered as firm. They point to the possibility of the presence of a new Higgs particle in the spectrum, in addition to the already observed 125 GeV state. In particular, there are excesses involving a diphoton resonance at invariant masses of about 95 GeV, 152 GeV and 650 GeV and an extra scalar might accompany the recent observation of a toponium at a mass of about 350 GeV. Several interpretations of these excesses have been attempted in extensions of the Standard Model. In this paper, we aim to explain them in the framework of a two Higgs doublet model supplemented by a relatively light pseudoscalar Higgs boson $a$ which would correspond to the putative resonance in most cases. This realistic 2HD+a scenario is attractive as it is has the virtue to pass all experimental constraints from high-precision experiments and collider searches and, at the same time, to allow for a viable explanation of the dark matter in the universe. We first update the present constraints on the model, in particular taking into account the latest results on dark matter and Higgs searches, as well the high-precision measurements, including those from Higgs and flavor physics. We then show that the additional Higgs states with the proper mass spectrum and adjusted couplings to fermions, would explain all the LHC excesses (but individually) while passing the former experimental constraints as well as the theoretical ones.

Figures (9)

• Figure 1: Production cross section of a 95 GeV pseudoscalar resonance (interpreted as the lightest $a$ state in the 2HD+a model) decaying into $\gamma \gamma$ as a function of $\sin\theta$. The scatter plot has been obtained by performing a parameter scan when accounting for theoretical constraints and experimental constraints from precision Higgs and electroweak measurements as well as flavor physics. The four different panels correspond, as reported on their top, to the Type-I, Type-II, Type-X and Type-Y. The color pattern of the model points follow corresponding values of $\tan\beta$.
• Figure 2: Model points in the $[\sin\theta,\tan\beta]$ plane obtained from the parameter scan of eq. (\ref{['eq:scan95']}) complying with the general constraints and having $M_a=95\,\hbox{GeV}$. The orange band corresponds to the region compatible with the experimental hint of a 95 GeV resonance decaying into $\gamma \gamma$.
• Figure 3: Values of the $pp\to A \to ah \to \bar{b} b \gamma \gamma$ (left) and $pp\to H \to Za \to \bar{b} b \gamma \gamma$ production cross sections as a function of $\sin\theta$ for $M_a=125\,\hbox{GeV}$ in the Type-I scenario; the color code follows the value of $\tan\beta$. The two panels correspond to the fixed values $M_A=300\,\hbox{GeV}$ (left) and $M_H=300\,\hbox{GeV}$ (right).
• Figure 4: Model points complying with DM constraints in the $[m_\chi, y_\chi]$ plane in the scenario $M_a=152\,\hbox{GeV}$. The two panels refer to two distinct scans with fixed values $M_A=300\,\hbox{GeV}$ (left) and $M_H=300\,\hbox{GeV}$ (right). In both cases, the Type-I scenario has been considered.
• Figure 5: Production cross section of a 365 GeV resonance, interpreted as the light pseudoscalar $a$ of the 2HD+a model, decaying into top pairs, as function of $\sin\theta$. The points of the scatter plot corresponds to parameter assignments of the model complying with theoretical and experimental constraints; the color pattern follows the value of $\tan\beta$. The different panels correspond the four types of Yukawa configurations reported on top of each plot.