Constraining the Little Higgs model of Schmaltz, Stolarski, and Thaler with recent results from the LHC

Abstract: In this paper, we use the latest Higgs measurements from ATLAS and CMS to constrain the parameter space of the model of Schmaltz, Stolarski and Thaler, a Little Higgs model with two Higgs doublets, which we will refer to as the BLH model. We account for all production and decay modes explored at ATLAS and CMS in two scenarios: a general case, which assumes the $h_0$ state is light ($m_{h_0} \approx 125$ GeV) and the masses of the other neutral scalars ($H_0$ and $A_0$) are allowed to vary, and a case with a near-degeneracy between the masses of the $h_0$ and $A_0$ and, for some choices of parameters, the $H_0$ states. The near-degeneracy scenario can result in an enhanced diphoton rate, as measured by ATLAS, but is largely ruled out by a combination of the $h_0 \rightarrow \tau<sup>+\tau<sup>-$ and the heavy $H_0 \rightarrow W<sup>+W<sup>-$ measurements. In the general case, we find large regions of parameter space that are in better agreement with either the ATLAS or CMS results than is the SM. However, a significantly enhanced diphoton rate is only possible through large contributions to the $h_0 \gamma \gamma$ effective coupling from charged Higgs bosons in a region of parameter space that borders on violation of perturbativity in the scalar sector.