Mass-degenerate Higgs bosons at 125 GeV in the Two-Higgs-Doublet Model

TL;DR

This paper explores the possibility that two nearly mass-degenerate Higgs bosons in the Two-Higgs-Doublet Model could explain observed excesses in gamma gamma events and the lack of significant ZZ* excess, suggesting a complex Higgs sector.

Contribution

It demonstrates how a pair of nearly degenerate Higgs bosons in the Two-Higgs-Doublet Model can account for current Higgs data anomalies and predicts observable differences in invariant mass peaks.

Findings

Degenerate Higgs bosons can explain gamma gamma excesses.

Different invariant mass peaks expected in ZZ* and gamma gamma channels.

Parameter space with specific nd eta values fits the data.

Abstract

The analysis of the Higgs boson data by the ATLAS and CMS Collaborations appears to exhibit an excess of h --> gamma\gamma events above the Standard Model (SM) expectations; whereas no significant excess is observed in h --> ZZ* --> {four lepton} events, albeit with large statistical uncertainty due to the small data sample. These results (assuming they persist with further data) could be explained by a pair of nearly mass-degenerate scalars, one of which is a SM-like Higgs boson and the other is a scalar with suppressed couplings to W+W- and ZZ. In the two Higgs doublet model, the observed \gamma\gamma and ZZ* --> {four lepton} data can be reproduced by an approximately degenerate CP-even (h) and CP-odd (A) Higgs boson for values of \sin(\beta-\alpha) near unity and 0.7 < \tan\beta < 1. An enhanced \gamma\gamma signal can also arise in cases where m_h ~ m_H, m_H ~ m_A, or m_h ~ m_H ~ m_A. Since the ZZ* --> {four lepton} signal derives primarily from a SM-like Higgs boson whereas the \gamma\gamma signal receives contributions from two (or more) nearly mass-degenerate states, one would expect a slightly different invariant mass peak in the ZZ* --> {four lepton} and \gamma\gamma channels. The phenomenological consequences of such models can be tested with additional Higgs data that will be collected at the LHC in the near future.