Precision measurements constraints on the number of Higgs doublets

TL;DR

This paper investigates how precision electroweak measurements constrain the number of Higgs doublets in extended Standard Model scenarios, analyzing various mass spectra and identifying conditions under which the number of Higgs doublets is limited.

Contribution

It provides a detailed analysis of the constraints on the number of Higgs doublets from electroweak precision data, considering different mass spectrum configurations and identifying scenarios with no or limited bounds.

Findings

Degenerate heavy Higgses impose no limit on N

Non-degenerate configurations lead to upper bounds on N

Lightest Higgs consistent with 125 GeV observed at LHC

Abstract

We consider an extension of the Standard Model with an arbitrary number $N$ of Higgs doublets (NHDM), and calculate their contribution to the oblique parameters $S$ and $T$. We examine the possible limitations on $N$ from precision measurements of these parameters. In view of the complexity of the general case of NHDM, we analyze several benchmark scenarios for the Higgs mass spectrum, identifying the lightest CP-even Higgs with the Higgs-like particle recently observed at the LHC with the mass of $\sim 125$ GeV. The rest of the Higgses are put above the mass scale of $\sim 600$ GeV, below which the LHC experiments do not detect any Higgs-like signals except for the former famous one. We show that, in a scenario, with all the heavy Higgses degenerate at any scale, there are no limitations on the number $N$ of the Higgs doublets. However, upper limits appear for certain not completely degenerate configurations of the heavy Higgses.