Advances in High Energy Physics

Volume 2017, Article ID 6139250, 7 pages

https://doi.org/10.1155/2017/6139250

## Sources of Charged Higgs Pair through Double or Triple Higgs Production at Linear Colliders

^{1}National Centre for Particle Physics, University of Malaya, 50603 Kuala Lumpur, Malaysia^{2}COMSATS Institute of Information Technology (CIIT), Islamabad 44000, Pakistan

Correspondence should be addressed to Ijaz Ahmed; moc.liamg@57demhaji

Received 17 September 2016; Accepted 14 December 2016; Published 8 February 2017

Academic Editor: Enrico Lunghi

Copyright © 2017 Ijaz Ahmed. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The publication of this article was funded by SCOAP^{3}.

#### Abstract

The production of triple Higgs , and pairwise charged Higgs boson is studied in the context of future linear colliders within the two-Higgs-doublet model (2HDM) type II. The aim is to compare sources of charged Higgs pair through the above processes, that is, double and triple Higgs production. Cross sections are calculated at the leading order in 2HDM type II and Minimal Supersymmetric Standard Model (MSSM). Several orders of magnitude (10^{4}) enhancement are observed in 2HDM compared to MSSM, while no sizable enhancement is seen in muon collider versus electron-positron collider. The analysis is based on a heavy charged Higgs with mass above 500 GeV. It is found that double charged Higgs production cross section (being the same in 2HDM and MSSM) is few femtobarns, while the triple Higgs production cannot exceed a fraction of femtobarn within the parameter space under study.

#### 1. Introduction

The main undisputed highlight of Run 1 of the Large Hadron Collider (LHC) at CERN [1, 2] is the discovery of the Standard Model (SM) Higgs boson. The measured signal strengths are quite in agreement with SM predictions. The mass of the Higgs signal is found to be near 125 GeV, which not only confirms the Higgs mechanism as a right approach towards giving masses to the electroweak particles and gauge bosons but also puts a question of possibility of existence of further Higgs bosons, as it is still not clear whether the Higgs sector is indeed minimal, containing only a single Higgs doublet. One of the straight forward ways to address such a question is simply to go beyond the SM by adding a second Higgs doublet to the field content of the model. A particularly well-motivated possibility along these lines is the Minimal Supersymmetric Standard Model (MSSM) [3] and the general (unconstrained) two-Higgs-doublet model (2HDM) [4, 5]. The general 2HDM Higgs sector contains two CP-even neutral Higgs bosons, , , a CP-odd (pseudo-scaler) neutral Higgs boson, , and pair of charged Higgs bosons, , whereas, is the SM-like Higgs boson and is the candidate for the signal observed at LHC.

The purpose of this paper is to take into account all current constraints on the type II CP-conserving 2HDM parameter space and determine the allowed ranges of the triple and double Higgs couplings to estimate their corresponding cross sections. This work would prepare the ground for collider studies. Therefore, two types of linear colliders, that is, and , are compared for all processes. Both of these types of processes have been extensively searched during the last years at Tevatron, Large Electron-Positron Collider (LEP), and currently Large Hadron Collider (LHC). The recent results from LHC exclude a large parameter space of the light charged Higgs, GeV, if BR and heavy charged Higgs at [6, 7]. Furthermore, a remarkable restriction over charged Higgs masses comes from Flavor Changing Neutral Current (FCNC), radiative B-meson decay, whose branching ratio [8] is measured with sufficient precision that becomes sensitive to new physics. The charged Higgs contribution in above branching ratio increases with decreasing . This channel has been studied by BaBar and Belle collaborations in detail [9, 10] and the up-to-date limit excludes charged Higgs lighter than 480 GeV at 95% CL [11]. Therefore, the analysis presented throughout the paper is based on GeV.

A phenomenological study of triple Higgs production, including event study and the effect of neutral Higgs masses, and , on the cross section can be found in [12] for GeV.

In order to choose right masses for Higgs bosons of 2HDM, one should be aware that the global fit to electroweak measurements requires to be [13]. This requirement does not allow large mass splitting between Higgs bosons. Therefore, we adopt degenerate masses for neutral Higgs bosons, that is, .

Regarding the neutral Higgs mass , recently CMS and ATLAS experiments have excluded a wide range of in MSSM via a study of channel at TeV [14, 15]. Higgs boson decays to gauge bosons such as , , and have not been studied for MSSM neutral Higgs bosons. They are, however, considered for the light SM Higgs boson as different sources of Higgs boson production. Our chosen MSSM points are outside the LHC excluded area if one sets GeV and .

This study is intended to be suitable at colliders or muon colliders. The muon collider is expected to get the integrated luminosity around 125 fb^{−1} at TeV and 440 fb^{−1} at TeV. This is a unique machine, to be designed to provide high luminosity, very small energy spread, excellent stability, and good shielding of muon beam decay backgrounds.

#### 2. Theoretical Framework

The theoretical basis is a two-Higgs-doublet model with the general potential as follows [16, 17]:

The free parameters of such a model are in the general basis. The CP violation or Flavor Changing Neutral Currents (FCNC) are not assumed as they are naturally suppressed via the Natural Flavor Conservation (NFC) mechanism by imposing symmetry on the Lagrangian [18, 19] leads to . Furthermore, we choose which takes the region of study very close to MSSM parameter space. With the above setting, that is, and , free parameters can alternatively be taken as , , , , , because there is a correspondence between Higgs boson masses and values. We use 2HDMC package [20] to ensure that chosen parameters are consistent with current experimental limits and respect also the potential unitarity, perturbativity, and stability. A point is chosen if it satisfies all above requirements. Figures 1 and 2 show Higgs boson masses used in the analysis and their corresponding and values extracted from 2HDMC. The choice of the default set of MSSM parameters is GeV, GeV, GeV, GeV, and GeV, which reflect the benchmark scenario.