Scrutinizing the alignment limit in two-Higgs-doublet models:mh=125  GeV

Abstract

In the alignment limit of a multi-doublet Higgs sector, one of the Higgs mass eigenstates aligns with the direction of the scalar field vacuum expectation values, and its couplings approach those of the Standard Model (SM) Higgs boson. We consider CP-conserving Two-Higgs-Doublet Models (2HDMs) of Type I and Type II near the alignment limit in which the lighter of the two CP-even Higgs bosons, h, is the SM-like state observed at 125 GeV. In particular, we focus on the 2HDM parameter regime where the coupling of h to gauge bosons approaches that of the SM. We review the theoretical structure and analyze the phenomenological implications of the regime of alignment limit without decoupling, in which the other Higgs scalar masses are not significantly larger than m h and thus do not decouple from the effective theory at the electroweak scale. For the numerical analysis, we perform scans of the 2HDM parameter space employing the software packages 2HDMC and Lilith, taking into account all relevant pre-LHC constraints, the latest constraints from the measurements of the 125 GeV Higgs signal at the LHC, as well as the most recent limits coming from searches for heavy Higgs-like states. We contrast these results with the alignment limit achieved via the decoupling of heavier scalar states, where h is the only light Higgs scalar. Implications for Run 2 at the LHC, including expectations for observing the other scalar states, are also discussed. *

Closing the wedge: Search strategies for extended Higgs sectors with heavy flavor final states

“…A type II 2HDM consists of doublets H u , coupling only to up-type quarks, and H d , coupling only to down-type quarks and leptons. The neutral scalar components of both these fields acquire vacuum expectation values, v u and v d , with For simplicity, we assume that we are in the (almost) alignment limit [3][4][5][6][7][8][9][10][11][12][13][14][15][16], in which, to first approximation, the mass eigenstates are given by the fields in the Higgs basis [26][27][28][29][30][31], where only one doublet field combination (H SM ) couples to gauge bosons and does not mix with the second orthogonal doublet combination (H NSM ). The observed Higgs boson (h) with a mass of 125 GeV is identified with the scalar arising from H SM , whereas the H NSM gives rise to H, A and the charged Higgs bosons.…”

“…This suggests that the Higgs sector is approximately aligned [3][4][5][6][7][8][9][10][11][12][13][14][15][16], either via decoupling or via alignment without decoupling. In the latter scenario, it becomes essential to directly search for the presence of extra Higgs bosons, which may have an unmeasurably small impact on the properties of the 125 GeV Higgs.…”

A simple criterium for CP conservation in the most general 2HDM

“…[18]). Moreover, one should 5 Let us remind that such condition (including all its forms discussed in [19]) is insufficient to establish CP conservation in the considered model in the general case, since does not guarantee the fulfillment of the condition (11b), i. e. non-appearance of CP odd vertices (12). doesn't contradict CP conservation.…”

“…The choice of the set of these parameters, describing the same physical reality, (choice of basis in the parameter space) is ambiguous. In the non-minimal models, like 2HDM, the observed situation with properties of Higgs boson similar to those in the SM (SM-like scenario [4] or alignment limit [5]) can be described by different non-equivalent sets of parameters.…”

Hierarchical versus degenerate 2HDM: The LHC run 1 legacy at the onset of run 2

“…Refs. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]). Various works have also discussed the constraints coming from LHC searches for neutral and charged scalars A 0 , H 0 , and H AE via A 0 → Zh, A 0 =H 0 → ττ, A 0 =H 0 → γγ, H 0 → ZZ=WW, H 0 → hh, H AE → tb, and H AE → τν (see e.g.…”