The THDMa Revisited

Abstract

The THDMa is a new physics model that extends the scalar sector of the Standard Model by an additional doublet as well as a pseudoscalar singlet and allows for mixing between all possible scalar states. In the gauge-eigenbasis, the additional pseudoscalar serves as a portal to the dark sector, with a priori any dark matter spins states. The option where dark matter is fermionic is currently one of the standard benchmarks for the experimental collaborations, and several searches at the LHC constrain the corresponding parameter space. However, most current studies constrain regions in parameter space by setting all but 2 of the 12 free parameters to fixed values. In this work, we performed a generic scan on this model, allowing all parameters to float. We applied all current theoretical and experimental constraints, including bounds from current searches, recent results from B-physics, in particular Bs→Xsγ, as well as bounds from astroparticle physics. We identify regions in the parameter space which are still allowed after these were applied and which might be interesting for an investigation of current and future collider machines.

Benchmarking LHC searches for light 2HDM+$\boldsymbol{a}$ pseudoscalars

“…Since for models with pseudoscalar mediators the DM direct detection (DD) constraints are weaker compared to models with scalar mediators, such models are more attractive from an astrophysical point of view since they often allow to reproduce the observed DM relic abundance in a wider parameter space and with less tuning. These features admit a host of missing transverse momentum (E miss T ) signatures at colliders which can be consistently compared and combined, making the 2HDM+a model one of the pillars of the LHC DM search programme [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22].…”

“…Since comprehensive discussions of the structure of the 2HDM+a model can be found in the articles [4,11,21,22] to which we refer the interested reader for further details, we will only review the ingredients of the model that are relevant for our study.…”

“…Here m h 125 GeV is the Higgs mass, v 246 GeV denotes the vacuum expectation value of the SM Higgs field and θ represents the mixing angle of the two CP-odd weak spin-0 eigenstates. The three quartic couplings λ 3 , λ P 1 and λ P 2 appear in the scalar potential of the 2HDM+a model and serve commonly as input parameters [4,11,21,22].…”

“…variation of one of the standard parameter choices recommended by the LHCDMWG in [11] all constraints that arise from Higgs and flavour physics, electroweak precision measurements and vacuum stability are automatically fulfilled for the choices (5). See the works [4,11,21,22] for details.…”

New Physics with missing energy at future lepton colliders -- Snowmass White Paper

“…We here report on results of a scan that allows all of the above novel parameters float in specific predefined ranges [60]. In such a scenario, it is not always straightforward to display bounds from specific constraints in 2-dimensional planes.…”