2HDMC - a two Higgs Doublet Model Calculator

• 2HDMs are among the simplest non-trivial extensions of the Standard Model Higgs sector and appear, for example, in the MSSM.Source: §1 · p. 2
• A general 2HDM can serve as an effective theory when searching for physics beyond the Standard Model.Source: §1 · p. 2
• The contribution presents 2HDMC for exploring the physics of general CP-conserving 2HDMs.Source: §1 · p. 2

2.1 General two Higgs doublet model potential

• The general model uses two complex SU(2)L doublets with hypercharge Y=1 in a gauge-invariant, renormalizable potential.Source: §2.1 · p. 2
• Requiring no explicit CP violation makes the potential parameters m2_12 and λ5−7 real, alongside m2_11, m2_22, and λ1−4.Source: §2.1 · p. 2

2.2 Electroweak symmetry breaking

• After symmetry breaking, the doublet vevs are parameterized by v1=v cosβ and v2=v e^iξ sinβ, with ξ set to zero to exclude spontaneous CP violation.Source: §2.2 · p. 2
• The proceedings description is explicitly limited and incomplete; the authors refer readers to [3] for a fuller account.Source: §2.2 · p. 2
• The physical parameterization uses Higgs masses and sβ−α alongside m2_12, λ6−7, and tanβ; 2HDMC also supports general and Higgs-basis choices.Source: §2.2 · p. 3

2.3 Possible additional symmetries

• The potential can impose U(1)PQ or exact Z2 symmetry; soft Z2 breaking with nonzero m2_12 leads to flavour-changing neutral currents beyond tree level.Source: §2.3 · p. 3
• 2HDMC provides setup methods for a tree-level MSSM model using mA and tanβ and for an inert doublet model.Source: §2.3 · p. 3

3. Theoretical constraints

• 2HDMC checks positivity, perturbativity, and tree-level unitarity as theoretical constraints on potential parameters.Source: §3 · p. 3
• Boundedness from below requires λ1 and λ2 to be positive, with additional conditions depending on whether λ6 and λ7 vanish.Source: §3 · p. 3
• Perturbativity is checked using 2→2 Higgs-scattering cross-sections, with a default upper limit of 4π on quartic Higgs couplings.Source: §3 · p. 3
• Tree-level unitarity is tested in HH and HVL scattering by limiting eigenvalues of the corresponding scattering matrices.Source: §3 · pp. 3–4

4. Yukawa sector

• The general Yukawa sector is parameterized by flavour-space matrices ρL, ρD, and ρU for leptons, down-type quarks, and up-type quarks.Source: §4 · p. 4
• The only stated constraint on each ρF matrix is that it be symmetric.Source: §4 · p. 4
• Non-diagonal ρF matrices lead to non-minimal flavour-violating charged currents and flavour-changing neutral currents; imposing Z2 symmetry restricts ρF to κF cotβ or −κF tanβ, yielding four types that the program can select directly.Source: §4 · p. 4

5. Partial decay widths

• 2HDMC calculates partial decay widths and branching ratios for a range of processes involving applicable Higgs bosons and Z or W bosons.The supplied passage does not specify the individual processes.Source: §5 · pp. 4–5
• H denotes any applicable Higgs boson, and V denotes Z or W.Source: §5 · p. 5

6. Experimental constraints

• The program calculates 2HDM contributions to the oblique parameters S, T, U, V, W, and X relative to the Standard Model with reference Higgs mass mref_h, and to the muon anomalous magnetic moment.The paper notes that taking existing experimental constraints into account is not a simple task and limits its own methods accordingly.Source: §6 · p. 5
• For collider and flavour limits, 2HDMC provides interfaces to HiggsBounds version 2 and SuperIso, respectively.Source: §6 · p. 5

7. Usage/parameter-setting/input-output

• 2HDMC uses a modular, object-oriented C++ structure and is available as a library or as ready-to-compile command-line programs.Source: §7 · p. 5
• The code requires a tested gcc compiler version 3.4 or 4 and the GNU Scientific Library; a template makefile and Demo test program are provided.Source: §7 · p. 5
• Its four main classes cover Standard Model inputs with running αs and quark masses, Higgs and Yukawa model specification, theoretical and experimental constraints, and Higgs and top-quark decay modes.Source: §7 · p. 5
• A LesHouches-style input/output format supports communication with other programs, and a 2HDM can be exported as a MadGraph/MadEvent user model for cross-section calculations [12].Source: §7 · p. 6

8. Summary and conclusions

• 2HDMC explores general CP-conserving 2HDMs from model definition and theoretical and experimental constraint checks to decay-width and scattering-cross-section calculations.The paper cites examples of its use in [13] [14] [15] [16].Source: §8 · p. 6