A Symmetric Two Higgs Doublet Model

1. A Symmetric Two Higgs Doublet Model Shreyashi Chakdar Colby College arXiv: 1805.XXXXX (Bossi, Chakdar) PHENO 2018 05/08/17

2. Where are we standing? Spont. Breaking of EW symmetry Higgs Self coupling? More scalar states? Higgs portal to Dark Matter?

3. Where are we standing? Higgs Self coupling? Spont. Breaking of EW symmetry Higgs portal to Dark Matter? More Scalar states?

4. Window into BSM: LHC NEW SCALAR STATES DARK MATTER

5. What is Symmetric 2 Higgs Doublet Model? • Symmetric 2HDM: 2HDM + interchange symmetry () • + two Higgs doublets with = = = 175 Gev • 5 physical scalar fields: and • Model has no flavor changing neutral current (FCNC) • Neutral Scalar behaves like the SM-like Higgs with = 125 GeV • Other neutral scalar can be much lighter in mass than the SM-like Higgs • This lighter neutral scalar , charged scalar and pseudoscalar do not have couplings to fermions; H don’t have 3 point couplings with gauge bosons • h has couplings to fermions and 3 point couplings to gauge bosons (same couplings as SM)

6. Model and Formalism • After the original interchange symmetry is spontaneously broken, residual symmetry remains unbroken • Unbroken Residual symmetry: , & other fields remain positive Lightest negative particle (H) is the DM candidate • As H does not couple to fermions, the mass limit on is lower than coming from LHC • gluon-gluon fusion process for production of a generic scalar boson • If < ighter scalar H can be produced via decays of SM-like Higgs (h HH) at LHC

7. Scalar Sector Snapshot

8. Mass Parameters • Minimisation condition ( + + 2 *) • = 125 GeV + + • From < + + + + ] • For H to be the DM candidate • From relic abundance of DM • Vacuum stability bounds: • Constraints from Collider: + ;

9. Phenomenological implications at the LHC • Neutral scalar boson h has same couplings as the SM-like Higgs boson (= 125 GeV) • All other scalars (and ) do not couple to the fermions • If < H can be produced from the decay of h, via the three-point coupling “hHH” • If is small, decay channel of h HH extra invisible decay mode of SM-like h at LHC • Invisible decay branching ratio of 125 GeV Higgs is taken as < • h HH channel decay width in this model is given by

10. The invisible Higgs decay channel • Invisible Higgs boson decays : the hardest Higgs boson decay modes to look for at LHC • In SM h invisible decays are only through process with BR ( 0.1%) • h coupling measurements set an indirect upper limit of 34% on h non-SM particles • The invisible Higgs Branching ratio constraints: • ATLAS/CMS has set upper limits on the Br () to be 0.25 (0.24) at 95% CL • CMS has put as observed (expected) upper limit of 0.28 (0.21) at 95% CL at 13 TeV with 35.9 on the invisible branching fraction of the 125 GeV Higgs boson • With High luminosity run with 3000 , LHC is expected to probe down to ~ 5% Global fits to the Higgs Coupling Direct searches for the invisible Higgs channels can be searched for in the mono-jet (hj), VBF (hjj) and associated Vh channels

11. Modes for searching Invisible Higgs at the LHC Feynman diagrams for some target invisible Higgs decay processes at the LHC: 1. jets from the VBF process ( 2. Associated production 3. Gluon fusion

12. The Invisible Higgs decay channel in this model • In this model, total decay width (4.08 MeV) of the 125 GeV SM-like Higgs boson: • + • where , , , , • If the upper bound of < 25%, the bound on the decay width : • GeV • Bound can be translated to a bound on effective coupling and : (1 ) ½ where effective coupling = 2(+ +) + 3(+ )

13. Parameter space scan • Shaded region corresponds to the allowed values of and corresponding to bound of < 25% • From direct detection, the intermediate mass range • 5 GeV - 40 GeV is ruled out • In the low mass region (< 5 GeV ) include preferred signal regions where cross-section is fixed by requiring correct amount of thermally produced DM Parameter space scan with variation in and shown in figure

14. Other phenomenological implications • DM candidate H can also be produced through unsuppressed 4-point coupling • Decay process with decay width GeV can be tested at the proposed ILC • can be produced via Drell-Yan and can decay through channel + H /A • with decay widths given by

15. Final Remarks • Model presents simple twist in the well studied 2HDM sector by adding extra • interchange symmetry • After the EWSB, the residual symmetry remains unbroken • This makes the lightest negative particle the neutral scalar H to be DM candidate • Neutral scalar as well as charged scalar and pseudoscalar don’t couple to fermions • H don’t have usual 3 point couplings but has corresponding 4 point couplings with • The scalar can be much lighter in mass than the SM-like Higgs and can be produced • through the h HH channel contributing to the Higgs invisible decays • The invisible decay BR < 25% puts a bound on the parameter space which is studied here

16. THANK YOU!