Lepton flavor violation at future (lepton) colliders: induced by - PowerPoint PPT Presentation

Lepton flavor violation at future (lepton) colliders: induced by neutral and doubly-charged scalars Yongchao Zhang Washington University in St. Louis January 11, 2019 Mini-Workshop: Theory - Physics Opportunities and Advanced Tools IAS, HKUST based on P. S. B. Dev, R. N. Mohapatra & YCZ, PRL120 (2018)221804 [1711.08430] P. S. B. Dev, R. N. Mohapatra & YCZ, PRD 98 (2018)075028 [1803.11167] P. S. B. Dev & YCZ, JHEP 1810 (2018)199 [1808.00943] (see also P. S. B. Dev, M. J Ramsey-Musolf & YCZ, PRD 98 (2018)055013 [1806.08499]) see also CEPC CDR [1811.10545] & CLIC Yellow Book [1812.02093]

Outline Motivations of the LFV processes Beyond SM neutral scalar H at future lepton colliders ◮ On-shell production ◮ Off-shell production ◮ Prospects at ILC and CEPC (CLIC in backup slides) Doubly-charged scalar H ±± at future lepton colliders ◮ On-shell production through the (LFV) Yukawa couplings ◮ Off-shell production ◮ Prospects at ILC and CEPC (CLIC in backup slides) Displaced LFV signals at future colliders ◮ Long-lived H ±± in type-II seesaw L ◮ DV prospects at HL-LHC, FCC-hh & ILC ◮ DV from H ±± in left-right models R Conclusion Yongchao Zhang (Wustl) LFV Jan 11, 2019 2 / 31

Why lepton-flavor violation (LFV) at future lepton colliders? Neutrino oscillations ⇒ lepton flavor violation why not in the charged lepton sector??? “Smoking-gun” signal beyond the SM; Clean SM background at lepton colliders, compared to the hadron colliders. ...Connection to neutrino mass generation (and other pheno) ◮ Beyond SM neutral scalar H from e.g. left-right model, sneutrino in RPV SUSY models; ◮ Doubly-charged scalar H ±± in type-II seesaw and its extensions like left-right model; ◮ Might also be connected to the heavy neutrino searches, effective 4-fermion interactions, or even DM pheno at future lepton colliders. (See the talks by R. Franceschini, J. Zupan, M. Ramsey-Musolf, O. Fischer, M. Mitra) Yongchao Zhang (Wustl) LFV Jan 11, 2019 3 / 31

Beyond SM neutral scalar H @ future lepton colliders

Well-motivated underlying models RPV SUSY: sneutrinos ( ˜ ν ) [Aulakh, Mohapatra ’82; Hall,Suzuki ’84; Ross, Valle ’85, Barbier+ ’04; Duggan, Evans, Hirschauer ’13] L RPV = 1 2 λ αβγ � L α � L β � E c γ Left-right symmetric models: the SU ( 2 ) R -breaking scalar H 3 [Dev, Mohapatra, YCZ ’16; ’16; ’17; Maiezza, Senjanovi´ c, Vasquez ’16] LFV couplings are generated at tree and loop level 2HDM: CP-even or odd (heavy) scalars from the 2nd doublet [Branco+ ’11; Crivellin, Heeck, Stoffer ’15] LFV couplings are induced from small deviation from the lepton-specific structure. Mirror models: singlet scalar connecting the SM leptons to heavy mirror leptons [Hung ’06, ’07; Bu, Liao, Liu ’08; Chang, Chang, Nugroho+ ’16; Hung, Le, Tran+ ’17] LFV couplings arise from the SM-heavy lepton mixing Yongchao Zhang (Wustl) LFV Jan 11, 2019 5 / 31

Effective LFV couplings Model-independent effective LFV couplings of H L Y = h αβ ¯ ℓ α, L H ℓ β, R + H . c . . For simplicity, we assume h αβ are real, symmetric, H is CP-even, hadrophobic and the mixing with the SM Higgs h is small. H might originate from a isospin singlet, doublet or triplet, depending on specific underlying models. 1 Effective Dim-4 couplings � = Effective 4-fermion couplings like Λ 2 (¯ ee )(¯ e µ ) [Kabachenko, Pirogov ’97; Ferreira, Guedes, Santos ’06; Aranda, Flores-Tlalpa, Ramirez-Zavaleta+ ’09; Murakami, Tait ’14; Cho, Shimo ’14] m H < √ s ⇒ on-shell production Yongchao Zhang (Wustl) LFV Jan 11, 2019 6 / 31

On-shell production of H at lepton colliders the e + e − process e + e − → ℓ ± α ℓ ∓ β + H e + e + e + e + e − ℓ + α γ, Z γ, Z γ, Z ℓ − ℓ − H ℓ − e − e − e − ℓ − e + β H H involving the charged-currents [ H decaying into visible particles] e + e − → ν α ¯ ν e + H ν e ¯ e + W ν α ℓ − e − H Yongchao Zhang (Wustl) LFV Jan 11, 2019 7 / 31

Laser photon in future lepton colliders In future lepton colliders, high luminosity photon beams can be obtained by Compton backscattering of low energy, high intensity laser beam off the high energy electron beam [Ginzburg et al ’83, ’84] . The effective photon luminosity distribution ( x = ω/ E e � 0 . 83 the fraction of electron energy carried away by the scattered photon, ξ = 4 ω 0 E e / m 2 e ) � � 4 x 2 1 1 4 x f γ/ e ( x ) = ( 1 − x ) + ( 1 − x ) − ξ ( 1 − x ) + , D ( ξ ) ξ 2 ( 1 − x ) 2 � � 1 − 4 ξ − 8 log ( 1 + ξ ) + 1 2 + 8 1 with D ( ξ ) = ξ − 2 ( 1 + ξ ) 2 , ξ 2 Yongchao Zhang (Wustl) LFV Jan 11, 2019 8 / 31

On-shell production of H at lepton colliders involving the laser photon(s) e ± γ → ℓ ± + H , γγ → ℓ ± α ℓ ∓ β + H ℓ + α γ e − H H γ ℓ − γ ℓ − β Yongchao Zhang (Wustl) LFV Jan 11, 2019 9 / 31

Constraints on the LFV couplings: on-shell On-shell production amplitudes depend linearly on the LFV couplings muonium anti-muonium oscillation: (¯ µ e ) ↔ ( µ ¯ e ) ( h e µ ) [Clark, Love ’03] µ − µ − e − e − H H µ + e + µ + e + Electron and muon g − 2 ( h e ℓ , h µℓ ) [Lindner, Platscher, Queiroz ’16] Bhabha scattering, LEP ee → ℓℓ data ( h e ℓ ) [OPAL ’03; L3 ’03; DELPHI ’05] H e − ℓ − µ e e h e µ h e µ H γ e + ℓ + Yongchao Zhang (Wustl) LFV Jan 11, 2019 10 / 31

Prospects of H : on-shell production 1 1 2 ) μ g - ( g - 2 ) μ ( 0.1 ee → μμ 0.1 2 ) e g - ( ee → μμ o n i ( g - 2 ) e a t n l l c i o s t i 10 - 2 o a l m i l u e + e - → ν e ν μ H c n i s o o | h e μ | u | h e μ | m m 10 - 2 u i n H o e H u μ → e μ m γ γ → 10 - 3 γ γ e + e - → e μ H e + e - → ν e ν μ H H e μ 10 - 3 → e - e + 10 - 4 e γ → μ H e γ → μ H s = 240 GeV s = 1 TeV 5 ab - 1 1 ab - 1 10 - 5 10 - 4 5 10 50 100 500 10 100 1000 m H [ GeV ] m H [ GeV ] γγ ( e γ ) channel: laser photon collision. Green bands: muon g − 2 anomaly (excluded). Assuming the dominant decay mode H → e ± µ ∓ . Very sadly, “Japanese science committee questions the project’s (ILC) multibillion-dollar price tag...” [ https://www.nature.com/articles/d41586-018-07833-9 ] CLIC could do better! Yongchao Zhang (Wustl) LFV Jan 11, 2019 11 / 31

Prospects of H : on-shell production 1 1 γγ → e τ H 0.1 0.1 ee → ττ ( g - 2 ) e ee → ττ e + e - → ν e ν τ H 10 - 2 → | h e τ | | h e τ | e + e - → ν e ν τ H 10 - 2 e H τ γ γ → e + e - → e τ H e + e - → e τ H 10 - 3 2 ) e g - ( 10 - 3 H e e γ → τ H γ → τ 10 - 4 s = 240 GeV s = 1 TeV 5 ab - 1 1 ab - 1 10 - 4 5 10 50 100 500 10 100 1000 m H [ GeV ] m H [ GeV ] γγ ( e γ ) channel: laser photon collision. Assuming the dominant decay mode H → e ± τ ∓ . Yongchao Zhang (Wustl) LFV Jan 11, 2019 12 / 31

Prospects of H : on-shell production 1 1 0.50 ( g - 2 ) μ 0.1 → μτ H 0.10 e - e + ( g - 2 ) μ | h μτ | | h μτ | e d 0.05 d l u x c e H 2 ( g - 2 ) μ excluded g ) μ - μ τ ( H → e - 10 - 2 τ e + μ → γ γ 10 - 2 H τ μ → s = 240 GeV s = 1 GeV γ γ 5 ab - 1 1 ab - 1 10 - 3 5 10 50 100 500 10 100 1000 m H [ GeV ] m H [ GeV ] ◮ γγ ( e γ ) channel: laser photon collision. ◮ Assuming the dominant decay mode H → µ ± τ ∓ . ◮ The muon g − 2 discrepancy can be directly tested at CEPC & ILC via the searches e + e − , γγ → µτ + H . Yongchao Zhang (Wustl) LFV Jan 11, 2019 13 / 31

Off-shell production of H at lepton colliders Off-shell production (at resonance when m H ≃ √ s ) might also be mediated by a (light) gauge boson Z ′ with LFV couplings [Heeck ’16] e + e − → ℓ ± α ℓ ∓ β ℓ − ℓ − e − e − α α H H ℓ + ℓ + e + e + β β Yongchao Zhang (Wustl) LFV Jan 11, 2019 14 / 31

Constraints on the LFV couplings: off-shell Off-shell production amplitudes depend quadratically on the LFV couplings constraints [ GeV − 2 ] process current data µ − → e − e + e − < 10 − 12 ee h e µ | / m 2 H < 6 . 6 × 10 − 11 | h † τ − → e − e + e − < 2 . 7 × 10 − 8 | h † ee h e τ | / m 2 H < 2 . 6 × 10 − 8 τ − → µ − e + e − < 1 . 8 × 10 − 8 | h † ee h µτ | / m 2 H < 1 . 5 × 10 − 8 τ − → µ + e − e − < 1 . 5 × 10 − 8 | h † e µ h e τ | / m 2 H < 1 . 9 × 10 − 8 τ − → e − γ < 3 . 3 × 10 − 8 ee h e τ | / m 2 H < 1 . 0 × 10 − 6 | h † τ − → µ − γ < 4 . 4 × 10 − 8 e µ h e τ | / m 2 H < 1 . 2 × 10 − 6 | h † | h † ee h e τ | / m 2 H < 1 . 1 × 10 − 7 < 5 . 0 × 10 − 13 ( g − 2 ) e | h † e µ h e τ | / m 2 H < 1 . 0 × 10 − 8 | h † ee h e τ | / m 2 H < 1 . 4 × 10 − 7 ee → ee , ττ Λ > 5 . 7 & 6 . 3 TeV | h † e µ h e τ | / m 2 H < 1 . 3 × 10 − 7 ee → µµ, ττ Λ > 5 . 7 & 7 . 9 TeV The µ → 3 e limit is so strong that the it leaves no hope to see any signal in the ee → e µ channel at future lepton colliders. Yongchao Zhang (Wustl) LFV Jan 11, 2019 15 / 31