Hunting relaxions and light (pseudo)scalars at LEP, the (HL)LHC and future lepton colliders . Elina Fuchs Weizmann Institute of Science, Israel [1610:02025] Flacke, Frugiuele, EF, Gupta, Perez [1807.10842] Frugiuele, EF, Perez, Schlaffer Beyond Standard Model: Where do we go from here? GGI Firenze , August 28, 2018
Challenges for naturalness at the TeV-scale ◮ symmetry-based theories of naturalness: New Physics ∼ TeV e.g. SUSY, composite Higgs ◮ under pressure by null-results at LHC how much tuning acceptable? still some blind spots survive ◮ novel ideas for naturalness with light NP instead of symmetry protection of Higgs mass: dynamical evolution � Relaxion Elina Fuchs (Weizmann) | Relaxion at colliders | 1
Outline 1 Introduction: relaxion for naturalness 2 Relaxion phenomenology 3 Relaxion searches Precision probes Direct searches Elina Fuchs (Weizmann) | Relaxion at colliders | 1
I. Brief introduction: relaxion for naturalness
Relaxion mechanism [Graham, Kaplan, Rajendran ’15] V ( H ) = µ 2 ( φ ) H † H + λ ( H † H ) 2 V ( φ ) = rg Λ 3 φ + ... µ 2 ( φ ) = − Λ 2 + g Λ φ scans m h during inflation 1. φ ≥ Λ /g ⇒ µ 2 > 0 , no vev 2. φ < Λ /g ⇒ µ 2 < 0 , sign flip, EWSB Elina Fuchs (Weizmann) | Relaxion at colliders | 2
Relaxion mechanism [Graham, Kaplan, Rajendran ’15] V ( H ) = µ 2 ( φ ) H † H + λ ( H † H ) 2 V ( φ ) = rg Λ 3 φ + ... µ 2 ( φ ) = − Λ 2 + g Λ φ scans m h during inflation 1. φ ≥ Λ /g ⇒ µ 2 > 0 , no vev 2. φ < Λ /g ⇒ µ 2 < 0 , sign flip, EWSB � � φ 3. backreaction V br = Λ 4 br cos f 4. φ ց ⇒ | µ 2 ( φ ) | , v 2 ր ⇒ ∆ V br ր 5. until φ stopped by sufficient barrier Elina Fuchs (Weizmann) | Relaxion at colliders | 2
Relaxion models (examples) ◮ minimal model: QCD (rel)axion, √ Λ 4 br = 4 πf 3 π y u v/ 2 � θ QCD × ◮ non-QCD strong sector, √ Λ 4 br ≃ yv ′ 3 v H / 2 ◮ double-field mechanism ( φ, σ ) [Espinosa, Grojean, Panico, Pomarol, Pujolas, Servant ’15] ◮ familon (PNGB of spontaneously broken flavour symmetry) with vector-like leptons in the backreaction sector [Gupta, Komargodski, Perez, Ubaldi ’15] backreaction sector and ◮ friction via particle production scale Λ br model-dependent [Hook, Marques-Tavares ’16] ◮ ... Elina Fuchs (Weizmann) | Relaxion at colliders | 3
II. Relaxion Phenomenology
Relaxion-Higgs mixing [Flacke, Frugiuele, EF, Gupta, Perez ’16] [Choi, Im ’16] √ j ≡ r 4 br = ˜ considering Λ 4 M 4 − j v j / br v 4 , here j = 2 (non-QCD) 2 minimum of V ( φ, h ) : ( φ 0 , v = 246 GeV ) , φ 0 : endpoint of rolling, s 0 ≡ sin ( φ 0 /f ) can be O (1) or smaller Mixing term in the relaxion-Higgs potential � � ˜ M 4 − j v j − 1 φ 0 V ( φ, h ) ⊃ sin hφ → diagonalise √ j f f 2 V ( h, φ ) ⊃ hφ : Measurable consequences of relaxion-Higgs mixing? Elina Fuchs (Weizmann) | Relaxion at colliders | 4
Relaxion properties I: mass & mixing Relaxion mass 100.000 � m φ ≃ r 2 br v 2 c 0 − 16 r 4 br s 2 f = 10 3 GeV 0 f 0.001 f ≤ 2 m φ v 10 6 GeV sin θ ≃ 8 r 4 br s 0 ˜ > M M v M ϕ [ GeV ] 10 - 8 10 9 GeV ˜ max (for f ≫ r 2 br v , 16 r 4 br s 2 0 ≪ c 0 ) 10 12 GeV 10 - 13 10 15 GeV 10 18 GeV 10 - 18 0.001 0.010 0.100 1 10 100 ˜ [ GeV ] M Elina Fuchs (Weizmann) | Relaxion at colliders | 5
Relaxion properties I: mass & mixing Relaxion mass 100.000 � m φ ≃ r 2 br v 2 c 0 − 16 r 4 br s 2 f = 10 3 GeV 0 f 0.001 f ≤ 2 m φ v 10 6 GeV sin θ ≃ 8 r 4 br s 0 ˜ > M M v M ϕ [ GeV ] 10 - 8 10 9 GeV ˜ max (for f ≫ r 2 br v , 16 r 4 br s 2 0 ≪ c 0 ) 10 12 GeV 10 - 13 10 15 GeV "Relaxion line": maximal mixing 10 18 GeV 10 - 18 depends linearly on mass 0.001 0.010 0.100 1 10 100 ˜ [ GeV ] M Elina Fuchs (Weizmann) | Relaxion at colliders | 5
Relaxion properties II: lifetime [Clarke, Foot, Volkas ’13] [Flacke, Frugiuele, EF, Gupta, Perez ’16] Relaxion lifetime ⊲ threshold effects 10 17 s 10 17 10 13 s had - pert ⊲ cτ φ ∝ (sin θ ) − 2 e μ π c τ 10 7 10 6 s ⊲ displaced vertex? 1 s τ ϕ [ s ] ⊲ decay outside detector? 10 - 3 sin 2 θ c τ = 2m ⊲ cosmological time scales? 1 10 - 13 10 - 3 10 - 6 φ possibly long-lived 10 - 9 10 - 23 10 - 6 10 - 4 0.01 1 m ϕ [ GeV ] Elina Fuchs (Weizmann) | Relaxion at colliders | 6
Relaxion couplings to SM: CP -even and -odd CP -even g hX = sin θ g hX , X = f ¯ f, V V Relaxion inherits SM Higgs couplings suppressed by mixing ⇔ Higgs portal (applicable to other light-scalar models) CP -odd � ˜ φ c γγ F µν + ˜ c Zγ F µν + ˜ c ZZ 4 F µν � 2 Z µν � 4 Z µν � Z µν L ⊃ 4 π f � +˜ c WW W µν + ˜ c GG W µν � 4 G µν � G µν 4 c model-dependent: backreaction sector ˜ Elina Fuchs (Weizmann) | Relaxion at colliders | 7
III. Relaxion Searches
Status ( CP -even interaction) LEP - 2 FCCee K →π + inv B → K μμ - 4 CHARM Log 10 [ sin θ ] HB SN 1987A S H - 6 I P τ = 1s - 8 r τ u i n h → unt LHC1 m i v e r i RG s s e a C - 10 max mix FCCee = τ 1 0 2 6 s - 12 0 2 4 6 8 10 Log 10 [ m ϕ / eV ] 5th force astro cosmo meson decays beam dump lepton collider LHC Relaxion mass and mixing span many orders of magnitude Elina Fuchs (Weizmann) | Relaxion at colliders | 8
Precision probes ◮ Higgs couplings sensitivity to BR ( h → NP) ? deviation from self-coupling λ ? ◮ Z total width? Elina Fuchs (Weizmann) | Relaxion at colliders | 9
New decay mode of the Higgs invisible and untagged final states Γ NP = Γ inv + Γ unt h h h total Higgs width Γ h = κ 2 Γ SM + Γ NP h h φ h c hφφ φ relaxion: 2 parameters → fit (as SM+singlet) ◮ BR ( h → NP) = BR ( h → unt) = BR ( h → φφ ) (GeV-scale relaxion decays inside detector) ◮ κ ≡ cos θ : universal coupling modifier Elina Fuchs (Weizmann) | Relaxion at colliders | 10
Triple-scalar coupling hφφ c φφh = r 4 br v 3 θ − 2 r 4 br v 2 θ s θ − r 4 br v 4 θ s θ − 2 r 4 br v 3 θ + r 4 br v 2 f 2 c 0 c 3 s 0 c 2 2 f 3 s 0 c 2 c 0 c θ s 2 θ + 3 vλc θ s 2 s 0 s 3 θ f f 2 f → r 4 br v 3 θ ≃ m 2 θ → 0 φ f 2 c 0 c 3 − v where s 0 , c 0 ≡ sin , cos ( φ 0 /f ) Untagged Higgs decays ◮ Global Higgs coupling fits allow (under model assumptions) to bound BR( h → NP), in particular h → untagged ⇒ bound on g hφφ containing term ∝ cos 3 θ ◮ here h → φφ = � does not vanish at θ → 0 expect sin θ -independent bound on m φ for θ → 0 : relaxion-specific Elina Fuchs (Weizmann) | Relaxion at colliders | 11
Upper bounds on BR ( h → NP) ◮ BR ( h → inv) available for all colliders ◮ BR ( h → NP) often not available for suitable assumptions Estimate via precision of couplings ◮ κ Z most precise → approximation of global κ ◮ rates constrain combination of κ and BR ( h → NP) � 1 − n · δ κ � 2 BR ( h → NP) ≤ 1 − κ Conservative estimate; 2-parameter fit would be stronger than multi- κ Elina Fuchs (Weizmann) | Relaxion at colliders | 12
Higgs self-coupling λ λ ≃ f 2 − 4 r 4 c 0 + 16 r 4 br s 2 v 2 � � br 0 8 ( f 2 − 4 c 0 r 4 br v 2 ) [Di Vita, Durieux, Grojean, Gu, Liu, Panico, Riembau, Vantalon ’17] ◮ HL-LHC, FCCee, CLIC, ILC may reach a sensitivity of 10 − 50% [Di Vita et al ’17, Abramowicz et al ’16] ◮ relaxion-induced deviations from SM prediction < 10% for sin 2 θ < 0 . 1 = ⇒ too small to be resolved Elina Fuchs (Weizmann) | Relaxion at colliders | 13
Z precision measurements Precision measurements at the Z -pole = Γ( Z → φf ¯ ◮ relaxion opens NP contribution: Γ NP f ) Z ◮ bounded by δ Γ LEP1 = 2 . 3 MeV → δ Γ TeraZ = 0 . 1 MeV [Bicer et al ’14] Z Z ◮ � theory improvement needed: Z = 0 . 5 MeV → δ Γ th , 3loop δ Γ th = 0 . 2 MeV [Freitas ’14] Z Elina Fuchs (Weizmann) | Relaxion at colliders | 14
Resulting indirect bounds ◮ Z and Higgs precision measurements ◮ lepton colliders powerful h → untagged: bound on mass independent of sin θ for small mixing Elina Fuchs (Weizmann) | Relaxion at colliders | 15
Direct probes: φ production as a light Higgs gg Production at the LHC 1000 W ϕ Z ϕ ◮ pp → φ (gg) 100 tt ϕ bb ϕ ◮ pp → Zφ, Wφ VBF 10 tφ, b ¯ ◮ pp → t ¯ σ [ pb ] bφ 1 ◮ pp → φjj (VBF) 0.100 0.010 Production at lepton colliders ◮ e + e − → Zφ 0.001 20 40 60 80 100 ◮ Z → Z ∗ φ , Z ∗ → ff m ϕ [ GeV ] Hadronic cross sections at 13 TeV (solid) measurements at and above Z -pole and leptonic ones at 240 GeV (dashed) for sin 2 θ = 1 . Elina Fuchs (Weizmann) | Relaxion at colliders | 16
Branching ratios 1 bb cc 0.100 ττ μμ γγ 0.010 BR ϕ 0.001 10 - 4 10 - 5 5 10 50 100 m ϕ [ GeV ] exploit all final states: suitable at lepton/hadron colliders Elina Fuchs (Weizmann) | Relaxion at colliders | 17
Searches for exotic Higgs decays h → φφ → XXY Y [e.g. CMS-PAS-HIG-17-024, ATLAS 1802.03388] -1 35.9 fb (13 TeV) ) (%) 25 CMS Observed Observed Median expected Median expected τ 2b2 68% expected 68% expected 95% expected 95% expected Preliminary 20 → aa Combined → B(h 15 (h) SM σ σ 95% CL limit on 10 5 0 15 20 25 30 35 40 45 50 55 60 m (GeV) a ◮ BR ( h → φφ → 4 b ) � O (10 − 3 ) at CEPC with √ s = 240 GeV [Liu. Wang, Zhang ’17] Elina Fuchs (Weizmann) | Relaxion at colliders | 18
Recommend
More recommend
