New neutrino interactions: Theoretical motivation and experimental - PowerPoint PPT Presentation

New neutrino interactions: Theoretical motivation and experimental probes Ingolf Bischer Cold Quantum Coffee, ITP 27 November 2018 Ingolf Bischer New neutrino interactions

Outline 1. Global picture of neutrino physics 2. General neutrino interactions 3. Experimental probes Ingolf Bischer New neutrino interactions

1. Global picture of neutrino physics Ingolf Bischer New neutrino interactions

Global picture of neutrino physics Status Quo ◮ Consistent with three-flavor picture: ◮ Mixing: NuFIT 3.2 (2018)   0 . 799 → 0 . 844 0 . 516 → 0 . 582 0 . 141 → 0 . 156 | U | 3 σ = 0 . 242 → 0 . 494 0 . 467 → 0 . 678 0 . 639 → 0 . 774     0 . 284 → 0 . 521 0 . 490 → 0 . 695 0 . 615 → 0 . 754 ◮ Masses: ∆ m 2 21 = (6 . 80 → 8 . 02) × 10 − 5 eV 2 ∆ m 2 31 = (2 . 399 → 2 . 593) × 10 − 3 eV 2 � m i < 0 . 72 eV (95%CL from Planck data (indirect)) ( m ν e < 0 . 2 eV future 90%CL KATRIN bound) [NuFIT 3.2; Esteban et al. 1611.01514], [PDG; Tanabashi et al. 2018] Ingolf Bischer New neutrino interactions

Global picture of neutrino physics Status Quo ◮ CP phase [NuFIT 3.2 (2018)] δ CP = (144 → 374) ◦ ◮ Minor anomalies: ◮ LSND/MiniBooNE: Short-baseline excess of ν e hinting at fourth generation sterile mixing? In simplest ways inconsistent with global picture . . . ◮ Reactor anomalies: discrepancy between predicted and observed fluxes - new physics or errors in nuclear physics predictions? [MiniBooNE; Aguilar-Arevalo et al. 1805.12028] [Neutrino-4; Serebrov et al. 1809.10561]] Ingolf Bischer New neutrino interactions

Global picture of neutrino physics Open questions ◮ Mass ordering? (although normal ordering statistically preferred) ◮ Dirac or Majorana? ◮ CP phase δ CP of the mixing matrix? ◮ Deep new physics reason explanation for small neutrino masses, likely connected with new interactions? ◮ 3+X generations of neutrinos? ◮ Significant dark matter amount constituted by sterile neutrinos? (“warm” dark matter) ◮ Baryogenesis via Leptogenesis? ⇒ Plenty of room for new physics in the neutrino sector Ingolf Bischer New neutrino interactions

2. General neutrino interactions Ingolf Bischer New neutrino interactions

General neutrino interactions Steady sources of neutrinos ◮ Nuclear reactors ∼ 1 MeV ◮ The Sun ∼ 100 keV-MeV ◮ Accelerators ∼ GeV (p on target → π ± , K ± , focus, inflight decay) ◮ Soon? Neutrino factory ( µ decay) ◮ Cosmic rays scattering in the atmosphere ∼ GeV-TeV Bursted sources of neutrinos ◮ Collapsing Supernovae (few second burst of thermal neutrinos) Ingolf Bischer New neutrino interactions

Standard neutrino interactions Reactor and accelerator neutrinos ◮ Reactors and accelerators controllable & sources rather well understood ◮ Still neutrino flux determination major theoretical and experimental challenge ◮ Interesting approaches: ◮ Choose observables which are not too sensitive to flux ◮ Compare two observables which have approximately the same relative flux dependence, such that the flux cancels Ingolf Bischer New neutrino interactions

Standard neutrino interactions Reactor and accelerator neutrinos ◮ Both sources typically below the weak scale ⇒ well-described by Fermi theory of effective interactions between four fermions Ingolf Bischer New neutrino interactions

Standard neutrino interactions Reactor and accelerator neutrinos ◮ Both sources typically below the weak scale ⇒ well-described by Fermi theory of effective interactions between four fermions ν α e α ν α e α − → W e β ν β e β ν β √ g 2 2 2 G F = 2 m 2 W Ingolf Bischer New neutrino interactions

Standard neutrino interactions Reactor and accelerator neutrinos ◮ Both sources typically below the weak scale ⇒ well-described by Fermi theory of effective interactions between four fermions Fermi Lagrangians (in flavor basis) √ L ( ν α γ µ P L ν α ) g ψ � g ν � � L NC = − 2 2 G F ψγ µ P X ψ X X = L , R √ � e β γ µ P L ν β � L ℓ 2 G F ( e α γ µ P L ν α ) CC = − 2 √ � u β γ µ P L d β � L q 2 G F ( e α γ µ P L ν α ) CC = − 2 Ingolf Bischer New neutrino interactions

Non-Standard neutrino interactions ◮ Idea: New high-energy physics may leave a similar trace like the “integrated out” W and Z bosons in the low-energy regime ⇒ Non-Standard modifications with respect to Fermi theory ν α e α ν α e α − → V e β ν β e β ν β Interaction strength ∝ g 2 V m 2 V Ingolf Bischer New neutrino interactions

Non-Standard neutrino interactions ◮ Idea: New high-energy physics may leave a similar trace like the “integrated out” W and Z bosons in the low-energy regime ⇒ Non-Standard modifications with respect to Fermi theory NSI Lagrangians (in flavor basis) √ � ν α γ µ P L ν β � � ǫ ψ, X L NSI � � NC = − 2 2 G F ψγ µ P X ψ αβ X = L , R √ � e α γ µ P L ν β � L NSI � ( u γ γ µ P X d γ ) ǫ X CC = − 2 2 G F αβ X = L , R ◮ ǫ ∝ m 2 g 2 current bounds ∼ 10 − 3 − 10 − 1 dep. on flavor g 2 ? NP W m 2 NP Ingolf Bischer New neutrino interactions

General neutrino interactions ◮ Idea: What is the most general four-fermion interaction Lagrangian if we admit right-handed neutrinos? Five Lorentz-invariant Lagrangians constructed from four Dirac spinors ψ i L S ( ψ 1 , ψ 2 , ψ 3 , ψ 4 ) = � � � � ψ 1 ψ 2 ψ 3 ψ 4 , L P ( ψ 1 , ψ 2 , ψ 3 , ψ 4 ) = ψ 1 γ 5 ψ 2 ψ 3 γ 5 ψ 4 � � � � , L V ( ψ 1 , ψ 2 , ψ 3 , ψ 4 ) = ψ 1 γ µ ψ 2 � � � � ψ 3 γ µ ψ 4 , L A ( ψ 1 , ψ 2 , ψ 3 , ψ 4 ) = ψ 1 γ µ γ 5 ψ 2 ψ 3 γ µ γ 5 ψ 4 � � � � , L T ( ψ 1 , ψ 2 , ψ 3 , ψ 4 ) = ψ 1 σ µν ψ 2 � � � � ψ 3 σ µν ψ 4 , σ µν = i 2[ γ µ , γ ν ] Ingolf Bischer New neutrino interactions

General neutrino interactions ◮ Idea: What is the most general four-fermion interaction Lagrangian if we admit right-handed neutrinos? ◮ For chiral fields more restrictive, e.g. with two left-handed neutrinos and two identically charged fermions ψ 1 , ψ 2 � � S ( ν L ψ 1 , R ) ψ 2 , R ν L ν L γ 5 ψ 1 , R ψ 2 , R γ 5 ν L � � � � P = − = − 1 2 ( ν L γ µ ν L ) � � V ψ 2 , R γ µ ψ 1 , R = 1 ν L γ µ γ 5 ν L ψ 2 , R γ µ γ 5 ψ 1 , R � � � � A 2 L T = 0 ◮ Only one independent structure for right-chiral partners ψ R ◮ Only V or A structure for left-chiral partners ψ L ⇒ NSI Ingolf Bischer New neutrino interactions

General neutrino interactions ◮ Idea: What is the most general four-fermion interaction Lagrangian if we admit right-handed neutrinos (required by masses)? GNI Lagrangians (in flavor basis) 10 NC = − G F � ǫ j ,ψ � � ν α O j ν β � � L GNI � � ψ O ′ � √ j ψ 2 αβ α,β j =1 10 CC = − G F � ǫ j ,ψ � � e α O j ν β � � � � L GNI u O ′ √ � j d 2 αβ α,β j =1 ◮ Ten parameters instead of two! Ingolf Bischer New neutrino interactions

General neutrino interactions ( ∼ ) O ′ j ǫ j O j j γ µ ( 1 − γ 5 ) γ µ ( 1 − γ 5 ) 1 ǫ L γ µ ( 1 + γ 5 ) γ µ ( 1 − γ 5 ) 2 ˜ ǫ L γ µ ( 1 − γ 5 ) γ µ ( 1 + γ 5 ) 3 ǫ R γ µ ( 1 + γ 5 ) γ µ ( 1 + γ 5 ) 4 ˜ ǫ R ( 1 − γ 5 ) 5 ǫ S 1 ( 1 + γ 5 ) 6 ˜ ǫ S 1 ( 1 − γ 5 ) γ 5 7 − ǫ P ( 1 + γ 5 ) γ 5 8 − ˜ ǫ P σ µν ( 1 − γ 5 ) σ µν ( 1 − γ 5 ) 9 ǫ T σ µν ( 1 + γ 5 ) σ µν ( 1 + γ 5 ) 10 ˜ ǫ T Ingolf Bischer New neutrino interactions

General neutrino interactions Some model examples Type-II seesaw: ◮ Add scalar triplet to SM: √ � ∆ + / ∆ ++ � 2 √ ∆ = ∆ 0 − ∆ + / 2 ◮ Yukawa couplings to lepton doublets ◮ Coupling to SM Higgs Ingolf Bischer New neutrino interactions

General neutrino interactions Some model examples Type-II seesaw: ν β φ ν α ν α ∆ 0 ∆ + ν β e σ e ρ φ e β φ φ e α ∆ ++ ∆ e σ e ρ φ φ | ǫ | � 10 − 3 [Malinsk´ y et al. 0811.3346] Ingolf Bischer New neutrino interactions

General neutrino interactions Some model examples ν α ν σ ν β φ φ ψ ψ ψ Loop-induced NSI: ◮ E.g. neutral singlet scalar φ ◮ ǫ ∝ m 2 | y ψ | 2 | y ν | 2 W m 2 g 2 φ [I.B., W. Rodejohann, X.-J. Xu 2018] Ingolf Bischer New neutrino interactions

General neutrino interactions Advantages: ◮ Model-independent parametrisation of new physics √ ◮ Indirect access to high energy scales m / g = ( 2 /ǫ G F ) 1 / 2 ◮ Experimentally accessible by cross section precision measurements ◮ Can potentially discriminate Dirac from Majorana nature of neutrinos ◮ Naturally arise in many BSM models (although often constrained to be small) Differences to usual NSI: ◮ Needs RH neutrinos and can be L -violating Ingolf Bischer New neutrino interactions

3. Experimental probes Ingolf Bischer New neutrino interactions