Implications of massive neutrinos

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1 Laboratoire de Physique Théorique-Orsay, Université Paris-Sud Implications of massive neutrinos Observations: what have we learned? Neutrino mass discovery new physics How to generate small neutrino masses? Seesaw realisations Implications for cosmology How to Disentangle between models? Collider Physics Asmaa Abada Wahran, les Andalouses, 02-0 May 2009

2 Neutrinos are the most elusive particles of the Standard Model Q em = 0, Q color = 0. informations on the essential features of the SM : left nature of the weak interaction and family structure Masses and Mixings The charged interaction is not diagonal in flavour space: L int = g 2 li L γ µ ν j L U ijw + µ + h.c., n=3 Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix (Chau-Keung) 0 U = c 2 c 3 s 2 c 3 s 3 e iδ s 2 c 23 c 2 s 23 s 3 e iδ c 2 c 23 s 2 s 23 s 3 e iδ s 23 c 3 s 2 s 23 c 2 c 23 s 3 e iδ c 2 s 23 s 2 c 23 s 3 e iδ c 23 c 3 o C A ne Diag iα, e iα 2, δ Dirac phase, α,2 Majorana phases, θ 2,θ 23, θ 3 (ν = ν) m, m 2, m 3 mass eingenvalues, if m 3 > 0, m,2 = m,2 e iα,2

3 P(ν α ν β ; L) = δ αβ 4 X j<k + 2 X j<k Transition Probabilities Re `U αj U βju αku βk sin 2 Im `U αj U βju αku βk sin m 2 jkl 2E m 2 jkl 4E!!, m 2 jk = m 2 j m 2 k. Oscillations are possible if ν are massive ( m 2 jk 0) and mix (U αj U βj 0) oscillation experiments do not give the nature : Dirac or Majorana : ν ν! n = 2: P(ν α ν β ) = sin 2 2θ sin 2 L L vac π, L vide = 4πE 2.48km m 2 E(GeV) m 2 (ev 2 ) oscillations arise when L L vac m2 L 4πE m2 (ev 2 ) E(GeV) L(km)

4 Accessible m 2 Depending on L et E neutrino sources : L(km) E(GeV) m 2 (ev 2 ) Source ν solar ν atmospheric ν des accelerators (long distance) 0. 0 ν accelerators (short distance) ν des reactors

5 Leptonic CP Assymetry CP (αβ) P(ν α ν β ) P( ν α ν β ) = 4 j>k Im ( U αj U βju αju βk ) sin ( m 2 jk Cannot be observed in appearance experiment ) L 2E CPT CP (eµ) = CP (µτ) = CP (τe) 6J l 2 l 23 l 3 J Im ( ) U e3 UeU µ3u µ sin2θ23 sin2θ 2 sinθ 3 sinδ (Jarlskog Invariant) ( ) l ij sin.27 m 2 ij (ev)2 L(km) E(GeV) θ 23 large (OK) and also m 2 3. θ 2 large (OK) and also m 2 2. θ 3 conditions the measurement: θ 3 > 0 : only upper limit θ 3 < 3 0 (95% CL)

6 Observations: Neutrinos and BAU The Standard Model do not explain Neutrino masses and mixings: Recent data: atmosphere, Solar, Terrestrial expts. Atmospheric ν and Reactor Data m 2 atm(ev 2 ) θ atm θ ± 0.2(0.6) m 2 sol(ev 2 ) Solar ν θ sol ±.3 Oscillations Cosmology Tritium Absolute mass scale ν m ν > p m 2 atm ev P i m ν i < ev m νe < 2.2 ev Majorana nature? (0νββ) CP phases? Majorana phases α,2 : no direct information : (0νββ)? Dirac CP Phase δ we first need to know θ 3 with good accuracy

7 () Need a high scale (> SM ) to generate small neutrino masses and mixings (2) Need dynamical mechanism to generate Baryon Asymmetry of the Universe (BAU) η B : Primordial abundances of light elements + CMB Anisotropies η B = n B n B n γ = (6.2 ± 0.6) 0 0 AIM: find models that are simultaneously consistent with () & (2) BAU from Leptogenesis? Favourite option: new physics at high scale M What is this new physics? How does it manifest? Heavy fields manifest in the low energy effective theory (SM) via higher dimensional operators δl d=5, δl d=6,...

8 m ν 0 New Physics Standard Model ν L and no ν R = No Dirac mass term: L md = m D ( ν L ν R + ν R ν L ) No Higgs triplet = No Majorana mass term: L mm = 2 M ij ν c L i ν Lj + h.c. Lepton symmetry is accidental = Non-renormalisable operators dim 5, 6... MS Effective theory of a larger one at a scale Λ { (φl ) O d=5 = T ( ) } φ =v Λ φl + h.c. m ν v 2 /Λ m ν m 2 atm ev 2 Λ 0 5 GeV. Remarkably near Λ GUT!!

9 Beyond the Standard Model Typically 3 possible ways to generate m ν 0: See-saw mechanism: towards GUT SO(0), can be achieved via. type I with RH neutrino exchange 2. type II with scalar triplet exchange 3. type III with fermionic triplet exchange Radiative corrections MSSM or various extensions +R/ p, Zee model, Extra dimensions alternative to the see-saw

10 3 ways to generate tree level O d=5 : Seesaw I, II, III Y Y t N R M R Y N R µ Σ R Σ R M Σ Y. Y t. type I (fermionic singlet) type II (scalar triplet) type III (fermionic triplet) m ν = 2 Y T N v2 M N Y N m ν = 2Y v 2 µ M 2 m ν = v2 2 Y T Σ M Σ Y Σ Minkowski,Gell-Man, Magg, Wetterich, Ma,Hambye et al. Ramond, Slansky Nussinov Bajc, Senjanovic, Lin Yanagida, Glashow Mohapatra, Senjanovic A.A., Biggio, Bonnet, Gavela, Mohapatra, Senjanovic Schechter, Valle Notari, Strumia, Papucci, Dorsn Ma, Sarkar Fileviez-Perez, Foot, Lew...

11 Seesaw Type I, SM + ν R L = L SM + λ ν Jk L k ν RJ H 2 ν R J M RJ ν c R J + λ α H c ē Rα l α, m D = λ ν v Majorana Eigenstates (3 3) : ν = L + L c = ν c m L m D M R m T D N = R + R c =N c M R M R m D 200 GeV M R 0 5 GeV m ν m 2 atm (0 2 0 ) ev λ ν O() λ ν h e M R few TeV

12 Baryo(Lepto)genesis requirements Sakharov 67 a. Baryon (Lepton) number violation 2. C & CP Violation 3. Out of equilibrium processes n B(L) n B( L) Out-of-equilibrium : decays of heavy particles in an expanding Universe H(T) Γ X α X M X Γ D < H T=MX a 4th constraint : B L must be violated if baryogenesis occurs > EW scale

13 History 985: Kuzmin, Rubakov & Shaposhnikov, following the discovery of fast B + L violation at T > T EW On the anomalous electroweak baryon number nonconservation in the early universe", Phys. Lett. B 55, 36 (985) 986: Fukugita &Yanagida, basic idea of leptogenesis Baryogenesis without grand unification", Phys. Lett. B 74, 45 (986) : a few remarkable works opened the way to quantitative leptogenesis, e.g.,luty, Baryogenesis via leptogenesis", Phys. Rev. D 45, 455 (992), Covi, Roulet,Vissani, CP violating decays in leptogenesis scenarios", P. L. B 384, 69 ( 96) 993: Farrar, Shaposhnikov, EW baryogenesis? Baryon asymmetry of the Universe in the MSM", Phys. Rev. Lett. 70, 2833 (993). 994: Gavela, Pene, et al., IMPOSSIBLE! Standard model CP violation and baryon asymmetry", Nucl. Phys. B 430, 345[& 382] (94),

14 > SK (2000): Evidence for neutrino oscillations + EW baryogenesis fails in SM and MSSM, fuel the interest on leptogenesis : a flourishing study begins: A.A, Buchmuller, Di Bari, Plumacher ; Davidson, Ibarra; Hambye, Yin Lyn, Papucci, Strumia; Grossman, Kashti, Nardi, Nir, Roulet; Pilaftsis, Underwood; Branco, Gonzalez Felipe, Joaquim, Masina, Rebelo, Savoy; : Guidice, Notari, Raidal, Riotto & Strumia, Towards a complete theory of thermal leptogenesis in the SM and MSSM", Nucl. Phys. B 685, 89 (2004) Buchmuller and Plumacher, Leptogenesis for pedestrians", Annals Phys. 35, 305 (2005)...in one flavour approximation

15 2000: First study of flavour effects in leptogenesis, Barbieri, Creminelli, Strumia and Tetradis, Baryogenesis through leptogenesis", Nucl. Phys. B 575, 6 (2000) Endoh, Morozumi & Xiong, Primordial lepton family asymmetries in seesaw model", Prog. Theor. Phys., 23 (2004) 2006: First quantitative study of flavour effects in leptogenesis, A.A, Davidson, Josse-Michaux, Losada & Riotto, Flavour issues Leptogenesis", JCAP 0604, 004 (2006); [hep-ph/060083] Nardi, Nir, Roulet & Racker, The importance of flavor in leptogenesis", JHEP 060, 64 (2006); [hep-ph/060084]. A.A, Davidson, Ibarra, Josse-Michaux, Losada & Riotto Flavour matters in leptogenesis", JHEP 0609, 00 (2006); [hep-ph/060528] 2006: Extensive analysis... (A.A, Antusch, Blanchet, Branco, Chun, Davidson, De Simone, Di Bari, Felipe, Joaquim, King, Losada, Pascoli, Petcov, Raffelt, Riotto, Strumia, Uhlig...)...

16 Leptogenesis Basic Leptogenesis Mechanism Fukugita and Yanagida 86. CP violating decay of a heavy particle through an L-violating interaction can produce a lepton asymmetry. 2. This lepton asymmetry is transformed into a baryon asymmetry through sphaleron SM interactions: B + L-current is anomalous but B L and /3B L α - currents are not η B = ( 24+4nH 42+9n H )η L

17 ) L violation ν R Majorana 2) C & CP asymmetry: ǫ = α ǫ αα= α α ( Γ(N Hl α ) Γ( N H l α ) ( Γ(N Hl α )+Γ( N H l α ) ) ) CP from the complexity of the λ ν Yukawa matrix 3) Out-of-equilibrium decay of N Γ N H(T=M ) η L K ǫ is produced.

18 Boltzmann Equations One Flavour Approx The lightest N is produced in the thermal bath after inflation * Y N n N s dy N dz = z sh(m ) (Y N Y eq N dy L dz = z [ ǫ γ sh(m ) (Y N D Y eq N is N abundance, Y L n l n l s )(γ D + γ S ), ) γ W = α Y αα L * z = M T, s : entropy density, ǫ : CP-asymmetry Y L ], Y eq L * γ D,γ S : interaction rates for the decay and scattering L = * γ W = function ( γ D,γ S, L = 2 ) washout factor is total lepton asymmetry

19 Constraints on neutrinos in One Flavour Approx - M << M 2 << M 3 ǫ 3 2 6π M m v 2, = 3 6π ( m = m 2 + m2 2 + m2 3 ) M v 2 ( m 2 atm + m2 sol ) m 3 If light ν spectrum is degenerate: ǫ = 0 If light ν spectrum is hierarchical ǫ 3 2 6π M m 2 atm v 2 (Davidson, Ibarra) λ O() & κ and η B (WMAP) M > GeV η B L max m : m < 0.5 ev (Buchmuller, Di Bari, Plumacher) 2- M = M 2 = M 3 ǫ = 0 3- Quasi-degenerate M 2 J M2 I << M2 J M2 I ǫ 0 m < ev (Hambye et al)

20 When is the one flavour approx valid? Thermal leptogenesis at T M when Γ N < H(M ) The one flavour approximation is correct when the interactions mediated by charged lepton Yukawa are out of equilibrium. Γ α h 2 αt * Ints involving the charged τ are out of equilibrium at T 0 2 GeV (Γ τ < H) * Ints involving the charged µ are out of equilibrium at T 0 9 GeV (Γ µ < H) * Ints involving the charged e are out of equilibrium at T 0 5 GeV (Γ e < H) The diagonal terms are the lepton asymmetries stored in each flavour The off-diagonal terms encode the quantum correlations between the flavour asymmetries One Flav approx valid for M > 0 2 GeV, below, Solve FLAVOURED BE.

21 One flavour dy αα L dz = z [ ǫαα γ sh(m ) (Y N D Y eq N ) γ αα W Y αα L Y eq L ], α dy αα L dz = ǫ αα = Γ(N Hl α ) Γ( N H l α ) Γ(N Hl α )+Γ( N H l α ) Y eq L Sum over flavour z [ (ǫee + ǫ sh(m ) µµ + ǫ ττ ) γ }{{} ( Y N D Y eq N ǫ ( γ ee Y ee W L + γ µµ Y µµ W L + γττy ) ττ W L }{{} z sh(m ) (γ ee W +γµµ W +γττ W ) Y L [ ǫ γ D (Y N Y eq N ) γ W ) ], Y L ] (One State Approx) Y eq L

22 Flavoured BE Y α B/3 L α asymmetry in lepton flavour α. Baryonic asymmetry: Y B 2 37 α Y α α ǫ α η α N Abundance: Y N (z) = κ (D(z) + S(z)) ( Y N (z) Y eq N (z) ), z = M /T Y α asymmetry: Y α (z) = ǫ α κ (D(z) + S(z)) ( Y N (z) Y eq N (z) ) κ α W(z) β A αβy β (z) Y L Abundance : Y Lα = A αβ Y β ; A = Washout parameters: κ α Γ N lα H(M N ) = λ αλ α m ev The CP-asymmetry: ǫ α = Γ N lα Γ N P lα α(γ N l α +Γ lα) = (8π) N Efficiency η α : need to solve BE 0 5/79 20/79 20/79 25/ /537 4/537 25/358 4/ /537 v2 M m m α C A m, κ = α κ α m m, [λλ ] j Im { ( (λ α )(λλ ) j (λ jα )} M 2 ) j g M 2

23 Consequences of treatment of flavours * CP asymmetry: Remember, in ONE FLAV APPROX, if light ν spectrum is degenerate (m i m): ǫ = 0 ǫ = α ǫ αα = 0 and ǫ αα 3M m 8πv 2 individual grows with absolute scale m ǫ αα have opposite sign but are weighted by different washout factors Can have successful leptogenesis in the case of degenerate light neutrino spectrum

24 * Efficiencies η α : κ α = κ β ; κ β = ; κ β = 30 Thermal initial N abundance (N N eq ) or dynamically generated (N = 0). 0 0 Η Α d Η Α Κ Α A diagonal Κ Α Full A Strong washout regime (κ α > ) : no flavour effect when A is diagonal Weak washout regime (κ α < ): effect only in dynamical N abundance case Pronounced flavour effect when non diagonal entries of A are considered Order of magnitude enhancement Josse-Michaux and A.A, JCAP 070 (2007) 009

25 Illustratif example Flavour α = ("e + µ") in the strong washout regime α = 2 (τ) in the weak washout regime: Y B significantly enhanced compared to the one flavour approximation treatment

26 * Influence of flavours : Y e+µ /Y τ (M GeV, ǫ e+µ + ǫ τ = 0 6 ) Dynamical initial N abundance (N = 0) or thermally generated (N N eq ) Y e Μ Y Τ Log 0 0 Y e Μ Y Τ.8 0 Y e Μ Y Τ 0 Log 0 Y e Μ Y Τ Κ e Μ Κ Τ Κ e Μ Κ Τ Y e Μ Y Τ 0 0 Y e Μ Y Τ Ε e Μ Ε Τ 0 2 Contour plot of Log 0 ( Ye+µ Y τ ) Ε e Μ Ε Τ 0 2 In principle, one should have Y e+µ ( )Y τ for ǫ e+µ ( )ǫ τ. But important influence of the wash-out parameters: Eg: in the thermal case, for κ e+µ /κ τ 0. and ǫ e+µ /ǫ τ 0.5 Y e+µ 2Y τ.

27 Y B = 2 37 BAU in the 3-flavour case α Y α α ǫ α η α For ǫ α ǫ α 0, define efficiency for BAU η B : Y B = ǫ η B κ α = κ β ; κ β = ; κ β = 30 0 Η B This is for ǫ α for all flavours Baryonic efficiency strongly depends on the flavour alignement Off diagonal A matrix: only a few percent effect in the case of ǫ α ǫ α 0 Κ Α

28 BAU in the 2-flavour case Effect of the off-diagonal A entries: YB tot diag /YB Κ e Μ Y B tot. Y B diag Κ e Μ Y B tot. Y B diag Κ Τ Dynamical Κ Τ Thermal 0 2 This is for ǫ e+µ = ǫ τ (= 0 6 ) Baryonic efficiency strongly depends on the flavour alignement Effects of the off diagonal A matrix in this case are as large as 40% Effect of A αβ : Dynamical case - constructive & destructive Thermal case - strictly constructive

29 An interesting example 3-flavour case in a democratic scenario Equal κ α and α ǫ α = 0: - ignoring the O(A) BAU= 0 - taking them into account BAU 0

30 Lower bound on N mass Solve the BE to obtain the WMAP-allowed (M m ) parameter space Input parameters : Yukawa couplings λ ( λ = M /2 N Rm/2 U v, Casas-Ibarra)

31 Dynamical M GeV M GeV m sol m atm m ev 0 9 m sol m atm m ev One Flavour approx Full flavour treatment Thermal M GeV m sol m atm M GeV m sol m atm m ev m ev

32 All points displayed comply with In summary: Y B Lower bounds for M N : GeV in the dynamical case M N GeV in the thermal case Dynamical case: m can take extremelly small values Effect of flavours: open the allowed interval for m

33 Light neutrino masses m = lightest neutrino mass M GeV m sol m atm m ev Dynamical M GeV m sol m atm m ev Thermal No bound on absolute scale of light neutrinos from the requirement of sucessful leptogenesis!

34 Now what is this new physics? Bottom up approach: use effective theory Neutrino masses require new heavy fields Effects at low energy: effective theorie approach Effective operators obtained when expanding the heavy field propagators in M heavy fermion: D/ +... D/ M M M M heavy scalar : D 2 M 2 M 2 D2 M L eff = L SM + c d=5 O d=5 + c d=6 O d=6 + c d=5 M ; cd=6 M 2...;

35 Dimension 5 : δl d=5 = 2 cd=5 αβ ( l c φ )( φ ) Lα l L β + h.c., m ν = v2 Y Y M R c d=5 v 2 M R Y M R M GUT Y 0 6 M R TeV Mass operator O d=5 violates lepton number L Majorana neutrinos O d=5 is common to all models of Majorana neutrinos

36 3 ways to generate tree level O d=5 : Seesaw I, II, III Y Y t N R M R Y N R µ Σ R Σ R M Σ Y. Y t. type I (fermionic singlet) type II (scalar triplet) type III (fermionic triplet) m ν = 2 Y T N v2 M N Y N m ν = 2Y v 2 µ M 2 m ν = v2 2 Y T Σ M Σ Y Σ Minkowski,Gell-Man, Magg, Wetterich, Ma,Hambye et al. Ramond, Slansky Nussinov Bajc, Senjanovic, Lin Yanagida, Glashow Mohapatra, Senjanovic A.A., Biggio, Bonnet, Gavela, Mohapatra, Senjanovic Schechter, Valle Notari, Strumia, Papucci, Dorsn Ma, Sarkar Fileviez-Perez, Foot, Lew...

37 Distinguishing among the 3 types of seesaw The O d=5 operator is the same for all extensions of SM responsible for neutrino masses and mixing (ν data, (ββ) 0ν,...) To distinguish the several seesaw mechanisms: produce the heavy states or use O d=6 operators

38 Dimension 6 operators Effective Lagrangian L eff = c i O i Model c d=5 c d=6 i Oi d=6 Fermionic Singlet Y T N M N Y N ( Y N M N ) M N Y N M 2 Y αβ Y γδ αβ ( ) ( φ ) l Lα φ i / l Lβ ( llα τ llβ ) (l Lγ τ llδ ) Scalar Triplet 4Y µ M 2 µ 2 M 4 ( ) ( φ τ φ )( φ ) Dµ D µ τ φ Fermionic Triplet Y T Σ M Σ Y Σ ( Y Σ M Σ 2 (λ 3 + λ 5 ) µ 2 M 4 ) M Σ Y Σ αβ ( φ φ ) 3 ( ) l Lα τ φ ( φ ) id/ τ llβ Fermions: if Y O(), c d=6 (c d=5 ) 2 and the smallness m ν would preclude observable effects from Oi d=6. Not the case for scalars!

39 Scalar triplet (type II) Y µ = (, 3, 2), L = 2 Yukawa coupling: Y ij (l L ) c ia (l L) jb (iτ 2 τ α ) ab α + h.c Scalar coupling: µφ t aφ b (iτ 2 τ α ) ( ) α + h.c. M 2 2 λ 2 ( ) 2 λ 3 ( φ φ )( ) +... d=5 Operator: Mass m ν = v 2 µ Y M 2 2 different scales µ, M possible to have Y O() M TeV (µ 00 ev)

40 Low energy effects of dimension 6 operators: ( )( ) 2M Y 2 ij Y kl lli γ µ l Lk llj γ µ l Ll LFV, constraints not suppressed by µ ( 2 µ2 M 4 µ φ φ ) ( µ φ φ ) 2λ 3 µ 2 M 4 ( φ φ ) 3 EW prec. data, couplings to gauge bosons 4 µ2 M 4 [ φ D µ φ ] [ φ D µ φ ] 2 µ2 M 4 ( φ φ ){ Y e le R φ + Y d qdφ Y u qiτ 2 uφ + h.c. } top physics... Direct LFV: d = 5 operator supressed by small scale µ; d = 6 operator not supressed

41 Testing seesaws Scalar seesaw (Type II): Lepton Flavour Violation µ eee, τ lll, µ eγ, τ eγ bounds on various combinations of Y M Fermionic seesaw (Type I and III): non unitarity NN αβ = ǫ Σ = v2 2 cd=6 αβ = v2 Y 2 Σ M M Σ Y Σ αβ Σ Type I: also Lepton Flavour Violation µ eγ, τ eγ, W, Z (semi) leptonique decays, Type III: same as Type I + tree level Lepton Flavour Violation (µ eee, τ lll) at tree level

42 µ eee and τ 3l which gives Bounds on Type II seesaw Γ(µ e + e e ) = m5 µ 92π 3 M 4 Y µe 2 Y ee 2 Br(µ e + e e ) Γ(µ e + e e ) Γ(µ e ν µ ν e ) = M 4 G 2 F For τ decays: Y eµ 2 Y ee 2 Γ(τ l + i l j l j ) = m5 τ 92π 3 M 4 Y τi 2 Y jj 2 (for any i and j) Γ(τ l + i l j l k ) = m5 τ 96π 3 M 4 Y τi 2 Y jk 2 (for any i, j, k with j k) Using exp. Brs (or upper limits) derive bounds for Yukawa couplings

43 ( Process Constraint on Bound ( M ) 2 ) TeV µ e + e e Y µe Y ee < τ e + e e Y τe Y ee < τ µ + µ µ Y τµ Y µµ < τ µ + e e Y τµ Y ee < τ e + µ µ Y τe Y µµ < τ µ + µ e Y τµ Y µe < τ e + e µ Y τe Y µe < non-observation of these LFV transitions bounds on M most stringent decay: µ eee M 294 TeV,for Y O()

44 µ eγ and τ lγ Radiative processes due to exchange between lepton fields of the ++ and + fields Br(l l 2 γ) = α 48π ΣY ll Y l2 l l G 2 F M 4 Br(l eν ν e ) Process Constraint on Bound ( ( M ) 2 ) TeV µ eγ Σ l=e,µ,τ Y lµ Y el < τ eγ Σ l=e,µ,τ Y lτ Y el <.05 τ µγ Σ l=e,µ,τ Y lτ Y µl < 8.4 0

45 Bounds on combinations of Y Combined bounds ( Process Yukawa Bound ( M ) 2 ) TeV µ eγ Y µµ Y µe + Y τµ Y τe < τ eγ Y ττ Y τe <.05 τ µγ Y ττ Y τµ < Other bounds on Y Stringent bounds from M W Y µe 2 < ( M ) TeV Additional bounds from Bhabha scattering, muon anomalous magnetic moment,...

46 ) Y < 0 ( M TeV) or stronger observation of µ eγ at MEG (sensitivity of 0 3?) for Y O() 5 TeV < M < 50 TeV for Y O(0 2 ) 0.5 TeV < M < 0.50 TeV if M turns out to be as low as O(TeV), possibility of clean signals in hadronic accelerators (Tevatron, LHC) The production of ++ and, decaying into pairs of same-sign leptons striking signals, free from SM backgrounds If observed, must verify whether a scalar-mediated Seesaw is at work observe in addition at least three LFV processes (to measure and disentangle the individual Y ij couplings)

47 Bounds on Yukawas in Type III Lepton Flavour Violation at tree level µ eee, τ 3l Lepton Flavour Violation at loop level µ eγ, τ eγ Z decays (Z eµ, Z eτ, Z µτ) W decays, Universality tests, Invisible Z width... For M TeV, Y < 0 2 l l γ versus l 3l Generic results: In type I seesaw (fermionic singlet): Γ(l γl ) >> Γ(l 3l ) In type III seesaw (fermionic triplet): Γ(l γl ) << Γ(l 3l ) a measurement of a Γ(l 3l ) in the next generation of expt. would rule out TeV Fermionic triplet seesaw as its origin

48 Summary Leptogenesis is an interesting minimal mechanism that can explain the BAU and simultaneously neutrino masses. Sucessfull leptogenesis Generates strong constraints on neutrino masses. All derived in FA. When interaction rates of the charged Yukawa couplings are faster than the leptogenesis rates in BEs, they should be " integrated out" and we work in flavour basis. Flavours are relevant for M < 0 2 GeV Resulting Flavoured BE are different and thus the solutions also Phenomenology: Leptogenesis can work even with degenerate light neutrinos spectra: ǫ αα can be bigger than ǫ No upper bound on neutrino mass scale from successfull leptogenesis Baryon asym can be enhanced in specific models

49 What is the new physics? How to disentangle between models? d=6 operators allow to discriminate among models of Majorana ν rich phenomenology (hep-ph/060083; hep-ph/060528; hep-ph/ )