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A. Yu. Smirnov

Sterile neutrinos:. searches & implications. A. Yu. Smirnov. International Centre for Theoretical Physics, Trieste, Italy. Planck 2011, May29, Lisbon. Sterile neutrino. n s. Light. No weak interactions: - singlets of the SM symmetry group. RH - components of neutrinos.

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A. Yu. Smirnov

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  1. Sterile neutrinos: searches & implications A. Yu. Smirnov International Centre for Theoretical Physics, Trieste, Italy Planck 2011, May29, Lisbon

  2. Sterile neutrino ns Light No weak interactions: - singlets of the SM symmetry group RH - components of neutrinos Couple with usual neutrinos via (Dirak) mass terms Mix with active neutrinos may have Majorana mass terms maximal mixing? Sov. Phys. JETP 26 984 (1968) in the context of idea of neutrino–antineutrino oscillations

  3. LSND is back? Large Scintillator Neutrino Detector p -> p+ -> m+ + nm -> e+ + ne + nm Los Alamos Meson Physics Facility ne + p  e+ + n decay at rest nm nm ->ne ne L = 30 m P = (2.64 +/- 0.67 +/- 0.45) 10-3 Oscillations? n Dm2 > 0.2 eV2 e+ 3.8s excess t 200 t mineral oil scintillator Cherenkov cone + scintillations

  4. Sterile neutrinos as solution of all the problems Plan: 1. New evidences? 2. The Sun: sterile shining 3. Searching for sterile in ice

  5. New evidences?

  6. MiniBooNE: anti-nu L = 541 m, <En> ~ 800 MeV 12 m diameter tank 450 t (mineral oil) 1280 PMT

  7. Reactor neutrino anomaly Revised value of cross-section G.Mention et al, arXiv: 1101.2755 Increase of the Mean flux by 3% Rreact = 0.937 +/- 0.027 2.14 s Dm2 > 1.5 eV2 sin2 2q = 0.17 +/- 0.1

  8. Gallium anomaly Calibration Source + reactor Gallex/GNO 51Cr SAGE 51 Cr, 37Ar RGa = 0.87 +/- 0.05 G.Mention et al, arXiv: 1101.2755 sin22q = 0.24 C Giunti, M. Laveder Dm2 = 2.15 eV2

  9. Controversial and not convincing Consistency With reactor anomaly global fit of data in terms of nu-sterile becomes better Limit on Ue4 becomes weaker |Ue4|2 : 0.02  0.04 Smaller values of Um4 are allowed to explain LSND/MiniBooNE – less tension with SBL experiment bounds |Um4|2 : 0.04  0.02 3 + 2 scheme Global fit n5 n4 Dm512 = 0.87 eV2 Dm412 = 0.47 eV2 Ue4 = 0.128 Ue5 = 0.138 J Kopp, M. Maltoni,T.Schwetz 1103.4570 [hep-ph] Um5 = 0.148 Um4 = 0.165

  10. Extra radiation in the Universe Effective number of neutrino species - WMAP-7 - Barion Acoustic Oscillations - Hubble constant E. Komatsu et al arXiv: 1001.4538 [astro-ph.CO] + 0.86 - 0.88 Neff = 4.34 (68 % CL) - WMAP–7 - Atacama Cosmology Telescope Neff = 5.3 +/- 1.3 (68% CL) J. Dunkley et al arXiv:1009.0866 [astro-ph.CO] D Neff = (0.02 – 2.2) (68% CL) J. Hamann et al PRL 105 (2010)181301 BBN Y. I. Izotov and T X Thuan Astrophys J 710 (2010) L67 + 0.80 - 0.70 Neff = 3.68 (68 % CL)

  11. Cosmological bounds E Giusarma et al 1102.4774 [astro-ph] J R Kristiansen, O Elgaroy 1104.0704 [astro-ph] LCDM Inverse approach: Dm2 < 0.25 eV2 wCDM + 2nS 1). w < -1 ruling out L 2). Age of the Universe 12.58 +/- 0.26 Gyr 68 % 95% too young? • WMAP • SDSS (red galaxy clustering) • Hubble (prior on H0 ) The oldest globular clusters 13.4 +/- 0.8 +/- 0.6 Gyr run 1 (blue) + BBN • Supernova Ia Union • Compilation 2 (in add) run 2 (red)

  12. Mass scales - LSND, MiniBooNE 40 - 70 MeV 1 MeV ns • Warm Dark matter • Pulsar kick ~ 10 keV 1 keV • - LSND, MiniBooNE • Reactor anomaly • Calibration experiments • - Extra radiation 0.5 - 2 eV 1 eV (2 – 4) 10-3 eV - Solar neutrinos - Extra radiation in the Universe 10-3 eV

  13. Mixing ne nm nt mee mem met … mmm mmt … … mtt meS mmS mtS Mass matrix nS … … … mSS For mSS ~ 1 eV tanqjS = mjS/mSS ~ 0.2 - is not small produces large corrections to the active neutrino mass matrix dmij ~ - tanqiStanqjS mSS ~ 0.04 mSS mSS >> mab , maS In general can not be considered as small perturbation! Effect can be small if J. Barry, W. Rodejohann, He Zhang arXiv: 1105.3911 Active neutrino spectrum is quasi degenerate meS mmS mtS have certain symmetry mSS ~ mab

  14. Applications mn = ma + dm Original active mass matrix e.g. from see-saw Induced mass matrix due to mixing with nu sterile dm can change structure (symmetries) of the original mass matrix completely (not a perturbation) produce dominant mt - block with small determinant Enhance lepton mixing Be origin of difference of Generate TBM mixing UPMNS and VCKM

  15. The Sun: shining in sterile P. C. de Holanda, A. Yu. S. 1012.5627 [hep-ph]

  16. Homestake BOREXINO SNO SuperKamiokande

  17. Problem? QArexp < QArLMA 2.55 +/- 0.25 SNU > 3.1 SNU No turn up of the spectrum in SK P. de Holanda, A.S. Phys. Rev. D69 (2004) 113002 hep-ph 0307266 Light sterile neutrino RD = Dm012 /Dm212 << 1 • << 1 - mixing angle of sterile- active neutrinos  dip in survival probability Motivation for the low energy solar neutrino experiments BOREXINO, KamLAND …

  18. Up-turn? pp 7Be CNO 8B SNO: LETA gap BOREXINO ne- survival probability from solar neutrino data vs LMA-MSW solution

  19. (3 + 1) scheme ne ns nt nm n3 Dm2atm mass n2 Dm2sun n0 Dm2dip n1

  20. Level crossing H D m012 > (0.2 - 2) 10-5 eV2 ne n2m sin2 2a= 10-4 - 10-3 ns non-adiabatic level crossing nm/t n0m sterile resonances n1m density

  21. Mixing scheme and transitions ns ne na n0 n1 n2 U = Uq Ua Uq - rotation in 12-plane on q12 ns mixes inn0and n1 Ua - rotation in 01- plane on a Scheme of transitions n2 n2m ne n1m ne n1 interference  wiggles n0m n0 ns P(nene) ~ |Ue1mA11 + Ue0mA01|2 |Ue1 |2 + |Ue2 m|2|Ue2|2

  22. Survival probability - dip - wiggles

  23. Spectra sin22a = 10-3 (red), 5 10-3 (blue) SK-I SNO-LETA P. De Holanda, A.S. SK-III Borexino SNO-LETA RD = 0.2 Dm2 = 1.5 10-5 eV2

  24. BOREXINO: Be line data excluded excluded RD = 0.007 - 0.07 Be Dm012 > 0.5 10-5 eV2 pep Predictions for pep-neutrinos RD = 0.07 - 0.115 P(pep) = 0.2 – 0.3 P(Be) = 0.55 pep-suppressed RD > 0.12 P(pep) = 0.53

  25. Fit of spectra c2 fit of spectra with sterile neutrino dip: SK-I, SK-III, SNO-LETA, SNO-NC, Borexino Best fit values: Dc2 = 7.5 sin2 2a ~ 10-3 Dm012 ~ 1.5 10-5 eV2 Interval with sin22a ~ (0.5 – 1) 10-3 D m012 = (1 – 2) 10-5 eV2 Dc2 > 6 m0 > 0.003 eV Alternative: mixing with level n2m sin22a ~ (0.5 – 1) 10-3 RD = Dm012 /Dm212 = 1.1

  26. Implications m0 ~ 0.003 eV M2 MPlanck m0 = M ~ 2 - 3 TeV mixing h vEW M sin2 2a ~ 10-3 h = 0.1 a ~ vEW M sin2 2b ~ 10-1 b ~

  27. Level crossing scheme P. De Holanda, A.S. Mixing with the third active state ns

  28. Extra radiation in the Universe Production of sterile in the Early universe Mixing of ns in n3 M Cirelli G Marandella A Strumia F Vissani n3 = cosb nt’ + sinb ns nt’ = cosq23 nt + sinq23 nm where Dm302 ~ 2.5 10-3 eV2 Atmospheric neutrinos: sin2b < 0.2 – 0.3 (90%) MINOS: sin2b < 0.23 (90%) tan2b

  29. Other consequences Atmospheric neutrinos ER ~ 12 GeV nt’ – ns resonance nmns resonance peak 10 – 15 GeV IceCube Deep Core Supernova neutrinos Additional suppression of ne flux

  30. Searching for sterile in Ice S Razzaque and A. S. arXiv:1104.1390 [hep-ph]

  31. Test H Nunokawa O L G Peres R Zukanovich-Funchal Phys. Lett B562 (2003) 279 nm - ns oscillations with Dm2 ~ 1 eV2 are enhanced in matter of the Earth in energy range 0.5 – few TeV This distorts the energy spectrum and zenith angle distribution of the atmospheric muon neutrinos, also modifies m/e ratio S Choubey JHEP 0712 (2007) 014 Can be tested by IceCube First data from IceCube • Check theoretical considerations, • generalize … • - perform analysis of the data

  32. IceCube

  33. IceCube results R. Abbasi et al, arXiv:1010.3980 [astro-ph.CO] Zenith angle distribution Unfolded neutrino spectrum April 2008 – May 2009 40 strings 100 GeV – 400 TeV 18 000 up-going muons

  34. (3 + 1) scheme ne ns nt nm LSND/MiniBooNE: vacuum oscillations n4 P ~ 4|Ue4 |2|Um4 |2 Dm2LSND mass Restricted by short baseline experiments CHOOZ, CDHS, NOMAD n3 Dm2atm n2 Dm2sun n1 With new reactor data: Dm412 = 1.78 eV2 Ue4 = 0.15 Um4 = 0.23

  35. Level crossing scheme Normal mass hierarchy in the flavor block; m0 ~ 1 eV Three new level crossings |Ue4 |2 |Um4 |2 are large enough, so that evel crossings are adiabatic Ve - Vs = 2 GF (ne – nn /2)

  36. nS - mass mixing scheme ns nt nm n0 n3 n2 Uf = U23 Ua ns mixes in the mass states n3andn0 ~ n0 = - sina n3 + cosa ns where ~ ~ n3 = cosa n3+ sina ns n3 = cosq23 nt + sinq23 nm ~ ~ n2 = cosq23 nm - sinq23 nt n2 = n2 ~ ns mixes with n3 ~ ~ ns, n3, n2 Propagation basis: Evolution is reduced to 2n-problem exactly

  37. Evolution Propagation basis ~ nf = U23 n ns ns ns ns ~ ~ nt nt n3 n3 A33 ~ ~ nm nm n2 n2 A22 decouples propagation projection projection S P(nmnm) = |cos2q23A22 + sin2q23A33 |2

  38. Survival probability Effect of phase shift for the nm - ntoscillations due to matter effects neutrinos antineutrinos MSW resonance dip

  39. Energy spectra

  40. Suppression factor S = N(osc.)/N(no osc.) Eth = 0.1 TeV

  41. Zenith angle distribution nS - mass mixing case Free normalization and tilt factor

  42. Bounds on mixing Illustrative fit in the simplest mixing scheme + 5% uncorrelated systematic errors LSND: sin2a > 0.04 Statistical errors + free normalization + tilt

  43. ns-nm - mixing ns nt nm n0 n3 n2 Uf = Ub U23 ns mixes with nm n0 = - sinb nm + cosb ns n3 = - cosb sinq23 nm + cos q23nt - sinb sinq23 ns n2 = - sinb cosq23 nm + sin q23nt - cosb cosq23 ns Propagation basis = flavor basis Evolution is not reduced to the 2n - evolution exactly

  44. Probabilities antineutrinos neutrinos

  45. Zenith angle distribution nS - nm mixing Free normalization and tilt factor Fit with sterile is even better Eth = 0.1 TeV

  46. Suppression factors Eth = 1 TeV Eth = 0.1 TeV

  47. Summary New evidences/hints of existence of sterile: MiniBooNE, reactors, Gallium calibration, solar, additional radiation in the Universe Convincing? Consistent? Controversial? Light sterile neutrino mixed in n1 or/and n2 with D m012 ~ 1.5 10-5 eV2 sin2 2a ~ 10-3 leads to the dip in the spectrum which explains an absence of the up turn of the spectrum, reduces prediction for the Ar production rate Being mixed in n3 with sin2b ~ 0.2 sterile can be generated in the Early Universe DNeff ~ 1, thus explaining additional radiation

  48. IceCube has high sensitivity to sterile mixing with D m012 ~ 1 eV2 sin2a > 0.01 Depending on values of parameters, Um4, Ut4 , Dm422 large variety of zenith angle distribution can be obtained. With present data only part of the parameter space relevant for LSND/MiniBooNE can be excluded and in some ranges the fit can be even improved. Future high statistics studies of the zenith angle distributions in different energy regions (with different energy thresholds) can provide sensitive search of sterile in whole parameter space and discriminate different mixing scenarios.

  49. MINOS bound E = 475 MeV E = 200 MeV

  50. Dependence on mixing scheme In general, the Hamiltonian H = D0 V0 x V0T + D2 V2 x V2T (i = 0, 2) ViT = ( USi , Ut i , Um i ), Di = Dmi32 / 2E In the lowest order at high energies H ~ D0 V0 x V0T V0T = ( US0 , Ut 0 , Um 0 ) P(nmnm) ~ | sin2q’A33(a) + cos2q’|2 tanq ’ = - Um 0 / Ut 0 sin2a = |Um 0|2 + | Ut 0|2 Dm032 = 1 eV2 |Um 0|2 ~ 0.02 – 0.04 LSND/MiniBooNE |Ut 0|2 < 0.5 MINOS, Atmospheric neutrinos

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