Sergio Palomares-Ruiz June 8, 2005 LS N D imits olutions ew iscoveries et’s peak about LSND eutrinos in elphi WIN’05 20th International Workshop on Weak Interactions and Neutrinos Delphi, Greece, June 6-11, 2005 The Anomaly

Sergio Palomares-Ruiz June 8, 2005 THE FACTS

Sergio Palomares-Ruiz June 8, 2005 “Non Standard” results Solar neutrino deficit 8 σ effect Atmospheric neutrino anomaly 14 σ effect Neutrino disappearance  m 2 21 = ( ) eV 2 sin 2  12 = (0.23 – 0.37) |  m 2 31 | = (1.4 – 3.3) eV 2 sin 2 2  23 > 0.90 Neutrino Oscillations Homestake, SAGE, GALLEX, SK, SNO + KamLAND SK and K2K Standard results sin 2  13 < M. Maltoni et al., New J. Phys. 6:122, 2004

Sergio Palomares-Ruiz June 8, 2005 “Standard” results Bugey ( e → e ) L = 15 m, 40 m, 95 m; E ~ few MeV →  m 2 ~ 0.01 – 1 eV 2 CHOOZ and Palo Verde ( e → e ) [for  13 small] L ~ 1000 m; E ~ few MeV →  m 2 ~ eV 2 CCFR (  →  ) L = km and km (2 detectors) 40 GeV < E < 230 GeV →  m 2 ~ 10 – 100 eV 2 CDHS (  →  ) L = km and km (2 detectors) E ~ GeV →  m 2 ~ 1 – 100 eV 2 No neutrino disappearance

Sergio Palomares-Ruiz June 8, 2005 “Standard” results NOMAD (  → e ) L = km; 1 GeV < E < 100 GeV →  m 2 ~ 1 – 100 eV 2 KARMEN (  → e ) L = 17.6 m; 16 MeV < E < 50 MeV →  m 2 ~ 0.1 – 10 eV 2 No neutrino appearance So far, so good! No short baseline neutrino “anomaly” Neutrino anomalies explained by oscillations between 3 neutrinos → 2 independent  m 2

Sergio Palomares-Ruiz June 8, 2005 LSND (  → e ) L = 30 m; 20 MeV < E < 52.8 MeV →  m 2 ~ 1 – 10 eV 2 It did see e appearance! Non-Standard result Neutrino appearance But…  m 2 atm +  m sol   m 2 LSND

Sergio Palomares-Ruiz June 8, 2005 The LSND experiment A. Aguilar et al., Phys. Rev. D64:112007, 2001 Neutrinos are produced from pion and muon decays  + →  +  (e + e )  - →  -  (e - e )  + → e + e   - → e - e  e Most  + decay at rest (97%) and also most  + Very few  - decays at rest (DAR) → 0.08% e backgrounds

Sergio Palomares-Ruiz June 8, σ effect A. Aguilar et al., Phys. Rev. D64:112007, 2001G. Drexlin, Nucl.Phys.Proc.Suppl.118: ,2003 e excess : 87.9 ± 22.4 ± 6.0 P (  → e ) = (0.264 ± ± 0.045) %

Sergio Palomares-Ruiz June 8, 2005 THE ESPECULATIONS

Sergio Palomares-Ruiz June 8, 2005 Classifying solutions With and without sterile neutrinos –With one and with more than one sterile With and without neutrino oscillations With and without CPT violation With non-standard and with standard processes With and without extra dimensions With problems and with problems Those we like and those we don’t like Those we have proposed and those we haven’t proposed No solution But if LSND is right, all imply NEW PHYSICS!

Sergio Palomares-Ruiz June 8, neutrino models  m 2 sol  m 2 atm  m 2 LSND e   s Steriles would participate in solar and atmospheric neutrino oscillations Ruled out at 5.1 σ Disfavored by SBL and atmospheric neutrino experiments M. Maltoni et al., New J. Phys. 6:122, 2004

Sergio Palomares-Ruiz June 8, neutrino models  m 2 sol  m 2 atm  m 2 LSND1  m 2 LSND2 M. Sorel, J. M. Conrad and M. H. Shaevitz, Phys. Rev. D66:033009,2002 Compatibility between SBL (including KARMEN) and LSND of 30%, instead of 3.6 % in the standard 3+1 model

Sergio Palomares-Ruiz June 8, 2005 CPT violating spectra  m 2 sol  m 2 atm e   The killer: reactor experiments Bugey and CHOOZ: need U e3 ' 1 P KamLAND ' 1  m 2 atm  m 2 LSND  m 2 KamLAND  m 2 LSND,atm H. Murayama and T. Yanagida, Phys. Lett. B520: , 2001 G.Barenboim, L. Borissov and J. Lykken, Phys.Lett.B534: ,2002 The killer: atmospheric experiments … for LSND  m 2, antineutrinos signal would wash out the up-down asymmetry produce a deficit of up-going muon events near the horizon Although there is some room for CPT violation with all-but-LSND data… G. Barenboim, L. Borissov and J. Lykken, hep-ph/ A. Strumia, Phys. Lett. B539:91-101,2002 M. C. González-García, M. Maltoni and T. Schwetz, Phys. Rev. D68:053007, 2003

Sergio Palomares-Ruiz June 8, models - U  4 constrained by CCFR and atmospherics, not CDHS → still some room - U e4 constrained by GALLEX ( e disappearance during test with a 51 Cr source) 2+2 models Too little sterile content on solar and atmospheric neutrino oscillations → Ruled out Hybrid models (3+1), (2+2) : no bound from solar neutrino data (3+1), (2+2) : similar to (2+2) → excluded 4 neutrinos + CPT violation Assuming the same  m 2 for neutrinos and antineutrinos but different mixings V. Barger, D. Marfatia and K. Whisnant, Phys. Lett. B576: ,2003

Sergio Palomares-Ruiz June 8, 2005 CPT violating decoherence Quatum gravity models involve singular space-time configurations: space-time foam → decoherence is the result of particle propagation due to the fuzzy properties of the background not necessarily related to mass differences between particles and antiparticles Simple model: effects only in the antineutrino sector and diagonal decoherence matrix → No spectral distortions at KamLAND Without KamLANDWith KamLAND G. Barenboim and N. E. Mavromatos, JHEP01:034, 2005 Pure decoherence Pure decoherence both Mixing + decoherence Mixing + decoherence both

Sergio Palomares-Ruiz June 8, 2005 Lorentz violation In the minimal Standard Model Extension (SME) with Lorentz violation, neutrinos are massless and oscillations are determined by 102 real constants controlling the Lorentz violation V. A. Kostelecký and M. Mewes, Phys. Rev. D69:016005, 2004 P (  → e ) ' |(h eff )  e | 2 L 2 → for LSND |(h eff )  e | 2 ~ (3 x GeV) 2 V. A. Kostelecký and M. Mewes, Phys. Rev. D70:076002, 2004 Unusual dependences for the oscillation phases: a L L and c L L E Predict, e.g., azimuthal dependence for atmospheric neutrinos Constraints (in the  -  sector): a L < few GeV c L < M. C. González-García and M. Maltoni. Phys. Rev. D70:033010, 2004 a L ~ GeV c L ~

Sergio Palomares-Ruiz June 8, 2005 LFV muon decay The  L = 2 decay:  + → e + + e +  (  = e, ,  ) could explain LSND data if Scale of new physics relatively low,  ~ GeV, → effects on low energy observables, e.g., the SM  parameter in the Michel spectrum These models predict  = 0 for  L = 2 decays → constrained by KARMEN BR KARMEN (90% CL) B. Armbruster et al., Phys. Rev. Lett. 90:181804, 2004 K. S. Babu and S. Pakvasa, hep-ph/ Predicted  = TWIST experiment Measured  = ± ± ± J. R. Musser et al., Phys. Rev. Lett. 94:101805, 2005

Sergio Palomares-Ruiz June 8, 2005 Mass varying neutrinos Matter effects on neutrinos due to the interaction with a very light and weakly coupled scalar particle could give rise to masses and mixings which are enviroment dependent Yukawa couplings V(  )´´ Nucleon number density LSND, KamLAND, K2K and Palo Verde are in matter Bugey and CHOOZ are in air KARMEN is 50% in matter and 50% in air CDHS is unknown It could accomodate 3+1 models: an experiment like Bugey but in matter should see disappearance Limits for 2+2 models are very model dependent D. B. Kaplan, A. E. Nelson and N. Weiner, Phys. Rev. Lett. 93:091801, 2004 K. M. Zurek, JHEP 0410:058, 2004

Sergio Palomares-Ruiz June 8, 2005 Shortcuts in extra dimesions In some theories with extra dimensions, SM particles propagate only in the brane, but non-SM particles can also do it in the bulk. If the brane is distorted → shortcuts s travel “faster” This induces an effective term in the hamiltonian which introduces resonant mixing driven by , the aspect ratio of the brane deformation The key point: evading CDHS bounds by a resonance in the range MeV No effect No bound If E res ~ 30 – 100 MeV → no signal in MiniBooNE If E res ~ 200 – 400 MeV → impressive signature in MiniBooNE H. Päs, S. Pakvasa and T. J. Weiler hep-ph/

Sergio Palomares-Ruiz June 8, 2005 Neutrino oscillations + decay The decay option: key ingredient to evade CDHS bounds For small U  4 and short baselines 3+1 model with a decay option… …but LSND explained (mainly) by oscillations CDHS compares measurements at two detectors: if D 1 = D 2, no difference This requires  4 / m 4 ~ and m 4 ~ few eV → g ~ In contradiction with laboratory bounds g < E. Ma, G. Rajasekaran and I. Stancu, Phys. Rev. D61:071302, 2000

Sergio Palomares-Ruiz June 8, 2005 Neutrino decay 3+1 model with a decay option… …but LSND explained by decay Good fit to data SPR, S. Pascoli and T. Schwetz, hep-ph/ As far as g e ´  U el g hl  0, we expect e and e appearance

Sergio Palomares-Ruiz June 8, 2005 Mixing of e with 4 is not required → we set U e4 = 0 Only CDHS and atmospherics constrain the model LSND and KARMEN compatibility SPR, S. Pascoli and T. Schwetz, hep-ph/

Sergio Palomares-Ruiz June 8, 2005 The rate of N’s is controlled by U  4 and that of e ’s by g he In order to be consistent with laboratory and supernova bounds, a typical value is g ~ With  -1 ~ L LSND (g m 4 ~ eV) → m 4 ~ 100 keV The MiniBooNE signal In addition, extending the model with an extra neutrino and allowing for complex couplings, the signal in the neutrino run might be suppressed SPR, S. Pascoli and T. Schwetz, hep-ph/

Sergio Palomares-Ruiz June 8, 2005 THE RIGHT ONE

Sergio Palomares-Ruiz June 8, 2005 ??

Sergio Palomares-Ruiz June 8, 2005 Conclusions Solar (8σ) and atmospheric neutrino (14σ) anomalies well understood in terms of oscillations LSND: the only (anti)neutrino appearance experiment with positive signal (3.3σ)… why shouldn’t it be right? Many possible solutions… … if LSND is right, (hopefully) one must be right If so, we might need to forget about our prejudices on sacred principles, modify the Standard Model of Cosmology… We all will have more fun! If anyone is in a hurry…

Sergio Palomares-Ruiz June 8, 2005 So we will wait for MiniBooNE! Oracular responses were given every month, on the 7th day, the birthday of Apollo …we could ask to Delphi’s Oracle Unfortunately…