Superluminal Neutrinos? Constraints and Constructions. John Ellis King s College London (& CERN)

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1 Versus and Superluminal Neutrinos? Constraints and Constructions John Ellis King s College London (& CERN)

2 Versus and Do neutrinos really travel faster than light? Do photons travel at the speed of light? Photon v c: 1997 Neutrino v c: 1999 Astrophysical constraints on photon v: 2005/7 SN and accelerator constraints on neutrino v: 2008 Interpretation of OPERA: 2011

3 History in the Making? 1862: Maxwell found that there should be electromagnetic waves travelling at approximately the (known) speed of light 1905: Einstein used universal speed of light as foundation of geometric description of physics 2011: OPERA finds 6-σ discrepancy between neutrino speed and that of light Life in the fast lane

4 MINOS Measurement of ν Speed Near & far detectors Uncertainties Published result almost 2 σ > 0

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6 SN 1987a Constraints Revisited JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

7 Constraints from Supernova 1987a Data from 3 experiments Supernova simulation Arrived hours before γ s!!! δv < 10-9 JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv: Possible E dependence of δv constrained by bunching

8 Constraints from SN1987a Fit to possible E-dependent time-lag Linear: Quadratic: Subluminal and superluminal cases JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

9 OPERA could improve on MINOS JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

10 Structure of CNGS Beam Energy Spectrum Time structure JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

11 Possible Distortion of Spill 100 ns resolution, linear delay by 5 ns/gev, corresponding to M νqg1 = GeV JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

12 Arrival Times for Different Energies 1000-event slices Higher energies later JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

13 Fits to Simulated OPERA Data Linear case Quadratic case Sensitivity Sensitivity JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

14 Fitting Edges of Spill Factor ~ 5 less sensitivity to energy dependence JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

15 Using 5ns Bunch Structure 5 ns spacing, 1 ns bunches Fit to quadratic case Including rock events Sensitivity Sensitivity JE, Harries, Mersegaglia, Rubbia & Sakharov: arxiv:

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17 The Main Result

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19 Special and General Relativity Sagnac effect (rotation of Earth during travel): : δt = ns Tends to increase travel time Smaller than total error, taken into account Schwartzschild effects ~ Neutrinos follow geodesic, re-evaluate Euclidean distance Non-inertial effects, redshifts of clocks, dipole field, frame-dragging all negligible Kiritsis & Nitti: OPERA public note 136

20 Comparison of Neutrino Constraints Cacciapaglia, Deandrea & Panizzi: arxiv: Giudice, Sibiryakov & Strumia: arxiv: Alexandre, JE & Mavromatos: arxiv: SN1987a excludes δv ~ E or E 2

21 Power-Law Fit to Neutrino Data Need δv ~ E n with n > 2.5 Giudice, Sibiryakov & Strumia: arxiv:

22 Could Neutrinos be Tachyons? v would approach c from above as E increases No non-trivial finite-dimensional unitary representations of Lorentz group for m 2 < 0 i.e., no spin-1/2 spinors Should spin 0 be quantized as bosons? No (Feinberg) vs Yes (Sudarshan) Problem of causality! Reinterpret backward emission of E < 0 as forward emission of E > 0? Deform/break Lorentz symmetry?

23 Lifshitz-Type Field Theory Time and space dimensions scale differently (Interesting for quantum gravity, mass generation) Anisotropy parameter z Model for neutrino velocity: Action: Dispersion relation: Group velocity: v g = > c Superluminal propagation: δv ~ E 2 J. Alexandre: arxiv: Alexandre, JE & Mavromatos: arxiv:

24 Lorentz-Violating Gauge Theory Background vector or axial U(1) gauge field: Dispersion relation: Group velocity: Subluminal propagation (so far ) Alexandre, JE & Mavromatos: arxiv:

25 Background Gauge Field Allow background gauge field: Disersion relations: (ν anti-ν) Subluminal group v: Include anisotropic background: Group velocity may be super- or subluminal: Dependent on direction! Alexandre, JE & Mavromatos: arxiv:

26 Suggests Exotic Possibilities Neutrino speed antineutrino speed? Speed depends on direction? Possibility of diurnal variation as Earth rotates If no diurnal variation, V aligned with Earth s rotation axis In this case: Neutrino going North (MINOS) subluminal Null effect for neutrinos travelling East-West (T2K) Alexandre, JE & Mavromatos: arxiv:

27 Condensed-Matter Analogues? Systems known with relativistic fermionic excitations: p ~ E: Superfluids & superconductors Graphene Motivation for our early work Can study versions with superluminality e.g., PT-symmetry breaking in honeycomb photonic lattice Homework for particle physicists? Kupnin & Volovik: cond-mat/ JE, Mavromatos, Nanopoulos & Volkov: 1999 Szameit, Rechtsman, Bahat-Treidel & Segev: arxiv:

28 Čerenkov Radiation by Neutrinos Possible if speed > light dominant process e + e - Bremsstrahlung Energy loss rate: Difference between initial/final energies, terminal energy E T : Sensitive to δ = 2 δv and its E dependence Applied to IceCube data suggests Does not apply to models with distorted metrics, nonlinear deformations of Lorentz symmetry Cohen & Glashow: arxiv:

29 Distortion of Energy Spectrum? Events seen up to very high energies >> <E ν > = 28.1 GeV No apparent distortion of kinematic observables (relevant to possibility of Čerenkov radiation)

30 Constraints from ICARUS No visible distortion of neutrino energy spectrum No excess of e + e - pairs Cohen & Glashow: arxiv: ICARUS Collaboration: arxiv:

31 Gravitational Čerenkov Radiation Possible if speed > gravity waves, assumed = c Gravitational Čerenkov radiation: with OPERA δv ~ , maximum propagation time: Excludes GZK neutrinos (E ν ~ GeV, t ~ 10 8 y) by many orders of magnitude IceCube sees no neutrinos with E ν > GeV: would have t max < 10-4 s Alexandre, JE & Mavromatos: arxiv:

32 Revisiting Lorentz Violation with SN ν s 2D SN simulations suggest ringing on millisec scale If seen can be used to bound Lorentz violation Detectable in IceCube? Analyze emissions using wavelets Smear with δv(e) Bound if pulses seen JE, Janka, Mavromatos, Sakharov & Sarkisyan: arxiv:

33 Revisiting Lorentz Violation with SN ν s Short time-scale power disappears for time delay τ > 0.04 (s/mev) Potential constraints in linear case in quadratic case For subluminal (superluminal) propagation Potential for strong bound on δv(e) JE, Janka, Mavromatos, Sakharov & Sarkisyan: arxiv:

34 Space-Time Foam?

35 Nature of Quantum Gravity Vacuum Expect quantum fluctuations in fabric of space-time In natural Planckian units: ΔE, Δx, Δt, Δχ ~ 1 Fluctuations in energy, space, time, topology of order unity Space-time foam J.A.Wheeler Induce Lorentz violation?

36 Probes of Lorentz Violation for Photons Time delay from distant object: Compare arrivals of photons of different energies from astrophysical source with small intrinsic δt Gamma-Ray Bursters, pulsars, active galaxies, Typical sensitivities: Amelino-Camelia, JE, Mavromatos, Nanopoulos + Sarkar: 1997

37 Robust Analysis of GRB Data Corrected treatment of redshift Improved lower limit: JE, Mavromatos, Nanopoulos, Sakharov + Sarkisyan: astro-ph/

38 Time Delay from Markarian 501? Arrival time delay of ~ 4 minutes reported for photons in highest-energy bin Sensitive to M QG1 ~ GeV MAGIC Collaboration: astro-ph/

39 Results for AGN Markarian 501 Significance of time delay < 95% Linear dispersion: (E/M QG1 ) One-σ range: M QG1 = (0.34 to 0.78) x GeV 95% CL lower limit: M QG1 > 0.26 x GeV Quadratic dispersion: (E/M QG2 ) 2 One-σ range: M QG2 = (0.47 to 1.1) x GeV 95% CL lower limit: M QG2 > 0.27 x GeV Cannot exclude initial time delay at source MAGIC Collaboration + JE, Mavromatos, Nanopoulos, Sakharov, Sarkisyan: arxiv:0708:2889 [astro-ph]

40 Analysis of AGN PKS Observation by HESS of multiple flaring of AGN at larger redshift with more statistics HESS Collaboration: arxiv:0706:0797 [astro-ph]

41 Analysis of AGN PKS Comparison between HESS data in different energy bins No significant differences in arrival times Lower limit on m QG > GeV HESS Collaboration: arxiv:1101:33650 [astro-ph]

42 Fermi Analysis of GRB Redshift z = ± γ energies up to 31 GeV No hint of energydependent time delay Lower limit on m QG depends sensitively on assumptions m QG > 1.2 to 102 m P Fermi Collaboration: arxiv: [astro-ph]

43 The Story so far No technical error found OPERA carried out test with separated bunches No theoretical error found Difficult to reconcile with other constraints (SN1987a, Cohen-Glashow radiation, ) No direct contradiction with other experiments Other experiments are preparing to check This is how science should be done (technical scrutiny, verification, tests, theory)

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45 Comparison of Electron Constraints Much stronger than ν constraints