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Slide 2 Robert Ehrlich George Mason University mason.gmu.edu/~rehrlich The Hunt for the Tachyon ABSTRACT: Despite the apparent conflict with relativity, some physicists have continued to seek evidence for the existence of hypothetical faster-than-light particles dubbed tachyons. In the past all claims of tachyons have, however, later been shown to be incorrect, or at least not reproducible. Nevertheless, the speaker believes that the tachyon is not some mythical beast, and that we may be on the verge of proving its existence. Specifically, he believes that the ever-surprising neutrino, or its electron flavor, is actually a tachyon. It might be useful to check out the speakers youtube video or a press release describing his latest research on the subject, both of which can be found on his web site: http://mason.gmu.edu/~rehrlich/http://mason.gmu.edu/~rehrlich/ Sound check (a biased view?) Slide 3 The phantom of the OPERA Sent bunches of neutrinos from CERN to a detector 730 km away Compared their time of flight to that of light, c Measured neutrino speed higher than c by 0.0000237 % photon Experiment has been redone by OPERA and others, and all now show a departure from c within the experimental uncertainty -- just the latest of a number of false sightings. This is not the greatest time to make the case for superluminal (FTL) neutrinos! The OPERA experiment (2011) NOT the way experiment was done! Slide 4 Many false sightings: all speed measurements so far consistent with v = c within experimental uncertainties, but we know that neutrinos (unlike photons) cannot have exactly v = c. Never settled: Negative results on speed measurements cannot rule out neutrinos being tachyons they only set more stringent limits, i.e., v closer to c. Pointless? Many people believe there is no point in even looking since Einstein said v > c is impossible! Conclusions from tachyon searches Slide 5 Nothing can go faster than light if it travels in in vacuum if it carries energy or information if it started out slower than light if it is measured locally within the space Slide 6 Why were tachyons first proposed? (1962) m is imaginary! Bilaniuk, O.-M. P.; Deshpande, V. K.; Sudarshan, E. C. G. "'Meta' Relativity". American Journal of Physics 30 718 (1962). How can you define the rest mass of tachyons which can never be at rest!?! Rest mass Relativistic mass Slide 7 Tachyons would fill a vacant niche Tachyon luxon tardyon Past light cone Future light cone Else- where Else- where 3 world lines Spacetime diagram (c = 1.0 here) Slide 8 Tachyons from A to B Tachyon kinematics is consistent with special relativity For v > c particles relativity says M 2 < 0 No passing through the light barrier from either side 3 distinct classes: tachyons, tardyons & luxons Neither required nor forbidden by theory They violate causality -- sending messages back in time??? Slide 9 How are the neutrino masses found? -- For some reaction where neutrino is emitted measure the missing (unobserved) energy E & momentum p -- Calculate the missing mass from: m 2 = E 2 p 2 (relation assumes c = 1) Why? The only known candidates for being tachyons are one of the 3 types of neutrinos. ANSWER: Only neutrinos have masses so close to zero that within the experimental uncertainty we do not know if m 2 > 0 or m 2 How could we tell if neutrinos are tachyons? 1. Find one type that can outrace light (v > c). 2. Find one type that has an imaginary rest mass, i.e., 3. Look for low energy neutrinos created in a brief pulse arrive before high energy ones Supernovae are the only way it could be done why? A. Chodos, and V. A. Kostelecky, Phys. Lett. B 150, 431 (1985; Least Sensitive test Wait until 2020 (Katrin) STATUS Need enormous distance to see spread in times due to energy variation. Slide 14 13 SN 1987A 1 st supernova whose neutrinos were observed Slide 15 Super-Kamiokande Neutrino detector: Currently the Worlds largest 14 Super K is hundreds of times more sensitive than what was available in 1987 Slide 16 What can SN tell us about the neutrino mass, m? How does arrival time ordinarily correlate with energy, E? Infinite energy neutrino 1/E 2 Lags lightLeads light Is arrival time relative to light & T is light travel time from SN Slope ~ 1/m 2 Slide 17 How about a tachyonic mass? (m 2 < 0) Infinite energy neutrino 1/E 2 The limited data on SN 1987 neutrinos hinted at a tachyonic neutrino. Ehrlich, R. Tachyonic neutrinos and the neutrino masses, Astropart. Phys., 41 (2013) 16, http://arxiv.org/pdf/1204.0484.pdf http://arxiv.org/pdf/1204.0484.pdf Slide 18 The actual data: 24 neutrinos from SN 1987A supports 2 mass values m 1 = 4 eV neutrinos m 2 = 21 eV neutrinos v > c neutrinos -- none observed R. Ehrlich, Evidence for two neutrino mass eigenstates from SN 1987A and the possibility of superluminal neutrinos, Robert Ehrlich, Astroparticle Physics 35, 625628 (2012) Slide 19 A 3 rd superluminal (v > c) neutrino to the rescue The flavor state masses can be very close to zero (and even negative) if one of the mass states has m 2 < 0 Slide 20 4 Dots are simulated data Both slope and intercept predicted & no background SN 1987A data for 17 min interval Including burst 12 MeV The one real data point available Would lie on line shown!!! Chances of the one event being due to random background? What if they found 2 more in looking at the data for the rest of the one hour? Slide 21 How could we tell if neutrinos are tachyons? 1. Find one type that can outrace light (v > c). 2. Find one type that has an imaginary rest mass, i.e., 3. Look for low energy neutrinos created in a brief pulse arrive before high energy ones Supernovae are the only way it could be done why? 4. Find an energetically forbidden decay in which one is emitted!!! A. Chodos, and V. A. Kostelecky, Phys. Lett. B 150, 431 (1985; Least Sensitive test Wait until 2020 (Katrin) Next SN in galaxy will tell Maybe seen already!!! STATUS New results Need enormous distance to see spread in times due to energy variation. Slide 22 New results: A peak just above the knee of the cosmic ray spectrum -- what is the knee & what on Earth does it have to do with tachyons? Slide 23 Recent work is based on experiment on high energy cosmic rays What is known about them Acceleration mechanism? Composition? Points of origin? Shape of spectrum, dN/dE? NASA Drawing of showers of charged particles created by incoming high energy cosmic rays 22 Slide 24 A Radical proposal: Missing protons? Slide 25 Missing protons interpreted as being due to the onset of proton beta decay at an energy E = E knee Proton beta decay (normally energetically forbidden) why? Inverse beta decay (allowed if proton has enough E & neutrino is a tachyon) Tachyons violate causality, or reverse their direction in time and the sign of their energy in certain reference frames, i.e., an emitted neutrino of energy E appears as an absorbed (anti) neutrino to a sufficiently rapidly moving observer moving with the proton at speed: Follows from the Lorentz Transformation 1 Ehrlich, R., "Implications for the Cosmic Ray Spectrum of a Negative Electron Neutrino Mass 2, Phys. Rev. D, 60, 17302 (1999) 24 From energy of knee deduce neutrino has: m 2 ~ -- 0.25 eV 2 Slide 26 p ne + v pe - v ne + v pe - v ne + v The p n p n p Decay chain Assume n p much slower than p n. Chain continues with energy loss at each step until p drops below the energy of the knee. The result is a pile up of neutrons at an energy a bit above the knee a small peak at around 4.5 PeV (+ 2.2 PeV) After 1999 prediction a 2 nd paper written in same year found a 4.5 PeV peak for CRs pointing back to Cygnus X-3. Chain Offers a way cosmic rays could mostly point back to their sources Slide 27 Cygnus X-3 paper 1 in which peak claimed 1. R. Ehrlich, Phys. Rev. D 60, 073005 (1999) using published data from: J. Lloyd-Evans et al., Nature, 305 (1983) 784. Counts above background vs energy Signal based on counts in 2.5% wide interval of phase, background based on the other 97.5% -- factor of 40 background suppression Animation 26 1 PeV 10 PeV 100 PeV 4.5 Slide 28 Any guesses? Reception to 4.5 PeV paper (1999) Was cited by 23 people over the years, but by the wrong ones! Great skepticism (extending to whether all reports of Cygnus X-3 claimed CR signals were genuine), in light of several high statistics subsequent experiments having negative results: The coffin nail CASA-MIA (1996) In addition, conventional wisdom is that except at very high energies, CRs being charged protons or nuclei are randomized sufficiently by galactic B-field so that none point back to sources. Also, neutrons could not survive the trip from any sources 27 Slide 29 Why 4.5 PeV signal from Cygnus X-3 only seen in some experiments? Obviously signal cannot show up in experiments that lack enough CRs with E ~ 4 PeV. CASA-MIA had only 0.09% of its data with E > 1.2 PeV Plus, being a weak signal 4.5 PeV peak only shows up when background suppressed by: -- cut on times of very rare major flares (Tibet & Marshak) -- cut on 2.5% phase window (Lloyd-Evans) 28 Slide 30 Other support for a peak near 4.5 PeV 29 Slide 31 The Tunka experiment Data is from the Tunka Collaboration (35 physicists, mainly Russians) 133 Cherenkov detectors (1 PeV) Data analyzed: 1.8 M events collected over 3 years 2009 -2012; energy resolution 15% & energy threshold 1 PeV. Tunka continues to take data. 30 Cherenkov Effect Slide 32 My connection to Tunka? I am not aware if Tunka has taken a position on my results. Around Jan 2013 I connected with Mikhail Zotov at MSU about some cosmic ray work he had done MZ had access to the Tunka data though he was not a member of the group. He provided me with his analysis of the data though he declined to be a coauthor on the paper based on it. 31 Absolutely none! Slide 33 New paper supporting 4.5 PeV peak Dont look at any one suspected source, but do a blind search for candidate sources anywhere in the sky, i.e, statistically significant excess of counts above what calculated background See how the excess number of candidate sources depends on energy & look for a peak near E = 4.5 + 2.2 PeV Data Suggests a peak in CR spectrum at 5.86 PeV consistent with previous claim of peak at 4.5 + 2.2 PeV 32 Slide 34 More on idea of a blind search 33 Tile the celestial sphere (with circles) & look for excess counts at various significance levels S in each circle. Do it for 3 circle sizes & shift whole pattern one degree at a time to do another search. Map of the sky In celestial coordinates declination = 0 Right ascension = 0 Expectation based on chance: Red : candidate sources Blue: candidate sinks Slide 35 How to look for a peak in spectrum if you do not know where sources are? Define candidate sources: Small region of sky from which cosmic rays of energy E appear to come in excessive numbers (rel. to bkgd.) Excessive is defined in statistical terms p < 1/2000 Candidate sources are not associated with any known objects Find number of candidate sources versus energy & look for a peak many more at some particular energy 34 Slide 36 Calculation of background: Time shuffling method Accurate means needed in order to know what the excess is at any location in the sky (in the absence of a real source) Use the Shuffling method which relies on the data itself & shuffles recorded times between events. Hinges on fact that any sky location (in celestial coordinates RA & declination) connects to many Earth-based coordinates (in azimuth, altitude, and t -- time event recorded. If no real sources the time shouldnt matter Earth-based coordinates: Altitude & azimuth North star Any source with a specific RA & declination changes its altitude & azimuth as the Earth rotates Slide 37 For E = 5.86 PeV energy bin many more large S > 0 excesses than chance predicts & no excess for S < 0 N S Standard Gaussian (sigma = 1) Candidate sources taken to have S > 3.3 sigma excess above background Basis of this definition? 68 candidate sources -- 48 above Gaussian 36 Slide 38 Numbers of excess candidate sources in each energy bin E (PeV) N N No excess seen for candidate sinks Not physically possible Candidate sources S > 3.3 Candidate sinks S < - 3.3 Slide 39 38 Locations of candidate sources Locations of candidate sinks Slide 40 Summary of the new evidence No single source identified, but the number of candidate sources (68) is much greater than chance would predict (20) in the energy bin centered on 5.86 PeV. Consistent with 1999 result (peak at 4.5 + 2.2 PeV) for Cygnus X-3, and with previous prediction of peak Number of candidate sinks consistent with chance (20) at all energies & none are physically possible Main Problem: Is the result replicable? 39 Slide 41 Now some fun stuff: Why v > c neutrinos might imply the ability to send signals back in time First, one-way signaling 40 Slide 42 Tachyons violate causality No absolute distinction between cause & effect! Consider a warning signal sent between approaching saucers to avoid a collision. Assume that the warning signal is sent using v > c tachyons. How would this appear on a spacetime diagram? Slide 43 distance time 42 Slide 44 43 Slide 45 Sending a message to your earlier self? Requires round trip signaling Which famous physicist first showed this could be done if faster-than-light particles existed & could be used to send signals? In what year? Paul Ehrenfest (1911) See wikipedia entry on tachyon anti-telephone for details Slide 46 Sending a message to your earlier self with the aid of a friend 45 u > cv < c Return signal from ship reaches you on Earth before you sent the original message provided: How much in your past? E.g., if u = 2c, v = 0.9c, L = 220 ly, get: T = -50 y Slide 47 A bit of philosophy on different ways to make big discoveries 46 Slide 48 Mistakes are very useful provided you learn how to spot them (a) Especially mistaken assumptions: time is absolute parity is conserved doctors can do no wrong only long term processes can lead to drastic changes on Earth tachyons are unphysical??? (b) Especially your own mistakes! 47 Slide 49 Mistakes & learning how to spot them (b) especially your own mistakes. The original paper presenting these results was so absurd, no reputable journal should publish it --fortunately for me! Initially: looked at ~20 suspected CR sources, e.g., The Crab put equal weight on MSU data & Tunka data used only one search radius calculated background wrong had no cut N > 50 (fooled by small numbers) focused only on E = 4.5 PeV energy bin thought 2 & 3 sigma signals were meaningful I had the great benefit of having a Russian collaborator Mikhail Zotov at MSU who had access to the Tunka data & who finally declined to be a coauthor. 48 Why? Slide 50 Two types of physicists seeking to make fundamental discoveries Pack hunters (1,046 Higgsians)Lone wolves Massive expensive apparatus & many years spent in preparation Analyze existing data in a novel way & takes little time to complete Problems: getting funding & you wont get the Nobel prize Problems: getting access to someone elses raw data & most of the time you will be wrong Advantage of getting advice from many highly knowledgeableexperts Advantage of not getting advice from many experts or crackpots It s better to be lucky than smart. Lone wolves may be stronger, more aggressive and far more dangerous than the average wolf that is a member of a pack. However, lone wolves have difficulty hunting, as wolves favorite prey, large ungulates, are nearly impossible for a single wolf to bring down alone. Instead, lone wolves will generally hunt smaller animals and scavenge carrion. Wikipedia entry 49 Slide 51 Jumping from failure to failure with undying enthusiasm is the secret of success. Savas Dimopoulos, a particle physicist, quoted in the 2/25/14 NY Times in connection with the discovery of the Higgs 50 Ehrlich corollary (courtesy of Kenny Rogers): You've got to know when to hold them & Know when to fold them. Slide 52 Special thanks to: Leonid Kuzmichev of Moscow State University, Head of the Tunka Collaboration & to Mikhail Zotov also of MSU for providing his analysis of the Tunka data. My web site http://mason.gmu.edu/~rehrlich has a link to a press release, a link to this presentation, and to the scientific paper on which it is based. 51 Slide 53 Why are most physicists tardycentric? Einstein said no v > c Many false sightings Imaginary rest mass Causality violated Instability of vacuum in field theory Flaky associations My guess what Einstein would think about these arguments Slide 54 Tardy- centrism mason.gmu.edu/~rehrlich