# Tag Info

26

It's very hard to imagine that there is any sensible model consistent with OPERA's results. (Aside from models of unaccounted-for systematic uncertainties in the experiment.) We know that we live in a world described to very high precision by Lorentz-invariant quantum field theory, so the most sensible way to look for Lorentz violation is to start with such ...

23

I am afraid that one has to go to a "very unusual segment" of theoretical literature if he wants any papers about superluminal neutrinos. Guang-jiong Ni has been authoring many papers about superluminal neutrinos a decade ago: http://arxiv.org/abs/hep-ph/0103051 http://arxiv.org/abs/hep-th/0201077 http://arxiv.org/abs/hep-ph/0203060 ...

19

They are probaby talking about supernovae, like how SN1987A was first detected by neutrinos before the light arrived. In that case neutrinos and photons are both produced in the core of the supernovae explosion, but they have dense clouds of gas to get through before they get to empty space and travel freely to us. Since the neutrinos are weakly interacting ...

16

Before I answer, a couple caveats: As Adam said, the universe isn't going to start behaving any differently because we discovered something. Right now it seems much more likely (even by admission of the experimenters) that it's just a mistake somewhere in the analysis, not an actual case of superluminal motion. Anyway: if the discovery turns out to be ...

16

Dark matter can be hot, warm or cold. Hot means the dark matter particles are relativistic (kinetic energy on the order of the rest mass or much higher), cold means they are not relativistic (kinetic energy much less than rest mass) and warm is in between. It is known that the total amount of dark matter in the universe must be about 5 times the ordinary ...

14

The calculation is done for 1987A here. Basically, the neutrinos' fractional speed increase from the new paper is $2.48\pm0.28\pm0.30\times10^{-5}$ (statistical / systematic errors, respectively) . SN1987a was $166\,912\pm10.1$ ly away, so multiplying the fraction by the travel time gives $4.14\pm0.97$ years. In reality, we got the neutrinos a few hours ...

11

Possible extragalactical sources for high energy neutrinos is still an open question. There are several candidates, look at this paper on arXiv. By the way, astrophysical neutrinos have been already detected more than 20 year ago by Kamiokande in Japan. They came from supernova SN 1987A, and helped to set an upper bound (of about $10\ \text{eV}$) on the sum ...

10

The historical formulation of the SM involved one Higgs doublet and only renormalizable couplings, the latter being due to the focus at the time on achieving a renormalizable formulation of the weak interactions. With these restrictions neutrinos are massless and do not oscillate. To get neutrino masses you need to extend this framework either by adding ...

10

Depends on the detection technology. Yes Cerenkov based detectors (SNO and Super-Kamiokande for instance, as well a many cosmic ray neutrino detector) are direction sensitive, and this is one of the design considerations that drive the use of this tricky technique. The best results come from quasi-elastic reactions like $\nu_l + n \to l^- + p$. The ...

10

Cute question! For a neutrino with mass $m$ and energy $E\gg m$, we have $v=1-\epsilon$, where $\epsilon\approx (1/2)(m/E)^2$ (in units with $c=1$). IceCube has detected neutrinos with energies on the order of 1 PeV, but that's exceptional. For neutrinos with mass 0.1 eV and an energy of 1 PeV, we have $\epsilon\sim10^{-32}$. The time of flight for ...

9

Whether or not neutrinos would be suitable for rapid trading, people have seriously considered their utility for signalling in difficult environments. I read an article a while back about a paper (published in Phys. Lett. B, but I can't access that from here) by Patrick Huber which proposed using neutrinos for through-the-earth communication to submarines as ...

9

The basis of all neutrino beams is a less exotic (protons most of the time) beam smashing some mundane target and making scads of assorted particles---many of them charged. Those charged particles are focused (and possible subjected to a second filtering for energy by using collimators and more magnets, though this step is not being done at CERN), then they ...

8

Great question. The experimental situation remains inconclusive. However, theoretically, there exists a damn good reason to think that the neutrinos have Majorana masses - and, consequently, the double beta decays should be possible. It's called the seesaw mechanism. The mechanism is justified by an intriguing observation: $$m_{\nu}:m_{Higgs} \approx ... 8 There are a couple of misconceptions here. The flavor states are not mass states. That is, the electron neutrino does not have a mass m_{\nu_e} and the muon neutrino a mass of m_{\nu_\mu}. Rather, there are two different basis' in which to examine the neutrino. So a neutrino known to be l flavored, is a mixture of mass states (numbered) like$$ ...

8

It is technically impossible to measure the speed of such a particle directly; and it all depend on "which" neutrino you are talking about. The speed is related to the momentum and the momentum to the energy. So you can have a neutrino of some MeV of total energy, another one of some GeV, etc. But in any cases, the answer will be "very very close" to c. ...

8

T2K is running right now. They might (probably) need to improve their understanding of the distance and timing. LBNE is still in the planning stages, but will have a longer baseline which could be very helpful disclaimer: I am vaguely involved in LBNE--specifically doing MC work for the near detector design.

8

Short answer: Unknown. Slightly longer answer: the situation you describer would obtain if neutrinos were Majorana particles (and thus not Dirac particles). It is favored by theorists because it feeds into a nice explanation of why the neutrinos are so light by comparison to the other massive particles. Experiments are underway that might settle the ...

7

Back when I was in graduate school in the 1990s, the standard reference for this sort of thing was Kolb and Turner's book The Early Universe. Even after all these years, that book's treatment of this subject is probably still a good place to look. Even if there's no asymmetry-producing process for neutrinos (like baryogenesis), you still expect a relic ...

7

The various theoretical options are very different in nature, and the answer to this question almost defines the option. 1) Relativity is wrong, there is objective absolute time, Lorentz symmetry is emergent (as in electrodynamics before Einstein), and going faster than light doesn't create any time-loop paradoxes. 2) Relativity is valid, but neutrinos, ...

7

Assuming relativity as we know and love it. Massless particles move at the speed of light. At the speed of light particles experience no time, and therefore the evolution of the wave function from a pure flavor state to a mixed state which is proportional $U\exp(-iEt)U^{*}$ where $E$ is the energy of the particular mass state, $t$ is the elapsed time, and ...

7

Humanity operates quite a number of spacecrafts in various places in the Solar System and communications with their on-board computers depends on the speed of light. This is because the frequency on which commands and data is sent and received varies with spacecraft and ground station's relative velocities by tens of kHz due to Doppler effect (the relative ...

6

Experimental measurements of neutrino speed have been performed. But thus far, they have all found that the neutrinos were going so close to the speed of light that no difference was detectable within the precision of the experiments. A couple measurements are described here: http://en.wikipedia.org/wiki/Neutrino#Speed

6

The gravitational field of a fast moving particle is from its energy, not its rest-mass. The source of the gravitational field is the energy divided by c2 if you are using unnatural units, or what used to be called "relativistic mass" before that term fell out of favor. The neutrinos we observe are moving at essentially the speed of light, so we cannot ...

6

Pasted text of the letter in English - the link also contains the original typed German letter. Open letter to the group of radioactive people at the Gauverein meeting in Tübingen. Zürich, Dec. 4, 1930 Physics Institute of the ETH Gloriastrasse Zürich Dear Radioactive Ladies and Gentlemen, As the bearer of these ...

6

It's a little strong to hold that the PMNS matrix is known. It's mostly known (with $\theta_{1,3}$ non-zero at five sigma just this week! Congratulations, Daya Bay!{*}), but the CP violating phase ($\delta_{CP}$) is basically unconstrained as are the Majorana phases (if they apply). Nor is the "maximal" mixing angle known to high precision a fact which is ...

5

Your question is equivalent to asking what the absolute mass of the neutrinos is, and the answer is currently unknown. We do have decent values for the differences of the squared masses for all three required neutrino states (one pair separated by about $7.7 \times 10^{-5}\text{ eV}^2$, and another one standing off from them by about $\pm 2.4 \times ... 5 The solar data analyzed with current solar models are in good agreement with reactor and atmospheric results for$\theta_{12}$and$\Delta m_{21}^2$. This is not, however, a very strong test of the models. References: The big SNO paper. SNO probed the solar neutrino spectrum in detail. On page 34 you'll find their spiffy comparison plot of flux for ... 5 While interesting, even potentially enormous for physics, you can still bet on the sun coming up tomorrow. One thing I like to point out to people who are enamored with the fact that science is constantly changing is that any new changes have to fit the old observations into them. The article even mentions this specifically. If it turns out that neutrinos ... 5 Yes. Beam neutrino experiments regularly observe events in which a single hadron appears in the detector. Such events are attributable to$Z$exchange reactions like$\nu + p \to \nu' + p' + \pi ${*}, or$\nu + p \to \nu' + p'$(where$p'$is energetic enough to register in the detector). Reactions with leptonic products are not obvious because ... 5 I'm not an expert in stellar physics by any means, but I can say this: the velocity discrepancy observed by OPERA,$\frac{v - c}{c} = 2.9\times 10^{-5}\$, would correspond to a delay ("prelay"?) of around 4 years for neutrinos coming from SN1987A. The observed delay was only 3 hours, which is smaller by a factor of roughly ten thousand. So if you assume that ...

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