# Tag Info

27

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 ...

25

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 ...

20

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 ...

19

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 ...

19

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 ...

18

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 ...

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 ...

13

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 ...

13

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 ...

12

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 ...

12

It seems that theoretically neutrino stars have been postulated. A google search came up with Supermassive neutrino stars and galactic nuclei. R.D. Viollier, D. Trautmann and G.B. Tupper. Phys. Lett. B 306 no. 1-2 (1993), pp. 79-85. The calculations have been done for you :) if you have access to a library: Abstract The characteristics of ...

11

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. ...

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

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 ...

10

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 $\pm 2.4 \times ... 10 The basis of all neutrino beams is a less exotic (protons most of the time) beam smashing some mundane target and making scads of assorted particles---many of them charged. Those charged particles are focused (and possible subjected to a second filtering for energy by using collimators and more magnets, though this step is not being done at CERN), then they ... 10 Instead of the massive compact objects which could serve as a 'replacement' for the supermassive black hole inside the galactic center (which are discussed in the Viollier and Tupper paper from Anna's answer) I would like to point another possibility: halos of degenerate neutrino gas around galactic clusters. The order of magnitude calculations for the ... 9 There are a couple of misconceptions here. The flavor states are not mass states. That is, the electron neutrino does not have a mass$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 $$... 9 Neutrinos are leptons, they have leptons number just like the charged leptons (electron, muon, tau). Weak interaction conserve not only the global lepton number, but the lepton flavor numbers as well. And that is how we identify their flavors: electron neutrinos participate in reactions that involve electrons and muon neutrinos participate in reaction that ... 9 No. Ordinary supernovas do not produce neutrinos of large enough energy to cause such a nuclear weapon meltdown, even if the inverse square law diminution of flux is not an issue. The original paper on which the NewScientist based its article is the preprint Sugawara, H., Hagura, H., Sanami, T. Destruction of Nuclear Bombs Using Ultra-High Energy ... 9 The answer is yes. Neutrino will travel faster than light in a medium with a refractive index (n) greater than one (which is the case of air). Indeed the speed of light in that medium will be v_{\text{medium}}=c/n where c=2.998\times10^8 m/s and n>1. Then, because neutrino interacts only very weakly (only through the weak nuclear force) with the ... 8 Great question. The experimental situation remains inconclusive. However, theoretically, there exists a damn good reason to think that the neutrinos have Majorana masses - and, consequently, the double beta decays should be possible. It's called the seesaw mechanism. The mechanism is justified by an intriguing observation:$$ m_{\nu}:m_{Higgs} \approx ... 8 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 ... 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 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, ... 8 Everything is affected by gravity. Gravity warps of space-time according to the Einstein Field Equations, and traveling on "geodesics" (shortest path curves) on that curved surface is how gravity is manifested. Thinking as though there is some sort of euclidean space underneath the non-euclidean space-time in which neutrinos can take a more direct ... 8 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 ... 8 An answer requires two order of magnitude estimates. Absorption by the planet The fraction$f_a$lost to absorption is roughly $$f_a = -\sigma N$$ where$N$is the mean number of nucleons along the neutrinos path and$\sigma$is the neutrino nucleon cross-section at the appropriate energy (a few MeV). We can expand the number to$$f_a = -\sigma ... 8 The problem is that because neutrinos have a very small mass they are generally moving at speeds near the speed of light. See the hot dark matter Wikipedia entry for more details. The high speed means their velocity is greater than any escape velocities found in the universe, so they aren't gravitationally bound to anything. I don't think it would even be ... 8 How do I stay alive to be killed by neutrinos? You wouldn't. The point is being made that even the beam of neutrinos with a supernova at one astronomical unit distance would be intense enough that enough of them would interact with the matter of your body to be lethal. So even the neutrinos would get you if all the other stuff - notably$\gamma\$s didn't. ...

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