Neutrinos 'must' have mass ?

[Widdekind]

Amongst the EW force-carrying bosons, it qualitatively seems like there is a progressive 'layering' of physical characteristics -- first, the Z⁰ boson gets mass (over photons); then, the W^+,- get electrical charge (over Z⁰s). And, somewhat seemingly similarly, electrons look like neutrinos, that have 'on-loaded' a 'burden' of charge. And more, are there any particles, that have electrical charge, w/o mass 'first' ? Or, are there any (fundamental) particles, having color-charge, w/o electrical-charge 'first' ? So, is it possible, to quantify, this qualitative argument, for why neutrino's 'must' have mass??

[MigL]

I could be wrong, but I seem to remember ( haven't done a search for info ) that when the supernova explosion was detected in the large Magellanic cloud, it was detected because of the increased incidence of neutrino detections in one of the experiments. The neutrinos arrived within hours of the magnitude increase of the star, ie the neutrinos travelled the distance as fast as the light did ( very large distance ). This would indicate massless neutrinos ( or extremely close to 0 ), although other experiments have put the mass at small but not inconsequential. Which is right ?

[ajb]

The "reason" why neutrinos lies in neutrino oscillations as a solution to the solar neutrino problem. In brief, a neutrino of one given flavour can later change flavour if the neutrino has a small, but non-zero mass. This small mass was not part of the original standard model, but has now been incorporated.

[csmyth3025]

As I understand it, neutrinos are leptons (in the same family as electrons). Also, neutrinos are thought by some to be their own antiparticles:

 

It is possible that the neutrino and antineutrino are in fact the same particle, a hypothesis first proposed by the Italian physicist Ettore Majorana. The neutrino could transform into an antineutrino (and vice versa) by flipping the orientation of its spin state. This change in spin would require the neutrino and antineutrino to have nonzero mass, and therefore travel slower than light, because such a spin flip, caused only by a change in point of view, can take place only if inertial frames of reference exist that move faster than the particle: such a particle has a spin of one orientation when seen from a frame which moves slower than the particle, but the opposite spin when observed from a frame that moves faster than the particle.

(ref. http://en.wikipedia....or_oscillations )

 

This leads to a curious situation in my mind. If neutrinos are their own antiparticles, then in the very early universe whatever number of neutrinos and (by identity) antineutrinos that existed (were initially created) would have remained relatively unchanged - since there would be no particle annihilation for neutrinos and their antiparticles.

 

Also, since neutrinos are produced in various types of nuclear reactions - but only rarely interact with matter once formed, it seems that over the history of the universe the number of neutrinos must have been steadily increasing and will continue to do so.

 

Does this steadily increasing proportion of neutrinos have any effect on the cosmos in general? I ask this in regard to the calculations that are made concerning the cosmological equation of state:

 

Non-relativistic matter

The equation of state of ordinary non-relativistic matter (e.g. cold dust) is , which means that it is diluted as , where is the volume. This means that the energy density red-shifts as the volume, which is natural for ordinary non-relativistic matter.

 

 

Ultra-relativistic matter

The equation of state of ultra-relativistic matter (e.g. radiation, but also matter in the very early universe) is which means that it is diluted as . In an expanding universe, the energy density decreases more quickly than the volume expansion, because radiation has momentum and, by the de Broglie hypothesis a wavelength, which is red-shifted.

(ref. http://en.wikipedia....tivistic_matter )

 

I'm not sure if neutrinos are treated as non-relativistic matter or as ultra-relativistic matter.

 

Chris

[ajb]

As I understand it, neutrinos are leptons (in the same family as electrons). Aneutrinos and their antiparticles.

 

Right, they are leptons and come in three varieties. The electron, muon and tau have a "partner" neutrino.

 

 

I ask this in regard to the calculations that are made concerning the cosmological equation of state:

 

It is now generally believed that neutrinos do not account for dark matter. As neutrinos are very light, they are treated as ultrarelativistic.

[csmyth3025]

Right, they are leptons and come in three varieties. The electron, muon and tau have a "partner" neutrino...

 

...It is now generally believed that neutrinos do not account for dark matter. As neutrinos are very light, they are treated as ultrarelativistic.

I wasn't quite thinking in terms of dark matter - but, rather, ordinary matter density and energy density.

 

In regard to regular (non-relativistic) mass, I take it that the amount of non-relativistic mass was fixed in the early moments of the big bang and, according to current thinking, has remained and will remain essentially unchanged:

 

The strong force acts between quarks. Unlike all other forces (electromagnetic, weak, and gravitational), the strong force does not diminish in strength with increasing distance. After a limiting distance (about the size of a hadron) has been reached, it remains at a strength of about 10,000 newtons, no matter how much further the distance between the quarks. In QCD this phenomenon is called color confinement; it implies that only hadrons, not individual free quarks, can be observed. The explanation is that the amount of work done against a force of 10,000 newtons (about the weight of a one-metric ton mass on the surface of the Earth) is enough to create particle-antiparticle pairs within a very short distance of an interaction. In simple terms, the very energy applied to pull two quarks apart will turn into new quarks that pair up again with the original ones. The failure of all experiments that have searched for free quarks is considered to be evidence for this phenomenon.The elementary quark and gluon particles affected are unobservable directly, but instead emerge as jets of newly created hadrons, whenever energy is deposited into a quark-quark bond, as when a quark in a proton is struck by a very fast quark (in an impacting proton) during a particle accelerator experiment.

(ref. http://en.wikipedia....he_strong_force )

 

and...

 

Unlike in electron-positron annihilation, proton-antiproton annihilation to two photons is expected to be extremely rare; one sensitive search for such events saw an excess of signal-like events but did not claim this as a direct detection.

(ref. http://en.wikipedia....on_annihilation )

 

These passages lead me to believe that any interaction involving quarks will not reduce the amount of quark (non-relativistic) mass in the universe.

 

On the other hand, neutrinos - which apparently do have a vanishingly small amount of non-relativistic mass - have been continuously created since the big bang from energetic nuclear reactions such as nuclear fission, nuclear fusion and, notably, stellar collapse:

 

The observations were consistent with theoretical supernova models in which 99% of the energy of the {SN 1987A} collapse is radiated away in neutrinos. The observations are also consistent with the models' estimates of a total neutrino count of 10⁵⁸ with a total energy of 10⁴⁶ joules...

(ref. http://en.wikipedia....trino_emissions )

 

This train of thought made me wonder if the proportion of non-relativistic mass (w = 0) compared to radiation (w = ¹/₃) in the universe is gradually increasing. Your response assures me, I believe, that this is not the case since the mass that neutrinos are thought to have is considered ultra-relativistic mass.

 

Indeed, it seems that the proportion of radiation and ultra-relativistic mass (w= ¹/₃) compared to non-relativitstic mass (w= 0) has and will remain essentially unchanged. Is this correct?

 

Chris

 

Edited to add last paragraph.

Edited June 29, 2011 by csmyth3025

[ajb]

Nucleosynthesis is the forming of light stable isotopes in the early Universe. One can use the big bang model to make predictions of the abundances of light elements and test this against observation.

[Mr Skeptic]

And more, are there any particles, that have electrical charge, w/o mass 'first' ?

 

That there won't be. To bring electric charge together requires energy, and so a ball of electric charge must have some rest mass.

[csmyth3025]

Indeed, it seems that the proportion of radiation and ultra-relativistic mass (w= ¹/₃) compared to non-relativitstic mass (w= 0) has and will remain essentially unchanged. Is this correct?

 

Chris

[Widdekind]

Indeed, it seems that the proportion of radiation and ultra-relativistic mass (w= ¹/₃) compared to non-relativitstic mass (w= 0) has and will remain essentially unchanged. Is this correct?

 

Chris

 

Radiation red-shifts, so that its energy, equal to its number density x energy per photon, scales as R^-4. Conversely, 'dust-like' (pressure-less) matter, having rest-mass, has a constant energy per particle, and its energy density scales as R^-3. Thus, there was once an era of "Radiation Domination", after which "Matter Dominated" the density:

 

http://www.newscientist.com/article/dn13414-universe-submerged-in-a-sea-of-chilled-neutrinos.html

 

During a core-collapse SN, the fusion of protons & electrons, into neutrons, also releases neutrinos:

 

[math]e^{-} + p^{+} \rightarrow n^0 + \nu_e[/math]

Therefore, the reverse reaction is surely physically possible:

 

[math]n^0 + \nu_e \rightarrow e^{-} + p^{+} [/math]

Now, except for the "invisible neutrino", that reaction looks allot like 11-minute-half-life neutron decay.

 

QUESTION: Is it possible, that neutron decay, is caused by the "harassment" of neutrons, by the Cosmic Neutrino Background ?? And, if so, could all radio-active decay be induced, by interactions, with the CNB ??

Edited July 22, 2011 by Widdekind