We know that while propagating through space, neutrinos changes their identities continuously.i.e., they oscillate from one flavour to another while travelling. This phenomenon suggest that neutrinos do feel time and therefore must be massive.

My question is that what will possibily happen if we decrease the background temperature(temperature of the medium in which neutrinos are propagating) to near absolute zero or increase it to thousands of kalvins? Is there any known tool for handling such situations?

(My current knowledge of neutrino oscillations is limited to vacuum case only. I will learn oscillations in matter in near future.)

  • $\begingroup$ What's "background temperature"? $\endgroup$ – safesphere Sep 27 '18 at 18:41
  • $\begingroup$ @safesphere temperature of the medium in which neutrinos are propagating. $\endgroup$ – Aman pawar Sep 27 '18 at 18:43
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    $\begingroup$ There is a huge discussion of neutrino oscillation in matter, including resonances (aka MSW effect). If you have a dense medium of electrons, the electron neutrino will get an effective mass that differs from the other flavors. The temperature, i.e. the average kinetic energy of the electrons, itself does not play a major role here, but the density of electrons, which is connected to the temperature, does. $\endgroup$ – user178876 Sep 27 '18 at 18:51

The effect of the space between the Sun and the Earth is entirely negligible. The chance that a neutrino interacts with a photon or a stray hydrogen atom (pretty much all there is in that gap) is incredibly small. Remember that neutrinos only act through the weak force.


A neutrino has a mean free path in lead of several light years.

It is conceivable there is an effect due to the temperature of the material that emits the neutrino. Though even this effect is very likely to be quite small. The temperature of the material in the Sun means that the interacting nuclei are moving with thermal energy. Higher temperature might mean they are moving faster if the neutrino happens to be emitted in the direction the nucleus is already moving due to thermal motion. So, looking at the same link, that means the cross section to interact is somewhat larger. It is also moving slightly faster so it will have a larger gamma factor and oscillate slower. But these will be fairly small.


Nuclei in the Sun will be going some few thousand km/s. Neutrinos are going very close to speed of light, or 3E5 km/s. So the difference will be a very small effect.

  • $\begingroup$ "Remember that neutrinos only act through the weak force. " This is not correct. Neutrinos interact through gravity too, it is just that they interact weakly. $\endgroup$ – Árpád Szendrei Sep 28 '18 at 5:27

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