Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A Do "thermal neutrinos" exist

  1. Aug 24, 2017 #1
    Would neutrinos emitted in the distant and early universe be slowed enough to become thermal neutrinos? Could these be detected?
  2. jcsd
  3. Aug 24, 2017 #2


    User Avatar
    2017 Award

    Staff: Mentor

    The cosmic neutrino background should be thermal. PTOLEMY is a plan to measure it.

    Neutrinos emitted by nuclear processes after the big bang are not thermal, even if they become slow in the very distant future their energy spectrum will look different.
  4. Aug 24, 2017 #3
    Do the cosmic background neutrinos remain in thermal equilibrium by interacting with matter? Or are they thermal simply because of the effects of expansion?
  5. Aug 24, 2017 #4

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The latter.

    Before decoupling, neutrinos were in thermal equilibrium with the "cosmic soup". It can be shown that after decoupling, expansion of the universe redshifts a thermal spectrum for radiation into a thermal spectrum. Weinberg in his book "Cosmology" demonstrates his on pages 101-102. Weinberg

    The above applies to massless neutrinos, which is a good approximation for some of the history of the universe. Their non-zero masses, however, gradually shift their spectrum away from a thermal spectrum. From "Relativistic Cosmology" by Ellis, Maartens, and MacCallum page 304:

  6. Aug 24, 2017 #5
    Terrific. Thanks very much.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted