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Homework Help: Cosmology thermodynamics

  1. May 18, 2012 #1
    1. The problem statement, all variables and given/known data
    Find the change in temperature due to conservation of entropy, which happens during reheating when pions ( [itex]\pi^{\pm},\ \pi^0[/itex] ) get out of thermodynamic equilibrium beneath 140 MeV.

    2. Relevant equations

    3. The attempt at a solution

    I tried to compare this to the exiting of neutrinos, but I had no luck with that.

    I have the connection of entropy and temperature:

    [itex]s(T)=\frac{2\pi^2}{45}g_{eff}^s T^3[/itex]

    where [itex]g_{eff}^s[/itex] are entropy degrees of freedom given by:

    [itex]g_{eff}^s=\sum_{b=1}^{N_b} g_b\left(\frac{T_b}{T}\right)^3+\frac{7}{8}\sum_{f=1}^{N_f}g_f\left(\frac{T_f}{T}\right)^3[/itex]

    I could find that looking at masses of all SM particles and seeing which are heavier than 140 MeV, and then putting them in. Only u, d, s quarks, electron, muon have lower masses than pions so I would count them out.

    But other than that I have no idea how to solve this :\

    Any help would be appreciated...
  2. jcsd
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