Viscosity in a Lepton-Photon Universe

Understand

We look at viscosity production in a universe consisting purely of leptons and photons.

• This is quite close to what the Universe actually look like when the temperature was between $10^{10}$ K and $10^{12}$ K ($1$ -- $100$ MeV).
• By taking the strong force and the hadronic particles out of the equation, we can examine how the viscous forces behave with all the 12 leptons present.
• By this we study how shear- and (more interestingly) bulk viscosity is affected during periods with particle annihilation.