relic abundances, CMYK

On the plane I worked out (for the first time since about 1993) how one calculates the relic abundance of an annihilating particle species in the expanding universe. Interactions (creation and annihilation processes) try to keep the species in thermal equilibrium (in abundance and in energy). The expansion of the universe dilutes the abundance and redshifts away the energy. The net creation rate (excess creation rate over annihilation rate) is proportional to the deficit in the abundance relative to the thermal equilibrium abundance. Kolb & Turner derive this with a very complicated argument, but it follows nicely from detailed balance (as they note, to their credit). The net creation rate is also proportional to the net mean effective annihilation cross section (sigma), which depends on the creation and destruction processes, the masses of the species and the decay products, and the energy distribution in the species and decay products (since you need to have sufficient energy to create new particles).

I also worked out some things related to RGB to CMYK conversion (in the context of our galaxy atlas). Most of the "algorithms" in use are wrong, because they don't consider the physics of "subtractive" color systems. I am going to write something up about this.