Primordial Fluctuations - Adiabatic/isocurvature Fluctuations

Adiabatic/isocurvature Fluctuations

Adiabatic fluctuations are density variations in all forms of matter and energy which have equal fractional over/under densities. So for example, an adiabatic photon overdensity of a factor of two would also correspond to an electron overdensity of two. For isocurvature fluctuations, the density variations for one component do not necessarily correspond to density variations in other components. While it is usually assumed that the initial fluctuations are adiabatic, the possibility of isocurvature fluctuations can be considered given current cosmological data. While the overall constraints are inconclusive, uncorrelated isocurvature cold dark matter modes are found to be unlikely.