Viable Gauge Choices in Cosmologies with Non-Linear Structures

Understand

A variety of gauges are used in cosmological perturbation theory.

• These are often chosen in order to attribute physical properties to a particular choice of coordinates, or otherwise to simplify the form of the resultant equations.
• Calculations are then performed with the understanding that they could have been done in any gauge, and that transformations between different gauges can be made at will.
• We show that this logic can be extended to the domain of large density contrasts, where different types of perturbative expansion are required, but that the way in which gauges can be chosen in the presence of such structures is severely constrained.