Disformal transformations as a change of units

Understand

A disformal transformation is a very useful tool to analyze a general effective theory description of inflation.

• It can for example be used to set the tensor sound speed to unity, such that the tensor power spectrum only depends on the Hubble parameter.
• However, the disformal transformation has also led to quite some confusion in recent literature.
• We hope to clarify that confusion by pointing out that a disformal transformation is nothing else than a change of units.