Is there the radion in the RS2 model ?

TL;DR

This paper investigates the RS2 model with matter on the brane and demonstrates that the radion field remains a physical degree of freedom due to boundary conditions, challenging previous assumptions that it could be gauged out.

Contribution

It shows that in the RS2 model with matter, the radion cannot be gauged away and is a genuine physical degree of freedom.

Findings

Radion field cannot be gauged out in the RS2 model with matter.

Boundary conditions at infinity preserve the radion as a physical mode.

Radion remains a physical degree of freedom in this setup.

Abstract

We analyse the physical boundary conditions at infinity for metric fluctuations and gauge functions in the RS2 model with matter on the brane. We argue that due to these boundary conditions the radion field cannot be gauged out in this case. Thus, it represents a physical degree of freedom of the model.