Modified Gravity: living without Birkhoff I. DGP

Understand

We consider the consequences of the absence of Birkhoff's theorem in theories of modified gravity.

• As an example, we calculate the gravitational force on a test particle due to a spherical mass shell in the Dvali-Gabadaze-Porrati model (DGP).
• We show that unlike in General Relativity, the force depends on the mass distribution.
• In particular, the gravitational force within a spherical mass shell depends on the geometric structure of the bulk, and is likely non-zero.