Modified TOV Equations in fR gravity (using xAct)

[varun naudiyal]

Hello guys,

I'm trying to derive the modified Tolman-Oppenheimer-Volkoff (TOV) equations for a general f(R) theory in Mathematica and I'm running into some issues with my workflow.

First, I use a VarAction function to get the general f(R) field equations. Then, in a separate notebook, I define a spherically symmetric metric using Cmetric and manually copy over the field equations from the first step. I have to do this because I can't find a way to specify metric components in the first notebook after deriving the general equations.

This two-notebook process is cumbersome and produces a very messy, unstructured expression for the final equations that is difficult to parse. I have to manually sort everything out and derive the end modified TOV equations. T~T please help 

I have three main questions:

1. How can I better structure or simplify the messy final output?

2. Is there a way to integrate this entire process into a single notebook?

3. How can I proceed further to derive the modified TOV in mathematica (and not manually as I'm doing rn)?

Any advice on how to improve this unholy mess would be greatly appreciated.