# Homework Help: General relativity - Covariant Derivative Of F(R)

1. Oct 18, 2012

### thecoop

In f(R) gravity as http://en.wikipedia.org/wiki/F(R)_gravity ,

i have problem with the term [ g_ab □ - ∇_a ∇_b ] F(R) , well

actually is [ ∇_b ∇_a - ∇_a ∇_b ] F(R) , but F is a function of Ricci Factor and Ricci Factor is expressed as a(t) ( scale factor ) . for the a = b = 0 i say this term becomes zero . is it true ?

2. Oct 18, 2012

### dextercioby

Can you re-write your post so that it makes (more) sense ?

3. Oct 19, 2012

### clamtrox

I don't know anything about f(R) gravity theories, but that expression is clearly zero if the torsion tensor vanishes.