Help understanding quadratic gravity

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Hi all.

I keep coming across the term "quadratic gravity" in various GR papers and don't entirely understand the concept as it doesn't seem to be explained anywhere. It seems to appear most frequently in the context of pp-waves. So I was hoping somebody could enlighten me as to what its all about :smile:

Thanks
 
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Doesn't that refer to extensions of General Relativity in which the Lagrangian includes terms that are quadratic in the Riemann tensor. That is, instead of just R you include R2, RμνRμν, etc.
 
Put like that it does make sense. Now I look at it, the action used in various papers does have the Ricci tensor squared in one form or another. Suppose I really should have noticed :biggrin:.
Thanks for the quick reply
 

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