Instabilities in the CDMT

Question

Could anyone explain or refer to references on why the CDMT f(R) gravity model suffers from Instabilities any why the sign of ${\mu}^{4}$ matters.

This post imported from StackExchange Physics at 2014-04-13 14:09 (UCT), posted by SE-user user38032

Comments

I don't know much about \(f(R)\) gravity, but I don't know whether this "CDMT \(f(R)\) model" is well-known among $f(R)$ gravity theorists. If it isn't you may want to give a short introduction to it if you want to attract good, or even original, answers.  

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This is a duplicate of http://www.physicsoverflow.org/14900/metric-%24f-r-%24-instability?show=14900#q14900

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@RonMaimon Yes, I agree. I hid the imported comment by "Jim" which said the same thing because I didn't realise that the "Metric $f(R)$ instability" question was imported here, so I thought it was irrelevant for us. Have you already posted it in the Close Vote Queue?