Help with second–order scalar perturbation action in xAct (scalar–Gauss–Bonnet with μ(ϕ,X))

[Ali Seidabadi]

Hi ,  I am trying to use xAct  to derive the second–order action for scalar perturbations in a non-minimal scalar–Gauss–Bonnet model on a flat FLRW background , and I would be very grateful for some guidance.

I have attached two Mathematica notebooks . Unfortunately, my notebook for the model is not working as expected and  I get various xAct warnings/errors and  Even when the code runs, the computation of the second–order Lagrangian is extremely slow / heavy .  Is the general strategy I am using appropriate for this kind of non-minimal Gauss–Bonnet model? and  In my notebooks, where exactly am I doing things incorrectly ?

Thank you very much in advance for any hints or comments.  

  Best regards,

 Ali .