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I'm trying to derive equation of motion in Higgs scalar-tensor theory with the Lagrangian given by $$\mathcal{L}=[\frac{1}{16\pi}\alpha \phi^{\dagger}\phi R+ \frac{1}{2}\phi^{\dagger}_{;\mu}\phi^{;\mu} - V(\phi)]\sqrt{-g} + \mathcal{L_M}\sqrt{-g}$$ and equation of motion for gravity is given by $$ R_{\mu\nu}-\frac{1}{2}Rg_{\mu\nu}+\frac{8\pi}{\alpha\phi^\dagger\phi}V(\phi)g_{\mu\nu}= \frac{8\pi}{\alpha\phi^\dagger\phi}T_{\mu\nu}-\frac{4\pi}{\alpha\phi^\dagger\phi}[\phi^\dagger_{;\mu}\phi_{;\nu} + \phi^\dagger_{;\nu}\phi_{;\mu}] + \frac{4\pi}{\alpha\phi^\dagger\phi}\phi^\dagger_{;\lambda}\phi^{;\lambda}g_{\mu\nu}-\frac{1}{\phi^\dagger\phi}[(\phi^\dagger\phi)_{;\mu;\nu}-(\phi^\dagger\phi)^{;\beta}_{\;\; ;\beta}g_{\mu\nu}]$$ I'm studying this paper in which the equation of motion is derived. I've got the LHS and the first term on the RHS but how do i calculate the last three terms on the RHS.
Also I'm following this paper which was quite helpful. It suggest using Euler Lagrange equation
$$ \frac{\partial{\mathcal{L}}}{\partial{g^{\mu\nu}}} - \partial_\kappa \frac{\partial{\mathcal{L}}}{\partial g^{\mu\nu}_{\;,\kappa}} + \partial_\kappa\partial_\lambda \frac{\partial{\mathcal{L}}}{\partial g^{\mu\nu}_{\; ,\kappa \lambda}} = 0$$

but still I could not get the last three terms on the RHS.

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  • $\begingroup$ First things first you are missing the Ricci curvature in the first term of your lagrangian. The other terms should come from the fact that in comparison to e.g. Einstein Hilbert the variation of $R_{\mu \nu}$ that you get from the variation of $R$ does not vanish as the total derivative does not work out due to the multiplicative factor. For seeing what this changes you can e.g. check out a combination of the Wikipedia pages for Einstein-Hilber action and Brans-Dicke theory (the latter has a similar effect and gives the reason for the extra terms) $\endgroup$ Commented Apr 19 at 15:27
  • $\begingroup$ Yes, thanks, I've corrected it now. Also, I've checked like thousands of sites and sources, and each of them just states that the equation of motion should be the following. None of them actually goes through the derivation of each step." $\endgroup$
    – kush
    Commented Apr 20 at 2:07

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