How Do Perturbation Equations Affect FRW Cosmology Metrics?

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Perturbation equations in FRW cosmology metrics are analyzed through the perturbed line element, revealing key relationships in the covariant derivative. The expansion leads to expressions for the energy-momentum tensor components, highlighting the roles of density perturbations and velocity fields. The equations indicate that certain terms, like ##3(1+w) \mathcal{H}(1+\delta)##, may be incorrectly included in the overall equation. The discussion emphasizes the importance of accurately deriving these terms to understand their impact on cosmological models. Clarification on the connection coefficients is also sought to resolve discrepancies in the equations.
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Homework Statement
##T^{00} = a^{-2} \bar{\rho}(1+\delta)##
##T^{0i} = a^{-2} \bar{\rho}(1+w)v^i##
##T^{ij} = a^{-2} \bar{\rho} [(1+\delta)\delta^{ij} - h^{ij}]##
Relevant Equations
##\nabla_{\mu} T^{\mu \nu} = 0##
The perturbed line element: ##g = a(\tau)^2[-d\tau^2 + (\delta_{ij} + h_{ij})dx^i dx^j]##
Expanding the covariant derivative with ##\nu = 0##, you get a few pieces. Here on keeping only terms linear in the perturbations,

##\partial_{\mu} T^{\mu 0} = a^{-2} \bar{\rho} \left[ \delta' - 2\mathcal{H} (1+\delta) + (1+w) i\mathbf{k} \cdot \mathbf{v} \right]##

here ##\mathcal{H} = a'/a## and ##i \mathbf{k} \cdot \mathbf{v} = \partial_i v^i##. Then

##\Gamma^{\mu}_{\mu \rho} T^{\rho 0} = a^{-2} \bar{\rho} \left[ 4\mathcal{H}(1+\delta) + \frac{1}{2} h' \right]##

##\Gamma^{0}_{\mu \rho} T^{\mu \rho} = a^{-2} \bar{\rho} \left[ \mathcal{H}(1+\delta)(1+3w) + \frac{1}{2} w h' \right]##

Overall,
##0 = a^{-2} \bar{\rho} \left[ \delta' + 3(1+w) \mathcal{H}(1+\delta) + (1+w) i \mathbf{k} \cdot \mathbf{v} + \frac{1}{2}(1+w)h'\right]##

but the term ##3(1+w) \mathcal{H}(1+\delta)## shouldn't be there. I can't see why not? For reference, the connection coefficients

1707826896803.png
 
At first, I derived that: $$\nabla \frac 1{\mu}=-\frac 1{{\mu}^3}\left((1-\beta^2)+\frac{\dot{\vec\beta}\cdot\vec R}c\right)\vec R$$ (dot means differentiation with respect to ##t'##). I assume this result is true because it gives valid result for magnetic field. To find electric field one should also derive partial derivative of ##\vec A## with respect to ##t##. I've used chain rule, substituted ##\vec A## and used derivative of product formula. $$\frac {\partial \vec A}{\partial t}=\frac...