Cosmological Perturbation Theory in $f(Q,T)$ Gravity

Understand

We developed the cosmological linear theory of perturbations for $f(Q,T)$ gravity, which is an extension of symmetric teleparallel gravity, with $Q$ the non-metricity and $T$ the trace of the stress-energy tensor.

• By considering an ansatz of $f(Q,T)=f_1(Q)+f_2(T)$, which has been broadly studied in the literature and the coincident gauge where the connection vanishes, we got equations consistent with $f(Q)$ gravity when $f_{T}=0$.
• In the case of the tensor perturbations, the propagation of gravitational waves was found to be identical to $f(Q)$, as expected.
• For scalar perturbations, outside the limit $f_T = 0$, we got that the coupling between $Q$ and $T$ in the Lagrangian produces a coupling between the perturbation of the density and the pressure.