On the junction conditions in $f\left(R\right)$-gravity with torsion

Junction conditions are discussed within the framework of $f\left(R\right)$-gravity with torsion. After deriving general junction conditions, the cases of coupling to a Dirac field and a spin fluid are explicitly dealt with. The main differences with respect to Einstein–Cartan–Sciama–Kibble theory $\left(f\right(R)=R)$ are outlined. (paper)