I am following a paper where a production function of this type is used.
$$Y=\left [\beta K^{- \rho}+\alpha \eta \left (\frac{K}{L} \right )^{-c(1+\rho)}L^{- \rho} \right ]^{-1/\rho}$$
It is a modified version of a CES where in addition there is the term $\alpha \eta \left (\frac{K}{L} \right )^{-c(1+\rho)}$ which multiply the $L$ factor.
I was therefore wondering. What may be the economic justification interpretation for adding this factor?