Longitudinal structure function $F_L$ at low $Q^2$ and low $x$ with model for higher twist: an update

A reanalysis of the model for the longitudinal structure function $F_L (x,Q^2)$ at low $x$ and low $Q^2$ was undertaken, in view of the advent of the EIC. The model is based on the photon-gluon fusion mechanism suitably extrapolated to the region of low $Q^2$. It includes the kinematic constraint $F_L\sim Q^4$ as $Q^2\rightarrow$ 0 and higher twist contribution which vanishes as $Q^2 \rightarrow \infty$. Revised model was critically updated and compared to the presently available data.