Determination of the $theta_{23}$ octant in long baseline neutrino experiments within and beyond the standard model

The recent data indicate that the neutrino mixing angle $theta_{23}$ deviates from the maximal-mixing value of 45$^circ$, showing two nearly degenerate solutions, one in the lower octant (LO) ($theta_{23}<45^circ$) and one in the higher octant (HO) ($theta_{23}>45^circ$). We investigate, using numerical simulations, the prospects for determining the octant of $theta_{23}$ in the future long baseline oscillation experiments. We present our results as contour plots on the ($theta_{23}-45^circ$, $delta$)--plane, where $delta$ is the $CP$ phase, showing the true values of $theta_{23}$ for which the octant can be experimentally determined at 3$,sigma$, 2$,sigma$ and 1$,sigma$ confidence level. In particular, we study the impact of the possible nonunitarity of neutrino mixing on the experimental determination of $theta_{23}$ in those experiments.