Issues Related to Matter Effect in DUNE

Due to its long baseline, DUNE provides an excellent avenue to probe Earth's matter effect and associated degeneracies. We study in detail the performance of DUNE to validate matter oscillation by excluding the vacuum scenario. Whatever be the values of oscillation parameters, we find that DUNE can feel Earth's matter at more than 2$\sigma$ confidence level. The relative 1$\sigma$ precision in the measurement of line-averaged constant Earth matter density ($\rho_{\mathrm{avg}}$) for maximal CP-violating choices of $\delta_{\mathrm{CP}}$ is around 10 to 15% depending on the choice of neutrino mass ordering. If CP phase turns out to be around -90$^{\circ}$ or 90$^{\circ}$, DUNE can measure $\rho_{\mathrm{avg}}$ with precision better than any other atmospheric and long-baseline experiments. We also observe new interesting degeneracies among $\rho_{\mathrm{avg}}$, $\delta_{\mathrm{CP}}$, and $\theta_{23}$. A detailed understanding of these degeneracies are essential to correctly assess the outcome of DUNE.