Study of nonstandard interactions mediated by a scalar field at the ESSnuSB experiment

In this paper, we study scalar mediator induced nonstandard interactions (SNSIs) in the context of the ESSnuSB experiment. In particular, we study the capability of ESSnuSB to put bounds on the SNSI parameters and also study the impact of SNSIs in the measurement of the leptonic $CP$ phase ${\delta }_{CP}$. Existence of SNSIs modifies the neutrino mass matrix and this modification can be expressed in terms of three diagonal real parameters (${\eta }_{ee}$, ${\eta }_{\mu \mu }$, and ${\eta }_{\tau \tau }$) and three off-diagonal complex parameters (${\eta }_{e\mu }$, ${\eta }_{e\tau }$, and ${\eta }_{\mu \tau }$). Our study shows that the upper bounds on the parameters ${\eta }_{\mu \mu }$ and ${\eta }_{\tau \tau }$ depend upon how $\Delta {m}_{31}^{2}$ is minimized in the theory. However, this is not the case when one tries to measure the impact of SNSIs on ${\delta }_{CP}$. Further, we show that the $CP$ sensitivity of ESSnuSB can be completely lost for certain values of ${\eta }_{ee}$ and ${\eta }_{\mu \tau }$ for which the appearance channel probability becomes independent of ${\delta }_{CP}$.