Nonstandard Neutrino Interactions as a Solution to the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>NO</mml:mi><mml:mi>ν</mml:mi><mml:mi mathvariant="normal">A</mml:mi></mml:math> and T2K Discrepancy
Sabya Sachi Chatterjee, A. Palazzo
Abstract
The latest data of the two long-baseline accelerator experiments $\mathrm{NO}\ensuremath{\nu}\mathrm{A}$ and T2K, interpreted in the standard three-flavor scenario, display a discrepancy. A mismatch in the determination of the standard $CP$ phase ${\ensuremath{\delta}}_{\mathrm{CP}}$ extracted by the two experiments is evident in the normal neutrino mass ordering. While $\mathrm{NO}\ensuremath{\nu}\mathrm{A}$ prefers values close to ${\ensuremath{\delta}}_{\mathrm{CP}}\ensuremath{\sim}0.8\ensuremath{\pi}$, T2K identifies values of ${\ensuremath{\delta}}_{\mathrm{CP}}\ensuremath{\sim}1.4\ensuremath{\pi}$. Such two estimates are in disagreement at more than 90% C.L. for 2 degrees of freedom. We show that such a tension can be resolved if one hypothesizes the existence of complex neutral-current nonstandard interactions (NSIs) of the flavor changing type involving the $e\ensuremath{-}\ensuremath{\mu}$ or the $e\ensuremath{-}\ensuremath{\tau}$ sectors with couplings $|{ϵ}_{e\ensuremath{\mu}}|\ensuremath{\sim}|{ϵ}_{e\ensuremath{\tau}}|\ensuremath{\sim}0.2$. Remarkably, in the presence of such NSIs, both experiments point towards the same common value of the standard $CP$ phase ${\ensuremath{\delta}}_{\mathrm{CP}}\ensuremath{\sim}3\ensuremath{\pi}/2$. Our analysis also highlights an intriguing preference for maximal $CP$ violation in the nonstandard sector with the NSI $CP$ phases having best fit close to ${\ensuremath{\phi}}_{e\ensuremath{\mu}}\ensuremath{\sim}{\ensuremath{\phi}}_{e\ensuremath{\tau}}\ensuremath{\sim}3\ensuremath{\pi}/2$, hence pointing towards imaginary NSI couplings.