Present and Future Bounds on Non-Standard Neutrino Interactions

We consider Non-Standard neutrino Interactions (NSI), described by four-fermion operators of the form $(\barν_α γν_β) (\bar{f} γf)$, where $f$ is an electron or first generation quark. We assume these operators are generated at dimension $\geq 8$, so the related vertices involving charged leptons, obtained by an SU(2) transformation $ν_δ \to e_δ$, do not appear at tree level. These related vertices necessarily arise at one loop, via $W$ exchange. We catalogue current constraints from $\sin^2 θ_W$ measurements in neutrino scattering, from atmospheric neutrino observations, from LEP, and from bounds on the related charged lepton operators. We estimate future bounds from comparing KamLAND and solar neutrino data, and from measuring $\sin^2 θ_W$ at the near detector of a neutrino factory. Operators constructed with $ν_μ$ and $ν_e$ should not confuse the determination of oscillation parameters at a $ν$factory, because the processes we consider are more sensitive than oscillations at the far detector. For operators involving $ν_τ$, we estimate similar sensitivities at the near and far detector.

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