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NSI

Non-standard neutrino interactions.

Introduced as a concept by Wolfenstein (Wolfenstein-oscillations-1978).

Theory

A possible BSM effect driven by physics at a higher energy scale $\Lambda$ that manifests at lower energies through sixth-order operators in the extended SM field theory (Ohlsson-nsi-2013) (check about higher energy scale). NSI is predicted by several neutrino mass models (Bischer-fieldtheory-2019).

Commonly modelled using an assumed new mediator particle Z' (Elisa-thesis-2023).

NC NSI manifests through impacts on the forward scattering between neutrinos and charged fermions in the Earth (matter effects) (Bhupal-nsi-2019).

The existence of NSI effects may resolve tensions in the standard oscillation parameters (Esteban-nsitension-2020). Additionally, detection or exclusions of NSI is relevant for interpretations of measurements of the oscillation parameters (Bhupal-nsi-2019) (check).

Our approach parametrizes the effect of NSI on the matter potential through six effective coupling parameters:

Parameter Label
$\epsilon_{e\mu}^\oplus$ "flavor-violating"
$\epsilon_{e\tau}^\oplus$ "flavor-violating"
$\epsilon_{\mu\tau}^\oplus$ "flavor-violating"
$\epsilon_{ee}^\oplus$ "flavor-universal"/"flavor-diagonal"
$\epsilon_{\mu\mu}^\oplus$ "flavor-universal"/"flavor-diagonal"
$\epsilon_{\tau\tau}^\oplus$ "flavor-universal"/"flavor-diagonal"

where $\epsilon_{\alpha\beta}^\oplus \approx \epsilon_{\alpha\beta}^e + \epsilon_{\alpha\beta}^p + Y_n^\oplus\epsilon_{\alpha\beta}^n$ (Thomas-DRAGON-2021).

The non-diagonal parameters are potentially complex (Thomas-DRAGON-2021):

$$ \begin{align*} \epsilon_{\alpha\beta}^\oplus &= |\epsilon_{\alpha\beta}^\oplus|e^{i\delta_{\alpha\beta}} \quad (\alpha \neq \beta) \end{align*} $$

For some reason, you can subtract off $\epsilon_{\mu\mu}^\oplus \times \mathbf{1}$ to reduce the parameters to five, and then the Hamiltonian is described by a total of eight real parameters (Thomas-DRAGON-2021):

  • $\vert\epsilon_{e\mu}^\oplus\vert$
  • $\vert\epsilon_{e\tau}^\oplus\vert$
  • $\vert\epsilon_{\mu\tau}^\oplus\vert$
  • $\epsilon_{ee}^\oplus - \epsilon_{\mu\mu}^\oplus$
  • $\epsilon_{\tau\tau}^\oplus - \epsilon_{\mu\mu}^\oplus$
  • $\delta_{e\mu}$
  • $\delta_{e\tau}$
  • $\delta_{\mu\tau}$

The parameters with minus signs in them are called the "nonuniversality strengths" (Thomas-DRAGON-2021).

This approach is mostly independent of the underlying model and mediator mass (Farzan-nsi-2018) (check).

Analyses

"What sets neutrino oscillation experiments apart from other experiments is their unique capability to probe BSM scenarios responsible for NSI independently of the new physics energy scale $\Lambda$" (– Thomas's paper) (Farzan-nsi-2018) (check).

DeepCore is most sensitive to $\epsilon_{\mu\tau}^\oplus$, but can constrain all effective NSI parameters (Thomas-DRAGON-2021).

IceCube analyses of NSI are

There were also IceCube NSI analyses done in 2017 (IC) (Salvado-ICnsi-2017), 2018 (DC) (IC-ICnsi-2018), and 2020 (DC) (Demidov-ICnsi-2020) (Thomas-DRAGON-2021).

Other experiments that have done NSI analyses are Super-K (2011) (SuperK-SuperKnsi-2011), MINOS (2013) (MINOS-MINOSnsi-2013), and COHERENT (2018) (Denton-COHERENTnsi-2018) (Thomas-DRAGON-2021).

Interpolating hypersurfaces are not computationally feasible for NSI analyses (Elisa-thesis-2023).