Direction of the neutrino magnetic moment

Determine the direction of the cosmic-neutrino magnetic moment relative to the electric field in the single-arm interferometer, including its possible time dependence under interferometer rotation, rather than assuming a fixed alignment angle.

Background

The effective interaction Hamiltonian depends on the angle between the neutrino magnetic-moment vector and the electric field, denoted by θμsE\theta_{\mu_s E}. Because the directional orientation of the magnetic moment affects the predicted interaction and phase shift, the paper simplifies the analysis by setting this angle to zero.

The authors explicitly state that the direction is unknown and note that rotating the interferometer could produce a time modulation of the cosmic-neutrino-background signal as the relative angle changes. A treatment of this directional and time-dependent scenario is not carried out in the paper.

References

Since we do not know the direction of $\vec{\mu}{s}$, we assume $\theta{\mu_{s} E} = 0$. Actually, one could rotate the interferometer to get the time modulation of the CNB signal since $\theta_{\mu_{s} E}$ would vary with time.

— Discovery Potentials for the Cosmic Neutrino Background using Single Arm Interferometer  (2608.24739 - Nugroho, 25 Aug 2026) in Section 2, “CNB and Photon Interaction”