Lorentz violation effects in two neutrino double-beta decay

Understand

Observable effects for the Lorentz invariance violation (LIV) at a low energy scale can also be investigated in double beta decay (DBD).

• For example, by comparing the theoretical predictions with a precise analysis of the summed energy spectra of electrons in $2\nu\beta\beta$ decay, one can constrain the $\mathring{a}_{of}^{(3)}$ coefficient that governs the time-like component of the Lorentz invariance violating operator that appears in the Standard Model extension theory.
• In this work, we perform calculations of the phase space factors and summed energy spectra of electrons as well as of their deviations due to LIV necessary in such experimental investigations.
• The Fermi functions needed in the calculation are built up with exact electron wave functions obtained by numerically solving the Dirac equation in a realistic Coulomb-type potential with the inclusion of the finite nuclear size and screening effects.