Impact of isovector pairing fluctuations on neutrinoless double- β decay in multireference covariant density functional theory

We extend the multireference covariant density-functional theory (MR-CDFT) by including fluctuations in quadrupole deformations and average isovector pairing gaps simultaneously for the nuclear matrix elements (NMEs) of neutrinoless double-beta (0νββ) decay in the candidate nuclei Ge76, Se82, Mo100, Te130, and Xe136 assuming the exchange of either light or heavy neutrinos. The results indicate a linear correlation between the predicted NMEs and the isovector pairing strengths, as well as the excitation energies of 21+ and 41+ states. By adjusting the pairing strengths based on the excitation energies of the 21+ states, we calculate the NMEs for 0νββ decay, which are reduced by approximately 12% to 62% compared with the results obtained in the previous studies by Song et al. [Phys. Rev. C 95, 024305 (2017)2469-998510.1103/PhysRevC.95.024305]. Additionally, upon introducing the average isovector pairing gap as an additional generator coordinate in the calculation, the NMEs increase by a factor ranging from 56% to 218%.