Abstract
Neutrinoless double beta decay ($0\nu\beta\beta$) is a crucial test for lepton number violation. Observation of this process would have fundamental implications for neutrino physics, theories beyond the Standard Model and cosmology. Focussing on so called short-range operators of $0\nu\beta\beta$ and their potential interplay with the standard light Majorana neutrino exchange, we present the first complete calculation of the relevant nuclear matrix elements, performed within the interacting boson model (IBM-2). Furthermore, we calculate the relevant phase space factors using exact Dirac electron wavefunctions, taking into account the finite nuclear size and screening by the electron cloud. The obtained numerical results are presented together with up-to-date limits on the standard mass mechanism and effective $0\nu\beta\beta$ short-range operators in the IBM-2 framework. Finally, we interpret the limits in the particle physics scenarios incorporating heavy sterile neutrinos, Left-Right symmetry and R-parity violating supersymmetry.
Highlights
The nature of neutrinos and especially the origin of their masses are a crucial open question
The values of light neutrino exchange nuclear matrix element (NME) Mν calculated in our approach are shown in the last column of Table IV
This, along with the large phase space factor (PSF) discussed below, makes 100Mo an ideal isotope to probe the corresponding mechanisms from a theoretical point of view
Summary
The nature of neutrinos and especially the origin of their masses are a crucial open question. In BSM scenarios, a neutrino mass insertion is not necessarily required, cf Fig. 1(b) In such cases, the decay rate is estimated as Γ0LνRββ ∼ v2Λ−O67 G2Fm4FQ5ββ∼ ð105 GeV=ΛO7 Þ6 × ð1026 yrÞ−1, with the SM Higgs vacuum expectation value (VEV) v 1⁄4 246 GeV and the scale ΛO7 of the exotic dim-7 operator. The decay rate is estimated as Γ0LνRββ ∼ v2Λ−O67 G2Fm4FQ5ββ∼ ð105 GeV=ΛO7 Þ6 × ð1026 yrÞ−1, with the SM Higgs vacuum expectation value (VEV) v 1⁄4 246 GeV and the scale ΛO7 of the exotic dim-7 operator Such long-range mechanisms via the exchange of light. We numerically evaluate all relevant NMEs within the interacting boson model (IBM-2) framework This will allow us to set upper limits on the effective couplings εI where we will highlight the exchange of heavy sterile neutrinos as an important example.
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