We present a new contribution of the R-parity violating (Rp / ) supersymmetry (SUSY) to neutrinoless double beta decay (0νββ) via the pion exchange between decaying neutrons.The pion coupling to the final state electrons is induced by the Rp / SUSY interactions. We have found this pion-exchange mechanism to dominate over the conventional two-nucleon one. The latter corresponds to direct interaction between quarks from two decaying neutrons without any light hadronic mediator like π-meson.The constraints on the certain Rp / SUSY parameters are extracted from the current experimental 0νββ-decay half-life limit. These constraints are significantly stronger than those previously known or expected from the ongoing accelerator experiments.12.60. Jv, 11.30.Er, 23.40.Bw Neutrinoless double beta decay (0νββ) has long been recognized as a sensitive probe of the new physics beyond the standard model (SM) (see [1]-[2]). Various mechanisms of 0νββ decay were proposed and studied in the last two decades. The conventional mechanism is based on the exchange of a massive Majorana neutrino between the two decaying neutrons. A new mechanism was found within supersymmetric (SUSY) models with R-parity violation (3B+L+2S where S, B and L are spin, baryon and lepton numbers.) It was later studied in more details in [4]. A complete analysis of this mechanism within the minimal supersymmetric standard model (MSSM) was carried out in [5].The nuclear 0νββ-decay is triggered by the 0νββ quark transition d + d → u + u + 2e − which is induced by certain fundamental interactions. It was a common practice to put the initial d-quarks separately inside the two initial neutrons of a 0νββ-decaying nucleus. This is the so called two-nucleon mode of the 0νββ-decay [see Fig. 1(a)]. If the above 0νββ quark transition proceeds at short distances, as in the case of R p / SUSY interactions, then the basic nucleon transition amplitude n + n → p + p + 2e − is strongly suppressed for relative distances larger than the mean nucleon radius.In this letter we propose a new pion-exchange SUSY mechanism which is based on the double-pion exchange between the decaying neutrons [ Fig. 1(b)]. At the quark level this mechanism implies the same short-distance R p / MSSM interactions as in [5]. However, it essentially differs from the previous consideration of the SUSY contribution to the 0νββ-decay at the stage of the hadronization. We assume that the R p / MSSM quark interactions induce ππ → 2e transition at the middle point of the diagram in Fig. 1(b). The importance of the pion-exchange currents in 0νββ-decay was first been pointed out by B. Pontecorvo [6]. Latter, this idea was quantitatively realized in [7]-[8] for the case of the heavy Majorana neutrino exchange. It was shown that the pion-exchange contribution can not be neglected in this case. We will show that in the case of the R p / MSSM induced quark transition the pion-exchange contribution absolutely dominates over the conventional two-nucleon mode.The R p -violating part of the superpotential breaki...
We discuss an extension of the standard model (SM) with vector and scalar leptoquarks. The renormalizable leptoquark Lagrangian consistent with the SM gauge symmetry is presented including the leptoquark-Higgs interactions previously not considered in the literature. We discuss the importance of these new interactions for leptoquark phenomenology. After the electro-weak symmetry breaking they generate non-trivial leptoquark mass matrices. These lead to mixing between different SU (2) L -multiplets of the leptoquarks and induce at low energies new effective 4-fermion lepton-quark vertices. The latter affect the standard leptoquark phenomenology. We discuss constraints on these interactions from the helicity-suppressed π → ν + e decay.
We have discovered a misprint in Eq. (12) of the paper. The units in this equation are incorrectly given. The correct equation reads L ¼ cγτ N ≃ 0.12γ 10 GeV m N 5 m W R 1 TeV 4 ½mm: ð12Þ
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