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Register a new userUncovering Multiple CP-Nonconserving Mechanisms of $betabeta$-Decay
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We consider the possibility of several different mechanisms contributing to the $betabeta$-decay amplitude in the general case of CP nonconservation: light Majorana neutrino exchange, heavy left-handed (LH) and heavy right-handed (RH) Majorana neutrino exchanges, lepton charge non-conserving couplings in SUSY theories with R-parity breaking. If the $betabeta$-decay is induced by, e.g., two non-interfering mechanisms, one can determine $|eta_i|^2$ and $|eta_j|^2$, $eta_i$ and $eta_j$ being the two fundamental parameters characterising these mechanisms, from data on the half-lives of two nuclear isotopes. In the case when two interfering mechanisms are responsible for the $betabeta$-decay, $|eta_i|^2$ and $|eta_j|^2$ and the interference term can be uniquely determined, in principle, from data on the half-lives of three nuclei. Given the half-life of one isotope, the positivity conditions $|eta_i|^2geq 0$ and $|eta_j|^2geq 0$ lead to stringent constraints on the half-lives of the other $betabeta$-decaying isotopes. These conditions, as well as the conditions for constructive (destructive) interference are derived and their implications are analysed in two specific cases. The method considered by us can be generalised to the case of more than two $betabeta$-decay mechanisms. It allows to treat the cases of CP conserving and CP nonconserving couplings generating the $betabeta$-decay in a unique way.
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In the near future, the neutrinoless double-beta ($0 ubetabeta$) decay experiments will hopefully reach the sensitivity of a few ${rm meV}$ to the effective neutrino mass $|m^{}_{betabeta}|$. In this paper, we tentatively examine the sensitivity of future $0 ubetabeta$-decay experiments to neutrino masses and Majorana CP phases by following the Bayesian statistical approach. Provided experimental setups corresponding to the sensitivity of $|m^{}_{betabeta}| simeq 1~{rm meV}$, the null observation of $0 ubetabeta$ decays in the case of normal neutrino mass ordering leads to a very competitive bound on the lightest neutrino mass $m^{}_1$. Namely, the $95%$ credible interval turns out to be $1.6~{rm meV} lesssim m^{}_1 lesssim 7.3~{rm meV}$ or $0.3~{rm meV} lesssim m^{}_1 lesssim 5.6~{rm meV}$ when the uniform prior on $m^{}_1/{rm eV}$ or on $log^{}_{10}(m^{}_1/{rm eV})$ is adopted. Moreover, one of two Majorana CP phases is strictly constrained, i.e., $140^circ lesssim rho lesssim 220^circ$ for both priors of $m^{}_1$. In contrast, if a relatively worse sensitivity of $|m^{}_{betabeta}| simeq 10~{rm meV}$ is assumed, the constraint becomes accordingly $0.6~{rm meV} lesssim m^{}_1 lesssim 26~{rm meV}$ or $0 lesssim m^{}_1 lesssim 6.1~{rm meV}$, while two Majorana CP phases will be essentially unconstrained. In the same statistical framework, the prospects for the determination of neutrino mass ordering and the discrimination between Majorana and Dirac nature of massive neutrinos in the $0 ubetabeta$-decay experiments are also discussed. Given the experimental sensitivity of $|m^{}_{betabeta}| simeq 10~{rm meV}$ (or $1~{rm meV}$), the strength of evidence to exclude the Majorana nature under the null observation of $0 ubetabeta$ decays is found to be inconclusive (or strong), no matter which of two priors on $m^{}_1$ is taken.
The precision of double-beta ($betabeta$) decay experimental half-lives and their uncertainties is reevaluated. A complementary analysis of the decay uncertainties indicates deficiencies due to small size of statistical samples, and incomplete collection of experimental information. Further experimental and theoretical efforts would lead toward more precise values of $betabeta$-decay half-lives and nuclear matrix elements.
In a separate paper we have discussed the possibility that six quark clusters can affect the rate of double-beta decay. In this article we develop the formalism needed in the evaluation of the energy of all six-quark cluster configurations, which can arise in a harmonic oscillator basis up to $2 hbar omega$ excitations. The symmetries that were found useful for this purpose were the combined spin color symmetry $SU_{cs}(6)$, the orbital symmetry $SU_{o}(6)$ and the isospin symmetry $SU_I(2)$.
We study double gamma ($gammagamma$) decay nuclear matrix elements (NMEs) for a wide range of nuclei from titanium to xenon, and explore their relation to neutrinoless double-beta ($0 ubetabeta$) NMEs. To favor the comparison, we focus on double-magnetic dipole transitions in the final $betabeta$ nuclei, in particular the $gammagamma$ decay of the double isobaric analog of the initial $betabeta$ state into the ground state. For the most probable decay with equal-energy photons, our large-scale nuclear shell model results show a good linear correlation between the $gammagamma$ and $0 ubetabeta$ NMEs. Our analysis reveals that the correlation holds for $gammagamma$ transitions driven by the spin or orbital angular momentum due to the dominance of zero-coupled nucleon pairs, a feature common to $0 ubetabeta$ decay. Our findings point out the potential of future $gammagamma$ decay measurements to constrain $0 ubetabeta$ NMEs, which are key to answer fundamental physics questions based on $0 ubetabeta$ experiments.
We study CP violation in chargino production and decay in the Minimal Supersymmetric Standard Model (MSSM) with complex parameters at an e^+ e^- linear collider with longitudinally polarized beams. We investigate CP-sensitive asymmetries by means of triple product correlations and study their dependence on the complex parameters M_1 and mu. We give numerical predictions for the asymmetries and their measurability at the future International Linear Collider. Our results show that the CP asymmetries can be measured in a large region of the MSSM parameter space.
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