arXiv subjects

L. Jokiniemi

Publications and source records attributed to L. Jokiniemi.

6 recordsLinked to original sources

arXiv2026

Two-neutrino double-weak decays of $^{126}$Xe and $^{134}$Xe from different many-body methods

We calculate the nuclear matrix elements and corresponding half-lives for the two-neutrino double-electron capture of $^{126}$Xe and the two-neutrino double-beta decay of $^{134}$Xe. We use different many-body methods: the proton-neutron quasiparticle random-phase approximation, the nuclear shell model, the microscopic interacting boson model, and an effective field theory for heavy nuclei. For both nuclei, all our half-life predictions are generally consistent with each other when including theoretical uncertainties for each method. Interestingly, for all calculations the lower range of the predicted $^{134}$Xe half-life is shorter than $T^{2\nu}_{1/2} \approx 2\times10^{24}$\,y, which may be within the reach of next-generation experiments. For $^{126}$Xe, our results typically predict one order of magnitude longer half-lives than those for $^{134}$Xe.

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arXiv2026

Global Ab initio Neutrino Mass Limits from Neutrinoless Double-Beta Decay

We present global limits for Majorana neutrino masses by combining latest results from neutrinoless double-beta ($0\nu\beta\beta$) decay searches and ab initio nuclear theory. Limits are derived in a Bayesian framework utilizing likelihood functions from a suite of $0\nu\beta\beta$-decay experiments in conjunction with nuclear matrix elements calculated from nuclear and electroweak forces derived from chiral effective field theory and implemented in the in-medium similarity renormalization group many-body approach. In contrast to nuclear models, ab initio results indicate that the current generation of $0\nu\beta\beta$-decay experiments have likely \textit{not} yet reached sensitivities required to probe the mass regime allowed by neutrino-oscillation data, where the combined bounds are notably stronger than those given by individual experiments. Finally, from predicted sensitivities of next-generation searches, we show that, while no one individual experiment fully covers the inverted mass ordering, this can be achieved from combined contributions from the four key isotopes: $^{76}$Ge, $^{100}$Mo, $^{130}$Te, and $^{136}$Xe.

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arXiv2026

Ab initio short-range nuclear matrix elements for neutrinoless double-beta decay

We present converged ab initio calculations of short-range neutrinoless double-beta ($0\nu\beta\beta$) decay nuclear matrix elements for the key experimental isotopes $^{76}$Ge, $^{82}$Se, $^{130}$Te and $^{136}$Xe. Starting from different nuclear forces derived from chiral effective field theory, we apply the in-medium similarity renormalization group to obtain an effective valence-space Hamiltonian along with consistently transformed $0\nu\beta\beta$-decay operators. We then obtain a range of values for the matrix elements that is consistent with, but generally smaller than, those from phenomenology. Finally, we combine our results with current limits from $0\nu\beta\beta$-decay searches to obtain constraints for the sterile-neutrino mixing-mass parameter space when considering the inclusion of a fourth, sterile neutrino.

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arXiv2023

Ab initio calculation of muon capture on $^{24}$Mg

In this work we study ordinary muon capture (OMC) on $^{24}$Mg from a first principles perspective. Starting from a particular two- and three-nucleon interaction derived from chiral effective field theory, we use the valence-space in-medium similarity renormalization group (VS-IMSRG) framework to construct effective Hamiltonians and muon-capture operators which nonperturbatively account for many-body physics outside the valence space. The obtained nuclear matrix elements are compared against those from the phenomenological shell model. The impact of including the correlations from the nuclear shell model (NSM) as well as including the induced two-body part is studied in detail. Furthermore, the effects of realistic bound-muon wave function on the operators is studied. Finally, predictions for capture rates to the lowest excited states in $^{24}$Na are given and compared with available data. It is found that the spectroscopic properties of $^{24}$Mg and its OMC daughter $^{24}$Na are fairly well described by both the NSM and VS-IMSRG, and that the effect of the hadronic two-body currents significantly reduces the OMC rates. Both models have some difficulties in matching the measured OMC rates, especially for the $2^+$ final states. This calls for further studies in other light nuclei with available OMC data.

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arXiv2022

Nuclear matrix elements for neutrinoless double beta decays and spin-dipole giant resonances

Nuclear matrix elements (NMEs) for neutrinoless double beta decays (DBDs) are required for studying neutrino physics beyond the standard model by DBD. The experimental spin-dipole (SD) giant resonance energy and the SD strength are shown for the first time to be closely related to the DBD-NME, and are used for studying the spin-isospin correlation and the quenching of the axial-vector coupling. So they are used to help the theoretical model calculation of the DBD-NME.

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arXiv2021

High-precision $Q$-value measurement and nuclear matrix elements for the double-$β$ decay of $^{98}$Mo

Neutrinoless double-beta ($0νββ$) decay and the standard two-neutrino double-beta ($2νββ$) decay of $^{98}$Mo have been studied. The double-beta decay $Q$-value has been determined as $Q_{ββ}=113.668(68)$ keV using the JYFLTRAP Penning trap mass spectrometer. It is in agreement with the literature value, $Q_{ββ}=109(6)$ keV, but almost 90 times more precise. Based on the measured $Q$-value, precise phase-space factors for $2νββ$ decay and $0νββ$ decay, needed in the half-life predictions, have been calculated. Furthermore, the involved nuclear matrix elements have been computed in the proton-neutron quasiparticle random-phase approximation (pnQRPA) and the microscopic interacting boson model (IBM-2) frameworks. Finally, predictions for the $2νββ$ decay are given, suggesting a much longer half-life than for the currently observed cases.

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