arXiv subjects

Jan Miśkiewicz

Publications and source records attributed to Jan Miśkiewicz.

4 recordsLinked to original sources

arXiv2026

Influence of configuration-interaction on isospin impurities and isospin symmetry breaking corrections to superallowed $0^+\rightarrow 0^+$ beta decays

The symmetry-conserving density functional theory (DFT)-based no-core configuration-interaction (DFT-NCCI) framework is applied for the first time to investigate the impact of configuration interaction (CI) on the Coulomb (isospin) impurity, $\alpha_{\rm C}$, in the ground and excited states of $^{10}$C, $^{10}$B, and $^{14}$N, as well as on the isospin-symmetry-breaking (ISB) correction to the superallowed $0^+ \rightarrow 0^+$ $\beta$ decay of $^{10}$C. We demonstrate, among other findings, that within the DFT-NCCI framework CI has a negligible effect on the ground-state isospin impurities, which are dominated by a single doorway state. In contrast, CI significantly modifies the impurities in excited states, including the isobaric analogue $I=0^+,\,T=1$ state in $^{10}$B. Hence, it also has a non-negligible impact on the ISB correction to the superallowed $\beta$ decay of $^{10}$C. Our calculations yield $\bar{\delta}_{\rm C}=0.45(4)\%$ when the Coulomb interaction is taken as the sole source of ISB, and $\bar{\delta}_{\rm ISB}=0.46(6)\%$ when short-range charge-symmetry-breaking (CSB) terms are included in addition. Hence, no statistically significant dependence of the ISB correction on the short-range CSB interaction is observed for this decay. Comparison with our previous results reveals a strong sensitivity to the nuclear symmetry energy, which governs the strength of the isospin-restoring force and whose value in finite nuclei remains difficult to constrain because of its intricate dependence on the momentum-dependent terms of the effective interaction.

nucl-th↗

arXiv2026

Skyrme SV density-functional analysis of the $2νββ$ decay in $^{76}$Ge

We present a theoretical study of the two-neutrino $0^+ \rightarrow 0^+$ double beta decay of $^{76}$Ge within the No-Core Configuration-Interaction framework based on the Skyrme SV density functional. We analyze three allowed decay scenarios distinguished by the $[n,m] \equiv [(νg_{9/2})^n, (πg_{9/2})^m]$ occupancy of the $0g_{9/2}$ intruder orbital, which remains conserved to high precision, as well as by the triaxiality of the daughter nucleus. The resulting $2νββ$ nuclear matrix element is found to depend strongly on the scenario. For the energetically favored $[4,2]$ occupancy, we obtain $|\mathcal{M}^{2ν}| = 0.069(7)$~MeV$^{-1}$. For the $[6,0]$ occupancy, the matrix element further depends on the triaxiality parameter $γ$ of the two coexisting, closely lying minima in $^{76}$Se, yielding $|\mathcal{M}^{2ν}| = 0.040(4)$~MeV$^{-1}$ at $γ= 17.7^\circ$ and $|\mathcal{M}^{2ν}| = 0.22(2)$~MeV$^{-1}$ at $γ= 41.9^\circ$. The latter result is consistent with the empirical value reported by A. S. Barabash, $|\mathcal{M}^{2ν}| = 0.204(14)$~MeV$^{-1}$, while the two former results are comparable to existing calculations based on energy-density-functional frameworks. Our calculations reveal challenges in the precise determination of the $|\mathcal{M}^{2ν}|$ for the $^{76}$Ge decay. The structural complexity, triaxiality, and shape coexistence identified in the analyzed nuclei imply a strong sensitivity to fine details of the interaction and configuration mixing. This, in turn, explains the difficulties in theoretical modeling of the $|\mathcal{M}^{2ν}|$ matrix elements for the $^{76}$Ge decay, which vary by almost an order of magnitude in the available literature.

nucl-th↗

arXiv2025

Two-neutrino $0^+ \to 0^+$ double beta decay of $^{48}\mathrm{Ca}$ within the DFT-NCCI framework

We present a seminal calculation of the nuclear matrix element for the two-neutrino double beta ($2νββ$) decay of ${}^{48}\text{Ca} \rightarrow {}^{48}\text{Ti}$ using a post-Hartree-Fock (HF) Density Functional Theory-based No-Core Configuration-Interaction (DFT-NCCI) framework developed by our group [Phys. Rev. C 94, 024306 (2016)]. In the present calculation, we utilize a variant of the approach that restores rotational symmetry and mixes states projected from self-consistent mean-field configurations obtained by solving the HF equations with the density-independent local Skyrme interaction. Our calculations yield $|\mathcal{M}_{2νββ}| = 0.056(6)$ MeV$^{-1}$ for the nuclear matrix element describing this process. This result is in very good agreement with shell-model studies - for example, with the calculations by Horoi {\it et al.\/} [Phys. Rev. C 75, 034303 (2007)], which yielded 0.054 (0.064) MeV$^{-1}$ for the GXPF1A (GXPF1) interactions, respectively. It is also in a reasonable agreement with the most recent experimental estimate from the review by Barabash, which is 0.068(6) MeV$^{-1}$, assuming quenching $qg_\text{A} \approx 1$. The consistency of our prediction with the shell-model results increases our confidence in the nuclear modeling of this second-order, very rare process which is of paramount importance for further modeling of the neutrinoless double beta ($0νββ$) decay process.

nucl-th↗

arXiv2021

Weighing the spacetime along the line of sight using times of arrival of electromagnetic signals

We present a new method of measuring the mass density along the line of sight, based on precise measurements of the variations of the times of arrival (TOA's) of electromagnetic signals propagating between two distant regions of spacetime. The TOA variations are measured between a number of slightly displaced pairs of points from the two regions. These variations are due to the nonrelativistic geometric effects (Roemer delays and finite distance effects) as well as the gravitational effects in the light propagation (gravitational ray bending and Shapiro delays). We show that from a sufficiently broad sample of TOA measurements we can determine two scalars quantifying the impact of the spacetime curvature on the light propagation, directly related to the first two moments of the mass density distribution along the line of sight. The values of the scalars are independent of the angular positions or the states of motion of the two clock ensembles we use for the measurement and free from any influence of masses off the line of sight. These properties can make the mass density measurements very robust. The downside of the method is the need for extremely precise signal timing.

gr-qc↗