arXiv subjects

Praveen C. Srivastava

Publications and source records attributed to Praveen C. Srivastava.

At least 19 recordsLinked to original sources

arXiv2026

Mirror and triplet energy differences in $sd$-shell nuclei using microscopic interactions with isospin-symmetry breaking effects

Starting from an isospin-symmetric microscopic interaction of Shin et al. [Phys. Rev. C 110, 034306 (2024)], we developed two isospin symmetry breaking (ISB) shell-model interactions by adding Coulomb interaction, as well as charge-symmetry breaking (CSB) and charge-independence breaking (CIB) components from the Argonne v18 (Av18) interaction at two different radial cutoffs, $r_c = 0.55$ and $0.70\ \mathrm{fm}$. With additional modifications to the proton single-particle energies, we then employed these interactions to calculate the Coulomb displacement energies (CDEs) and triplet displacement energies (TDEs) of the isobaric multiplet masses for nuclei with $|T_z| = 1/2$ and $T = 1$ across the $sd$-shell to test their validity and applicability, and compared with the USDCm interaction. We found that both ISB interactions show important roles of the CSB and CIB components in the CDEs and TDEs. In addition, we investigated mirror energy differences (MEDs) in the low-energy spectra of nuclei around $A$ = 20, and triplet energy differences (TEDs) in the $A$ = 18 and 22 systems. They are generally well described by the ISB interactions, although some discrepancies remain. Furthermore, the calculated $E2$ transition strengths obtained with the ISB interactions are shown to be in good agreement with experimental data, indicating small ISB effects in these transitions. Overall, both the ISB interactions provide a consistent and physically motivated framework for describing ISB effects, while the phenomenological USDCm interaction achieves closer agreement with experiment due to a larger number of adjustable parameters.

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arXiv2026

Multipartite entanglement study in $fp$-shell nuclei

In this study, we present multipartite entanglement results for the Ca and Ti isotopic chains obtained from nuclear shell-model wavefunctions. Our investigation focuses on the first excited $2^+_1$ states, which exhibit signatures of shell closures at $N=28$ and $N=32$. We calculate the 4- and 6-tangles, together with their corresponding network representations, providing a detailed picture of the underlying many-body correlations among nucleons. The primary objective of this work is to investigate the influence of shell closures on higher-order $n$-tangles, thereby gaining insight into the evolution of multipartite entanglement in medium-mass nuclei.

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arXiv2026

Ab initio study of $β$-decay and pairing in $N=Z$ nuclei

We investigate the $β$-decay properties of $rp$-process waiting-point nuclei $^{72}$Kr, $^{68}$Se, and $^{64}$Ge from realistic nuclear forces based on chiral effective field theory. The \textit{ab initio} valence-space in-medium similarity renormalization group method is employed for this purpose to consistently derive Hamiltonians and Gamow-Teller operators from chiral two- and three-nucleon interactions. The calculated half-lives and branching ratios indicate that nearly the entire decay intensity is confined within 1 MeV of excitation energy in the daughter nuclei. We address the isoscalar and isovector pairing and their impact on ground state properties of these waiting-point nuclei, along with several other $N=Z$ systems in the $fp$-shell. Our results do not provide evidence for an isoscalar condensate or any dominant isovector pairing condensate-like phase in these $N=Z$ nuclei. We present the full $B(\mathrm{GT})$ strength distributions and discuss the influence of pairing correlations on them. The present work provides a microscopic picture of $β$-decay strengths and pairing in $N=Z$ nuclei far from the stability line.

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arXiv2026

Large-scale shell-model investigation of $2ν$ECEC in $^{132}$Ba and $^{78}$Kr

We present a theoretical investigation of two-neutrino double electron capture ($2ν$ECEC) in $^{132}$Ba and $^{78}$Kr based on large-scale shell-model calculations. The nuclear matrix elements (NMEs) for the $2ν$ECEC process in $^{132}$Ba and $^{78}$Kr are calculated using the SN100PN and GWBXG effective interactions, respectively. The reliability of the employed interactions is first examined through a comparison of the calculated and experimental spectroscopic properties of the parent, intermediate, and granddaughter nuclei involved in the decay. We also examine the cumulative contribution of the $2ν$ECEC NME with respect to the $1^+$ state energies in the intermediate nuclei. The present results provide an updated and improved shell-model estimate of the $2ν$ECEC NME and half-life for $^{78}$Kr relative to earlier studies, and a baseline theoretical prediction for $^{132}$Ba that may assist future experimental efforts in constraining this rare decay mode.

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arXiv2026

Entanglement study in the island of inversion region using \textit{ab initio} approach

Quantum entanglement provides a unique perspective for probing nuclear structure. In this work, we employ quantum entanglement measures, including proton-neutron entanglement entropy, mutual information, and quantum relative entropy, to investigate the evolution of entanglement patterns as we approach neutron-rich nuclei. The study is carried out in the vicinity of the $N=20$ island of inversion region consisting of even-$A$ Ne, Mg, and Si isotopes, and also for isotones corresponding to $N=20$. The state-of-the-art \textit{ab initio} valence space in-medium similarity renormalization group method has been used for this purpose. We have highlighted the role of proton-neutron entanglement entropy in the formation of the island of inversion region. Mutual information provides insight into the strength of correlations between proton-proton, neutron-neutron, and proton-neutron single-particle states. While these correlations are relatively weak between protons and neutrons in the ground states, they become comparable to like-particle correlations in excited states. The quantum relative entropy is also studied between $0^+$ and $2^+$ states of the Ne, Mg, and Si isotopes, as well as $N=20$ isotones, using the Kullback-Leibler divergence and Jensen-Shannon divergence. We have performed these calculations by expressing the nuclear wavefunctions in a Slater-determinant basis and analyzing them through complementary partitions, including proton-neutron and mode-resolved factorizations.

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arXiv2025

Shell model study of isobaric analog states for $T_z= \pm 2$ nuclei using isospin non-conserving interactions

In order to comprehend the process underlying mirror energy differences in mirror pairs, we have performed shell-model calculations for $T_z= \pm 2$ $sd$-shell nuclei in the mass range $A$= 20 to 36 and neutron number varying from $N$= 8 to 20. Isospin-symmetry breaking (ISB) is responsible for the mirror energy difference of excited states. We have investigated the {\color{black}isospin non-conserving} interactions: USDC and USDCm to explore the low-lying energy spectra, mirror energy differences, isoscalar ($M_0$), isovector ($M_1$) matrix elements, \textit{E2} transition probability, magnetic ($μ$), and quadrupole moments ($Q$) of mirror-pair and compared them with their available experimental data. The impact of single-particle states on weakly bound and unbound nuclear states are investigated, especially those of the $s$-wave. We have also analyzed single proton/neutron separation energies and proton/neutron occupancy for ($T_z$=-2)/($T_z$=+2) $sd$-shell nuclei.

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arXiv2025

Collectivity and isomers in the Pb isotopes

In the present work, we aim to study collectivity in the Pb isotopes in the framework of nuclear shell model. We have performed shell-model calculations using KHH7B effective interaction. The model space of KHH7B interaction consists of 14 orbitals. We have reported results for even-even $^{196-206}$Pb isotopes for spectra and electromagnetic properties. The shell model results for isomeric states are also reported. Our results will be useful to compare upcoming experimental data.

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arXiv2025

Ab initio study of island of inversion in odd-$A$ nuclei: Structure of $^{31,33}$Mg

We study the $N=20$ island of inversion region in the odd-$A$ Ne and Mg isotopes from the fundamental nuclear forces based on chiral two- and three-nucleon potentials. The state-of-the-art \textit{ab initio} valence space in medium similarity renormalization method was used for this purpose. Our study focuses on the evolution of single-particle states and discusses their transition into the island of inversion through particle-hole excitations across the $N=20$ shell gap. The computed low-lying states and magnetic moments are in good agreement with the experimental data. We presented the rotational band structures, established via $E2$ transitions, in $^{31}$Mg and $^{33}$Mg, which emerge from both normal and intruder configurations at low excitation energies. Our results suggest the presence of weak, moderate, and strongly prolate-deformed configurations at low energy in both isotopes. The present work offers valuable insights into the configurations and shapes of low-lying states in nuclei within the island of inversion, enhancing our understanding of the structures of exotic nuclei from first principles.

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arXiv2025

Forbidden non-unique $β^{-}$ transitions and $g_A$-sensitive electron spectral-shapes

In the present work, we have done a systematic study of beta decay properties such as electron spectral-shapes, shape factors, and log$ft$ values for the higher forbidden non-unique $β^{-}$ transitions in the mass region A=85-123. We have performed the nuclear shell model (SM) calculations to explore the sensitivity of the electron spectral-shapes for different axial-vector coupling constants $g_{A}=0.8-1.27$. The effective interactions GWBXG, G-matrix, SNET and SN100PN are used for different model spaces. In the present work, we have computed the electron spectral-shapes of $^{85}$Br, $^{87}$Rb, $^{93}$Zr, $^{97}$Zr, $^{101}$Mo, $^{115}$Cd, $^{117}$Cd, $^{119}$In, $^{123}$Sn and $^{135}$Cs by constraining the small relativistic nuclear matrix element from conserved vector-current hypothesis (CVC). We have found that the electron spectral-shapes are strongly dependent on $g_{A}$ except the second forbidden non-unique $β^{-}$ transition $^{93}$Zr.

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arXiv2025

Weak interaction rates of $sd$-shell Urca pairs in stellar environment using a shell-model approach

In this work, the weak interaction rates of $sd$-shell nuclei in the hot and dense stellar environment are calculated using the shell model. The {\it ab initio} effective interactions are employed for the calculation of Gamow-Teller strengths and weak rates in addition to the phenomenological interaction. The weak rates are evaluated in a fine grid of density and temperature. The electron capture and $β^-$-decay rates of Urca pairs of nuclei with $A = 23, 25, 29, 31$ and 33 are evaluated as a function of $\log_{10} ρY_e$ and the corresponding Urca density is obtained. The screening effects are also included for the evaluation of these stellar weak rates. In addition, the intrinsic cooling strength is evaluated for $A=29,31$ and 33 Urca pairs in neutron star crusts. The stellar weak rates, along with the neutrino energy emitted and the gamma heat production, are tabulated for $A = 29-39$ nuclei.

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arXiv2025

Evolution of shell structure at $\mathbf{N=32}$ and 34: Insights from realistic nuclear forces

We investigated the evolution of shell structure at $N=32$ and 34 in neutron-rich nuclei beyond the stability line using realistic nuclear forces, employing the state-of-the-art valence-space in-medium similarity renormalization group method. The shell gaps are discussed from the excitation energies of the first $2^+$ states and the evolution of effective single-particle energies. We addressed different components of the nuclear interaction--central, spin-orbit, and tensor--and their roles in the development of shell gaps far from stability. The calculated results align well with the available experimental data and suggest a strengthening of the $N=34$ subshell gap and a weakening of the $N=32$ subshell gap below Ca. Additionally, the low-energy structures of the exotic $N=32$ isotones below Ca revealed that their ground states exhibit large deformation and coexist with a weakly deformed band at low excitation energy. The present work demonstrates essential components of the nuclear force in shaping magic numbers far from stability and provides deeper insights into the structure of exotic nuclei from the underlying nuclear forces.

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arXiv2025

Study of entanglement in Ne, Mg, and Si isotopic chains

In this article, we have presented the results for mode entanglement and its evolution in Ne, Mg, and Si isotopic chains. A detailed study has also been conducted on the role of nuclear forces with the assistance of the spin-tensor decomposition of two-body interaction into three components: central, spin-orbit, and tensor. This study can shed light on the high entanglement entropy observed for $N=Z$ nuclei and the importance of the tensor component on the proton-neutron entanglement entropy.

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arXiv2025

Modification of single-hole-like states by configuration mixing in the $^{99-131}$In

Large-scale shell-model calculations are performed for the $9/2^+_{\rm g.s.}$, $1/2^-_1$, $3/2^-_1$, and $5/2^-_1$ states in the odd-$A$ indium isotopes with $N=50-82$. The calculated energy levels, electromagnetic moments, and spectroscopic factors exhibit remarkable agreement with the experimental data due to significant configuration mixing for the neutron numbers away from the closed shells. The $1/2^-_1$ energy levels closely follow the trend of effective single-particle energies, which are determined using the fractional occupancies of neutron orbitals. However, configuration mixing with the proton $p_{3/2}$ and $f_{5/2}$ orbitals in the actual shell-model calculations plays a crucial role in accurately reproducing the positions of the $1/2^-_1$ levels, ensuring better agreement with the experimental data across the entire isotopic chain.

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arXiv2025

Ab initio no-core shell-model study of $^{20-23}$Na isotopes

We have done a systematic no-core shell-model study of $^{20-23}$Na isotopes. The low-energy spectra of these sodium isotopes consisting of natural and un-natural parity states were reported, considering three realistic interactions: inside nonlocal outside Yukawa (INOY), charge-dependent Bonn 2000 (CDB2K), and the chiral next-to-next-to-next-to-leading order (N$^3$LO). We also present the mirror energy differences in the low-energy spectra of $|T_z|$ = 1/2 mirror pair ($^{21}$Na - $^{21}$Ne). Apart from the energy spectra, we have also reported the electromagnetic transition strengths and moments. Finally, considering all three realistic interactions, we report the point-proton radii and neutron skin thicknesses.

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arXiv2024

Nuclear structure properties of $^{193-200}$Hg isotopes within large-scale shell model calculations

Large-scale shell-model calculations have been performed to study the nuclear structure properties of Hg isotopes with mass varying from $A=193$ to $A=200$. The shell-model calculations are carried out in the 50 $\leq Z \leq$ 82 and 82 $ \leq N \leq$ 126 model space using monopole-based truncation. We present detailed studies on low-energy excitation spectra, energy systematics, and collective properties of Hg isotopes, such as reduced transition probabilities, quadrupole, and magnetic moments along the isotopic chain. The evolution of wave function configurations with spin is analyzed in the case of even-$A$ Hg isotopes. The shell-model results are in reasonable agreement with the experimental data and predictions are made where experimental data are unavailable. The shapes of Hg isotopes are also investigated through the energy-surface plots.

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arXiv2024

Large-scale shell-model study of 2$ν$ECEC process in $^{78}$Kr

In this work, we present the systematic study of $2ν$ECEC process in the $^{78}$Kr using large-scale shell-model calculations with the GWBXG effective interaction. We first validate the efficiency of the utilized interaction by comparing the theoretical low-lying energy spectra, the kinematic moment of inertia, and reduced transition probabilities with the experimental data for both the parent and grand-daughter nuclei $^{78}$Kr and $^{78}$Se, respectively. Additionally, we examine the shell-model level densities of the $1^+$ states in the intermediate nucleus $^{78}$Br, comparing them with the predictions from the Back-shifted Fermi gas model. We analyze the variation of cumulative nuclear matrix elements (NMEs) for the $2ν$ECEC process in $^{78}$Kr as a function of $1^+$ state energies in the intermediate nucleus $^{78}$Br up to the saturation level. Our estimated half-life for $^{78}$Kr, extracted from the shell-model predicted NMEs, shows good agreement with the experimental value. The Gamow-Teller transitions from the lowest $1^+$ state of $^{78}$Br via both the EC$+β^+$ and $β^-$-channels are also discussed.

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arXiv2024

Systematic shell-model analysis of $2νββ$ decay of $^{76}$Ge and $^{96}$Zr to the ground and excited states of $^{76}$Se and $^{96}$Mo

In this work, we have studied the $2νββ$ decay of $^{76}$Ge and $^{96}$Zr isotopes utilizing large-scale shell-model calculations. The GWBXG effective interaction has been employed in the calculation of $2νββ$-decay nuclear matrix elements (NMEs). We have tested the effective interaction by comparing the predicted spectroscopic properties, such as energy spectra and transition probabilities, with the available experimental data. The variation of cumulative NMEs with respect to the $1^+$ state energies of the intermediate nucleus is also studied, corresponding to $0^+_{\rm g.s.}\rightarrow0^+_{\rm g.s.}$, $0^+_{\rm g.s.}\rightarrow0^+_{2}$, and $0^+_{\rm g.s.}\rightarrow2^+_{1}$ transitions between the parent and grand-daughter nuclei. The effective values of axial-vector coupling strength ($g_A^{\rm eff}$) are calculated using the predicted NMEs and experimental half-lives for $0^+_{\rm g.s.}\rightarrow0^+_{\rm g.s.}$ transitions. The extracted half-lives for $0^+_{\rm g.s.}\rightarrow0^+_{2}$, and $0^+_{\rm g.s.}\rightarrow2^+_{1}$ transitions using the shell-model predicted NMEs are consistent with the recent experimental data. The comparison of the shell-model predicted NMEs with previous NMEs available in the literature is discussed. Also, the computed branching ratios for the $2νββ$ decay of $^{76}$Ge and both the $2νββ$ and single-$β$ decay of $^{96}$Zr are reported corresponding to the calculated $g_A^{\rm eff}$ values.

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arXiv2024

Isoscalar, isovector and orbital contributions in $M1$ transitions from analogous $M1$ and Gamow-Teller transitions in $T=\frac{1}{2}$ mirror nuclei

The isoscalar and isovector components and their contributions to $M1$ transitions are discussed in the odd-$A$, $T=1/2$ mirror nuclei with mass number ranging from $A=23$ to 37. The orbital contributions in various $M1$ transitions and ground state magnetic moments are calculated by comparing analogous $M1$ and Gamow-Teller transitions between mirror pairs. The orbital contributions in different $M1$ transitions are explained on the basis of configurations of the initial and final states involved. In magnetic moments, the orbital contributions are found to be dependent on the deformation and single-particle nature of the states. All the $T=1/2$ mirror pairs are studied using isospin non-conserving interaction. The results are also compared with predictions from \textit{ab initio} effective interaction derived from realistic nuclear forces.

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