arXiv subjects

Michael Gennari

Publications and source records attributed to Michael Gennari.

13 recordsLinked to original sources

arXiv2026

Recent Progress in Ab-Initio Nuclear Theory for Precision Physics Searches in Muonic Atoms and Superallowed $\beta$ Decays

Precision tests of the Standard Model at low energy are increasingly limited by nuclear-structure theory rather than by experiment. We review two such cases: the two-photon-exchange correction to the Lamb shift in muonic atoms, and the \texorpdfstring{$\gamma W$}{gamma-W} box radiative correction to superallowed \texorpdfstring{$\beta$}{beta} decays. Although they probe different physics, both are governed by the same generalized hadronic tensor, so that the chiral effective field theory Hamiltonians and currents, Lanczos-based response methods, and Bayesian uncertainty quantification developed for one carry over directly to the other. We summarize recent ab initio progress in light nuclei and its impact on nuclear charge radii, on the helium isotope-shift puzzle, and on the extraction of \texorpdfstring{$V_{ud}$}{Vud} for the top-row CKM unitarity test, and state a future outlook.

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arXiv2026

Future directions in nuclear $\beta$ decay at FRIB and beyond

Motivated by the opportunities presented for studies relevant to nuclear structure, astrophysics, and fundamental symmetries with nuclear $\beta$ decay, the Facility for Rare Isotope Beams (FRIB) Theory Alliance topical program ``Future Directions in Nuclear $\beta$ Decays at FRIB'' was held in September of 2025. This white paper summarizes the main points of discussion over the two-week program, and it aims to provide a snapshot of the current status of the field while also highlighting important questions and opportunities for future work. We provide an overview of the experimental tools and techniques that enable modern $\beta$ decay studies, discuss the current state of nuclear many-body approaches used to study $\beta$ decays, and highlight the important science questions that can be addressed by weak decays.

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arXiv2026

A Phenomenological Extension for Microscopic Optical Potentials

Microscopic optical potentials constructed from realistic nucleon-nucleon interactions via multiple-scattering theory provide a first-principles description of nucleon-nucleus scattering. Nevertheless, such approaches often neglect medium corrections beyond Pauli blocking and fail to fully capture higher-order scattering contributions, leading to systematic under-prediction of absorption and deficiencies in angular distributions at low and intermediate energies. In this work we introduce a phenomenological correction scheme with an energy-dependent term designed to mimic correlation effects, dispersive contributions, and multi-step scattering processes. The correction is implemented in a minimal form to preserve the predictive character of the underlying microscopic model, while enabling improved flexibility in describing experimental observables. Applications to proton and neutron elastic scattering on light-mass nuclei demonstrate that the modified potentials yield enhanced agreement with measured differential cross sections, without sacrificing the microscopic foundation. This approach provides a practical pathway for incorporating missing medium and higher-order effects into optical model analyses relevant for nuclear structure and reaction studies.

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arXiv2026

Halo Nuclei from Ab Initio Nuclear Theory

A realistic description of halo nuclei, characterized by low-lying breakup thresholds, requires a proper treatment of continuum effects. We have developed an ab initio approach, the no-core shell model with continuum (NCSMC), capable of describing both bound and unbound states in light nuclei in a unified way. With chiral two- and three-nucleon interactions as the only input, we can predict structure and dynamics of halo and other light nuclei and, by comparing to available experimental data, test the quality of chiral nuclear forces. We review NCSMC calculations of weakly bound states and resonances of exotic halo nuclei $^6$He, $^8$B, $^{11}$Be, and $^{15}$C. For the latter, we discuss its production in the capture reaction $^{14}$C(n,$\gamma$)$^{15}$C. We highlight challenges of a description of $^6$He as a Borromean n-n-$^4$He system. Finally, we present calculations of excited states in $^{10}$Be exhibiting a one-neutron halo structure and a large scale no-core shell model investigation of $^{11}$Li as a precursor of a full n-n-$^9$Li NCSMC study.

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arXiv2026

Inelastic nucleon-nucleus scattering from a microscopic point of view

We apply to the nucleon-nucleus inelastic process a fully coherent microscopic multiple scattering approach. Our study addresses the complexities inherent in characterizing inelastic scattering events, offering a comprehensive theoretical model grounded in the reaction theory. The approach is based on the distorted-wave approximation and requires the knowledge of three potentials, which give the initial and final distorted wave functions and the transition potential. All of them are derived just like the microscopic optical potential for elastic nucleon-nucleus scattering we derived in previous papers of ours within the framework of the Watson multiple scattering theory and adopting the impulse approximation. The potentials are obtained by folding nonlocal ab initio nuclear densities from the No-Core Shell Model (NCSM) with a nucleon-nucleon $t$ matrix computed with a chiral interaction consistent with the one used in the calculation of the density. The only difference in the formal expressions of the three potentials resides in the nuclear density, where we use the ground and excited state densities of the target and the transition density. By extending methods traditionally applied to elastic scattering, we incorporate the effects of inelastic transitions enabling an accurate description of the experimental differential cross section. The predictive power of our numerical results is benchmarked against empirical data of inelastic proton scattering off $^{12}$C, for the transition to the $2^+$ state at 4.44 MeV, in a range of projectile energies of 65-300 MeV. The generally good description of the experimental cross sections as functions of the scattering angle gives clear evidence of the reliability and robustness of a model that does not contain any free adjustable parameters.

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arXiv2025

Towards a microscopic description of nucleus-nucleus collisions

We present the first results of a comprehensive microscopic approach to describe nucleus-nucleus elastic collisions by means of an optical potential derived at first order in multiple-scattering theory and computed by folding the projectile and target nuclear densities with the nucleon-nucleon $t$ matrix, which describes the interaction between each nucleon of the projectile and each nucleon of the target. Chiral interactions are consistently used in the calculation of the $t$ matrix and of the nonlocal nuclear densities, which are computed within the ab initio no-core shell model. Cross sections calculated for $\alpha$ collisions on $^{12}$C and $^{16}$O at projectile energies in the range 100-300 MeV are presented and compared with available data. For momentum transfer $q$ up to about $1.0$ fm$^{-1}$ our results are in good agreement with the experimental data, whereas for higher momenta a reduction of the imaginary contributions is needed.

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arXiv2024

An $\textit{ab initio}$ strategy for taming nuclear-structure dependence of $ V_{ud} $ extractions: the $ {}^{10}\mathrm{C} \rightarrow {}^{10}\mathrm{B} $ superallowed transition

We report the first \textit{ab initio} calculation of the nuclear-structure-dependent radiative correction $ \delta_{ \mathrm{NS} } $ to the $ {}^{10}\mathrm{C} \rightarrow {}^{10}\mathrm{B} $ superallowed transition, computed with the no-core shell model and chiral effective field theory. We obtain $\delta_{ \mathrm{NS} } = - 0.422 (29)_{ \mathrm{nuc} } (12)_{ n,\mathrm{el} } $ with a $1.6$-times reduction in the total uncertainty when compared to the current literature estimate based on the shell model and Fermi gas picture. This work paves the way for a precise determination of $V_{ud}$ from superallowed beta decays within a systematically improvable framework.

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arXiv2023

Effective field theory analysis of the Coulomb breakup of the one-neutron halo nucleus 19C

We analyse the Coulomb breakup of 19C measured at 67A MeV at RIKEN. We use the Coulomb-Corrected Eikonal (CCE) approximation to model the reaction and describe the one-neutron halo nucleus 19C within Halo Effective Field Theory (EFT). At leading order we obtain a fair reproduction of the measured cross section as a function of energy and angle. The description is insensitive to the choice of optical potential, as long as it accurately represents the size of 18C. It is also insensitive to the interior of the 19C wave function. Comparison between theory and experiment thus enables us to infer asymptotic properties of the ground state of 19C: these data put constraints on the one-neutron separation energy of this nucleus and, for a given binding energy, can be used to extract an asymptotic normalisation coefficient (ANC). These results are confirmed by CCE calculations employing next-to-leading order Halo EFT descriptions of 19C: at this order the results for the Coulomb breakup cross section are completely insensitive to the choice of the regulator. Accordingly, this reaction can be used to constrain the one-neutron separation energy and ANC of 19C.

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arXiv2022

Ab initio no-core shell model description of $^{10-14}$C isotopes

We present a systematic study of the $^{10-14}\text{C}$ isotopes within the \textit{ab initio} no-core shell model theory. We apply four different realistic nucleon-nucleon (NN) interactions: (i) the charge-dependent Bonn 2000 (CDB2K) potential (ii) the inside non-local outside Yukawa (INOY) potential (iii) the next-to-next-to-next-to-leading order (N$^3$LO) potential, and (iv) the optimized next-to-next-to-leading order (N$^2$LO$_{opt}$) potential. We report the low-lying energy spectra of both positive and negative parity states for the $^{10-14}\text{C}$ isotopes and investigate the level structures. We also calculate electromagnetic properties such as transition strengths, quadrupole and magnetic moments. The dependence of point-proton radii on the harmonic oscillator frequency and basis space is shown. We present calculations of the translation invariant one-body density matrix in the no-core shell model and discuss isotopic trends in the density distribution. The maximum basis space reached is $10 \hbar Ω$ for $^{10}\text{C}$ and $8 \hbar Ω$ for $^{11-14}\text{C}$, with a maximum M-scheme dimension of $1.3 \times 10^{9}$ for $^{10}\text{C}$. We found that while the INOY interaction gives the best description of the ground state energies, the N$^3$LO interaction best reproduces the point-proton radii.

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arXiv2022

Elastic proton scattering off non-zero spin nuclei

In recent years, we constructed a microscopic optical potential (OP) for elastic nucleon-nucleus ($NA$) scattering using modern approaches based on chiral theories for the nucleon-nucleon ($NN$) interaction. The OP was derived at first order of the spectator expansion in Watson multiple scattering theory and its final expression was a folding integral between the $NN$ $t$ matrix and the nuclear density of the target. Two- and three-body forces are consistently included both in the target and in the projectile description. The purpose of this work is to apply our microscopic OP to nuclei characterized by a ground state of spin-parity quantum numbers $J^π\ne 0^+$. We extended our formalism to include the spin of the target nucleus. The full amplitudes of the $NN$ reaction matrix are retained in the calculations starting from two- and three-body chiral forces. We show a remarkable agreement with experimental data for the available observables and, simultaneously, provide reliable estimates for the theoretical uncertainties. This work paves the way toward a full microscopic approach to inelastic $NA$ scattering, showing that the derivation of optical potentials between states with $J^π\ne 0^+$ is completely under control.

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arXiv2020

Impact of Three-Body Forces on Elastic Nucleon-Nucleus Scattering Observables

In a previous series of papers we investigated the domain of applicability of chiral potentials to the construction of a microscopic optical potential (OP) for elastic nucleon-nucleus scattering. The final expression of the OP was a folding integral between the nucleon-nucleon ($NN$) $t$ matrix and the nuclear density of the target. In these calculations $NN$ and three-nucleon ($3N$) chiral interactions were used for the target density and only the $NN$ interaction for the $NN$ $t$ matrix. The purpose of this work is to achieve another step towards the calculation of a more consistent OP introducing the $3N$ force also in the dynamic part of the OP. In the present work this is approximated with a density dependent $NN$ interaction obtained after the averaging over the Fermi sphere. In practice, in our model the $3N$ force acts as a medium correction of the bare $NN$ interaction used to calculate the $NN$ $t$ matrix. Even if the $3N$ force is treated in an approximate way, this method naturally extends our previous model of the OP and allows a direct comparison of our present and previous results. We consider as case studies the elastic scattering of nucleons off $^{12}$C and $^{16}$O. We present results for the differential cross section and the spin observables for different values of the projectile energy. From the comparison with the experimental data and with the results of our previous model we assess the importance of the $3N$ interaction in the dynamic part of the OP. Our analysis indicates that the contribution of the $3N$ force in the $t$ matrix is small for the differential cross section and it is sizable for the spin observables, in particular, for the analyzing power. A chiral expansion order-by-order analysis of the scattering observables confirms the convergence of our results at the next-to-next-to-next-to-leading-order, as already established in our previous work.

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arXiv2020

Elastic Antiproton-Nucleus Scattering from Chiral Forces

Elastic scattering of antiprotons off $^4$He, $^{12}$C, and $^{16,18}$O is described for the first time with a totally microscopic approach based on the calculation of an optical potential (OP) describing the antiproton-target interaction. The OP is derived using the recent antiproton-nucleon ($\bar{p}N$) chiral interaction to calculate the $\bar{p}N$ $t$ matrix, while the target densities are computed with the ab initio no-core shell model using chiral interactions as well. Our results are in a good agreement with the existing experimental data and the results computed at different chiral orders of the $\bar{p}N$ interaction display the convergence pattern expected from the theory.

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arXiv2018

Microscopic optical potentials derived from ab initio translationally invariant nonlocal one-body densities

We derive a microscopic optical potential for intermediate energies using ab initio translationally invariant nonlocal one-body nuclear densities computed within the no-core shell model (NCSM) approach utilizing two- and three-nucleon chiral interactions as the only input. The optical potential is derived at first-order within the spectator expansion of the non-relativistic multiple scattering theory by adopting the impulse approximation and using the same chiral nucleon-nucleon interaction as that used to compute densities. The ground state local and nonlocal densities of 4,6,8He, 12C, and 16O are calculated and applied to optical potential construction. The differential cross sections and the analyzing powers for the elastic proton scattering off of these nuclei are then calculated for different values of the incident proton energy. The impact of nonlocality and the COM removal is discussed. The use of nonlocal densities has a substantial impact on the differential cross sections and improves agreement with experiment in comparison to results generated with the local densities especially for light nuclei.

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