arXiv subjects

Peter Gysbers

Publications and source records attributed to Peter Gysbers.

6 recordsLinked to original sources

arXiv2026

Future directions in nuclear $β$ decay at FRIB and beyond

Motivated by the opportunities presented for studies relevant to nuclear structure, astrophysics, and fundamental symmetries with nuclear $β$ decay, the Facility for Rare Isotope Beams (FRIB) Theory Alliance topical program ``Future Directions in Nuclear $β$ 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 $β$ decay studies, discuss the current state of nuclear many-body approaches used to study $β$ decays, and highlight the important science questions that can be addressed by weak decays.

nucl-th↗

arXiv2022

Nuclear ab initio calculations of 6He $β$-decay for beyond the Standard Model studies

Precision measurements of $β$-decay observables offer the possibility to search for deviations from the Standard Model. A possible discovery of such deviations requires accompanying first-principles calculations. Here we compute the nuclear structure corrections for the $β$-decay of $^6$He which is of central interest in several experimental efforts. We employ the impulse approximation together with wave functions calculated using the ab initio no-core shell model with potentials based on chiral effective field theory. We use these state-of-the-art calculations to give a novel and comprehensive analysis of theoretical uncertainties. We find that nuclear corrections, which we compute within the sensitivity of future experiments, create significant deviation from the naive Gamow-Teller predictions, making their accurate assessment essential in searches for physics beyond the Standard Model.

nucl-th↗

arXiv2022

Ab initio prediction of the $^4{\rm He}(d,γ)\,^6\rm Li$ big bang radiative capture

The rate at which helium ($^4$He) and deuterium ($d$) fuse together to produce lithium-6 ($^6$Li) and a $γ$ ray, $^4$He$(d,γ)^6$Li, is a critical puzzle piece in resolving the roughly three orders of magnitude discrepancy between big bang predictions and astronomical observations for the primordial abundance of $^6$Li. The accurate determination of this radiative capture rate requires the quantitative and predictive description of the fusion probability across the big bang energy window ($30$ keV $\lesssim E\lesssim 400$ keV), where measurements are hindered by low counting rates. We present first-principles (or, ab initio) predictions of the $^4$He$(d,γ)^6$Li astrophysical S-factor using validated nucleon-nucleon and three-nucleon interactions derived within the framework of chiral effective field theory. By employing the ab initio no-core shell model with continuum to describe $^4{\rm He}$-$d$ scattering dynamics and bound $^6\rm Li$ product on an equal footing, we accurately and consistently determine the contributions of the main electromagnetic transitions driving the radiative capture process. Our results reveal an enhancement of the capture probability below 100 keV owing to previously neglected magnetic dipole (M1) transitions and reduce by an average factor of 7 the uncertainty of the thermonuclear capture rate between $0.002$ and $2$ GK.

nucl-th↗

arXiv2021

Constraining new physics with a novel measurement of the $^{23}$Ne $β$-decay branching ratio

Measurements of the beta-neutrino correlation coefficient (a$_{βν}$) in nuclear beta decay, together with the Fierz interference term (b$_F$), provide a robust test for the existence of exotic interactions beyond the Standard Model of Particle Physics. The extraction of these quantities from the recoil ion spectra in $β$-decay requires accurate knowledge, decay branching ratios, and high-precision calculations of higher order nuclear effects. Here, we report on a new measurement of the $^{23}$Ne $β$-decay branching ratio, which allows a reanalysis of existing high-precision measurements. Together with new theoretical calculations of nuclear structure effects, augmented with robust theoretical uncertainty, this measurement improves on the current knowledge of a$_{βν}$ in $^{23}$Ne by an order of magnitude, and strongly constrains the Fierz term in beta decays, making this one of the first extractions to constrain both terms simultaneously. Together, these results place bounds on the existence of exotic tensor interactions and pave the way for new, even higher precision, experiments.

nucl-ex↗

arXiv2021

Improving Hamiltonian encodings with the Gray code

Due to the limitations of present-day quantum hardware, it is especially critical to design algorithms that make the best possible use of available resources. When simulating quantum many-body systems on a quantum computer, straightforward encodings that transform many-body Hamiltonians into qubit Hamiltonians use $N$ of the available basis states of an $N$-qubit system, whereas $2^N$ are in theory available. We explore an efficient encoding that uses the entire set of basis states, where terms in the Hamiltonian are mapped to qubit operators with a Hamiltonian that acts on the basis states in Gray code order. This encoding is applied to the commonly-studied problem of finding the ground state energy of a deuteron with a simulated variational quantum eigensolver (VQE). It is compared to a standard "one-hot" encoding, and various trade-offs that arise are analyzed. The energy distribution of VQE solutions has smaller variance than the one obtained by the one-hot encoding even in the presence of simulated hardware noise, despite an increase in the number of measurements. The reduced number of qubits and a shorter-depth variational ansatz enables the encoding of larger problems on current-generation machines. This encoding also demonstrates improvements for simulating time evolution of the same system, producing circuits for the evolution operators with reduced depth and roughly half the number of gates compared to a one-hot encoding.

quant-ph↗

arXiv2017

Bifurcations of self-similar solutions for reversing interfaces in the slow diffusion equation with strong absorption

Bifurcations of self-similar solutions for reversing interfaces are studied in the slow diffusion equation with strong absorption. The self-similar solutions bifurcate from the time-independent solutions for standing interfaces. We show that such bifurcations occur at the bifurcation points, at which the confluent hypergeometric functions satisfying Kummer's differential equation is truncated into a finite polynomial. A two-scale asymptotic method is employed to obtain the asymptotic dependencies of the self-similar reversing interfaces near the bifurcation points. The asymptotic results are shown to be in excellent agreement with numerical computations.

nlin.PS↗