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

Precision measurements of beta-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 beta-decay of He-6 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. (C) 2022 The Author(s). Published by Elsevier B.V

Radiative capture and decays in ab initio nuclear theory

Atomic nuclei exhibit many phenomena not limited to excited states, decays, reactions, and clustering. Nuclear processes control the evolution of stars and explain the abundances of chemical elements in the universe. Nuclear physics can be used to answer fundamental questions about underlying particle physics and cosmology, such as the symmetry between matter and antimatter or the nature of neutrinos. The discrepancy between theoretical predictions and observations motivates improved theory and can provide evidence for new physics. A predictive model of nuclei is needed as input for experimental tests and for astrophysical models. Nuclei are complex strongly-interacting quantum many-body systems. Accurate the- oretical techniques are required to predict the rate of nuclear decay processes, the cross section of nuclear reactions and the distribution of the emitted particles. Ab initio nuclear theory takes advantage of the recent rapid increase in computing power to calculate nuclear structure and reactions solely from realistic interactions between the constituent nucleons. In this thesis, we first present beta-decay calculations using the ab initio no-core shell model. Our calculations provide an explanation for the quenching of Gamow-Teller beta- decays, provide nuclear structure corrections to the beta-spectrum necessary to interpret experiments seeking to find new physics and provide estimates for the hypothetical process of neutrinoless double-beta decay. Second, we present radiative capture calculations using the no-core shell model with continuum, an extension which places bound and scattering states on equal footing. The rate of radiative capture reactions in big bang nucleosynthesis is required to estimate the abundance of isotopes in the early universe. In addition, anomalies in recent radiative capture experiments claim the discovery of a new boson. Comparing to these experiments requires prediction of the distribution of electron-positron pairs produced by radiative capture.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Exploring the book problem: Text design, mental representations of space, and Spatial Presence in readers

Based on the MEC model of Spatial Presence, an experiment (N = 34) was conducted that explores the development of Spatial Presence in readers of text. Two techniques for text writing that may facilitate Spatial Presence were derived from the model and implemented in the stimulus production: the number of verbal spatial descriptions (cues) was varied (low versus high), and one text version included repeated instructions to imagine the portrayed space as vividly as possible. Findings indicate that the mental representation of described spaces is more vivid if much space-related information is presented by the text, but Spatial Presence is higher if less spatial cues are provided. These partially surprising results are discussed with respect to the MEC model and future directions of cross-media theorizing about Spatial Presence

Ab initio prediction of the ^4{\rm He}(d,\gamma)\,^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 $\gamma$ ray, $^4$He$(d,\gamma)^6$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$(d,\gamma)^6$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

Ab initio prediction of the ^4{\rm He}(d,\gamma)\,^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 $\gamma$ ray, $^4$He$(d,\gamma)^6$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$(d,\gamma)^6$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.Comment: 5 pages, 2 figures and 6 pages supplemental materia

Ab Initio Prediction of the He4(d,γ)Li6 Big Bang Radiative Capture

International audienceThe rate at which helium (He4) and deuterium (d) fuse together to produce lithium-6 (Li6) and a γ ray, He4(d,γ)Li6, is a critical puzzle piece in resolving the discrepancy between big bang predictions and astronomical observations for the primordial abundance of Li6. 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≲E≲400  keV), where measurements are hindered by low counting rates. We present first-principle (or, ab initio) predictions of the He4(d,γ)Li6 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 He4-d scattering dynamics and bound Li6 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