arXiv subjects

Helen Meyer

Publications and source records attributed to Helen Meyer.

8 recordsLinked to original sources

arXiv2026

Elastic deuteron-deuteron scattering within Nuclear Lattice Effective Field Theory

We calculate low-energy deuteron-deuteron scattering in the spin-quintet $^{5}S_2$ channel using nuclear lattice effective field theory. The calculation combines chiral interactions at next-to-next-to-next-to-leading order, implemented through wavefunction matching, with the adiabatic projection method. Because the radial cluster basis develops small norm-matrix eigenvalues at large Euclidean projection time, we investigate two stabilization procedures: Tikhonov regularization and projection onto well-resolved norm eigenmodes. The two procedures yield consistent Coulomb-subtracted phase shifts within their statistical and numerical uncertainties. A Coulomb-modified effective-range analysis gives ${}^5a_{dd} = (12.96 \pm 0.26)\,\mathrm{fm}$ and ${}^5r_{dd} = (3.62 \pm 0.79)\,\mathrm{fm}$. The phase shifts are more negative, and the scattering length is substantially larger than in previous calculations, corresponding to a stronger effective repulsion in the $^{5}S_2$ channel. These results provide a first nuclear-lattice benchmark for deuteron-deuteron scattering and establish a basis for future coupled-channel calculations of the deuteron-induced reactions relevant to big-bang nucleosynthesis.

nucl-th↗

arXiv2026

Fine-tunings in radiative $\alpha$-particle capture on $^{12}$C at astrophysical energies

We investigate the fine-tuning of radiative alpha-particle capture on carbon, $\alpha(^{12}{\rm C},^{16}{\rm O})\gamma$, at astrophysical energies. Utilizing results from cluster effective field theory for this reaction, we find that the low-energy data of the astrophysical S-factor allow for only very small variations in the electromagnetic fine-structure constant $\alpha$, namely $|\delta \alpha/\alpha| \leq 0.2\,$ per mille, in both the $E1$ and the $E2$ radiative capture.

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arXiv2025

Lattice calculation of the Sn isotopes near the proton dripline

We present the first $\textit{ab initio}$ lattice calculations of the proton-rich tin isotopes $^{99}$Sn to $^{102}$Sn using nuclear lattice effective field theory with high-fidelity two- and three-nucleon forces. For a given set of three-nucleon couplings, we reproduce binding energies with $\sim 1\%$ accuracy for the even-even systems, and obtain energy splitting and two-nucleon separation energies in agreement with experiment. Our results confirm the $N=50$ shell closure and reveal that the binding energy of $^{99}$Sn lies below values extrapolated from heavier isotopes.

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arXiv2025

Fine-tunings in nucleosynthesis and the emergence of life: Status and perspectives

We discuss the fine-tunings of nuclear reactions in the Big Bang and in stars and draw some conclusions on the emergence of the light elements and the life-relevant elements carbon and oxygen. We also stress how to improve these calculations in the future. This requires a concerted effort of different communities, especially in nuclear reaction theory, lattice QCD for few-nucleon systems, stellar evolution calculations, particle physics and philosophy.

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arXiv2025

Bounds on variations of the strange quark mass from Big Bang nucleosynthesis

We analyze the effect of a variation of the strange nucleon matrix element $\langle N| m_s \bar{s}s|N\rangle$ on the abundances of the light elements produced in the Big Bang. For that, we vary the nucleon mass in the leading eight reactions that involve neutrons, protons and the four lightest nuclei. We use various available Big Bang nucleosynthesis codes and find that the measured deuterium and $^4$He abundances set strict limits on the nucleon mass variations. This translates into an upper bound of possible variations of the strange quark mass, $\left| \Delta m_s/m_s \right| \leq 5.1\%$.

hep-ph↗

arXiv2024

A study of the fine-structure constant dependence of radiative capture in Halo-EFT

We study the fine-structure constant dependence of the rates of some selected radiative capture reactions within the framework of so-called Halo Effective Field Theory in order to assess the adequacy of some assumptions made on the Coulomb penetrability. We find that this dependence deviates from that implied by a parameterization of the cross sections of this effect via a simple penetration factor. Some features of this fine-structure dependence are discussed, in particular its potential impact on the abundances of the light elements in primordial nucleosynthesis.

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arXiv2024

Improved Constraints on the Variation of the Weak Scale from Big Bang Nucleosynthesis

We present an improved calculation of the light element abundances in the framework of Big Bang nucleosynthesis as a function of the Higgs vacuum expectation value $v$. We compare the methods of our calculation to previous literature including the recently published work of Burns et al. [1]. The PDG result for the $^4$He abundance can be explained within $2\sigma$ by $-0.014 \leq \delta v / v \leq 0.026$, for deuterium we find the constraint $-0.005 \leq \delta v / v \leq -0.001$. These bounds are more stringent than what was found earlier.

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arXiv2023

The electromagnetic fine-structure constant in primordial nucleosynthesis revisited

We study the dependence of the primordial nuclear abundances as a function of the electromagnetic fine-structure constant $α$, keeping all other fundamental constants fixed. We update the leading nuclear reaction rates, in particular the electromagnetic contribution to the neutron-proton mass difference pertinent to $β$-decays, and go beyond certain approximations made in the literature. In particular, we include the temperature-dependence of the leading nuclear reactions rates and assess the systematic uncertainties by using four different publicly available codes for Big Bang nucleosynthesis. Disregarding the unsolved so-called lithium-problem, we find that the current values for the observationally based $^{2}$H and $^{4}$He abundances restrict the fractional change in the fine-structure constant to less than $2\%$, which is a tighter bound than found in earlier works on the subject.

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