The axion-baryon coupling in SU(3) heavy baryon chiral perturbation theory

In the past, the axion-nucleon coupling has been calculated in the framework of SU(2) heavy baryon chiral perturbation theory up to third order in the chiral power counting. Here, we extend these earlier studies to the case of heavy baryon chiral perturbation theory with SU(3) flavor symmetry and derive the axion coupling to the full SU(3) baryon octet, showing that the axion also significantly couples to hyperons. As studies on dense nuclear matter suggest the possible existence of hyperons in stellar objects such as neutron stars, our results should have phenomenological implications related to the so-called axion window.Comment: 45 pages, 1 figur

Pion axioproduction: The Delta resonance contribution

The process of pion axioproduction, $aN\to\pi N$, with an intermediate $\Delta$ resonance is analyzed using baryon chiral parturbation theory. The $\Delta$ resonance is included in two ways: First, deriving the $a\Delta N$-vertices, the axion is brought into contact with the resonance, and, second, taking the results of $\pi N$ elastic scattering including the $\Delta$, it is implicitly included in the form of a pion rescattering diagram. As a result, the partial wave cross section of axion-nucleon scattering shows an enhancement in the energy region around the $\Delta$ resonance. Because of the isospin breaking, the enhancement is not as pronounced as previously anticipated. However, since the isospin breaking here is much milder than that for usual hadronic processes, novel axion search experiments might still exploit this effect.Comment: 13 pages, 5 figure

Precision calculation of the axion-nucleon coupling in chiral perturbation theory

We derive the axion-nucleon interaction Lagrangian in heavy baryon chiral perturbation theory up to next-to-next-to-leading order. The effective axion-nucleon coupling is calculated to a few percent accuracy.Comment: 20 page

Growth of well-ordered iron sulfide thin films

In this paper a growth recipe for well-ordered iron sulfide films and the results of their characterisation are presented. The film was studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). XRD data reveal that the film has a NiAs-like structure with Fe vacancies, similar to iron sulfides such as pyrrhotite and smythite, although no indication of any ordering of these vacancies was observed. LEED and STM results show that the film exhibits a 2 × 2 surface reconstruction. XPS data provide additional evidence for a large number of Fe vacancies, and the oxidation states of the Fe and S in the film are analysed

Challenges and solutions of environmental scanning electron microscopy characterisation of biomaterials:Application to hygro-expansion of paper

Most methodologies to measure the moisture-induced deformation (hygro-expansion) of paper microconstituents, including fibres and interfibre bonds, are low resolution or time-consuming. Hence, here, a novel method is proposed and validated to measure high-resolution full-field strain maps of paper microconstituents during hygro-expansion, based on environmental scanning electron microscopy (ESEM). To this end, a novel climate stage enables accurate control of the relative humidity (RH) near the specimen in the ESEM from 0%–100%. The fibre surface, which is decorated a priori with a microparticle pattern, is captured during RH change. Subsequently, correlating the fibre surface using a dedicated global digital image correlation algorithm enables high-resolution hygro-expansion strain maps. Method optimisation involved performing contrast enhancement, scan-correction to reduce ESEM artefacts and a background correction, resulting in a strain resolution of (Formula presented.). Method validation revealed that the fibres' crystallinity is affected by the electron beam, even for minimal invasive electron beam settings. Interestingly, however, the fibres consistently exhibit conventional hygro-expansion behaviour during the drying slopes. Using the optimised procedure, hygro-expansion characterisation of two interfibre bonds and four interfibre bond cross-sections revealed the competition between the low longitudinal and large transverse fibre hygro-expansion in the bonded area.</p

θ\theta-dependence of light nuclei and nucleosynthesis

We investigate the impact of the QCD vacuum at nonzero $\theta$ on the properties of light nuclei, Big Bang nucleosynthesis, and stellar nucleosynthesis. Our analysis starts with a calculation of the $\theta$-dependence of the neutron-proton mass difference and neutron decay using chiral perturbation theory. We then discuss the $\theta$-dependence of the nucleon-nucleon interaction using a one-boson-exchange model and compute the properties of the two-nucleon system. Using the universal properties of four-component fermions at large scattering length, we then deduce the binding energies of the three-nucleon and four-nucleon systems. Based on these results, we discuss the implications for primordial abundances of light nuclei, the production of nuclei in stellar environments, and implications for an anthropic view of the universe.Comment: 20 pages, 9 figure

QCD θ\theta-vacuum energy and axion properties

At low energies, the strong interaction is governed by the Goldstone bosons associated with the spontaneous chiral symmetry breaking, which can be systematically described by chiral perturbation theory. In this paper, we apply this theory to study the $\theta$-vacuum energy density and hence the QCD axion potential up to next-to-leading order with $N$ non-degenerate quark masses. By setting $N=3$, we then derive the axion mass, self-coupling, topological susceptibility and the normalized fourth cumulant both analytically and numerically, taking the strong isospin breaking effects into account. In addition, the model-independent part of the axion-photon coupling, which is important for axion search experiments, is also extracted from the chiral Lagrangian supplemented with the anomalous terms up to $\mathcal{O}(p^6)$.Comment: 22 pages, 1 figure, 2 tables; Version to appear in JHE