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Light elements were produced in the first few minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis (BBN) 1 , 2 . Among the light elements produced during BBN 1 , 2 , deuterium is an excellent indicator of cosmological parameters because its abundance is highly sensitive to the primordial baryon density and also depends on the number of neutrino species permeating the early Universe. Although astronomical observations of primordial deuterium abundance have reached percent accuracy 3 , theoretical predictions 4 – 6 based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D( p , γ ) 3 He reaction. Here we show that our improved cross-sections of this reaction lead to BBN estimates of the baryon density at the 1.6 percent level, in excellent agreement with a recent analysis of the cosmic microwave background 7 . Improved cross-section data were obtained by exploiting the negligible cosmic-ray background deep underground at the Laboratory for Underground Nuclear Astrophysics (LUNA) of the Laboratori Nazionali del Gran Sasso (Italy) 8 , 9 . We bombarded a high-purity deuterium gas target 10 with an intense proton beam from the LUNA 400-kilovolt accelerator 11 and detected the γ-rays from the nuclear reaction under study with a high-purity germanium detector. Our experimental results settle the most uncertain nuclear physics input to BBN calculations and substantially improve the reliability of using primordial abundances to probe the physics of the early Universe. High-precision cross-sections of the nuclear reaction that burns deuterium to create helium-3 are used to produce theoretical estimates of the primordial baryon density that are in agreement with recent astronomical observations.

The 4He monopole form factor is studied by computing the transition matrix element of the electromagnetic charge operator between the 4He ground-state and the p+3H and n+3He scattering states. The nuclear wave functions are calculated using the hyperspherical harmonic method, by starting from Hamiltonians including two- and three-body forces derived in chiral effective field theory. The electromagnetic charge operator retains, beyond the leading order (impulse approximation) term, also higher order contributions, as relativistic corrections and meson-exchange currents. The results for the monopole form factor are in fair agreement with recent MAMI data. Comparison with other theoretical calculations are also provided.

Starting from a complete set of relativistic nucleon–nucleon contact operators up to order O(p4) of the expansion in the soft (relative or nucleon) momentum p, we show that non-relativistic expansions of relativistic operators involve twenty-six independent combinations, two starting at O(p0), seven at order O(p2) and seventeen at order O(p4). This demonstrates the existence of two low-energy free constants that parameterize interactions dependent on the total momentum of the pair of nucleons P. The latter, through the use of a unitary transformation, can be removed in the two-nucleon fourth-order contact interaction of the Chiral Effective Field Theory, generating a three-nucleon interaction at the same order. Within a hybrid approach in which this interaction is considered together with the phenomenological potential AV18, we show that the LECs involved can be used to fit very accurate data on the polarization observables of the low-energy p-d scattering, in particular the Ay asymmetry.

We present a theoretical study of three- and four-nucleon continuum within the hyperspherical harmonics method, using a representative variety of realistic nucleon–nucleon potential models, i.e. one of phenomenological type, the Argonne v 18 (AV18), one obtained within chiral effective field theory up to next-to-next-to-next-leading order, the Idaho N3LO (I-N3LO), and a “low-k” model derived from the CD-Bonn potential. In particular, the convergence pattern for the four-nucleon system is found to be problematic for the P-waves phase-shifts in the case of the AV18 potential at higher energies. An extrapolation procedure is presented and discussed. Finally, we present the theoretical results for p − d and p − 3 scattering observables at two selected energies, and we compare these with the available experimental data. In particular, some spread in the unpolarized cross section and in some polarization observables has been observed using the three potential models, in particular for A =  4. Furthermore the well known discrepancy in the vector polarization observables remains for the three potential models.

The application of the hyperspherical harmonic approach to the case of non-local two-body potentials is described. Given the properties of the hyperspherical harmonic functions, there are no difficulties in considering the approach in both coordinate and momentum space. The binding energies and other ground-state properties of A = 3 and 4 nuclei are calculated using the CD Bonn 2000 and N3LO two-body potentials. The results are shown to be in excellent agreement with corresponding ones obtained by other accurate techniques. [PUBLICATION ABSTRACT]

This work investigates the muon capture reactions 2 H( μ − , ν μ ) nn and 3 He( μ − , ν μ ) 3 H and the contribution to their total capture rates arising from the axial two-body currents obtained imposing the partially-conserved-axial-current (PCAC) hypothesis. The initial and final A = 2 and 3 nuclear wave functions are obtained from the Argonne v 18 two-nucleon potential, in combination with the Urbana IX three-nucleon potential in the case of A  = 3. The weak current consists of vector and axial components derived in chiral effective field theory. The low-energy constant entering the vector (axial) component is determined by reproducting the isovector combination of the trinucleon magnetic moment (Gamow-Teller matrix element of tritium beta-decay). The total capture rates are 393.1(8) s −1 for A = 2 and 1488(9) s −1 for A  = 3, where the uncertainties arise from the adopted fitting procedure.

Realistic nuclear potentials, derived within chiral perturbation theory, are a major breakthrough in modern nuclear structure theory, since they provide a direct link between nuclear physics and its underlying theory, namely the QCD. As a matter of fact, chiral potentials are tailored on the low-energy regime of nuclear structure physics, and chiral perturbation theory provides on the same footing two-nucleon forces as well as many-body ones. This feature fits well with modern advances in ab-initio methods and realistic shell-model. Here, we will review recent nuclear structure calculations, based on realistic chiral potentials, for both finite nuclei and infinite nuclear matter.

In the first part of the contribution, we discuss the results of a recent benchmark calculation of n − 3 H and p − 3 He phase-shifts below the trinucleon disintegration thresholds. Three different methods—Alt, Grassberger and Sandhas, Hyperspherical Harmonics, and Faddeev–Yakubovsky—have been used and their results are compared. For both n − 3 H and p − 3 He we observe a rather good agreement between the three different theoretical methods. In the second part of the contribution, we study the longitudinal asymmetry in the 3 He( n , p ) 3 H reaction in order to obtain information about the parity-violating components of the nucleon–nucleon interaction.

We review our recent work on the derivation of the nuclear electromagnetic charge and current operators in chiral perturbation theory, based on time-ordered perturbation theory. We then discuss the strategies for fixing the relevant low-energy constants, and compare the resulting predictions for the electric and magnetic form factors of the deuteron and trinucleons with experimental data, using as input accurate nuclear wave functions derived with realistic potentials.

Purpose To compare a time-domain (Stratus) and a spectral-domain (Spectralis) optical coherence tomography (OCT) device in assessing foveal thickness in healthy subjects. Methods In this observational study 40 healthy subjects (40 eyes) underwent Stratus OCT and Spectralis OCT measurements of foveal thickness using three consecutive horizontal and vertical B-scan. Paired samples t -test was used to compare means between Stratus and Spectralis OCT measurements. Coefficient of variation (CoV) was used to compare dispersion in datasets. Pearson's correlation coefficient was used to quantify linear relation between Spectralis and Stratus OCT measurements. To assess agreement between Spectralis and Stratus OCT foveal thickness measurements, the Bland and Altman plots were used. Results Sample age ranged from 19 to 49 years (mean 33.25, standard deviation (SD) ±4.22). The Spectralis OCT foveal thickness measurements resulted significantly higher than those obtained with Stratus OCT (227.64±11.74 vs 144.36±12.25  μ m, and 227.63±11.43 vs 144.92±12.34  μ m, for horizontal and vertical foveal thickness, respectively) ( P <0.05). Coefficient of variations were 5.16 and 5.02% using Spectralis OCT, and 8.49 and 8.51% using Stratus OCT. Mean Spectralis/Stratus ratio was 1.58 for both horizontal and vertical measurements. A linear relation between the two technologies was found (r horiz =0.899 and r vert =0.869) ( P <0.001). Conclusions A good correlation between Stratus and Spectralis OCT foveal measurements was found, independently of retinal thickness. This preliminary study suggests the existence of a conversion factor between Stratus and Spectralis OCT when measuring healthy foveal thickness.