In this work we have studied the lithium problem in nonstandard cosmological models. In particular, by using the public code alterbbn, we have included in the computation of the primordial light nuclei abundances, the effects of the inclusion of dark energy and dark entropy, along with the variation of the fine structure constant and the Higgs vacuum expectation value. In order to set constrains on the variation of the fundamental constants we have compared our theoretical results with the available observational data. We have found that the lithium abundance is reduced for not-null variation at the $3\sigma$-level of both constants.

The nonmesonic weak decay of $\mathrm{\Lambda }$ hypernuclei is studied within a microscopic diagrammatic approach which is extended to include the $\mathrm{\Lambda }N-\mathrm{\Sigma }N$ strong interaction coupling. We adopt a nuclear matter formalism which, through the local density approximation, allows us to model finite hypernuclei. One-meson-exchange potentials are used for the weak and strong four-baryon interactions. The rates for the neutron- and proton-induced weak decays, $\mathrm{\Lambda }N\to nN$ and $\mathrm{\Lambda }N\to \mathrm{\Sigma }N\to nN$ ($N=n$ or $p$; $\mathrm{\Sigma }={\mathrm{\Sigma }}^{-}, {\mathrm{\Sigma }}^0$, and ${\mathrm{\Sigma }}^{+}$), are predicted for ${}_{\mathrm{\Lambda }}{}^{12}\mathrm{C}, {}_{\mathrm{\Lambda }}{}^{28}\mathrm{Si}, {}_{\mathrm{\Lambda }}{}^{56}\mathrm{Fe}$, and ${}_{\mathrm{\Lambda }}{}^{208}\mathrm{Pb}$. The $\mathrm{\Lambda }N-\mathrm{\Sigma }N$ coupling turns out to provide a contribution of about 23% (5%) to the total neutron-induced rate (proton-induced rate). Again as an effect of the hyperon coupling, the total one-nucleon-induced rate increases by about 9%, while the ${\mathrm{\Gamma }}_n/{\mathrm{\Gamma }}_p$ ratio increases by about 17%. The saturation property of the nonmesonic rates with increasing hypernuclear mass number is clearly obtained and explained. The above percentage modifications remain almost unaltered through the hypernuclear mass number. All the non-negligible changes introduced by the $\mathrm{\Lambda }N-\mathrm{\Sigma }N$ coupling lead to a definite improvement of our predictions once compared with the available KEK and FINUDA data.

The electric-octupole $E3$ transition strengths from the first $3^{-}$ state to the ground-state transition in $sd$ shell even-even nuclei with $A=16$ to 40 are investigated within the shell model framework using the effective (0+1)$\hslash \omega$ PSDPF interaction. For this type of transition, new effective charges for protons and neutrons have been determined. Their values 1.36 e for protons and 0.48 e for neutrons are close to those obtained previously for electric-quadrupole $E2$ transitions in $sd$ shell nuclei. The calculated $E3$ transition strengths from the ${3_1}^{-}\to {0_{\mathrm{gs}}}^{+}$ transitions are compared to a compilation of experimental $E3$ data for even-even nuclei throughout the $sd$ shell.

The lifetime of the $2_1^{+}$ state of ${}^{212}\mathrm{Po}$ was measured in the ${}^{208}\mathrm{Pb}$(${}^{12}\mathrm{C},{}^8\mathrm{Be}$)${}^{212}\mathrm{Po}$ transfer reaction by $\gamma$-ray spectroscopy employing the recoil distance Doppler shift (RDDS) method. The derived absolute $B\left(E2\right)$ value of 2.6(3) W.u. indicates a low collectivity and contradicts previous claims of $\alpha$-cluster components in the structure of the $2_1^{+}$ state. It is demonstrated that a consistent description of the properties of the $2_1^{+}-4_1^{+}-6_1^{+}-8_1^{+}$ sequence in ${}^{212}\mathrm{Po}$ cannot be achieved in the framework of a single-$j$ shell-model calculation, either. This puzzle is traced to the properties of the seniority-2 configurations in ${}^{210}\mathrm{Pb}$ and ${}^{210}\mathrm{Po}$.

In this paper we study the monopole pairing correlation in $0^{+}$ states of semimagic nuclei under random interactions. We calculate overlaps between $S$-pair wave functions and exact shell-model wave functions. No dominance of the $S$-pair components is shown: In a single-$j$ shell $0^{+}$ states have random overlaps with the $S$-pair wave function; in a multi-$j$ space the $0_1^{+}$ state has a small overlap with the $S$-pair wave function, and this is particularly pronounced if the single-particle splitting is small and/or the spins $j$ of single-particle orbits are large. For the $0_1^{+}$ state in a multi-$j$ space, the generalized seniority scheme and the seniority truncation of the shell model provide similar results. We study the odd-even staggering of one-neutron separation energies under random interactions. The odd-even staggering phenomenon survives in random samples where all the even members have spin-zero ground states but disappears in random samples where all the even members have spin-nonzero ground states.

Background: Weakly bound and unbound nuclear states appearing around particle thresholds are prototypical open quantum systems. Theories of such states must take into account configuration mixing effects in the presence of strong coupling to the particle continuum space.

Purpose: To describe structure and decays of three-body systems, we developed a Gamow coupled-channel (GCC) approach in Jacobi coordinates by employing the complex-momentum formalism. We benchmarked the complex-energy Gamow shell model (GSM) against the new framework.

Methods: The GCC formalism is expressed in Jacobi coordinates, so that the center-of-mass motion is automatically eliminated. To solve the coupled-channel equations, we use hyperspherical harmonics to describe the angular wave functions while the radial wave functions are expanded in the Berggren ensemble, which includes bound, scattering, and Gamow states.

Results: We show that the GCC method is both accurate and robust. Its results for energies, decay widths, and nucleon-nucleon angular correlations are in good agreement with the GSM results.

Conclusions: We have demonstrated that a three-body GSM formalism explicitly constructed in the cluster-orbital shell model coordinates provides results similar to those with a GCC framework expressed in Jacobi coordinates, provided that a large configuration space is employed. Our calculations for $A=6$ systems and ${}^{26}\mathrm{O}$ show that nucleon-nucleon angular correlations are sensitive to the valence-neutron interaction. The new GCC technique has many attractive features when applied to bound and unbound states of three-body systems: it is precise, is efficient, and can be extended by introducing a microscopic model of the core.

Nuclear spins and precise values of the magnetic dipole and electric quadrupole moments of the ground states of neutron-rich ${}^{73\text{–}78}\mathrm{Cu}$ isotopes were measured using the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the CERN On-Line Isotope Mass Separator (ISOLDE) facility. The nuclear moments of the less exotic ${}^{73,75}\mathrm{Cu}$ isotopes were remeasured with similar precision, yielding values that are consistent with earlier measurements. The moments of the odd-odd isotopes, and ${}_{29}^{78}\mathrm{Cu}$ ($N=49$) in particular, are used to investigate excitations of the assumed doubly magic ${}^{78}\mathrm{Ni}$ core through comparisons with large-scale shell-model calculations. Despite the narrowing of the $Z=28$ shell gap between $N\sim 45$ and $N=50$, the magicity of $Z=28$ and $N=50$ is restored toward ${}^{78}\mathrm{Ni}$. This is due to weakened dynamical correlations, as clearly probed by the present moment measurements.

Background: In our recent work [M. J. Ermamatov et al., Phys. Rev. C 94, 024610 (2016)], the two-neutron transfer induced by the $({}^{18}\mathrm{O},{}^{16}\mathrm{O})$ reaction was studied for ${}^{16}\mathrm{O}$ nucleus. Theoretical analysis of the low-lying states of ${}^{18}\mathrm{O}$ indicates that the transfer to the ground state proceeds predominantly through simultaneous transfer of the two-neutron system.

Purpose: In this work, we extend our previous theoretical analysis towards high-lying states of the ${}^{18}\mathrm{O}$ nucleus. In order to achieve a comprehensive picture, we revisit the experimental data for the ${}^{16}\mathrm{O}(t,p){}^{18}\mathrm{O}$ reaction at 15 MeV bombarding energy. We also include new experimental cross sections for the high-lying states of the ${}^{18}\mathrm{O}$ residual nucleus, populated in the ${}^{16}\mathrm{O}({}^{18}\mathrm{O},{}^{16}\mathrm{O}){}^{18}\mathrm{O}$ reaction at 84 MeV.

Method: The same spectroscopic parameters of the target nucleus were used as input in the coupled channel calculations for the transfer induced by triton and ${}^{18}\mathrm{O}$ projectiles. Simultaneous two-neutron transfer is calculated within the coupled reaction channel approach, using the extreme cluster and independent coordinate models. The sequential process is calculated within the distorted-wave Born approximation.

Results: Theoretical calculations reproduce the ${}^{16}\mathrm{O}(t,p){}^{18}\mathrm{O}$ data well, leading to natural parity states in the ${}^{18}\mathrm{O}$ nucleus without the need of adjustable parameters. The same methods are applied to the ${}^{16}\mathrm{O}({}^{18}\mathrm{O},{}^{16}\mathrm{O}){}^{18}\mathrm{O}$ data and a good agreement is observed.

Conclusions: Detailed analyses show the importance of a simultaneous mechanism for the two-neutron transfer reactions. In transferring two neutrons, the pairing correlation plays an important role.

The rate of the $T=1, 2^{+}$ to $T=1, 0^{+}$ transition in ${}^{10}\mathrm{B}$ ($T=1, T_z=0$) is compared to the analog transitions in ${}^{10}\mathrm{Be}$ ($T=1, T_z=-1$) and ${}^{10}\mathrm{C}$ ($T=1, T_z=+1$) to provide constraints on ab initio calculations using realistic nuclear forces. The relevant state in ${}^{10}\mathrm{B}$, at $E_x=5.164$ MeV, is particle unbound. Therefore, a determination of the $B\left(E2\right)$ electromagnetic transition rate requires a precise and accurate determination of the width of the state, as well as the $\alpha$-particle and $\gamma$-ray branching ratios. Previous measurements of the $\alpha$-particle branching ratio are just barely in agreement. We report on a new study of the $\alpha$-particle branch by studying the ${}^{10}\mathrm{B}(p,p^{\prime }){{}^{10}\mathrm{B}}^{*}$ reaction in inverse kinematics with the HELIOS spectrometer. The $\alpha$-particle branching ratio that we observe, $0.144\pm 0.027$, is in good agreement with the evaluated value and improves the associated uncertainty. The resulting experimental $B\left(E2\right)$ value is $7.0\pm 2.2 e^2{\mathrm{fm}}^4$ and is more consistent with a flat trend across the $A=10$ triplet than previously reported. This is inconsistent with Green's function Monte Carlo predictions using realistic three-nucleon Hamiltonians, which overpredict the $B\left(E2\right)$ value in ${}^{10}\mathrm{C}$ and ${}^{10}\mathrm{B}$.

The structure of the low- and medium-spin levels of the ${}^{211}\mathrm{Po}$ nucleus have been studied with in-beam $\gamma$-ray spectroscopy with the ${}^{208}\mathrm{Pb}(\alpha ,n){}^{211}\mathrm{Po}$ fusion-evaporation reaction. The level scheme was further extended with levels of the configurations $\pi {\left(h_{9/2}\right)}_{2^{+}-4^{+}}^2\otimes \nu g_{9/2}$, $\pi {\left(h_{9/2}\right)}_{8^{+}}^2\otimes \nu g_{9/2}$, $\pi {\left(h_{9/2}\right)}_{2^{+}-4^{+}}^2\otimes \nu i_{11/2}$, $\pi {\left(h_{9/2}\right)}_{2^{+}-4^{+}}^2\otimes \nu j_{15/2}$, $\pi {\left(h_{9/2}{f}_{7/2}\right)}_{8^{+}}\otimes \nu g_{9/2}$, and $\pi {\left(h_{9/2}\right)}_{0^{+}}^2\otimes \nu {\left(g_{9/2}\right)}_{0^{+}}^2{\left(s_{1/2}\right)}^{-1}$. The single-particle neutron states $\nu d_{5/2}$ and $\nu s_{1/2}$ were also identified. Furthermore, a number of states feeding the low-spin structures were added.

The bremstrahlung-induced fission of ${}^{234}\mathrm{U}$ and ${}^{232}\mathrm{Th}$ has been studied at the superconducting Darmstadt linear accelerator (S-DALINAC) in the excitation energy region close to the fission barrier. Fission-fragment mass and total kinetic energy (TKE) distributions from ${}^{234}\mathrm{U}$ were studied for the first time in this energy region. The results have been analysed in terms of fission modes, and a dominant yield of the mass-asymmetric standard-2 mode was found in both nuclei. No strong dependence of the fission-mode weights on the excitation energy of the compound nucleus was found. Correlations among mass, TKE, and angular distributions have also been investigated. A correlation in the form of an increased anisotropy for far-asymmetric masses and low TKE were found in both fissioning systems. A possible interpretation of this correlation in terms of fission modes is discussed.

We analyze recent $K^{+}$ meson photoproduction data from the CLAS collaboration for the reactions $\gamma p\to K^{+}\mathrm{\Lambda }$ and $\gamma p\to K^{+}{\mathrm{\Sigma }}^0$, fitting measured forward-angle differential cross sections to the form $A{e}^{Bt}$. We develop a quantitative scheme for determining the kinematic region where the fit is to be done, and, from the extracted $t$-slope $B$, determine whether single-Reggeon exchange can explain the production mechanism. We find that, in the region $5<s<8.1{\mathrm{GeV}}^2$, production of the $K^{+}\mathrm{\Lambda }$ channel can be explained by single $K^{+}$ Reggeon exchange, but the $K^{+}{\mathrm{\Sigma }}^0$ production channel cannot. We verify these conclusions by fitting the data to a differential cross section produced by the interfering sum of two exponential amplitudes.

The decay of $\alpha$ particle from a nucleus is viewed as a quantum resonance state of a two-body scattering process of the $\alpha$+daughter nucleus pair governed by a novel nucleus-nucleus potential in squared Woods-Saxon form. By the application of the rigorous optical model (OM) potential scattering ($S$-matrix) theory the genuineness of the potential for the system is established by giving a good explanation of the elastic scattering and reaction cross sections data of the $\alpha$+nucleus pair. From the pole position in the complex momentum ($k$) plane of the $S$ matrix of the real part of the OM potential defined above, the energy and width of the resonance state akin to the decaying state of emission of $\alpha$ particle are extracted and from this width, the result of the $\alpha$-decay half-life is derived to account for the experimental result of the half-life in the cases of a large number of $\alpha$ emitters including heavy and superheavy nuclei. The $S$ matrix of the real OM potential is replaced by an analytical function expressed in terms of exact Schrödinger solutions of a global potential that closely represents the real Coulomb-nuclear interaction in the interior and the pure Coulomb wave functions outside, and the resonant poles of this $S$ matrix in the complex momentum plane are used to give satisfactory results of decay half-lives of $\alpha$ coming out from varieties of nuclei.

The thermonuclear rate of the ${}^{46}\mathrm{Cr}(p,\gamma ){}^{47}\mathrm{Mn}$ reaction has been determined using a newly evaluated proton separation energy of $S_p\left({}^{47}\mathrm{Mn}\right)=380\pm 30\mathrm{keV}$ and nuclear structure information from the mirror nucleus ${}^{47}\mathrm{Ti}$. The astrophysical impact of this new rate and previously available rates has been investigated through one-zone postprocessing type-I x-ray burst calculations. The present ${}^{46}\mathrm{Cr}(p,\gamma ){}^{47}\mathrm{Mn}$ rate leads to a mass fraction at $A=46$ that is 60 times larger than that obtained using a statistical model rate. The new results constrain the calculated maximum and minimum mass fractions at $A=46$ and $A=48$ to be within factors of 12 and 4, respectively. Experimental studies of the level structure of ${}^{47}\mathrm{Mn}$ near the proton threshold are required to improve these model predictions.

The ${}^{15}\mathrm{O}(\alpha ,\gamma ){}^{19}\mathrm{Ne}$ reaction is expected to trigger the initial path for breakout from the CNO hydrogen-burning cycles to the rapid proton capture $\left(rp\right)$ process in type I x-ray bursts on accreting neutron stars. The thermonuclear reaction rate has a major impact on models of type I x-ray burst observables and it depends on the small $\alpha$-particle branching ratio, ${\mathrm{\Gamma }}_{\alpha }/\mathrm{\Gamma }$, of the 4.03 MeV state in ${}^{19}\mathrm{Ne}$. Attempts to measure ${\mathrm{\Gamma }}_{\alpha }/\mathrm{\Gamma }$ by populating the 4.03 MeV state using nuclear reactions have only led to strong upper limits. In the present work, we report the first experimental evidence that the 4.03 MeV ${}^{19}\mathrm{Ne}$ state is populated in ${}^{20}\mathrm{Mg} \beta$-delayed proton emission. This new channel has the potential to provide the necessary sensitivity to detect a finite value of ${\mathrm{\Gamma }}_{\alpha }/\mathrm{\Gamma }$.

The isotope ${}^{35}\mathrm{Mg}$ was spectroscopically studied via nucleon-removal reactions from ${}^{36}\mathrm{Mg}$ and ${}^{37}\mathrm{Al}$ secondary beams at intermediate energies. The experiment's aim was to clarify the level structure of this nucleus located in between the $N=20$ and 28 shell quenchings. De-excitation $\gamma$-ray energies, exclusive cross sections, and parallel momentum of outgoing ${}^{35}\mathrm{Mg}$ for several final states were measured and compared to structure calculations in the shell model and antisymmetrized molecular dynamics framework and the eikonal reaction calculation, further developing the level scheme of ${}^{35}\mathrm{Mg}$. It was found that a large fraction of the one-neutron knockout reaction goes into unbound states of ${}^{35}\mathrm{Mg}$, which may explain missing $f$-wave strength.

We study the binary mass distribution for the recently predicted thermally fissile neutron-rich uranium and thorium nuclei using a statistical model. The level density parameters needed for the study are evaluated from the excitation energies of the temperature-dependent relativistic mean field formalism. The excitation energy and the level density parameter for a given temperature are employed in the convolution integral method to obtain the probability of the particular fragmentation. As representative cases, we present the results for the binary yields of ${}^{250}\mathrm{U}$ and ${}^{254}\mathrm{Th}$. The relative yields are presented for three different temperatures: $T=1$, 2, and 3 MeV.

The two-particle Green's function and $T$ matrix including pphh correlations in infinite nuclear matter are evaluated by a diagonalization of the effective total Hamiltonian. This diagonalization procedure corresponds to the same eigenvalue problem as for the pphh Random Phase Approximation. The effective Hamiltonian is nonHermitian and, for specific density domains and partial waves, yields pairs of complex conjugated eigenvalues and eigenfunctions representing in-medium bound states of two nucleons. The occurrence of these complex poles of the two-particle in-medium Green's function indicates the well known pairing instability. It is shown that the corresponding bound-state wave functions contain momentum dependencies of the BCS gap function, so that the latter can be found from a single diagonalization procedure for the effective Hamiltonian matrix. The approach is illustrated by calculations for ${}^{1}S_0$ and ${}^{3}PF_2$ gap functions in neutron matter which essentially coincide with the results found by a direct solving of the BCS gap equation. However the developed approach shows a new interesting feature, i.e., the gap closure and a phase transition point at very low density in the case of coupled channels ${}^{3}SD_1$ in symmetric nuclear matter. This finding goes beyond the conventional BCS treatment and is discussed in the context of transition from Bose-Einstein condensation of quasideuterons to the formation of BCS pairing.

The effects of finite particle number sampling on the net baryon number cumulants, extracted from fluid dynamical simulations, are studied. The commonly used finite particle number sampling procedure introduces an additional Poissonian (or multinomial if global baryon number conservation is enforced) contribution which increases the extracted moments of the baryon number distribution. If this procedure is applied to a fluctuating fluid dynamics framework, one severely overestimates the actual cumulants. We show that the sampling of so-called test particles suppresses the additional contribution to the moments by at least one power of the number of test particles. We demonstrate this method in a numerical fluid dynamics simulation that includes the effects of spinodal decomposition due to a first-order phase transition. Furthermore, in the limit where antibaryons can be ignored, we derive analytic formulas which capture exactly the effect of particle sampling on the baryon number cumulants. These formulas may be used to test the various numerical particle sampling algorithms.

We study the scattering of dark matter particles off various light nuclei within the framework of chiral effective field theory. We focus on scalar interactions and include one- and two-nucleon scattering processes whose form and strength are dictated by chiral symmetry. The nuclear wave functions are calculated from chiral effective field theory interactions as well and we investigate the convergence pattern of the chiral expansion in the nuclear potential and the dark matter–nucleus currents. This allows us to provide a systematic uncertainty estimate of our calculations. We provide results for ${}^2\mathrm{H}$, ${}^3\mathrm{H}$, and ${}^3\mathrm{He}$ nuclei, which are theoretically interesting, and the latter is a potential target for experiments. We show that two-nucleon currents can be systematically included but are generally smaller than predicted by power counting and suffer from significant theoretical uncertainties even in light nuclei. We demonstrate that accurate high-order wave functions are necessary in order to incorporate two-nucleon currents.