The description of nuclei as a system of $\alpha$ particles is considered using a two-variable integrodifferential equation describing $A$-boson systems. The method is based on the assumption that two-body forces are the dominant ones within the system. This allows the expansion of the $A$-body wave function in Faddeev components which in turn can be expanded in potential harmonics that result either in a coupled system of differential equations in the hyper-radius $r$ or, when projected on the $r_{ij}$ space, in a single two-variable, integrodifferential equation that includes the two-body correlations exactly. The formalism can be readily applied to systems of up to $A\sim 20$. Going beyond this number one encounters increasingly difficult numerical problems stemming mainly from the structure of the kernel in the integral. However, these problems can be eliminated by transforming the equation, when $A\to \infty$, into a new one having a kernel which has a simple analytical form and is easy to use in calculations. We employed the transformed equation to investigate the possibility of describing nuclei consisting of $A$ $\alpha$ particles. It was found that for the Ali-Bodmer potential the $A=5$ system, i.e., the ${}^{20}$Ne, is the most stable while the $A=10$ system, i.e., the ${}^{40}$Ca, the binding energy has a maximum. Various aspects concerning the formation of $A\alpha$ nuclei are discussed.

The influence of entrance channel isospin, charge asymmetry, and bombarding energy on the competition between the complete fusion followed by the decay of compound nucleus and quasifission channels is treated within the dinuclear system model. The charge (mass) distributions of the products in the reactions ${}^{16,22}$O+${}^{27}$Al, ${}^{92,78}$Kr+${}^{40}$Ca, ${}^{86}$Kr${+}^{48}$Ca, ${}^{122}$Sn+${}^{12}$C, ${}^{32}$S+${}^{100}$Mo, ${}^{48}$Ca+${}^{144,154}$Sm, and ${}^{20,28}$Ne+${}^{181}$Ta are calculated at bombarding energies above the Coulomb barrier. The evolution of charge distribution of the complex fragments from the excited rotating nucleus ${}^{134}$Xe with increasing angular momentum and excitation energy is demonstrated.

We study heavy-ion inelastic scattering processes in neutron-rich nuclei including the full response to the different multipolarities. Among these we focus in particular on the excitation of low-lying dipole states commonly associated to the pygmy dipole resonance. The multipole response is described within the Hartree-Fock plus RPA formalism with Skyrme interaction. We show how the combined information from reactions processes involving the Coulomb and different mixtures of isoscalar and isovector nuclear interactions can provide a clue to reveal the characteristic features of these states. We have performed calculation for the excitation of ${}^{132}$Sn generated in the reactions with ${}^4$He, ${}^{40}$Ca, and ${}^{48}$Ca at several incident energies, as well as for the system ${}^{17}$O $+{}^{208}$Pb. Our results suggest that the investigation of the PDR states can be better carried out at low incident energies (below 50 MeV/nucleon). In fact, at these energies the PDR peak is relatively stronger than the giant dipole resonance (GDR) one and the narrow width of the low-lying quadrupole and octupole states should not blur its presence.

Theoretical studies of the production of real thermal photons in relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are performed. The space-time evolution of the colliding system is modelled using music, a 3+1D relativistic hydrodynamic simulation, using both its ideal and viscous versions. The inclusive spectrum and its azimuthal angular anisotropy are studied separately, and the relative contributions of the different photon sources are highlighted. It is shown that the photon $v_2$ coefficient is especially sensitive to the details of the microscopic dynamics like the equation of state, the ratio of shear viscosity over entropy density, $\eta /s$, and to the morphology of the initial state.

We study the thermalization process of charm quarks in hot and dense matter. The diffusion of heavy quarks is calculated via a Langevin equation, both for a static medium as well as for a quark-gluon plasma (QGP) medium generated by a (3 $+$ 1)-dimensional hydrodynamic model. We define two criteria for the thermalization of the heavy quarks and observe thermalization times that are longer than the lifetime of the QGP phase for reasonable values of the diffusion constant.

We calculate the thermal photon transverse momentum spectra and elliptic flow in $\sqrt{s_{NN}}=200$ GeV $\text{Au}+\text{Au}$ collisions at the Relativistic Heavy Ion Collider (RHIC) and in $\sqrt{s_{NN}}=2.76$ TeV $\text{Pb}+\text{Pb}$ collisions at the Large Hadron Collider (LHC), using an ideal hydrodynamical framework which is constrained by the measured hadron spectra at RHIC and LHC. The sensitivity of the results to the QCD-matter equation of state and to the photon emission rates is studied, and the photon $v_2$ is discussed in light of the photonic $p_T$ spectrum measured by the PHENIX Collaboration. In particular, we make a prediction for the thermal photon $p_T$ spectra and elliptic flow for the current LHC $\text{Pb}+\text{Pb}$ collisions.

Excited states in the $Z=19$, $N=29$ neutron-rich ${}^{48}$K isotope have been studied using deep-inelastic transfer reactions with a thick target at Gammasphere and with a thin target at the PRISMA-CLARA spectrometer. The lowest excited states were located; they involve a proton hole in the $s_{1/2}$ or $d_{3/2}$ orbital coupled to a $p_{3/2}$ neutron. A new 7.1(5)-ns, $5^{+}$ isomer, the analog of the $7/2^{-}$ isomer in ${}^{47}$K, was identified. Based on the observed $\gamma$-decay pattern of the isomer a revised spin-parity assignment of $1^{-}$ is proposed for the ground state of ${}^{48}$K.

The pairing gaps, heat capacities, and level densities are calculated within the BCS-based quasiparticle approach, including the effect of thermal fluctuations on the pairing field within the pairing model plus noncollective rotation along the $z$ axis for ${}^{60}$Ni and ${}^{72}$Ge nuclei. The analysis of the numerical results obtained shows that, in addition to the pairing gap, the heat capacity can also serve as a good observable to detect the appearance of the pairing reentrance in hot rotating nuclei, whereas such a signature in the level density is rather weak.

Excited states in ${}^{32}$P have been investigated up to high spins using $\gamma$-ray spectroscopic techniques following the ${}^{18}$O(${}^{16}$O, $np$)${}^{32}$P fusion-evaporation reaction. Sixteen new transitions have been observed, and the level scheme has been extended up to $E_x=9.637$ MeV. The multiclover Indian National Gamma Array (INGA) facilitated angular correlation and linear polarization measurements for spin-parity assignments. Branching ratios have been determined. The level scheme is indicative of excitation of nucleons across the $sd$-$fp$ shell gap. The experimental observables were successfully interpreted by large-basis cross shell model calculations without resorting to any reduction of the single-particle energies of the $f_{7/2}$ and $p_{3/2}$ orbitals. These results suggest that any lowering of single-particle energies may not be required if an appropriate choice of valence space and effective interaction is made.

The fusion reaction ${}^{40}$Ca + ${}^{40}$Ca was very recently reinvestigated by the Legnaro group and cross sections down to $\mu$b were measured. In the present work this reaction is analyzed within the coupled-channel formalism including $2^{+}$, $3^{-}$, and $5^{-}$ phonon states. The heavy-ion entrance channel potential is calculated within the double-folding prescription and comprises a direct local term and a local equivalent of the nonlocal knock-on exchange component. The single-particle densities entering the folding integrals are prescribed according to the density matrix expansion. Coupling potentials are calculated from the $G$-matrix Michigan three-range Yukawa-type semirealistic nucleon-nucleon interaction (M3Y) as well as one modern parametrization of the density-dependent Gogny effective interaction. Realistic deformation parameters are used. The best fit to the data is not pointing to a possible maximum in the astrophysical $S$-factor as in a previous study on sub-barrier fusion involving ${}^{48}$Ca projectiles.

Structure functions and polarization observables in elastic scattering of longitudinally polarized electrons on polarized deuterons are considered within the approximation of one-photon plus two-photon exchange. It is shown that the contribution of two-photon exchange to the generalized deuteron structure function $\mathcal{A}$ is of the order of few percent, while the contribution to the generalized structure function $\mathcal{B}$ is of the order of 10$\%$–20$\%$. We have found that the components $T_{20}$ and $T_{21}$ of the tensor analyzing power are mainly determined by one-photon exchange but that $T_{22}$ is mainly determined by interference between one-photon exchange and two-photon exchange. We have also considered the polarization observables $T_{11}$, $C_{21}$, and $C_{22}$, which are proportional to the imaginary part of the reaction amplitude and vanish in the framework of one-photon exchange.

We derive the leading one-loop contribution to the one-pion exchange and short-range two-nucleon electromagnetic current operator in the framework of chiral effective field theory. The derivation is carried out using the method of unitary transformation. Explicit results for the current and charge densities are given in momentum and coordinate space.

We consider nucleon-nucleon ($NN$) interactions from chiral effective field theory. In this work we restrict ourselves to the elastic $NN$ scattering. We apply the $N/D$ method to calculate the $NN$ partial waves taking as input the one-pion exchange discontinuity along the left-hand cut. This discontinuity is amenable to a chiral power counting as discussed by Lacour, Oller, and Meißner [Ann. Phys. (NY) 326, 241 (2011)], with one-pion exchange as its leading order contribution. The resulting linear integral equation for a partial wave with orbital angular momentum $\ell \ge 2$ is solved in the presence of $\ell -1$ constraints, so as to guarantee the right behavior of the $D$- and higher partial waves near threshold. The calculated $NN$ partial waves are based on dispersion relations and are independent of regulator. This method can also be applied to higher orders in the calculation of the discontinuity along the left-hand cut and extended to triplet coupled partial waves.

The $n$-${}^3$H and $p$-${}^3$He elastic phase shifts below the trinucleon disintegration thresholds are calculated by solving the four-nucleon problem with three different realistic nucleon-nucleon interactions (the I-N3LO model by Entem and Machleidt, the Argonne $v_{18}$ potential model, and a low-$k$ model derived from the CD-Bonn potential). Three different methods—Alt-Grassberger-Sandhas, hyperspherical harmonics, and Faddeev-Yakubovsky—have been used and their respective results are compared. For both $n$-${}^3$H and $p$-${}^3$He we observe a rather good agreement between the three different theoretical methods. We also compare the theoretical predictions with the available experimental data, confirming the large underprediction of the $p$-${}^3$He analyzing power.

Antiproton scattering off ${}^3\mathrm{He}$ and ${}^4\mathrm{He}$ targets is considered at beam energies below 300 MeV within the Glauber-Sitenko approach, utilizing the $\overline{N}N$ amplitudes of the Jülich model as input. A good agreement with available data on differential $\overline{p}{}^4\mathrm{He}$ cross sections and on $\overline{p}{}^3\mathrm{He}$ and $\overline{p}{}^4\mathrm{He}$ reaction cross sections is obtained. Predictions for polarized total $\overline{p}{}^3\mathrm{He}$ cross sections are presented, calculated within the single-scattering approximation and including Coulomb-nuclear interference effects. The kinetics of the polarization buildup is discussed.

A collective mass tensor derived from the cranking approximation to the adiabatic time-dependent Hartree-Fock-Bogoliubov (ATDHFB) approach is compared with that obtained in the Gaussian overlap approximation (GOA) to the generator coordinate method. Illustrative calculations are carried out for one-dimensional quadrupole fission pathways in ${}^{256}$Fm. It is shown that the collective mass exhibits strong variations with the quadrupole collective coordinate. These variations are related to the changes in the intrinsic shell structure. The differences between collective inertia obtained in cranking and perturbative cranking approximations to ATDHFB, and within GOA, are discussed.

The level density of 2${}^{+}$ states in ${}^{40}$Ca has been extracted in the energy region of the isoscalar giant quadrupole resonance from a fluctuation analysis of high-energy-resolution ($p,p^{\prime }$) data taken at incident energies of 200 MeV at the K600 magnetic spectrometer of iThemba LABS, South Africa. Quasifree-scattering cross sections were calculated to estimate their role as a background contribution to the spectra and found to be small. The shape of the background was determined from the discrete wavelet transform of the spectra using a biorthogonal wavelet function normalized at the lowest particle separation threshold. The experimental results are compared to widely used phenomenological and microscopic models.

Octupole vibrational states were studied in the nucleus ${}^{150}\mathrm{Nd}$ via inelastic proton scattering with $10.9-$MeV protons, which are an excellent probe to excite natural parity states. For the first time in ${}^{150}\mathrm{Nd}$, both the scattered protons and the $\gamma$ rays were detected in coincidence, giving the possibility to measure branching ratios in detail. Using the coincidence technique, the $B\left(E1\right)$ ratios of the decaying transitions for 10 octupole vibrational states and other negative-parity states to the yrast band were determined and compared to the Alaga rule. The positive and negative-parity states revealed by this experiment are compared with interacting boson approximation calculations performed in the $spdf$ boson space. The calculations are found to be in good agreement with the experimental data, for both positive and negative-parity states.

One of the striking features of particle production at high beam energies is the near-equal abundance of matter and antimatter in the central rapidity region. In this paper we study how this symmetry is reached as the beam energy is increased. In particular, we quantify explicitly the energy dependence of the approach to matter-antimatter symmetry in proton-proton and in heavy-ion collisions. Expectations are presented also for the production of more complex forms of antimatter such as antihypernuclei.

Dilepton production in $\mathrm{In}+\mathrm{In}$ collisions at 158$A$ GeV is studied within the microscopic parton-hadron-string dynamics (PHSD) transport approach that incorporates explicit partonic degrees of freedom and dynamical hadronization as well as the more familiar hadronic dynamics in the final reaction stages. A comparison to the data of the NA60 Collaboration shows that the measured dilepton yield is well described by including the collisional broadening of vector mesons, while simultaneously accounting for the electromagnetic radiation of the strongly coupled quark-gluon plasma (sQGP) via off-shell quark-antiquark annihilation, quark annihilation with additional gluon bremsstrahlung, and the gluon-Compton scattering mechanisms. In particular, the spectra in the intermediate mass range (1 GeV $⩽M⩽2.5$ GeV) are dominated by quark-antiquark annihilation in the nonperturbative QGP. Also, the observed softening of the transverse mass spectra at intermediate masses (1 GeV $⩽M⩽2.5$ GeV) is approximately reproduced. Furthermore, for dileptons of low masses ($M<0.6$ GeV), we find a sizable contribution from the quark annihilation with additional gluon bremsstrahlung, thus providing another possible window for probing the properties of the sQGP.