The $Q$ values for double-electron capture in ${}^{102}$Pd, ${}^{106}$Cd, and ${}^{144}$Sm have been measured by Penning-trap mass spectrometry. The results exclude at present all three nuclides from the list of suitable candidates for a search for resonant neutrinoless double-electron capture.

We report a measurement of the modification of the effective precession frequency of polarized ${}^3$He atoms in response to a dressing field in a room-temperature cell. The ${}^3$He atoms were polarized using the metastability spin-exchange method. An oscillating dressing field was then applied perpendicular to the constant magnetic field. Modification of the ${}^3$He effective precession frequency was observed over a broad range of the amplitude and frequency of the dressing field. The observed effects are compared with calculations based on quantum optics formalism.

The nucleus ${}^{46}$Ti has been studied with the reaction ${}^{42}$Ca(${}^7$Li,$p$2n)${}^{46}$Ti at a bombarding energy of 31 MeV. Thin target foils backed with a thick Au layer were used. Five new levels of negative parity were observed. Several lifetimes have been determined with the Doppler shift attenuation method. Low-lying experimental negative-parity levels are assigned to three bands with $K^{\pi }=3^{-}$, $0^{-}$, and $4^{-}$, which are interpreted in terms of the large-scale shell model, considering particle-hole excitations from $d_{3/2}$ and $s_{1/2}$ orbitals. Shell model calculations were performed using a few effective interactions. However, good agreement was not achieved in the description of either negative- or positive-parity low-lying levels.

A Skyrme-type momentum-dependent nucleon-nucleon force distinguishing isospin effect is parametrized and further implemented in the Lanzhou quantum molecular dynamics model, which leads to a splitting of nucleon effective mass in nuclear matter. Based on the isospin- and momentum-dependent transport model, we investigate the influence of momentum-dependent symmetry potential on several isospin-sensitive observables in heavy-ion collisions. It is found that symmetry potentials with and without the momentum dependence but corresponding to the same density dependence of the symmetry energy result in different distributions of the observables. The midrapidity neutron/proton ratios at high transverse momenta and the excitation functions of the total ${\pi }^{-}/{\pi }^{+}$ and $K^0/K^{+}$ yields are particularly sensitive to the momentum dependence of the symmetry potential.

Correlations of azimuthal angles observed at the Relativistic Heavy Ion Collider have gained great attention due to the prospect of identifying fluctuations of parity-odd regions in the field sector of QCD. Whereas the observable of interest related to parity fluctuations involves subtracting opposite-sign from same-sign correlations, the STAR collaboration reported the same-sign and opposite-sign correlations separately. It is shown here how momentum conservation combined with collective elliptic flow contributes significantly to this class of correlations, although not to the difference between the opposite- and same-sign observables. The effects are modeled with a crude simulation of a pion gas. Although the simulation reproduces the scale of the correlation, the centrality dependence is found to be sufficiently different in character to suggest additional considerations beyond those present in the pion gas simulation presented here.

A study of the assault frequency and preformation factor of the $\alpha$-decay description is performed from the experimental $\alpha$-decay constant and the penetration probabilities calculated from the generalized liquid-drop model (GLDM) potential barriers. To determine the assault frequency a quantum-mechanical method using a harmonic oscillator is introduced and leads to values of around ${10}^{21}$ s${}^{-1}$, similar to the ones calculated within the classical method. The preformation probability is around ${10}^{-1}$–${10}^{-2}$. The results for even-even Po isotopes are discussed for illustration. While the assault frequency presents only a shallow minimum in the vicinity of the magic neutron number 126, the preformation factor and mainly the penetrability probability diminish strongly around $N=126$.

The electromagnetic charge operator in a two-nucleon system is derived in chiral effective field theory ($\chi$EFT) up to order $eQ$ [or next-to-next-to-next-to-next-to-leading order (N4LO)], where $Q$ denotes the low-momentum scale and $e$ is the electric charge. The specific form of the N3LO and N4LO corrections from, respectively, one-pion-exchange and two-pion-exchange depends on the off-the-energy-shell prescriptions adopted for the nonstatic terms in the corresponding potentials. We show that different prescriptions lead to unitarily equivalent potentials and accompanying charge operators. Thus, provided a consistent set is adopted, predictions for physical observables will remain unaffected by the nonuniqueness associated with these off-the-energy-shell effects.

The recently measured $\gamma *\gamma *\to {\pi }^0$ anomalous form factor is analyzed using the $D4/D8\overline{D8}$ holographic approach to QCD. The half-on-shell transition form factor is vector meson dominated and is shown to exactly tie to the charged-pion form factor. The holographic result compares well with the data for the lowest vector resonance.

We investigate the charged pion photoproduction off the proton target with the $\Delta \left(1232\right)$ baryon, i.e., $\gamma p\to {\pi }^{-}{\Delta }^{++}\left(1232\right)$ and $\gamma p\to {\pi }^{+}{\Delta }^0\left(1232\right)$, based on the effective Lagrangian method, beyond the resonance region, $\sqrt{s}\gtrsim 2$ GeV. We employ the $\pi$- and $\rho$-meson Regge trajectories in the $t$ channel, in addition to the proton and $\Delta$ pole, in the $s$ and $u$ channels, respectively, and the contact-interaction contributions. A specific scheme for the form factor which satisfies the Ward-Takahashi identity, crossing symmetry, and on-shell condition is taken into account. We also consider a smooth interpolation between the Regge and Feynman propagators for the $t$-channel meson exchanges as a function of the Mandelstam variable $s$. We present the numerical results for the energy and angular dependences of the cross sections and the double- and single-polarization observables. It turns out that the present framework reproduces the experimental data qualitatively very well. In particular, the interpolation between the two propagators plays a crucial role in reproducing the high-energy experimental data correctly. The ${\pi }^{+}$ decay-angle distribution is also studied using the ${\Delta }^{++}$-decay frame, i.e., the Gottfried-Jackson frame. The present results will be a useful guide for future high-energy photon-beam experiments.

High-spin states in ${}^{139}$Nd were investigated using the reaction ${}^{96}$Zr(${}^{48}$Ca,5$n$) at a beam energy of 195 MeV and $\gamma$-ray coincidences were acquired with the Euroball spectrometer. Apart from several dipole bands at medium excitation energy, three quadrupole bands have been observed at high spin. Linking transitions connecting two of the high-spin bands to low-energy states have been observed. Calculations based on the cranked-Nilsson-Strutinsky formalism have been used to assign configurations for the high-spin quadrupole bands.

Lifetime measurements have been made in the ground-state band of the transitional nucleus ${}^{138}$Gd from coincidence recoil-distance Doppler-shift data. ${}^{138}$Gd nuclei were produced using the ${}^{106}$Cd (${}^{36}$Ar, 2$p$2$n$) reaction with a beam energy of 190 MeV. Reduced transition probabilities have been extracted from the lifetime data collected with the Köln plunger placed at the target position of the JUROGAM-II array. The $B\left(E2\right)$ values have been compared with predictions from X(5) critical-point calculations, which describe the phase transition between vibrational and axially symmetric nuclear shapes, as well as with IBM-1 calculations at the critical point. While the excitation energies in ${}^{138}$Gd are consistent with X(5) predictions, the large uncertainties associated with the measured $B\left(E2\right)$ values cannot preclude vibrational and rotational contributions to the low-lying structure of ${}^{138}$Gd. Although experimental knowledge for the low-lying $\gamma$ and $\beta$-vibrational bands in ${}^{138}$Gd is limited, potential-energy surface calculations suggest an increase in $\gamma$ softness in the ground-state band. In order to more fully account for the effects of $\gamma$ softness, the X(5) and IBM-1 calculations need to be extended to include the $\gamma$ degree of freedom for ${}^{138}$Gd.

We test the hypothesis of partially conserved axial current in high-energy diffractive neutrino production of pions. Since the pion pole contribution to the Adler relation (AR) is forbidden by conservation of the lepton current, the heavier states, like the $a_1$ pole, $\rho$-$\pi$ cut, etc., control the lifetime of the hadronic fluctuations of the neutrino. We evaluate the deviation from the AR in diffractive neutrino production of pions on proton and nuclear targets. At high energies, when all the relevant time scales considerably exceed the size of the target, the AR explicitly breaks down on an absorptive target, such as a heavy nucleus. In this regime, close to the black disk limit, the off-diagonal diffractive amplitudes vanish, while the diagonal one, $\pi \to \pi$, which enters the AR, maximizes and saturates the unitarity bound. At lower energies, in the regime of short lifetime of heavy hadronic fluctuations the AR is restored, i.e., it is not altered by the nuclear effects.

α decay of ${}^{271-294}$115 superheavy nuclei is studied using the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The predicted α half-lives of ${}^{287}$115 and ${}^{288}$115 nuclei and their decay products are in good agreement with experimental values. Comparison of α and spontaneous fission half-lives predicts four-α chains and three-α chains, respectively, from ${}^{287}$115 and ${}^{288}$115 nuclei and are in agreement with experimental observation. Our study predicts two-α chains from ${}^{273,274,289}$115, three-α chains from ${}^{275}$115, and four-α chains consistently from ${}^{284,285,286}$115 nuclei. These observations will be useful for further experimental investigation in this region.

An investigation of the yrast structure of the odd-$Z$ ${}^{159}$Ho nucleus to high spin has been performed. The ${}^{159}$Ho nucleus was populated by the reaction ${}^{116}$Cd(${}^{48}$Ca,$p4n\gamma$) at a beam energy of 215 MeV, and resulting $\gamma$ decays were detected by the Gammasphere spectrometer. The $h_{11/2}$ yrast band has been significantly extended up to $I^{\pi }=75/2^{-}$ (tentatively $79/2^{-}$). A lower frequency limit for the second ${\left(h_{11/2}\right)}^2$ proton alignment was extracted consistent with the systematics of this alignment frequency, indicating an increased deformation with neutron number in the Ho isotopes. The energy-level splitting between the signature partners in the $h_{11/2}$ structures of the Ho isotopes and the neighboring $N=92$ isotones is discussed.

An importance-sampling iterative algorithm for diagonalizing shell model Hamiltonian matrices is reviewed and implemented in a spin uncoupled basis. Shell model spaces of dimensions up to $N\lesssim {10}^9$ are considered. The analysis shows that about $10\%$ of the basis states are enough to bring the eigenvalues to convergence. This fraction of states, however, is insufficient to lead to convergence of the transition strengths, thereby limiting the applicability of the method to not too large spaces. In its domain of validity, the method yields a large number of eigensolutions and can be usefully adopted for rather complete studies of low-energy spectroscopy. This is done here for ${}^{132,134}$Xe isotopes. The calculation yields spectra and electromagnetic responses in fairly good agreement with the available experimental data and unveils the properties of the low-energy states of these isotopes, including their proton-neutron symmetry.

The quasiparticle energy spectrum of the Hartree-Fock-Bogoliubov (HFB) equations contains discrete bound states, resonances, and nonresonant continuum states. We study the structure of the unbound quasiparticle spectrum of weakly bound nuclei within several methods that do not rely on imposing scattering or outgoing boundary conditions. Various approximations are examined to estimate resonance widths. It is shown that the stabilization method works well for all HFB resonances except for very narrow ones. The Thomas-Fermi approximation to the nonresonant continuum has been shown to be very effective, especially for coordinate-space HFB calculations in large boxes that involve huge amounts of discretized quasiparticle continuum states.

An interpretation is suggested of the recently published experimental data on the alternating parity bands in ${}^{240}$Pu. The interpretation is based on the assumption that the main role in the description of the properties of the alternating parity bands plays the octupole mode which preserves the axial symmetry. The mathematical technique of the supersymmetric quantum mechanics is used for the realization of the model with the two-center octupole wave functions. A good description of the parity splitting and of the ratio of the dipole and quadrupole transitional moments is obtained for the first two bands.

The $N>82$ even neodymium isotopes were studied in the framework of the IBA-2 model. The analysis was performed by using a very schematic Hamiltonian, particularly suited to investigate the U(5) $\to$ SU(3) transition. The evolution of the excitation energy patterns and of the spectroscopic properties along the isotopic chain can be correctly reproduced when the role played by states of mixed symmetry character is also taken into account.

Eigenfunctions of the collective Bohr Hamiltonian with the Morse potential have been obtained by using the asymptotic iteration method (AIM) for both $\gamma$-unstable and rotational structures. $B\left(E2\right)$ transition rates have been calculated and compared to experimental data. Overall good agreement is obtained for transitions within the ground-state band, while some interband transitions appear to be systematically underpredicted in $\gamma$-unstable nuclei and overpredicted in rotational nuclei.