I address the issue of coherent and incoherent photoproduction of pseudoscalar mesons on nuclei at high photon energies in the peripheral region, characterized by small momentum transfer. The reactions considered give prominent background to photoproduction in the electromagnetic field of a nucleus. For this reason, a detailed knowledge of their cross sections is necessary for correct determination of the radiative decay widths of neutral mesons. Particular attention is paid to transitions to the discrete bound levels, as well as to the giant resonance states. Numerical results are presented for photoproduction of $\eta$ mesons on ${}^{12}\mathrm{C}$.

Based on the high-statistics data of the CLAS Collaboration on the $\gamma p\to \varphi p$ reaction in the center-of-mass energy range of 2.2 GeV to 2.8 GeV, we investigate the possible existence of strange molecular partners of $P_c$ states, i.e., $N^{*}\left(2080\right)$ and $N^{*}\left(2270\right)$ as $K^{*}\mathrm{\Sigma }$ and $K^{*}{\mathrm{\Sigma }}^{*}$ molecular states. In addition to the $t$-channel Pomeron exchange, $t$-channel meson exchange including pseudoscalar meson $(\pi ,\eta )$, scalar meson $[\sigma ,a_0\left(980\right),f_0\left(980\right)]$, axial-vector meson $f_1\left(1285\right)$, tensor meson $f_2\left(1270\right)$, as well as $s$- and $u$-channel proton exchange, the inclusion of the $s$-channel $N^{*}\left(2080\right)$ and $N^{*}\left(2270\right)$ states can fit the data very well. The fitted coupling constants of these $N^{*}$ molecular states to $p\varphi$ and $\gamma p$ are consistent with the results calculated directly from the relevant hadronic triangle diagrams of the hadronic molecular picture.

The ${\beta }^{-}$ decay $Q$ value of ${}^{136}\mathrm{Cs}$ $(J^{\pi }=5^{+}, t_{1/2}\approx 13 \mathrm{d})$ was measured with the JYFLTRAP Penning trap setup at the Ion Guide Isotope Separator On-Line facility of the University of Jyväskylä, Finland. The monoisotopic samples required in the measurements were prepared with a new scheme utilized for the cleaning, based on the coupling of dipolar excitation with Ramsey's method of time-separated oscillatory fields and the phase-imaging ion-cyclotron-resonance technique. The $Q$ value is determined to be 2536.83(45) keV, which is $\approx 4$ times more precise and 11.4(20) keV $(\approx 6\sigma )$ smaller than the adopted value in the most recent Atomic Mass Evaluation AME2020. The daughter, ${}^{136}\mathrm{Ba}$, has a $4^{+}$ state at 2544.481(24) keV and a $3^{-}$ state at 2532.653(23) keV, both of which can potentially be ultralow $Q$-value end states for the ${}^{136}\mathrm{Cs}$ decay. With our new ground-to-ground state $Q$ value, the decay energies to these two states become $-7.65\left(45\right)$ keV and 4.18(45) keV, respectively. The former is confirmed to be negative at the level of $\approx 17\sigma$, which verifies that this transition is not a suitable candidate for neutrino mass determination. On the other hand, the slightly negative $Q$ value makes this transition an interesting candidate for the study of virtual $\beta \text{−}\gamma$ transitions. The decay to the $3^{-}$ state is validated to have a positive low $Q$ value which makes it a viable candidate for neutrino mass determination. For this transition, we obtained a shell-model-based half-life estimate of $2.1_{-0.8}^{+1.6}\times {10}^{12}$ yr. Furthermore, the newly determined low reaction threshold of 79.08(54) keV for the charged-current ${\nu }_e+{}^{136}\mathrm{Xe}$ $\left(0^{+}\right)\to {}^{136}\mathrm{Cs}^{*}+e^{-}$ neutrino capture process is used to update the cross sections for a set of neutrino energies relevant to solar ${}^7\mathrm{Be}$, pep, and CNO neutrinos. Based on our shell-model calculations, the new lower threshold shows event rates of 2–4 percent higher than the old threshold for several final states reached by the different species of solar neutrinos.

The entanglement properties of systems in which elastic and inelastic reactions occur in projectile-target interactions is studied. A new measure of entanglement, the scattering entropy, based on the unitarity of the $S$ matrix (probability conservation), is suggested. Using simple models for both low- and high-energy interactions, the amount of entanglement is found to track with the strength of the inelastic interaction. The familiar example of the classical “black disk,” or total absorption, model is found to correspond to maximum entanglement. An analysis of high-energy $pp$ scattering data shows that entanglement is near maximum for laboratory energies greater than about 1 GeV, showing that the total absorption model is a reasonable starting point for understanding the data.

The first experiment using radioactive beams post-accelerated by the HIE-ISOLDE facility has enabled to obtain a precise set of $B\left(E2\right)$ transition probabilities in neutron-rich ${}^{74,76}\mathrm{Zn}$ isotopes. The resulting $B(E2$; $2_1^{+}\to 0_1^{+}$) values are consistent with those determined in earlier REX-ISOLDE measurements. While the $B(E2$; $4_1^{+}\to 2_1^{+}$) transition probability in ${}^{76}\mathrm{Zn}$ is also in agreement with earlier Coulomb-excitation results, the value obtained for ${}^{74}\mathrm{Zn}$ is considerably lower. For the first time, a spectroscopic quadrupole moment of the $2_1^{+}$ state was measured for an exotic nucleus in this mass region. A detailed comparison is presented with large-scale shell-model and Monte Carlo shell-model calculations.

We performed a measurement of the ${}^{52}\mathrm{Cr}(d,p){}^{53}\mathrm{Cr}$ reaction at 16 MeV using the Florida State University Super-Enge Split-Pole Spectrograph (SE-SPS) and observed 26 states. While all of the states observed here had been seen in previous ($d,p$) experiments, we changed five $L$ assignments from those reported previously and determined $L$ values for nine states that had not had such assignments made previously. The $g_{9/2}$ neutron strength observed in ${}^{53}\mathrm{Cr}$ in the present work and in the $N=29$ isotones ${}^{49}\mathrm{Ca}, {}^{51}\mathrm{Ti}$, and ${}^{55}\mathrm{Fe}$ via ($d,p$) reactions is much smaller than the sum rule for this strength. Most of the observed $L=4$ strength in these nuclei is located in states near 4 MeV excitation energy. The remaining $g_{9/2}$ strength may be located in the continuum or may be fragmented among many bound states. A covariant density-functional theory calculation provides support for the hypothesis that the $g_{9/2}$ neutron orbit is unbound in ${}^{53}\mathrm{Cr}$. The ($\alpha ,{}^3\mathrm{He}$) reaction may provide a more sensitive probe for the missing $g_{9/2}$ neutron strength. In addition, particle-$\gamma$ coincidence experiments may help resolve some remaining questions in this nucleus.

Our previous investigation within the time-dependent nuclear energy-density functional theory showed that the nuclear superfluids contained inside cold neutron stars could become gapless under certain circumstances. The absence of a gap in the energy spectrum of quasiparticle excitations leads to a specific heat that is comparable to that in the normal phase in sharp contrast with the exponential suppression in the BCS phase of type ${}^{1}S_0$ pairing. Here, we further study gapless superfluidity within the same microscopic framework focusing on hydrodynamic properties. In particular, we calculate the mass fraction transported by the normal fluid of quasiparticle excitations, and we find that it can be finite even at zero temperature. We derive an approximate analytical formula for arbitrary neutron-proton superfluid mixtures. We also present numerical results for neutron stars. Our study suggests that the dynamics of neutron stars may be much more complicated than previously thought. The realization of gapless superfluidity in neutron stars and its implications are discussed.

A microscopic self-consistent triaxial relativistic Hartree-Bogoliubov theory in continuum (TRHBc), which simultaneously takes into account the triaxiality and pairing correlations as well as continuum effects, is established and applied to explore the novel halo phenomenon in aluminum isotopes. The experimental proton drip line and the available data of neutron separation energies and charge radii are reproduced well without any free parameters. The neutron-richest odd-odd aluminum isotope observed so far, ${}^{42}\mathrm{Al}$, is predicted to be triaxially deformed with $\beta =0.35$ and $\gamma ={42}^{\circ }$. Its one-neutron separation energy is predicted to be 0.68 MeV, in agreement with the AME2020, and the neutron rms radius is 3.94 fm, remarkably larger than the empirical value. The density distribution of the valance neutron, which extends much farther in space than the core, suggests a possible neutron halo in ${}^{42}\mathrm{Al}$. The dominant components responsible for the spatial extension of the halo are revealed by the single-neutron orbitals around the Fermi energy. A novel phenomenon, the exchange of the intermediate and short axes between the triaxial core with $\beta =0.38$ and $\gamma ={50}^{\circ }$ and the triaxial halo with $\beta =0.79$ and $\gamma =-{23}^{\circ }$ is found. Future experiments to explore the halo phenomenon and the novel shape decoupling in ${}^{42}\mathrm{Al}$ are highly demanded.

Neutron scattering off neutron halos can provide important information about the internal structure of nuclei close to the neutron drip line. In this work, we use halo effective field theory to study the $s$-wave scattering of a neutron and the spin-parity $J^P={\frac{1}{2}}^{+}$ one-neutron halo nuclei ${}^{11}\mathrm{Be}, {}^{15}\mathrm{C}$, and ${}^{19}\mathrm{C}$ at leading order. In the $J=1$ channel, the only inputs to the Faddeev equations are their one-neutron separation energies. In the $J=0$ channel, the neutron-neutron scattering length and the two-neutron separation energies of ${}^{12}\mathrm{Be}, {}^{16}\mathrm{C}$, and ${}^{20}\mathrm{C}$ enter as well. The numerical results show that the total $s$-wave cross sections in the $J=1$ channel at threshold are of the order of a few barns. In the $J=0$ channel, these cross sections are of the order of a few barns for $n\text{−}{}^{11}\mathrm{Be}$ and $n\text{−}{}^{19}\mathrm{C}$ scattering, and about 60 $\mathrm{mb}$ for the $n\text{−}{}^{15}\mathrm{C}$ scattering. The appearance of a pole in $pcot\delta$ close to zero in all three cases indicates the existence of a virtual Efimov state close to threshold in each of the ${}^{12}\mathrm{Be}, {}^{16}\mathrm{C}$, and ${}^{20}\mathrm{C}$ systems. Observation of this pole would confirm the presence of Efimov physics in halo nuclei. The dependence of the results on the neutron-core scattering length is also studied.

We present a semimicroscopic study of the ${}^{16}\mathrm{C}{(d,p)}^{17}\mathrm{C}$ transfer reaction. The ${}^{17}\mathrm{C}$ overlap integrals and spectroscopic factors are obtained from a microscopic cluster model, involving many ${}^{16}\mathrm{C}+n$ configurations. This microscopic model provides a fair description of the ${}^{17}\mathrm{C}$ bound-state energies. The ${}^{16}\mathrm{C}+d$ scattering wave functions are defined in the continuum discretized coupled channel (CDCC) method, where the deuteron breakup is simulated by pseudostates. The transfer cross sections are in good agreement with recent data. We confirm the ${}^{16}\mathrm{C}\left(2^{+}\right)+n$ structure of the ground state, and show that deuteron breakup effects have a significant influence on the cross sections. We study the ${}^{17}\mathrm{C}{(p,d)}^{16}\mathrm{C}$ reverse reaction and suggest that the cross section to the $2^{+}$ state should be large. A measurement of the ground-state cross section would provide a strong test of the microscopic wave functions.

We investigate neutrinoless double-beta decay ($0\nu \beta \beta$) in the minimal extension of the standard model of particle physics, the $\nu \mathrm{SM}$, where gauge-singlet right-handed neutrinos give rise to Dirac and Majorana neutrino mass terms. We focus on the associated sterile neutrinos and argue that the usual evaluation of their contributions to $0\nu \beta \beta$, based on mass-dependent nuclear matrix elements, is missing important contributions from neutrinos with ultrasoft and hard momenta. We identify the hadronic and nuclear matrix elements that enter the new contributions, and calculate all relevant nuclear matrix elements for ${}^{136}\mathrm{Xe}$ using the nuclear shell model. Finally, we illustrate the impact on $0\nu \beta \beta$ rates in specific neutrino mass models and show that the new contributions significantly alter the $0\nu \beta \beta$ rate in most parts of the $\nu \mathrm{SM}$ parameter space.

Using a ($3+1$)-dimensional hybrid framework with parametric initial conditions, we study the rapidity-dependent directed flow $v_1\left(y\right)$ of identified particles, including pions, kaons, protons, and lambdas in heavy-ion collisions. Cases involving $\mathrm{Au}+\mathrm{Au}$ collisions are considered, performed at $\sqrt{s_{NN}}$ ranging from 7.7 to 200 GeV. The dynamics in the beam direction is constrained using the measured pseudorapidity distribution of charged particles and the net proton rapidity distribution. Within this framework, the directed flow of mesons is driven by the sideward pressure gradient from the tilted source, and that of baryons mainly due to the initial asymmetric baryon distribution with respect to the beam axis driven by the transverse expansion. Our approach successfully reproduces the rapidity- and beam energy-dependence of $v_1$ for both mesons and baryons. We find that the $v_1\left(y\right)$ of baryons has strong constraining power on the initial baryon stopping, and together with that of mesons, the directed flow probes the equation of state of the dense nuclear matter at finite chemical potentials.

Background: Calculations of the structure of the low-lying states of nuclei with $Z=97–109$ play an important role in understanding the properties of nuclei belonging to the new region of the nuclide chart, which is available now for experimental study.

Purpose: To calculate quasiparticle-phonon structure and the reduced $\gamma$-transition probabilities for the excited states with excitation energies below 1 MeV for odd-proton nuclei with $Z=97-109$.

Methods: The quasiparticle-phonon model, which takes into account the quasiparticle-phonon interaction of different multipolarities, is used as a basis for the calculations.

Results: The quasiparticle-phonon structure and the $\gamma$-reduced transition probabilities of odd-proton nuclei ${}^{263,265,267,269}\mathrm{Mt}$, ${}^{259,261,263,265}\mathrm{Bh}$, ${}^{255,257,259,261,263}\mathrm{Db}$, ${}^{251,253,255,257,259,261}\mathrm{Lr}$, ${}^{249,251,253,255}\mathrm{Md}$, ${}^{245,247,249,251}\mathrm{Es}$, and ${}^{243,245,247}\mathrm{Bk}$ are calculated. The $\alpha$-decay chains starting from ${}^{263,265,267,269}\mathrm{Mt}$ are analyzed.

Conclusion: The structure of the nuclear states with excitation energies below 1 MeV in the considered nuclei is mainly exhausted by the one-quasiparticle component. However, in some isotopes the quasiparticle-phonon admixtures plays an important role to destroy the smooth isotopic dependence of energy of the states. The nuclei in the $\alpha$-decay chains starting from ${}^{263,265,267,269}\mathrm{Mt}$ have up to two $\alpha$-decay lines. The number of $\alpha$-decay lines could be different in the $\alpha$-decay chain and in the direct production of the nucleus.

I present a method, IMSRG-Net, which utilizes machine-learning techniques as a solver for the in-medium similarity renormalization group (IMSRG). The primary objective of IMSRG-Net is to approximate the Magnus operators $\mathrm{\Omega }\left(s\right)$ in the IMSRG flow equation, thereby offering an alternative to the computationally intensive part of IMSRG calculations. The key idea of IMSRG-Net is its design of the loss function inspired by physics-informed neural networks to encode the underlying physics, i.e., the IMSRG flow equation, into the model. Through training on a dataset comprising ten data points with flow parameters up to $s=20$, capturing approximately one-eighth to one-quarter of the entire flow, IMSRG-Net exhibits remarkable accuracy in extrapolating the ground-state energies and charge radii of ${}^{16}\mathrm{O}$ and ${}^{40}\mathrm{Ca}$. Furthermore, this model demonstrates effectiveness in deriving effective interactions for a valence space.

The capture and evaporation residue cross sections (ERCSs) for heavy ion fusion reactions are calculated by using the dinuclear system model. The calculation results are in good agreement with the experimental data of reactions ${}^{48}\mathrm{Ca}+{}^{244}\mathrm{Pu}$ and ${}^{48}\mathrm{Ca}+{}^{248}\mathrm{Cm}$. To investigate the possibility of synthesizing superheavy nuclei (SHN) with $Z>118$ using the ${}^{54}\mathrm{Cr}$ projectile, a comparative analysis is conducted between the ERCSs obtained with ${}^{48}\mathrm{Ca}$ and ${}^{54}\mathrm{Cr}$ projectiles for the synthesis of SHN with $Z=114–118$. The analysis further investigates the variation trends of ERCSs, capture cross sections, fusion probabilities, and survival probabilities with an increasing compound nucleus proton number ($Z_{\mathrm{CN}}$). Furthermore, we predict the ERCSs for the synthesis of new elements $Z=119, Z=120, Z=121$, and $Z=122$ through the reactions ${}^{54}\mathrm{Cr}+{}^{243}\mathrm{Am}, {}^{54}\mathrm{Cr}+{}^{248}\mathrm{Cm}, {}^{54}\mathrm{Cr}+{}^{249}\mathrm{Bk}$, and ${}^{54}\mathrm{Cr}+{}^{249}\mathrm{Cf}$, respectively. However, the obtained results fall below the detectable limits of currently available facilities. Thus, to successfully synthesize SHN with $Z>118$, experimental efforts must focus on increasing the beam intensity and improving separation and detection techniques.

The magnetic field plays a crucial role in various novel phenomena in heavy-ion collisions. We solve the Maxwell equations numerically in a medium with time-dependent electric conductivity by using the finite-difference time-domain (FDTD) algorithm. We investigate the time evolution of magnetic fields in two scenarios with different electric conductivities at collision energies ranging from $\sqrt{s_{\text{NN}}}=7.7$ to 200 GeV. Our results suggest that the magnetic field may not persist long enough to induce a significant splitting between the global spin polarizations of $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ at freeze-out stage. However, our results do not rule out the possibility of the magnetic field influencing the spin (anti-)alignment of vector mesons.

A two-body ${}^{15}\mathrm{O}+{}^2\mathrm{He}$ cluster model is applied to continuum discretized coupled channel (CDCC) calculations for the 136-MeV ${}^{17}\mathrm{Ne}+{}^{208}\mathrm{Pb}$ system. With ${}^{15}\mathrm{O}+{}^2\mathrm{He}$ binding potential parameters tuned so that either of the two $B(E2;1/2_1^{-}\to 5/2_1^{-})$ values for ${}^{17}\mathrm{Ne}$ available in the literature are reproduced, the calculations provide a reasonable description of the elastic scattering data. A comparison of the predicted breakup angular distributions with the measured inclusive ${}^{15}\mathrm{O}$ production cross section supports the conclusion of previous coupled channel calculations that the larger of the two $B(E2;1/2_1^{-}\to 5/2_1^{-})$ values may be excluded since the calculation based on it significantly over predicts the forward angle data. Further calculations find that the 1.908-MeV $1/2^{+}$ resonance of ${}^{17}\mathrm{Ne}$ cannot be simultaneously described with the 1.288-MeV $3/2^{-}$ and 1.764-MeV $5/2^{-}$ resonances by an internally consistent calculation within the two-body model. Arguments based on $Q$-value matching considerations that a large peak in the measured inclusive ${}^{15}\mathrm{O}$ cross section centered at ${\theta }_{\mathrm{lab}.}={55}^{\circ }$ which the CDCC calculations fail to describe is due to $1p$ stripping to the giant quadrupole resonance in ${}^{209}\mathrm{Bi}$ are supported by distorted wave Born approximation calculations, providing a novel illustration of $Q$-value matching in action.