Kaon photo- and electroproduction off a proton near the production threshold are investigated by utilizing an isobar model. The background amplitude of the model is constructed from Feynman diagrams, whereas the resonance term is calculated by using the multipole formalism. It is found that both pseudoscalar and pseudovector models can nicely describe the available photoproduction data up to $W=50$ MeV above the threshold. The $\Lambda$ resonance $S_{01}(1800)$ is found to play an important role in improving the model. In the case of double polarization observables $O_{x^{\prime }}$ and $O_{z^{\prime }}$ our result corroborates the finding of Sandorfi et al. (arXiv:0912.3505 [nucl-th]). Due to the large contributions of the $K^{*}$ and $K_1$ vector mesons, extending the model to the case of electroproduction is almost impossible unless either special form factors that strongly suppress their contributions are introduced or all hadronic coupling constants are refitted to both photo- and electroproduction databases, simultaneously. It is also concluded that investigation of the kaon electromagnetic form factor is not recommended near the threshold region.

The total and differential cross sections for associated strangeness production in the $\mathit{pp}\to {\mathit{pK}}^{+}{K}^{-}p$ and $\mathit{pp}\to {\mathit{pK}}^{+}{\pi }^0{\Sigma }^0$ reactions have been studied in a unified approach using an effective Lagrangian model. It is assumed that both the $K^{-}p$ and ${\pi }^0{\Sigma }^0$ final states originate from the decay of the $\Lambda (1405)$ that was formed in the production chain $\mathit{pp}\to p(N^{*}(1535)\to K^{+}\Lambda (1405))$. The available experimental data are well reproduced, especially the ratio of the two total cross sections, which is much less sensitive to the particular model of the entrance channel. The significant coupling of the $N^{*}(1535)$ to $\Lambda (1405)K$ is further evidence for large $s\mathrm{s̄}$ components in the quark wave function of the $N^{*}(1535)$.

Expressing explicitly the parameters of the standard Skyrme interaction in terms of the macroscopic properties of asymmetric nuclear matter, we show in the Skyrme-Hartree-Fock approach that unambiguous correlations exist between observables of finite nuclei and nuclear matter properties. We find that existing data on neutron skin thickness $\Delta r_{\mathit{np}}$ of Sn isotopes give an important constraint on the symmetry energy $E_{\mathrm{sym}}({\rho }_0)$ and its density slope $L$ at saturation density ${\rho }_0$. Combining these constraints with those from recent analyses of isospin diffusion and the double neutron/proton ratio in heavy-ion collisions at intermediate energies leads to a more stringent limit on $L$ approximately independent of $E_{\mathrm{sym}}({\rho }_0)$. The implication of these new constraints on the $\Delta r_{\mathit{np}}$ of ${}^{208}\mathrm{Pb}$ as well as the core-crust transition density and pressure in neutron stars is discussed.

Yields, correlation shapes, and mean transverse momenta $p_T$ of charged particles associated with intermediate- to high-$p_T$ trigger particles ($2.5<p_T<10$ GeV/$c$) in $d+$ Au and Au $+$ Au collisions at $\sqrt{s_{{}_{\mathit{NN}}}}=200$ GeV are presented. For associated particles at higher $p_T\gtrsim 2.5$ GeV/$c$, narrow correlation peaks are seen in $d+$ Au and Au $+$ Au, indicating that the main production mechanism is jet fragmentation. At lower associated particle $p_T<2$ GeV/$c$, a large enhancement of the near- ($\Delta \varphi ~0$) and away-side ($\Delta \varphi ~\pi$) associated yields is found, together with a strong broadening of the away-side azimuthal distributions in Au $+$ Au collisions compared to $d+$ Au measurements, suggesting that other particle production mechanisms play a role. This is further supported by the observed significant softening of the away-side associated particle yield distribution at $\Delta \varphi ~\pi$ in central Au $+$ Au collisions.

We show how the measured particle ratios can be used to provide nontrivial information about the critical temperature of the QCD phase transition. This is obtained by including the effects of highly massive Hagedorn resonances on statistical models, which are used to describe hadronic yields. The inclusion of Hagedorn states creates a dependence of the thermal fits on the Hagedorn temperature, $T_H$, which is assumed to be equal to $T_c$, and leads to an overall improvement of thermal fits. We find that for $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy Ion Collider at $\sqrt{s_{\mathit{NN}}}=200$ GeV the best square fit measure, ${\chi }^2$, occurs at $T_c~176$ MeV and produces a chemical freeze-out temperature of $172.6$ MeV and a baryon chemical potential of $39.7$ MeV.

A microscopic approach has been employed to study the kaon productions in heavy-ion collisions. The momentum-integrated Boltzmann equation has been used to study the evolution of strangeness in the system formed in heavy-ion collisions at relativistic energies. The kaon productions have been calculated for different center-of-mass energies ($\sqrt{s_{\mathit{NN}}}$) ranging from the Alternating Gradient Synchrotron (AGS) to the Relativistic Heavy Ion Collider (RHIC). The results have been compared with available experimental data. We obtain a nonmonotonic hornlike structure for $K^{+}/{\pi }^{+}$ when plotted with $\sqrt{s_{\mathit{NN}}}$ with the assumption of an initial partonic phase beyond a certain threshold in $\sqrt{s_{\mathit{NN}}}$. However, a monotonic rise of $K^{+}/{\pi }^{+}$ is observed when a hadronic initial state is assumed for all $\sqrt{s_{\mathit{NN}}}$. Experimental values of $K^{-}/{\pi }^{-}$ are also reproduced within the ambit of the same formalism. Results from scenarios where the strange quarks and hadrons are formed in equilibrium and evolve with and without secondary productions have also been presented.

The search for mesons with non-quark-antiquark (exotic) quantum numbers has gone on for nearly 30 years. Currently there is experimental evidence of three isospin one states, the ${\pi }_1(1400)$, the ${\pi }_1(1600)$, and the ${\pi }_1(2015)$. For all of these states, there are questions about their identification and even if some of them exist. In this article, we will review both the theoretical work and the experimental evidence associated with these exotic quantum number states. We find that the ${\pi }_1(1600)$ could be the lightest exotic quantum number hybrid meson, but observations of other members of the nonet would be useful.

The differential cross sections for the neutrino-induced weak charged current production of strange particles in the threshold energy region are presented. The general representation of the weak hadronic current is newly developed in terms of eighteen unknown invariant amplitudes to parametrize the hadron vertex. The Born-term approximation is used for the numerical calculations in the framework of the Cabibbo theory and $\mathrm{SU}(3)$ symmetry. For unpolarized octet baryons four processes are investigated, whereas in the case of polarized baryons only one process is chosen to study the sensitivity of the differential cross section to the various polarizations of the initial-state nucleon and the final-state hyperon.

The center-depressed nuclear charge distributions are investigated with the parametrized distribution and the relativistic mean-field theory, and their corresponding charge form factors are worked out with the phase shift analysis method. The central depression of nuclear charge distribution of ${}^{46}\mathrm{Ar}$ and ${}^{44}\mathrm{S}$ is supported by the relativistic mean-field calculation. According to the calculation, the valence protons in ${}^{46}\mathrm{Ar}$ and ${}^{44}\mathrm{S}$ prefer to occupy the $1d_{3/2}$ state rather than the $2s_{1/2}$ state, which is different from that in the less neutron-rich argon and sulfur isotopes. As a result, the central proton densities of ${}^{46}\mathrm{Ar}$ and ${}^{44}\mathrm{S}$ are highly depressed, and so are their central charge densities. The charge form factors of some argon and sulfur isotopes are presented, and the minima of the charge form factors shift upward and inward when the central nuclear charge distributions are more depressed. Besides, the effect of the central depression on the charge form factors is studied with a parametrized distribution, when the root-mean-square charge radii remain constant.

We analyze the recently measured $v_2$ fluctuation in the context of establishing the degree of fluidity of the matter produced in heavy ion collisions. We argue that flow observables within systems with a non-negligible mean free path should acquire a “dynamical” fluctuation, due to the random nature of each collision between the system’s degrees of freedom. Because of this, $v_2$ fluctuations can be used to estimate the Knudsen number of the system produced at the Relativistic Heavy Ion Collider (RHIC). To illustrate this quantitatively, we apply the UrQMD model, with scaled cross sections, to show that collisions at RHIC have a Knudsen number at least one order of magnitude below the expected value for an interacting hadron gas. Furthermore, we argue that the Knudsen number is also bound from below by the $v_2$ fluctuation data, because too small a Knudsen number would break the observed scaling of $v_2$ fluctuations due to the onset of turbulent flow. We propose, therefore that $v_2$ fluctuation measurements, together with an understanding of the turbulent regime for relativistic hydrodynamics, will provide an upper as well as a lower limit for the Knudsen number. We also argue that an energy scan of $v_2$ fluctuations could shed light on the onset of the fluid regime.

At Large Hadron Collider energy, the expected large multiplicities suggest the presence of collective behavior even in $\mathit{pp}$ collisions. A hydrodynamical approach has been applied to estimate the expected elliptic flow measured by the azimuthal asymmetry parameter $v_2$ in $\mathit{pp}$ collisions at $\sqrt{s}=14\hspace{0.5em}\mathrm{TeV}$. $v_2$ of ${\pi }^{-}$ is found to be strongly dependent on the parton density profile inside a proton [e.g., surface diffuseness parameter ($\xi$)]. For $\xi =0.105\hspace{0.5em}\mathrm{fm}$, $v_2$ is found to be positive and larger compared to that at $\xi =0.25\hspace{0.5em}\mathrm{fm}$. The centrality dependence of $v_2$ has also been studied.

We solve the relativistic Riemann problem in viscous matter using the relativistic Boltzmann equation and the relativistic causal dissipative fluid-dynamical approach of Israel and Stewart. Comparisons between these two approaches clarify and point out the regime of validity of second-order fluid dynamics in relativistic shock phenomena. The transition from ideal to viscous shocks is demonstrated by varying the shear viscosity to entropy density ratio $\eta /s$. We also find that a good agreement between these two approaches requires a Knudsen number $\text{Kn}<1/2$.

The effect of nucleon-nucleon correlations in symmetric nuclear matter at finite temperature is studied beyond BCS theory. Starting from a Hartree-Fock description of nuclear matter with the Gogny effective interaction, we add correlations corresponding to the formation of preformed pairs and scattering states above the superfluid critical temperature within the in-medium $T$-matrix approach, which is analogous to the Nozières-Schmitt-Rink theory. We calculate the critical temperature for a BEC superfluid of deuterons, of a BCS superfluid of nucleons, and in the crossover between these limits. The effect of the correlations on thermodynamic properties (equation of state, energy, entropy) and the liquid-gas phase transition is discussed. Our results show that nucleon-nucleon correlations beyond BCS play an important role for the properties of nuclear matter, especially in the low-density region.

Vector analyzing power for the proton-${}^6\mathrm{He}$ elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target, which works at a low magnetic field of 0.09 T. The results are found to be incompatible with a $t$-matrix folding model prediction. Comparisons of the data with $g$-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The $\alpha$-core distribution in ${}^6\mathrm{He}$ is suggested to be a possible key for understanding the nuclear structure sensitivity.

The structure of proton unbound ${}^{30}\mathrm{S}$ states is important for determining the ${}^{29}\mathrm{P}$($p,\gamma$)${}^{30}\mathrm{S}$ reaction rate, which influences explosive hydrogen burning in classical novae and type I x-ray bursts. The reaction rate in this temperature regime had been previously predicted to be dominated by two low-lying, unobserved, $J^{\pi }=$ $3^{+}$ and $2^{+}$ resonances above the proton threshold in ${}^{30}\mathrm{S}$. To search for these levels, the structure of ${}^{30}\mathrm{S}$ was studied using the ${}^{32}\mathrm{S}$($p,t$)${}^{30}\mathrm{S}$ transfer reaction with a magnetic spectrograph. We have confirmed a previous detection of a state near 4700 keV, which had tentatively been assigned $J^{\pi }=3^{+}$. We have also discovered a new state at 4814(3) keV, which is a strong candidate for the other important resonance ($J^{\pi }=2^{+}$). The new ${}^{29}\mathrm{P}$($p,\gamma$)${}^{30}\mathrm{S}$ reaction rate is up to 4–20 times larger than previously determined rates over the relevant temperature range. The uncertainty in the reaction rate due to uncertainties in the resonance energies has been significantly reduced.

We investigate the influence of phenomenological three-nucleon interactions on the systematics of ground-state energies and charge radii throughout the whole nuclear mass range from ${}^4\mathrm{He}$ to ${}^{208}\mathrm{Pb}$. The three-nucleon interactions supplement unitarily transformed two-body interactions constructed within the unitary correlation operator method or the similarity renormalization group approach. To be able to address heavy nuclei as well, we treat the many-body problem in Hartree-Fock plus many-body perturbation theory, which is sufficient to assess the systematics of energies and radii, and limit ourselves to regularized three-body contact interactions. We show that even with such a simplistic three-nucleon interaction a simultaneous reproduction of the experimental ground-state energies and charge radii can be achieved, which is not possible with unitarily transformed two-body interactions alone.

Technical concepts are presented that improve the self-consistent treatment of vector mesons in a hot and dense medium. First applications concern an interacting gas of pions and $\rho$ mesons. As an extension of earlier studies, we thereby include random-phase-approximation-type vertex corrections and further use dispersion relations to calculate the real part of the vector-meson self-energy. An improved projection method preserves the four transversality of the vector-meson polarization tensor throughout the self-consistent calculations, thereby keeping the scheme void of kinematical singularities.