We study scalar, pseudoscalar, vector, and axial-vector mesons with nonstrange and strange quantum numbers in the framework of a linear sigma model with global chiral $U(N_f{)}_L\times U(N_f{)}_R$ symmetry. We perform a global fit of meson masses, decay widths, as well as decay amplitudes. The quality of the fit is, for a hadronic model that does not consider isospin-breaking effects, surprisingly good. We also investigate the question whether the scalar $\overline{q}q$ states lie below or above 1 GeV and find the scalar states above 1 GeV to be preferred as $\overline{q}q$ states. Additionally, we also describe the axial-vector resonances as $\overline{q}q$ states.

The chiral phase transition of the strongly interacting matter is investigated at nonzero temperature and baryon chemical potential (${\mu }_B$) within an extended ($2+1$) flavor Polyakov constituent quark-meson model that incorporates the effect of the vector and axial vector mesons. The effect of the fermionic vacuum and thermal fluctuations computed from the grand potential of the model is taken into account in the curvature masses of the scalar and pseudoscalar mesons. The parameters of the model are determined by comparing masses and tree-level decay widths with experimental values in a ${\chi }^2$-minimization procedure that selects between various possible assignments of scalar nonet states to physical particles. We examine the restoration of the chiral symmetry by monitoring the temperature evolution of condensates and the chiral partners’ masses and of the mixing angles for the pseudoscalar $\eta -{\eta }^{\prime }$ and the corresponding scalar complex. We calculate the pressure and various thermodynamical observables derived from it and compare them to the continuum extrapolated lattice results of the Wuppertal-Budapest collaboration. We study the $T-{\mu }_B$ phase diagram of the model and find that a critical endpoint exists for parameters of the model, which give acceptable values of ${\chi }^2$.

The existence of quark matter inside the heaviest neutron stars has been the topic of numerous recent studies, many of them suggesting that a phase transition to strongly interacting conformal matter inside neutron stars is feasible. Here we examine this hybrid star scenario using a soft and a stiff hadronic model, a constituent quark model with three quark flavors, and applying a smooth crossover transition between the two. Within a Bayesian framework, we study the effect of up-to-date constraints from neutron star observations on the equation-of-state (EOS) parameters and various neutron star observables. Our results show that a pure quark core is only possible if the maximum mass of neutron stars is below $\sim 2.35M_{\odot }$. However, we also find, consistent with other studies, that a peak in the speed of sound, exceeding $1/3$, is highly favored by astrophysical measurements, which might indicate the percolation of hadrons at $\sim 3–4n_0$. Even though our prediction for the phase transition parameters varies depending on the specific astrophysical constraints utilized, the position of the speed of sound peak only changes slightly, while the existence of pure quark matter below $\sim 4n_0$, using our parametrization, is disfavored. On the other hand, the preferred range for the EOS shows signs of conformality above $\sim 4n_0$. Additionally, we present the difference in the upper bounds of radius estimates using the full probability density data and sharp cutoffs and stress the necessity of using the former.

The boundary of the first order chiral phase transition region is studied in the $m_{\pi }-m_K-{\mu }_B$ space using the one-loop optimized perturbation theory for the resummation of the perturbative series. Chiral perturbation theory for mesons and baryons is used for the $T=0$ parametrization of the model. The surface of second order transition points bends with increasing ${\mu }_B$ towards the physical point of the $m_{\pi }-m_K$ mass plane allowing for the existence of the critical end point in the ${\mu }_B-T$ plane at the physical point. The location and scaling region of the CEP is explored.

We comment on the paper of S. Postnikov et al. [ Phys. Rev. D 82, 024016 (2010)] and give a modified formula that needs to be taken into account when calculating the tidal Love number of neutron stars in case a first order phase-transition occurs at nonzero pressure. We show that the error made when using the original formula tends to zero as $p\to 0$, and we estimate the maximum relative error to be $\sim 5\%$ if the density discontinuity is at larger densities.

The Cosmic-Ray Extremely Distributed Observatory (CREDO) is a newly formed, global collaboration dedicated to observing and studying cosmic rays (CR) and cosmic-ray ensembles (CRE): groups of at least two CR with a common primary interaction vertex or the same parent particle. The CREDO program embraces testing known CR and CRE scenarios, and preparing to observe unexpected physics, it is also suitable for multi-messenger and multi-mission applications. Perfectly matched to CREDO capabilities, CRE could be formed both within classical models (e.g., as products of photon–photon interactions), and exotic scenarios (e.g., as results of decay of Super-Heavy Dark Matter particles). Their fronts might be significantly extended in space and time, and they might include cosmic rays of energies spanning the whole cosmic-ray energy spectrum, with a footprint composed of at least two extensive air showers with correlated arrival directions and arrival times. As the CRE are predominantly expected to be spread over large areas and, due to the expected wide energy range of the contributing particles, such a CRE detection might only be feasible when using all available cosmic-ray infrastructure collectively, i.e., as a globally extended network of detectors. Thus, with this review article, the CREDO Collaboration invites the astroparticle physics community to actively join or to contribute to the research dedicated to CRE and, in particular, to pool together cosmic-ray data to support specific CRE detection strategies.