Search Results (11)

We review the in-medium modifications of effective masses (Lorentz scalar potentials or phenomenon of mass shift) of the heavy–heavy and heavy–light mesons in symmetric nuclear matter and their nuclear bound states. We use a combined approach with the quark–meson coupling (QMC) model and an effective Lagrangian. As demonstrated by the cases of pionic and kaonic atoms, studies of the meson–nucleus bound state can provide us with important information on chiral symmetry in a dense nuclear medium. In this review, we examine the mesons, $K,K^{\ast },D,D^{\ast },B,B^{\ast },\eta ,{\eta }^{\prime },\varphi ,{\eta }_c,J/\psi ,{\eta }_b,\mathsf{{\rm Y}}$, and $B_c$, where our emphasis is on the heavy mesons. In addition, we also present some new results for the $B_c$-nucleus bound states. Full article

There is evidence that the properties of hadrons are modified in a nuclear medium. Information about the medium modifications of the internal structure of hadrons is fundamental for the study of dense nuclear matter and high-energy processes, including heavy-ion and nucleus–nucleus collisions. At the moment, however, empirical information about medium modifications of hadrons is limited; therefore, theoretical studies are essential for progress in the field. In the present work, we review theoretical studies of the electromagnetic and axial form factors of octet baryons in symmetric nuclear matter. The calculations are based on a model that takes into account the degrees of freedom revealed in experimental studies of low and intermediate square transfer momentum $q^2=-Q^2$: valence quarks and meson cloud excitations of baryon cores. The formalism combines a covariant constituent quark model, developed for a free space (vacuum) with the quark–meson coupling model for extension to the nuclear medium. We conclude that the nuclear medium modifies the baryon properties differently according to the flavor content of the baryons and the medium density. The effects of the medium increase with density and are stronger (quenched or enhanced) for light baryons than for heavy baryons. In particular, the in-medium neutrino–nucleon and antineutrino–nucleon cross-sections are reduced compared to the values in free space. The proposed formalism can be extended to densities above the normal nuclear density and applied to neutrino–hyperon and antineutrino–hyperon scattering in dense nuclear matter. Full article

The pseudo-spin symmetry (PSS) provides an important angle to understand nuclear microscopic structure and the novel phenomena found in unstable nuclei. The relativistic Hartree–Fock (RHF) theory, that takes the important degrees of freedom associated with the $\pi$-meson and $\rho$-tensor ($\rho$-T) couplings into account, provides an appropriate description of the PSS restoration in realistic nuclei, particularly for the pseudo-spin (PS) doublets with high angular momenta ($\tilde{l}$). The investigations of the PSS within the RHF theory are recalled in this paper by focusing on the effects of the Fock terms. Aiming at common artificial shell closures appearing in previous relativistic mean-field calculations, the mechanism responsible for the PSS restoration of high-$\tilde{l}$ orbits is stressed, revealing the manifestation of nuclear in-medium effects on the PSS, and thus, providing qualitative guidance on modeling the in-medium balance between nuclear attractions and repulsions. Moreover, the essential role played by the $\rho$-T coupling, that contributes mainly via the Fock terms, is introduced as combined with the relations between the PSS and various nuclear phenomena, including the shell structure and the evolution, novel halo and bubble-like phenomena, and the superheavy magicity. As the consequences of the nuclear force in complicated nuclear many-body systems, the PSS itself and the mechanism therein can not only deepen our understanding of nuclear microscopic structure and relevant phenomena, but also provide special insight into the nature of the nuclear force, which can further enrich our knowledge of nuclear physics. Full article

In this paper, we report a study of the low-lying states of deformed ²¹Ne within the framework of the quantum-number projected generator coordinate method (PGCM), starting from a chiral two-nucleon-plus-three-nucleon ($NN+3N$) interaction. The wave functions of states are constructed as a linear combination of a set of axially deformed Hartree–Fock–Bogliubov (HFB) wave functions with different quadrupole deformations. These HFB wave functions are projected onto different angular momenta and the correct neutron and proton numbers for ²¹Ne. The results of the calculations based on the effective Hamiltonians derived by normal-ordering the $3N$ interaction with respect to three different reference states, including the quantum-number projected HFB wave functions for ²⁰Ne, ²²Ne, and an ensemble of them with equal weights, are compared. This study serves as a key step towards ab initio calculations of odd-mass deformed nuclei with the in-medium GCM. Full article

We have studied wake effects on the dissociation of heavy quarkonia states J/ψ and Y by introducing an in-medium modification to the inter-quark potential. The wakes in the quark–gluon plasma were modeled using linear response theory using a dynamic dielectric function obtained from kinetic theory (Boltzmann equation) with a Bhatnagar–Gross–Krook (BGK) collision term. The in-medium modified potential was used to investigate the dissociation character depending on various parameters such as the velocity of quarkonium moving through the medium and the collision frequency. We have also calculated critical values of the dissociation temperature. Modifications of the dissociation energy due to wake-field effects were found. Full article

We explore the emergence of the collisional broadening of hadrons under the influence of different media using the hadronic transport approach SMASH (Simulating Many Accelerated Strongly interacting Hadrons), which employs vacuum properties and contains no a priori information about in-medium effects. In this context, we define collisional broadening as a decrease in the lifetime of hadrons, and it arises from an interplay between the cross-sections for inelastic processes and the available phase space. We quantify this effect for various hadron species, in both a thermal gas in equilibrium and in nuclear collisions. Furthermore, we distinguish the individual contribution of each process and verify the medium response to different vacuum assumptions; we see that the decay width that depends on the resonance mass leads to a larger broadening than a mass-independent scenario. Full article

In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (${\overline{\sigma }}_3=f_{K^{\pm }}-f_{K^0}$) and the third generator of the matrix of the explicit symmetry breaking [$h_3=m_{a_0}^2\left(f_{K^{\pm }}-f_{K^0}\right)$] are estimated in terms of the decay constants of the neutral ($f_K^0$) and charged Kaon ($f_{K^{\pm }}$) and the mass of $a_0$ meson. Both quantities ${\overline{\sigma }}_3$ and $h_3$ are then evaluated, at finite baryon (${\mu }_B$), isospin chemical potential (${\mu }_I$), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the ($T-{\mu }_I$) phase diagram In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (${\overline{\sigma }}_3=f_{K^{\pm }}-f_{K^0}$) and the third generator of the matrix of the explicit symmetry breaking [$h_3=m_{a_0}^2\left(f_{K^{\pm }}-f_{K^0}\right)$] are estimated in terms of the decay constants of the neutral ($f_K^0$) and charged Kaon ($f_{K^{\pm }}$) and the mass of $a_0$ meson. Both quantities ${\overline{\sigma }}_3$ and $h_3$ are then evaluated, at finite baryon (${\mu }_B$), isospin chemical potential (${\mu }_I$), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the ($T-{\mu }_I$) phase diagram. The in-medium modifications of pseudoscalars ($J^{pc}=0^{-+}$), scalars ($J^{pc}=0^{++}$), vectors ($J^{pc}=1^{--}$), and axial-vectors ($J^{pc}=1^{++}$) meson states are then analyzed in thermal and dense medium. We conclude that the QCD phase diagram ($T-{\mu }_I$) is qualitatively similar to the ($T-{\mu }_B$) phase diagram. We also conclude that both temperature and isospin chemical potential enhance the in-medium modifications of the meson states $a_0$, $\sigma$, ${\eta }^{\prime }$, $\pi$, $f_0$, $\kappa$, $\eta$, K, $\rho$, $\omega$, ${\kappa }^{*}$, $\varphi$, $a_1$, $f_1$, $K^{*}$, and $f_1^{*}$. Regarding their chemical potential, at high temperatures the various meson states likely dissolve into colored partonic phase. In this limit, the meson masses form a universal bundle. Thus, we conclude that the increase in the chemical potential similar to temperature derives the colorless confined meson states into the colored deconfined parton phase. Full article

Total pion yields and ${\pi }^{-}/{\pi }^{+}$ ratios in two Sn+Sn collision systems, ${}^{132}$Sn+${}^{124}$Sn (neutron rich) and ${}^{108}$Sn+${}^{112}$Sn (neutron poor) at $E=270A$ MeV, are significant observables in SAMURAI Pion-Reconstruction and Ion-Tracker (S$\pi$RIT) experiments. Based on a recently developed transport model, DaeJeon Boltzmann–Uehling–Uhlenbeck (DJBUU), we investigate the isospin-dependent inmedium effects by including density- and isospin-dependent cross sections for $\mathsf{\Delta }$ baryon productions. We compare our results with the S$\pi$RIT data by considering these effects. We find that the yields as well as the ratios strongly depend on the in-medium effect, especially isospin-dependent in-medium cross sections for $\mathsf{\Delta }$ resonances. Full article

In the first part of this work we study the color coherence phenomenon by considering the well-known quark-antiquark antenna with an in-medium hard gluon emission and an extra very soft emission outside it—double antenna. By discussing the coherence effects in terms of the survival probability, we generalize previous studies of the antenna radiation to the case of more than two emitters. After providing support to the jet quenching picture with effective emitters in the QCD cascade, we present a novel setup of an antenna splitting inside the medium taking into account the finite formation time of the dipole, which turns out to be an important scale. We read into the role of coherence and the relevant time scales which control the scenario, while also providing theoretical support for vacuum-like emissions early in the medium. Finally, by mapping the spectrum of in-medium splittings through the corresponding kinematical Lund diagram, we appreciate regimes of a close correspondence to a semi-classical description. Full article

Exploiting a stiff equation of state of the relativistic mean-field model MKVORH $\varphi$ with $\sigma$ -scaled hadron effective masses and couplings, including hyperons, we demonstrate that the existing neutron-star cooling data can be appropriately described within “the nuclear medium cooling scenario” under the assumption that different sources have different masses. Full article

This review focuses on the demonstration of an interrelation between various in-medium effects, which are manifested in the phenomena occurring in neutron stars and heavy-ion collisions. More specifically, the equation of state of a baryon-rich cold hadron matter is considered. It is done within the relativistic mean-field approach with $\sigma$ field-scaled hadron masses and couplings, and a cut-mechanism is discussed leading to an increase of the stiffness of the dense baryon matter. Then, I discuss the role of the viscosity and thermal conductivity in description of the first-order phase transitions occurring in heavy-ion collisions and neutron stars. Next, the p-wave polarization effects on pion and kaon spectra are studied beyond the mean-field level. In particular, the pion softening effect is detailed. Then, a role of in-medium effects in neutrino radiation of neutron stars is discussed and effects of the bulk and shear viscosities in the problem of r-mode damping in young rapidly rotating pulsars are considered. Full article