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The global spin alignment of vector mesons has been observed by the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). It provides a unique opportunity to probe the correlation between the polarized quark and antiquark in the strongly coupled quark-gluon plasma (sQGP) produced in relativistic heavy ion collisions, opening a new window to explore the properties of sQGP. In addition, spin alignments of vector mesons have also been observed in other high-energy particle collisions such as e + e − annihilations at high energies where hadron production is dominated by quark fragmentation mechanism. The results obtained are quite different from those obtained in heavy ion collisions where quark coalescence/combination mechanism dominates suggesting strong dependence on hadronization mechanisms. So comprehensive studies in different hadronization processes are needed. In this article, we present a brief review of theoretical and experimental advances in the study of vector meson’s spin alignments in a variety of high-energy particle collisions, with emphasis on hadronization mechanisms.

The rho meson has long been successfully identified with a dynamical gauge boson of Hidden Local Symmetry (HLS) Hlocal in the non-linear sigma model G/H gauge equivalent to the model having the symmetry Gglobal×Hlocal, with G=[SU(2)L×SU(2)R]≃O(4),H=SU(2)V≃O(3). However, under a hitherto unproven assumption that its kinetic term is dynamically generated, together with an ad hoc choice of the auxiliary field parameter “a=2”, we prove this assumption, thereby solving the long-standing mystery. The rho meson kinetic term is generated simply by the large N limit of the Grassmannian model G/H=O(N)/[O(N−3)×O(3)] gauge equivalent to O(N)global×[O(N−3)×O(3)]local, extrapolated to N=4, O(4)global×O(3)local, with all the phenomenologically successful “a=2 results”, i.e., ρ-universality, KSRF relation, and the Vector Meson Dominance, realized independently of the parameter “a”. This in turn establishes validity of the large N dynamics at the quantitative level directly by the experiments. The relevant cutoff reads Λ≃4πFπ for N=4, which is regarded as a matching scale of the HLS as a “magnetic dual” to QCD. Skyrmion is stabilized by such a dynamically generated rho meson without recourse to the underlying QCD, a further signal of the duality. The unbroken phase with a massless rho meson may be realized as a novel chiral-restored hadronic phase in the hot/dense QCD.

The roles of the lightest vector mesons ρ and ω in the multi-Skyrmion states are studied using the hidden local symmetry approach up to the next-to-leading order, including the homogeneous Wess-Zumino terms. The low-energy constants in the effective field theory are determined using the Sakai-Sugimoto model and the flat-space five-dimensional Yang-Mills action. With only two inputs, m ρ and f π , it is possible to determine all low-energy constants without ambiguity. The vector meson effects can be investigated by sequentially integrating vector mesons, and their geometry can be elucidated by comparing the results using the low-energy constants estimated from the Sakai-Sugimoto model and the flat-space five-dimensional Yang-Mills action. We found that the ρ meson reduces the masses of the multi-Skyrmion states and increases the overlaps of their constituents, whereas the ω meson repulses the constituents of the multi-Skyrmion states and increases their masses. Therefore, these vector mesons are crucial in the Skyrme model approach to nuclei. We also found that the warping factor, an essential element in the holographic model of QCD, affects the properties of the multi-Skyrmion states and cannot be ignored.

In this paper, we analyze the application of an analytical gluon distribution based on double-asymptotic scaling to the photoproduction of vector mesons in coherent pp, pA, and AA collisions at LHC energies, using the color dipole formalism. Predictions for the rapidity distribution are presented for ρ0, J/ψ, ψ(2S), and Υ(1S) mesons photoproduction. An analysis of the uncertainties associated with different implementations of the dipole–proton amplitude is performed. The vector meson photoproduction accompanied by electromagnetic dissociation is also analyzed.

The star matter composed of nucleons deep inside compact stars, such as neutron stars, is believed to be very dense, such that various types of new concepts and physical phenomena are naturally expected due to the nontrivial strong correlations between hadrons. The possibility of revealing the hidden scale symmetry in dense baryonic matter has been discussed recently, to uncover the pseudo-conformal phase in dense star matter. In the pseudo-conformal phase, the trace of the energy–momentum tensor becomes density-independent, and the speed of sound approaches the conformal velocity in scale symmetric matter. Interestingly, it is also observed that the effective nucleon mass becomes a density-independent finite quantity, which can be identified as the chiral invariant mass of the parity doublet model, indicating that the parity doubling is an emergent phenomenon. In this paper, we will discuss how parity-doubling symmetry emerges inside the core of a compact star as a consequence of the interplays between ω vector mesons and nucleons (or dilaton, χ, equivalently) and between the chiral symmetry and the scale symmetry.

We study the reactions γγ → π 0 π 0 , π + π − , , K + K − , ηη and π 0 η based on a chiral Lagrangian with dynamical light vector mesons as formulated within the hadrogenesis conjecture. At present our chiral Lagrangian contains five unknown parameters that are relevant for the photon-fusion reactions. They parameterize the strength of interaction terms involving two vector meson fields. These parameters are fitted to photon-fusion data γγ → π 0 π 0 , π + π − , π 0 η and to the decay η → π 0 γγ . In order to derive gauge invariant reaction amplitudes in the resonance region constraints from maximal analyticity and exact coupled-channel unitarity are used. Our results are in good agreement with the existing experimental data from threshold up to about 0.9 GeV for the two-pion final states. The a 0 meson in the π 0 η channel is dynamically generated and an accurate reproduction of the γγ → π 0 η data is achieved up to 1.2 GeV. Based on our parameter sets we predict the γγ → , K + K − , ηη cross sections.

In this paper, we prove the existence of topologically non-trivial solutions of the two-dimensional Adkins–Nappi model of nuclear physics; to this end, we minimize the energy functional by using the classical Skyrme ansatz, as well as a non-radially symmetric generalization of it. In both cases, we show that the minimization procedure preserves the topological degree of the minimization sequence.

Electromagnetic and weak semileptonic decays of light mesons with the production of pairs l + l − and lν l are calculated within the quark model based on an effective four-quark interaction. Quark diagrams with meson vertices VPA, VVP and VPP are considered. Theoretical estimations for decay widths are obtained. The dominant role of channels with axial-vector meson in weak decays are shown. A number of predictions for future experiments are presented.

In this paper, a systematic investigation is conducted to explore the potential molecular states formed by heavy meson pairs D(∗)D(∗) and D(∗)D¯(∗) with the complex scaling method, in the framework of the one-boson-exchange (OBE) model. The exchange interactions are mediated by the pseudoscalar, scalar and vector mesons(π, σ, ρ, ω). The interaction potential within the OBE model is derived using the Bonn approximation, followed by the application of the complex scaling method to determine the bound and resonant states. The results demonstrate that the D(∗)D(∗) and D(∗)D¯(∗) systems can form not only multiple bound states, but also several P-wave resonant states. In the hadronic molecular state framework, the X(3872), Tcc+, and Zc(3900) states can be consistently explained as bound states, while the G(3900) can be interpreted as a P-wave resonant state. Furthermore, we also predict other new bound and resonant states, which have the potential to be observed experimentally.

We investigate the decays of \\[B^0_s\\], \\[B^0\\] and \\[B^-\\] into \\[ _c\\] plus a scalar or vector meson in a theoretical framework by taking into account the dominant process for the weak decay of \\[B\\] meson into \\[ _c\\] and a \\[qq\\] pair. After hadronization of this \\[qq\\] component into pairs of pseudoscalar mesons we obtain certain weights for the pseudoscalar meson-pseudoscalar meson components. In addition, the \\[B^0\\] and \\[B^0_s\\] decays into \\[ _c\\] and \\[ ^0\\], \\[K^*\\] are evaluated and compared to the \\[ _c\\] and \\[ \\] production. The calculation is based on the postulation that the scalar mesons \\[f_0(500)\\], \\[f_0(980)\\] and \\[a_0(980)\\] are dynamically generated states from the pseudoscalar meson-pseudoscalar meson interactions in S-wave. Up to a global normalization factor, the \\[ \\], \\[K K\\] and \\[ \\] invariant mass distributions for the decays of \\[B^0_s _c ^+ ^-\\], \\[B^0_s _c K^+ K^-\\], \\[B^0 _c ^+ ^-\\], \\[B^0 _c K^+ K^-\\], \\[B^0 _c ^0 \\], \\[B^- _c K^0 K^-\\] and \\[B^- _c ^- \\] are predicted. Comparison is made with the limited experimental information available and other theoretical calcualtions. Further comparison of these results with coming LHCb measurements will be very valuable to make progress in our understanding of the nature of the low lying scalar mesons, \\[f_0(500), f_0(980)\\] and \\[a_0(980)\\].