Vector Meson Couplings Research Articles

Vertex corrections due to the triangle singularity mechanism in the light axial vector meson couplings to K*K¯+ c.c.

The light axial vector mesons can couple to $K^*\bar{K}+c.c.$ in an $S$ wave at the tree level. Due to the near-threshold $S$-wave interactions the couplings can be affected by the final state interactions. It is of peculiar interest that the pion exchange between $K^*\bar{K}+c.c.$ can go through a triangle diagram which is within the kinematics of the triangle singularity (TS). This mechanism will introduce energy dependence and a $D$-wave amplitude to the vertex couplings. Hence, it should be necessary to investigate the role played by the $K^*\bar{K}+c.c.$ threshold in order to have a better understanding of the light axial vector spectrum.

Neutron star properties with careful parametrization in the vector and axial-vector meson extended linear sigma model

The existence of quark matter inside the cores of heavy neutron stars is a possibility which can be probed with modern astrophysical observations. We use a vector and axial-vector meson extended quark-meson model to describe quark matter in the core of neutron stars. We discover that an additional parameter constraint is necessary in the quark model to ensure chiral restoration at high densities. By investigating hybrid star sequences with various parameter sets, we show that low sigma meson masses are needed to fulfill the upper radius constraints and that the maximum mass of stable hybrid stars is only slightly dependent on the parameters of the crossover-type phase transition. Using this observation and results from recent astrophysical measurements, a constraint of $2.5<{g}_{V}<4.3$ is set for the constituent quark--vector meson coupling. The effect of a nonzero bag constant is also investigated, and we observe that its effect is small for values adopted in previous works.

Super-exceptional embedding construction of the heterotic M5: Emergence of SU(2)-flavor sector

A new super-exceptional embedding construction of the heterotic M5-brane's sigma-model was recently shown to produce, at leading order in the super-exceptional vielbein components, the super-Nambu-Goto (Green-Schwarz-type) Lagrangian for the embedding fields plus the Perry-Schwarz Lagrangian for the free abelian self-dual higher gauge field. Beyond that, further fields and interactions emerge in the model, arising from probe M2- and probe M5-brane wrapping modes. Here we classify the full super-exceptional field content and work out some of its characteristic interactions from the rich super-exceptional Lagrangian of the model. We show that SU(2)×U(1)-valued scalar and vector fields emerge from probe M2- and M5-branes wrapping the vanishing cycle in the A1-type singularity; together with a pair of spinor fields of U(1)-hypercharge ±1 and each transforming as SU(2) iso-doublets. Then we highlight the appearance of a WZW-type term in the super-exceptional PS-Lagrangian and find that on the electromagnetic field it gives the first-order non-linear DBI-correction, while on the iso-vector scalar field it has the form characteristic of the coupling of vector mesons to pions via the Skyrme baryon current. We discuss how this is suggestive of a form of SU(2)-flavor chiral hadrodynamics emerging on the single (N=1) M5 brane, different from, but akin to, holographic large-N QCD.

Weak magnetic field corrections to light vector or axial mesons mixings and vector meson dominance

Weak magnetic-field-induced corrections to effective coupling constants describing light vector meson mixing and vector meson dominance (VMD) are derived. The magnetic field must be weak with respect to an effective quark mass M* such that: or . On that basis, a flavor SU(2) quark–quark interaction due to a non-perturbative one gluon exchange is considered. By means of methods usually applied to the Nambu—Jona-Lasinio and global color models, the equations for leading light vector/axial meson coupling to a background electromagnetic field are derived. The corresponding effective coupling constants are resolved in structureless mesons and long-wavelength limits. Some of the resulting coupling constants are redefined, so as to become magnetic-field-induced corrections to vector or axial meson couplings. Due to the approximated chiral symmetry of the model, light axial meson mixing induced by the magnetic field is also obtained. Numerical estimates are presented for the coupling constants and some of the corresponding momentum-dependent form factors. The contributions of the induced VMD and vector meson mixing couplings for the low-momentum pion electromagnetic form factor and for the (off-shell) charge symmetry violation potential at the constituent quark level are estimated. The relative overall weak magnetic-field-induced anisotropic corrections are of the order of , where n = 2 or n = 1, respectively.

Chiral constraints on the isoscalar electromagnetic spectral functions of the nucleon from leading order vector meson couplings

Using baryon chiral perturbation theory including vector mesons, we analyze various continuum contributions to the isoscalar electromagnetic spectral functions of the nucleon induced by the leading order couplings.

Third family of compact stars within a nonlocal chiral quark model equation of state

A class of hybrid compact star equations of state is investigated that joins by a Maxwell construction a low-density phase of hadronic matter, modeled by a relativistic meanfield approach with excluded nucleon volume, with a high-density phase of color superconducting two-flavor quark matter, described within a nonlocal covariant chiral quark model. We find the conditions on the vector meson coupling in the quark model under which a stable branch of hybrid compact stars occurs in the cases with and without diquark condensation. We show that these hybrid stars do not form a third family disconnected from the second family of ordinary neutron stars unless additional (de)confining effects are introduced with a density-dependent bag pressure. A suitably chosen density dependence of the vector meson coupling assures that at the same time the $2~$M$_\odot$ maximum mass constraint is fulfilled on the hybrid star branch. A twofold interpolation method is realized which implements both, the density dependence of a confining bag pressure at the onset of the hadron-to-quark matter transition as well as the stiffening of quark matter at higher densities by a density-dependent vector meson coupling. For three parametrizations of this class of hybrid equation of state the properties of corresponding compact star sequences are presented, including mass twins of neutron and hybrid stars at 2.00, 1.39 and 1.20 $M_\odot$, respectively. The sensitivity of the hybrid equation of state and the corresponding compact star sequences to variations of the interpolation parameters at the 10% level is investigated and it is found that the feature of third family solutions for compact stars is robust against such a variation. This advanced description of hybrid star matter allows to interpret GW170817 as a merger not only of two neutron stars but also of a neutron star with a hybrid star or of two hybrid stars.

Electromagnetic couplings of radially excited light vector mesons from QCD sum rules

The couplings of unflavored vector mesons to the $e^+e^-$ annihilation are an important source of information on the nature and structure of these resonances which play a prominent role in the hadron phenomenology. The couplings of many radially excited heavy vector mesons are measured, while the corresponding couplings for light vector mesons are not known. We propose a phenomenological method allowing to estimate these unknown couplings. The method is suggested by our observation that the electromagnetic coupling of the $n$-th radial excitation of $S$-wave heavy vector meson decouples from the $e^+e^-$ annihilation with nearly exponential rate with $n$. It becomes natural to assume that the same effect takes place in the light vector mesons and this would allow to estimate the unknown couplings. We tested this assumption with the help of a generalized version of borelized QCD spectral sum rules saturated by a linear radial trajectory of meson states taken from the phenomenology. This leads to a consistent setup which is able to predict the decoupling rate. The calculated rate turned out to be almost the same as in the heavy vector mesons. Our result may be interpreted as an effective account for non-trivial electromagnetic formfactor in meson decays to $e^+e^-$, thus looking beyond the large-$N_c$ limit. On the one hand, we argue that the given decoupling does not necessary contradict to the previous large-$N_c$ results for the Regge like meson spectra.

There is only one set of the correct values of fF, fD and fS coupling constants in SU(3) invariant Lagrangian of the vector-meson-baryon interactions

One can prove, there is generally eight various ω − ø mixings forms in elementary particle physics, which on one side give different forms of the vector-meson-nucleon coupling constants through fF, fD and fS in SU(3) invariant Lagrangian of the vector-meson-baryon interactions, and on the other side different signs of the universal vector-meson coupling constants fρ, fω and fø. Identical set of numerical values of fF, fD and fS is evaluated only in that case, if the same ω − ø mixing is applied to a derivation of the vectormeson-nucleon coupling constant forms and also to the signs of the universal vector-meson coupling constants fρ, fω and fø.

Dispersion theoretical analysis of the nucleon form factors

We review the achievements of the project C.2 , that deals with a dispersion theoretical analysis of the nucleon form factors. We have analyzed the world data for the space-like and time-like form factors to extract nucleon radii and vector meson coupling constants. Our proton charge radius r P E ≃ 0.85 fm has gained prominence in the so-called proton radius puzzle, see Ref. [1]. We also have analyzed the strong energy dependence of the e + e − → pp amplitude at the nucleon-antinucleon threshold, two-photon exchange effects and isospin violation in the isovector nucleon form factors.

Effects of Tensor Couplings on Nucleonic Direct URCA Processes in Neutron Star Matter**Supported by the National Natural Science Foundation of China under Grant Nos 11447165, 11373047 and 11265009, and the Youth Innovation Promotion Association of Chinese Academy of Sciences under Grant No 2016056.

The relativistic neutrino emissivity of the nucleonic direct URCA processes in neutron star matter is investigated within the relativistic Hartree—Fock approximation. We particularly study the influences of the tensor couplings of vector mesons ω and ρ on the nucleonic direct URCA processes. It is found that the inclusion of the tensor couplings of vector mesons ω and ρ can slightly increase the maximum mass of neutron stars. In addition, the results indicate that the tensor couplings of vector mesons ω and ρ lead to obvious enhancement of the total neutrino emissivity for the nucleonic direct URCA processes, which must accelerate the cooling rate of the non-superfluid neutron star matter. However, when considering only the tensor coupling of vector meson ρ, the neutrino emissivity for the nucleonic direct URCA processes slightly declines at low densities and significantly increases at high densities. That is, the tensor coupling of vector meson ρ leads to the slow cooling rate of a low-mass neutron star and rapid cooling rate of a massive neutron star.

Numerical values of thefF,fD, andfScoupling constants in the SU(3) invariant interaction Lagrangian of the vector-meson nonet with1/2+octet baryons

It is demonstrated how an utilization of all existing experimental information on electric and magnetic nucleon form factors, to be described by the Unitary and Analytic (U\&A) nucleon electromagnetic structure model in space-like and time-like regions simultaneously, can provide numerical values of $f^F$, $f^D$, $f^S$ coupling constants in $SU(3)$ invariant interaction Lagrangian of the vector-meson nonet with $1/2^+$ octet baryons. The latter, together with universal vector-meson coupling constants $f_V$, play an essential role in a prediction of $1/2^+$ octet hyperon electromagnetic form factors behaviors.

Relativistic mean-field models with scaled hadron masses and couplings: Hyperons and maximum neutron star mass

An equation of state of cold nuclear matter with an arbitrary isotopic composition is studied within a relativistic mean-field approach with hadron masses and coupling constants depending self-consistently on the scalar mean-field. All hadron masses decrease universally with the scalar field growth, whereas meson–nucleon coupling constants can vary differently. More specifically we focus on two modifications of the KVOR model studied previously. One extension of the model (KVORcut) demonstrates that the equation of state stiffens if the increase of the scalar-field magnitude with the density is bounded from above at some value for baryon densities above the saturation nuclear density. This can be realized if the nucleon vector–meson coupling constant changes rapidly as a function of the scalar field slightly above the desired value. The other version of the model (MKVOR) utilizes a smaller value of the nucleon effective mass at the nuclear saturation density and a saturation of the scalar field in the isospin asymmetric matter induced by a strong variation of the nucleon isovector–meson coupling constant as function of the scalar field. A possibility of hyperonization of the matter in neutron star interiors is incorporated. Our equations of state fulfill majority of known empirical constraints including the pressure-density constraint from heavy-ion collisions, direct Urca constraint, gravitational-baryon mass constraint for the pulsar J0737-3039B, and the constraint on the maximum mass of the neutron stars.

Compact stars in a SU(3) quark-meson model

The recent observations of the massive pulsars PSR J1614-2230 and of PSR J0348+0432 with about two solar masses implies strong constraints on the properties of dense matter in the core of compact stars. Effective models of QCD aiming to describe neutron star matter can thereby be considerably constrained. In this context, a chiral quark-meson model based on a SU(3) linear $\sigma$-model with a vacuum pressure and vector meson exchange is discussed in this work. The impact of its various terms and parameters on the equation of state and the maximum mass of compact stars are delineated to check whether pure quark stars with two solar masses are feasible within this approach. Large vector meson coupling constant and a small vacuum pressure allow for maximum masses of two or more solar masses. However, pure quark stars made of absolutely stable strange quark matter, so called strange stars, turn out to be restricted to a quite small parameter range.

Equivalence Between Vector Meson Dominance and Unitarised Chiral Perturbation Theory

It is explicitly shown that either the approximate solution of the integral equation for the inverse of the pion form facto,r or the result of the Pad\(\text{\'e}\) approximant method of resumming the one loop Chiral Perturbation Theory (CPTH) are equivalent to the standard vector meson dominance (VMD) models, using the vector meson coupling to two pseudoscalars given by the KSRF relation. Inconsistencies between the one loop CPTH and its unitarised version (or the VMD model) are pointed out. The situation is better for the CPTH calculation of the scalar form factor and the related S-wave $\pi \pi$ scattering. The branching ratios of \(\tau \to \pi^+ \pi^0 \nu \), \(\tau \to K \pi \nu \), \(\tau \to K^+ \eta \nu\) and $\tau \to K^+ \bar{K^0} \nu\) using only two inputs as the \(\rho\) and \(K^*\) masses, or the two corresponding rms radii, agree with the experimental data. Using the same number of parameters, the corresponding one loop CPTH calculation cannot explain the $\tau$ data.

Equation of state with an extended SU(3) quark-meson model under conditions prevailing in core collapse supernovae

The quark-meson model is investigated for the two- and three-flavor case extended by contributions of vector mesons under conditions encountered in core-collapse supernova matter. Typical temperature ranges, densities and electron fractions, as found in core-collapse supernova simulations, are studied by implementing charge neutrality and local beta-equilibrium with respect to weak interactions. Within this framework, we analyze the resulting phase diagram and equation of state (EoS) and investigate the impact of undetermined parameters of the model. The EoS turns out to be relatively independent on the entropy per baryon but there are significant changes when going from the two-flavor to the three-flavor case due to the nontrivial contribution from the strange quarks which stay massive even at high densities. While an increasing vector meson coupling constant leads to a substantial stiffening of the EoS, we find that the impact of changing the scalar meson mass is equally strong and results in a softening of the EoS for increasing values.

Phase diagrams in nonlocal Polyakov-Nambu-Jona-Lasinio models constrained by lattice QCD results

Based on lattice QCD-adjusted SU(2) nonlocal Polyakov--Nambu--Jona-Lasinio (PNJL) models, we investigate how the location of the critical endpoint in the QCD phase diagram depends on the strenght of the vector meson coupling, as well as the Polyakov-loop (PL) potential and the form factors of the covariant model. The latter are constrained by lattice QCD data for the quark propagator. The strength of the vector coupling is adjusted such as to reproduce the slope of the pseudocritical temperature for the chiral phase transition at low chemical potential extracted recently from lattice QCD simulations. Our study supports the existence of a critical endpoint in the QCD phase diagram albeit the constraint for the vector coupling shifts its location to lower temperatures and higher baryochemical potentials than in the case without it.

Three-body couplings in RMF and its effects on hyperonic star equation of state

We develop a relativistic mean field (RMF) model with explicit three-body couplings and apply it to hyperonic systems and neutron star matter. Three-baryon repulsion is a promising ingredient to answer the massive neutron star puzzle; when strange hadrons such as hyperons are taken into account, the equation of state (EOS) becomes too soft to support the observed two-solar-mass neutron star. We demonstrate that it is possible to consistently explain the massive neutron star and hypernuclear data when we include three-body couplings and modify the hyperon–vector meson couplings from the flavor SU(3) value.

Neutron Star Properties in the Chiral Quark–Meson Coupling Model

We study the properties of neutron stars using the chiral quark–meson coupling model, in which the quark–quark hyperfine interaction due to the exchanges of gluon and pion based on chiral symmetry is considered. We also examine the effects of hyperons and Δ-isobars in a neutron star. Extending the SU(6) spin-flavor symmetry to more general SU(3) flavor symmetry in the vector–meson couplings to baryons, the maximum mass of neutron star can reach the recently observed massive pulsar mass, $${1.97 \pm 0.04 M_{\odot}}$$ . In this calculation, Λ and Ξ are generated in a neutron star, while Σ and Δ-isobars do not appear.

EQUATION OF STATE FOR MASSIVE NEUTRON STARS

Using relativistic Hartree-Fock approximation, we investigate the properties of the neutron-star matter in detail. In the present calculation, we consider not only the tensor coupling of vector mesons to octet baryons and the form factors at interaction vertexes but also the internal (quark) structure change of baryons in dense matter. The relativistic Hartree-Fock calculations are performed in two ways: one is the calculation with the coupling constants determined by SU(6) (quark model) symmetry, the other is with the coupling constants based on SU(3) (flavor) symmetry. For the latter case, we use the latest Nijmegen (ESC08) model. Then, it is very remarkable that the particle composition of the core matter in SU(3) symmetry is completely different from that in SU(6) symmetry. In SU(6) symmetry, all octet baryons appear in the density region below $\sim 1.2$ fm$^{-3}$, while, in the ESC08 model, only the \Xi^- hyperon is produced. Furthermore, the medium modification of the internal baryon structure hardens the equation of state for the core matter. Taking all these effects into account, we can obtain the maximum neutron-star mass which is consistent with the recently observed mass, 1.97 \pm 0.04 M_\sun (PSR J1614-2230). We therefore conclude that the extension from SU(6) symmetry to SU(3) symmetry in the meson-baryon couplings and the internal baryon-structure variation in matter certainly enhance the mass of neutron star. Furthermore, the effects of the form factor at vertex and the Fock contribution including the tensor coupling due to the vector mesons are indispensable to describe the core matter. In particular, the Fock term is very vital in reproducing the preferable value of symmetry energy, a_4 (\simeq 30 - 40 MeV), in nuclear matter.

Effects of Fock term, tensor coupling and baryon structure variation on a neutron star

The equation of state for neutron matter is calculated within relativistic Hartree–Fock approximation. The tensor couplings of vector mesons to baryons are included, and the change of baryon internal structure in matter is also considered using the quark–meson coupling model. We obtain the maximum neutron-star mass of ∼2.0M⊙, which is consistent with the recently observed, precise mass, 1.97±0.04M⊙. The Fock contribution is very important and, in particular, the inclusion of tensor coupling is vital to obtain such large mass. The baryon structure variation in matter also enhances the mass of a neutron star.