Meson-nucleon Coupling Constants Research Articles

ΔS = 0 hadronic parity violation in next-to-leading order QCD: Anomalous dimension matrices and their implications

We construct the effective Hamiltonian for hadronic parity violation in strangeness-nonchanging (ΔS=0) processes in next-to-leading order (NLO) in QCD, for all isosectors, and at a renormalization scale of 2GeV, thus extending our earlier leading-order (LO) analysis [1,2]. Hadronic parity violation, studied in the context of the low-energy interactions of nucleons and nuclei, exposes the complex interplay of weak and strong interactions in these systems, and thus supports our extension to NLO. Here we exploit the flavor-blind nature of QCD interactions to construct the needed anomalous dimension matrices from those computed in flavor physics, which we then use to refine our effective Hamiltonian and finally our predicted parity-violating meson-nucleon coupling constants, to find improved agreement with few-body experiments.

Toward a unified treatment of ΔS=0 parity violation in low-energy nuclear processes

We revisit the unified treatment of low-energy hadronic parity violation espoused by Desplanques, Donoghue, and Holstein to the end of an ab initio treatment of parity violation in low-energy nuclear processes within the standard model. We use our improved effective Hamiltonian and precise nonperturbative assessments of the quark charges of the nucleon within lattice quantum chromodynamics (QCD) to make new assessments of the parity-violating meson-nucleon coupling constants. Comparing with recent, precise measurements of hadronic parity violation in few-body nuclear reactions, we find improved agreement with these experimental results, though some tensions remain. We thus note the broader problem of comparing low-energy constants from nuclear and few-nucleon systems, considering, too, unresolved theoretical issues in connecting an ab initio, effective Hamiltonian approach to chiral effective theories. We note how future experiments and lattice QCD studies could sharpen the emerging picture, promoting the study of hadronic parity violation as a laboratory for testing ``end-to-end'' theoretical descriptions of weak processes in hadrons and nuclei at low energies.

A_{1} meson-nucleon coupling constant at finite temperature from the soft-wall AdS/QCD model

We study the temperature dependence of the a_1 meson-nucleon coupling constant in the framework of the soft-wall AdS/QCD model with thermal dilaton field. Profile functions for the axial-vector and fermion fields in the AdS-Schwarzschild metric are presented. It is constructed an interaction Lagrangian for the fermion-axial-vector-thermal dilaton fields system in the bulk of space-time. From this Lagrangian integral representation for the g_{a_1NN} coupling constant is derived. The temperature dependence of this coupling constant is numerically analyzed.

Temperature dependence of ρ meson-nucleon coupling constant from the AdS/QCD soft-wall model

We investigate the dependence of the $\rho$ meson-nucleon coupling constant on the temperature of the medium using the soft-wall model of AdS/QCD. The finite temperature profile functions for the vector and fermion fields are applied to the model having a thermal dilaton field. The interaction Lagrangian in the bulk between these fields is written as in zero temperature case and includes minimal- and magnetic-type interactions. The temperature dependence of the $g_{\rho NN}(T)$ coupling constant and its terms are plotted. We observe that the coupling constant and its separate terms become zero at the medium temperature near the Hawking temperature of phase transition.

A1-meson-baryon coupling constants in the framework of soft-wall and hard-wall AdS/QCD models

We calculate the [Formula: see text]-meson-nucleon ([Formula: see text]-baryon) coupling constant in the framework of soft-wall and hard-wall AdS/QCD models. Interaction Lagrangian in the bulk of AdS space was written for a minimal gauge coupling, a magnetic type coupling and a triple coupling of bulk fields. Applying AdS/CFT correspondence from the bulk interaction Lagrangian, we obtain holographic expressions for the [Formula: see text]-axial-vector meson-nucleon ([Formula: see text]-baryon) coupling constant in the boundary QCD theory. Numerical results for the [Formula: see text] coupling constant in the framework of both models are close to the known phenomenological estimates. The [Formula: see text]-axial-vector meson-[Formula: see text]-baryon coupling constant was considered in the framework of hard-wall model.

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.

IR-improved soft-wall AdS/QCD model for baryons

We construct an infrared-improved soft-wall AdS/QCD model for baryons by considering the infrared-modified 5D conformal mass and Yukawa coupling of the bulk baryon field. The model is also built by taking into account the parity-doublet pattern for the excited baryons. When taking the bulk vacuum structure of the meson field to be the one obtained consistently in the infrared-improved soft-wall AdS/QCD model for mesons, we arrive at a consistent prediction for the baryon mass spectrum in even and odd parity. The prediction shows a remarkable agreement with the experimental data. We also perform a calculation for the $\rho(a_1)$ meson-nucleon coupling constant and obtain a consistent result in comparison with the experimental data and many other models.

ρ Meson-Nucleon Coupling Constant from the Soft-Wall AdS/QCD Model

In the framework of the soft-wall model of AdS/QCD we calculated the $\rho$ meson nucleon coupling constant. Bulk-to boundary propagators for the free vector and spinor fields are presented, whose boundary values correspond to $\rho$ meson and to the nucleon respectively. The interaction Lagrangian between these fields is written in the bulk of AdS space and includes magnetic type interactions as well. Using the AdS/CFT correspondence from the bulk interaction action we derived the $g_{\rho NN}$ coupling constant in the boundary QCD. We found that the soft-wall model result for the $g_{\rho NN}$ constant is more close to empirical values than the one obtained in the hard-wall model.

Nuclear Matter Properties from a Chiral Soliton Model

We present a recent investigation on properties of nuclear matter within a chrial soliton approach which includes the explicit scalar dilaton-quarkonium meson saturating the quark loop contribution to the scale anomaly of QCD. We discuss the binding energy per nucleon, the compressibility of nuclear matter and the behavior of meson–nucleon coupling constants according to the density variations in the system.

Parity-violating asymmetry in the reactions 6Li $(n,\alpha)$ 3H and 10B $(n,\alpha)^{7}$ Li* $\rightarrow$ 7Li $+$ $\gamma$

We present two experiments measuring the parity-violating asymmetry (P-odd) of tritons emission in the reaction 6Li(n,α)3H and γ-quanta emission in the reaction 10B(n,α)7Li* → 7Li + γ with polarized cold neutrons, aiming at estimation of the weak meson-nucleon coupling constants. These experiments started in the PNPI, Gatchina and continued in the ILL, Grenoble. We describe an integral method to measure P-odd asymmetry and the two experiments. The results of our measurements are: \(\alpha{}_{P-odd}^{6Li}=(-8.8\pm2.1)\cdot10^{-8}\) and \(\alpha{}_{P-odd}^{10B}=(0.8\pm3.9)\cdot10^{-8}\).

Mesons and nucleons from holographic QCD in a unified approach

We investigate masses and coupling constants of mesons and nucleons within a hard wall model of holographic QCD in a unified approach. We first examine an appropriate form of fermionic solutions by restricting the mass coupling for the five dimensional bulk fermions and bosons. We then derive approximated analytic solutions for the nucleons and the corresponding masses in a small mass coupling region. In order to treat meson and nucleon properties on the same footing, we introduce the same infrared (IR) cut in such a way that the meson-nucleon coupling constants, i.e., gπNN and gρNN are uniquely determined. The first order approximation with respect to a dimensionless expansion parameter, which is valid in the small mass coupling region, explicitly shows difficulties to avoid the IR scale problem of the hard wall model. We discuss possible ways of circumventing these problems.

Validity of the relativistic impulse approximation for elastic proton-nucleus scattering at energies lower than 200 MeV

We present the first study to examine the validity of the relativistic impulse approximation (RIA) for describing elastic proton-nucleus scattering at incident laboratory kinetic energies lower than 200 MeV. For simplicity we choose a (208)Pb target, which is a spin-saturated spherical nucleus for which reliable nuclear structure models exist. Microscopic scalar and vector optical potentials are generated by folding invariant scalar and vector scattering nucleon-nucleon (NN) amplitudes, based on our recently developed relativistic meson-exchange model, with Lorentz scalar and vector densities resulting from the accurately calibrated PK1 relativistic mean field model of nuclear structure. It is seen that phenomenological Pauli blocking (PB) effects and density-dependent corrections to sigma N and omega N meson-nucleon coupling constants modify the RIA microscopic scalar and vector optical potentials so as to provide a consistent and quantitative description of all elastic scattering observables, namely, total reaction cross sections, differential cross sections, analyzing powers and spin rotation functions. In particular, the effect of PB becomes more significant at energies lower than 200 MeV, whereas phenomenological density-dependent corrections to the NN interaction also play an increasingly important role at energies lower than 100 MeV.

FROM HADRONIC PARITY VIOLATION TO PARITY-VIOLATING ELECTRON SCATTERING AND TESTS OF THE STANDARD MODEL

Searches for parity violation in hadronic systems started soon after the evidence for parity violation in β-decay of 60 Co was presented by Madame Chien-Shiung Wu and in π and μ decay by Leon Lederman in 1957. The early searches for parity violation in hadronic systems did not reach the sensitivity required and only after technological advances in later years was parity violation unambiguously established. Within the meson-exchange description of the strong interaction, theory and experiment meet in a set of seven weak meson-nucleon coupling constants. Even today, after almost five decades, the determination of the seven weak meson-nucleon couplings is incomplete. Parity violation in nuclear systems is rather complex due to the intricacies of QCD. More straight forward in terms of interpretation are measurements of the proton-proton parity-violating analyzing power (normalized differences in scattering yields for positive and negative helicity incident beams), for which there exist three precision experiments (at 13.6, at 45, and 221 MeV). To-date, there are better possibilities for theoretical interpretation using effective field theory approaches. The situation with regard to the measurement of the parity-violating analyzing power or asymmetry in polarized electron scattering is quite different. Although the original measurements were intended to determine the electro-weak mixing angle, with the current knowledge of the electro-weak interaction and the great precision with which electro-weak radiative corrections can be calculated, the emphasis has been to study the structure of the nucleon, and in particular the strangeness content of the nucleon. A whole series of experiments (the SAMPLE experiment at MIT-Bates, the G0 experiment and HAPPEX experiments at Jefferson Laboratory (JLab), and the PVA4 experiment at MAMI) have indicated that the strange quark contributions to the charge and magnetization distributions of the nucleon are tiny. These measurements if extrapolated to zero degrees and zero momentum transfer have also provided a factor five improvement in the knowledge of the neutral weak couplings to the quarks. Choosing appropriate kinematics in parity-violating electron-proton scattering permits nucleon structure effects on the measured analyzing power to be precisely controlled. Consequently, a precise measurement of the ‘running’ of sin 2θw or the electro-weak mixing angle has become within reach. The [Formula: see text] experiment at Jefferson Laboratory is to measure this quantity to a precision of about 4%. This will either establish conformity with the Standard Model of quarks and leptons or point to New Physics as the Standard Model must be encompassed in a more general theory required, for instance, by a convergence of the three couplings (strong, electromagnetic, and weak) to a common value at the GUT scale. The upgrade of CEBAF at Jefferson Laboratory to 12 GeV, will allow a new measurement of sin 2θW in parity-violating electron-electron scattering with an improved precision to the current better measurement (the SLAC E158 experiment) of the ‘running’ of sin 2θW away from the Z0 pole. Preliminary design studies of such an experiment show that a precision comparable to the most precise individual measurements at the Z0 pole (to about ±0.00025) can be reached. The result of this experiment will be rather complementary to the [Formula: see text] experiment in terms of sensitivity to New Physics.

Relativistic Hartree–Bogoliubov theory and the isospin dependence of the effective nuclear force

The role of the isospin dependence of the effective Lagrangian of the Relativistic Mean Field Theory (RMF) is investigated. The standard RMF density functional based on non-linear meson-exchange terms is extended to include density dependent meson–nucleon coupling constants. The new variation of the RMF, in which the isospin dependence enters in both isoscalar and isovector channels, provides improved description of the equation of state of neutron matter, better isovector properties of finite nuclei such as neutron skin thickness, more accurate nuclear masses and a consistent description of both isovector and isoscalar giant resonances.

P- and T-violating πNN form factor

The form factor of the parity and time-reversal violating (PTV) pion–nucleon interaction is calculated from one-loop vertex diagrams. The degrees of freedom included in the effective Lagrangian are nucleons, pions, η, ρ and ω mesons. We show that by studying the form factor one can constrain the PTV meson–nucleon coupling constants. We evaluate the mean square radius associated with the PTV πNN vertex. Using the mean square radius, we estimate the effect of the PTV πNN vertex on the neutron electric dipole moment, and find a very small correction. We also extract the renormalisation group β function and use it to discuss evolution of the PTV πNN coupling constant beyond the hadronic mass scale.

Parity-nonconserving observables in thermal neutron capture on a proton

We calculate parity nonconserving observables in the processes where a neutron is captured on a proton at the threshold energy radiating a photon. Various potential models such as Paris, Bonn and Argonne $v18$ are used for the strong interactions, and the meson-exchange description is employed for the weak interactions between hadrons. The photon polarization $P_\gamma$ in the unpolarized neutron capture process and photon asymmetry $A_\gamma$ in the polarized neutron capture process are obtained in terms of the weak meson-nucleon coupling constants. $A_\gamma$ turns out to be basically insensitive to the employed strong interaction models and thus can be uniquely determined in terms of the weak coupling constants, but $P_\gamma$ depends significantly on the strong interaction models.

Parity violation in nuclear systems

Experimental measurements of Parity Non-Conserving (PNC) asymmetries in simple nuclear systems represent always a key-tool for the study of the weak nucleon-nucleon interaction and consequently an accurate experimental method for the determination of the meson-nucleon weak coupling constants of the underlying theory. Recent theoretical analysis on the deuteron photodisintegration with polarized photons, a few MeV above threshold, have drastically improved previous theoretical estimates. Based on that, the feasibility of measuring the photon asymmetry A γ in the reaction \( \bar \gamma + d \to n + p \) with the 10-MeV CW Linac at the Institute of Accelerating Systems and Applications (IASA) is considered here. A brief review on previous experimental results obtained in the deuteron photodisintegration and in the thermal-neutron radiative capture on protons (inverse reaction) is given. The most important parameters in the design of a nuclear parity experiment are presented and the crucial factors, such as beam intensity, beam polarization and neutron detection techniques with the required high accuracy are outlined.

Covariant density functional theory for isospin properties of nuclei far from stability

The standard relativistic mean-field density functionals based on non-linear meson exchange terms are extended to include density dependent meson-nucleon coupling constants. Special care is taken for the density dependence in the isovector channel. This provides not only an improved description of the equation of state for neutron matter and asymmetric nuclear matter but also for isovector properties of finite nuclei far from stability such as the neutron skin thickness. In particular it improves nuclear binding energies considerably as compared earlier applications of relativistic density functional theory to nuclear mass tables. An average root mean square deviation of 900 keV is found.

P- andT-odd two-nucleon interaction and the deuteron electric dipole moment

The nuclear physics relevant to the electric dipole moment (EDM) of the deuteron is addressed. The general operator structure of the $P$- and $T$-odd nucleon-nucleon interaction is discussed and applied to the two-body contributions of the deuteron EDM, which can be calculated in terms of $P$- and $T$-odd meson-nucleon coupling constants with only small model dependence. The one-body contributions, the EDMs of the proton and the neutron, are evaluated within the same framework. Although the total theoretical uncertainties are sizable, we conclude that, compared to the neutron, the deuteron EDM is competitive in terms of sensitivity to $\mathit{CP}$ violation, and complementary with respect to the microscopic sources of $\mathit{CP}$ violation that can be probed.

Vacuum polarization effects in relativistic nuclear pairing

In the present work we discuss the contribution of the vacuum polarization on the nuclear pairing, in the context of the relativistic Hartree-Fock-Bogoliubov (HFB) approximation. The polarization effects on the pairing, as a function of Fermi momentum, is shown with the scalar and vector meson-nucleon coupling constants scaled by a parameter x. We have obtained that the nuclear pairing is affected by the vacuum polarization.