We study light scalar mesons in the AdS/QCD soft-wall model with a background dilaton field. The masses and decay constants are compatible with experiment and QCD determinations if $a_0(980)$ and $f_0(980)$ are identified as the lightest scalar mesons; moreover, the states are organized in linear Regge trajectories with the same slope of vector mesons. Comparing the two-point correlation function of scalar operators in AdS and QCD, information about the condensates can be derived. Strong couplings of scalar states to pairs of light pseudoscalar mesons turn out to be small, at odds with experiment and QCD estimates: this discrepancy is related to the description of chiral symmetry breaking in this model.
We show that AdS/QCD generates predictions for the rate of diffractive rho meson electroproduction that are in agreement with data collected at the HERA electron-proton collider.
We present a study of electroexcitation of nucleon resonances with higher spins, in a soft-wall AdS/QCD model, comparing our results with existing data from the CLAS Collaboration at JLab, from MAMI, and other experiments.
We investigate the transverse charge densities of the deuteron in a soft-wall AdS/QCD model by considering both the unpolarized and the transversely polarized cases. The deuteron form factors are derived from the soft-wall AdS/QCD model and it is shown that the calculated results agree with the phenomenological parametrization and experimental data. The transverse charge densities of the deuteron are also derived from the soft-wall AdS/QCD model, and we notice slight deviations from those of the phenomenological parametrization.
In this manuscript, a unified approach to hadron physics from holographic point of view is described. After introduction of a general setup for meson-nucleon system based on the bottom-up approach of QCD (AdS/QCD), as an illustration, we specifically examine meson-nucleon couplings. This is an example of the notion we call "holographic unification" in hadron physics.
We demonstrate another success of the AdS/QCD correspondence by showing that an AdS/QCD holographic light-front wavefunction for the $ρ$ meson generates predictions for the cross-sections of diffractive $ρ$ production that are in agreement with data collected at the HERA electron-proton collider.
We use an AdS/QCD holographic wavefunction to generate predictions for the rate of diffractive ρ-meson electroproduction that are in reasonable agreement with data collected at the HERA electron-proton collider.
We study further the soft-wall AdS/QCD model with a cubic potential for the bulk scalar. We analyze the spectra of pseudoscalar, scalar, vector and axial-vector mesons. We also study the spin-1/2 nucleon spectrum and the pion-nucleon coupling. All of them have a good agreement with the experimental data.
We present a study of the $N^*(1535)$ resonance electroexcitation in a soft-wall AdS/QCD model. Both the transverse $A_{1/2}^p$ and longitudinal $S_{1/2}^p$ helicity amplitudes are calculated resulting in good agreement with data and with the MAID parametrization.
By using a new parametrization of the dilaton field and including a cubic term in the bulk scalar potential, we realize linear confinement in both meson and nucleon sectors within the framework of soft-wall AdS/QCD. At the same time this model also correctly incorporate chiral symmetry breaking. We compare our resulting mass spectra with experimental data and find good agreement between them.
Hybrid mesons with exotic quantum numbers $J^{PC}=1^{-+}$ are examined in soft-wall AdS/QCD. The predicted mass spectrum is compared to the measured values of the candidates $π_1(1400)$, $π_1(1600)$ and $π_1(2015)$. Thermal effects are analysed through the spectral function in the AdS-Black Hole model, and the differences with the Hawking-Page description are discussed.
The purpose of this paper is to further study the soft-wall AdS/QCD model with constrained IR background. By including a quartic bulk scalar potential we study various meson and nucleon spectra. This model naturally realizes the asymptotical linearity of these mass spectra simultaneously, together with correctly pattern of explicit and dynamical chiral symmetry breaking. The agreement between the theoretical calculations and the experimental data is good.
We show that the nucleon spectrum in a hard-wall AdS/QCD model can be improved by use of a relatively large IR cutoff. All of the spin-1/2 nucleon masses listed in PDG can be fit quite well within 11%. The average error is remarkably only 4.66%.
We investigate light scalar mesons and glueballs in the $Dp-Dq$ hard-wall models, including $D3-Dq$, $D4-Dq$, and $D6-Dq$ systems. It is found that only in the $D4-D6$ and $D4-D8$ hard wall models, the predicted masses of the ${\bar q} q$ scalar meson $f_0$, scalar glueball are consistent with their experimental or lattice results. This indicates that $D4-D6$ and $D4-D8$ hard-wall models are favorite candidates of the realistic holographic QCD model.
We study the mass spectrum and decay constants of light and heavy mesons in a soft-wall holographic approach, using the correspondence of string theory in Anti-de Sitter space and conformal field theory in physical space-time.
We propose a modification of soft-wall holographic model that in combination with the light-front holographic QCD leads to a broad hydrogen-like degeneracy of the same sort as the degeneracy observed experimentally in the spectrum of light mesons.
We construct an improved soft-wall AdS/QCD model with a cubic coupling term of the dilaton and the bulk scalar field. The background fields in this model are solved from the Einstein-dilaton system with a nontrivial dilaton potential, which has been shown to be able to reproduce the equation of state from lattice QCD with two flavors. The chiral transition behaviors are investigated in the improved soft-wall AdS/QCD model with the solved gravitational background, and the crossover transition can be realized. Our study provides a possibility to address the deconfining and chiral phase transitio…
Holographic soft-wall model is successful in the phenomenology of hadrons. Here with the use of generalized parton distributions (GPDs) obtained from AdS/QCD, perturbative effects are entered into the formalism. Perturbations are incorporated in the formalism through the evolution of GPDs according to the DGLAP like equations. Evolved proton GPDs are compared with a phenomenological model to show that we can get good improvements of the holographic model. It seems that combining the holographic soft-wall model with perturbative effects to some extent, gives the correct physics of GPDs.
We calculate gravitational form factors of vector mesons using a holographic model of QCD. These provide restrictions on the generalized parton distributions of vector mesons, via the sum rules connecting stress tensor form factors to GPDs. We concentrate on the traceless part of the stress tensor, which suffices to fix the momentum and angular momentum sum rules. The vector mesons appear noticeably more compact measured by the gravitational form factors than by the charge form factor.
We use the soft-wall AdS/QCD model to investigate the finite-temperature effects on the spectral function in the vector channel. The dissociation of the vector meson tower onto the AdS black hole leads to the in-medium mass shift and the width broadening in a way similar to the lattice QCD results for the heavy quarkonium at finite temperature. We also show the momentum dependence of the spectral function and find it consistent with screening in a hot wind.
We derive a holographic soft-wall approach in five dimensional AdS-Schwarzschild space for the description of mesons at finite temperature. In this first application we consider the small temperature limit and derive analytical expression for the mass spectrum of mesons with adjustable quantum numbers $n$ (radial number), $L$ (angular orbital momentum) and $J$ (total angular momentum). We explicitly separate the contribution at zero temperature and the leading order temperature correction. The temperature corrections arise from the temperature dependence of the dilaton parameter (which is the …
Recently we derived a soft-wall AdS-Schwarzschild approach at small temperatures for the description of hadrons with integer spin and adjustable number of constituents (mesons, tetraquarks, dibaryons, etc.). In the present paper we extend our formalism to states with half-integer spin (baryons, pentaquarks, etc.), presenting analytical results for the temperature dependence of their masses and form factors.
We incorporate chiral symmetry breaking in a soft-wall version of the AdS/QCD model by using a modified dilaton profile and a quartic term in the bulk scalar potential. This allows one to separate the dependence on spontaneous and explicit chiral symmetry breaking. The resulting mass spectra in the scalar, vector and axial-vector sectors compares favorably with the respective QCD resonances.
By requiring the correct Regge behavior in both meson and nucleon sectors, we determine the infrared asymptotic behavior of various background fields in the soft-wall AdS/QCD model, including the dilaton, the warp factor, and the scalar VEV. We then use a simple parametrization which smoothly connect these IR limits and their usual UV limits. The resulting spectrum is compared with experimental data, and the agreement between them is good.
The primary gaol of this paper is to analyze the mass spectrum of the vector rho mesons by using the soft-wall AdS/QCD device. The theory is characterized by a form of the dilaton field which satisfies the constraint for having the correct Regge behavior as well as the constraint for the non-existence of the spurious massless scalar mode in the spectrum. The spectrum we obtained is in good agreement with the experimental data.
We report on the results of our recent research published in [1] that shows that AdS/QCD generates predictions for the rate of diffractive ρ-meson electroproduction that are in agreement with data collected at the HERA electron-proton collider [2,3]. Preliminary results of this research were presented in [4].
Generalized parton distributions of a deuteron in an AdS/QCD hard-wall model
Institute of Physics, Ministry of Science and Education（阿塞拜疆科学与教育部物理研究所）；Institute for Physical Problems, Baku State University（巴库国立大学物理问题研究所）；Center for Theoretical Physics, Khazar University（哈扎尔大学理论物理中心）；Western Caspian University（西里海大学）
We compute the rate for diffractive $ϕ$ electro-production using the Color Glass Condensate dipole model. The model parameters are obtained from fits to the most recent combined HERA data on inclusive deep inelastic scattering. As for the $ϕ$ meson, we use an AdS/QCD holographic light front wavefunction. Our predictions are compared to the available data collected at the HERA collider.
We present an improved study of the electromagnetic form factors of the nucleon and of the Roper-nucleon transition using an extended version of the effective action of soft-wall AdS/QCD. We include novel contribution from additional non-minimal terms, which do not renormalize the charge and do not change the normalization of the corresponding form factors, but the inclusion of these terms results in an important contribution to the momentum dependence of the form factors and helicity amplitudes.
We study light scalar mesons in the AdS/QCD soft-wall model with a background dilaton field, to investigate the features of this approach in describing QCD properties in the strong coupling regime. We find that the masses and decay constants are compatible with experiment and QCD determinations if $a_0(980)$ and $f_0(980)$ are identified as the lightest scalar mesons; moreover, the states are organized in linear Regge trajectories with the same slope of vector mesons. Strong couplings of scalar states to pairs of light pseudoscalar mesons turn out to be small, at odds with experiment and QCD e…
We give a further study on the improved soft-wall AdS/QCD model with two flavors. The chiral transition behaviors are studied in the case of finite chemical potential, with the chiral phase diagram obtained at zero quark mass. The thermal spectral functions of the vector and axial-vector mesons are calculated, and the in-medium melting properties of the mesons are investigated. We find that the chiral transition behaviors and the meson melting properties at finite chemical potential can be qualitatively described by the improved soft-wall AdS/QCD model, except in the region of large chemical p…
We discuss a holographic soft-wall model developed for the description of mesons and baryons with adjustable quantum numbers n, J, L, S. This approach is based on an action which describes hadrons with broken conformal invariance and which incorporates confinement through the presence of a background dilaton field.
We investigate the hybrid exotic meson with $J^{PC}=1^{-+}$ within the framework of an AdS/QCD model. Introducing a holographic field dual to the operator for hybrid exotic meson, we obtain the eigen-value equation for its mass. Fixing all free parameters by QCD observables such as the $ρ$-meson mass, we predict the masses of the hybrid exotic meson. The results turn out to be $1476 \mathrm{MeV}$ for the ground state, and $2611 \mathrm{MeV}$ for the first excited one. Being compared with the existing experimental data for the $π_1(1400)$, which is known to be $m_{π_1} = 1351\pm30 \mathrm{MeV}$…
We present a study of the flavor form factors in the framework of a hard-wall AdS/QCD model and compare with the available experimental data. We obtain the flavor form factors by decomposing the Dirac and Pauli form factors for the nucleons using the charge and isospin symmetry. Further, we present a detailed study of the flavor structures of the charge and anomalous magnetization densities in the transverse plane. Both the unpolarized and the transversely polarized nucleons are considered here. We compare the AdS/QCD results with two standard phenomenological parametrizations.
In this talk we study the Green's function of two vector and one axial-vector currents within the soft-wall anti-de-Sitter (AdS) model of Qunatum Chromodynamics (QCD), with a quadratic dilaton and chiral symmetry broken through a field X which gains a vacuum expectation value. We compare our predictions at high energies with the Operator Product Expansion both in the massless quark limit and for mq different from 0. The soft-wall model yields a zero magnetic susceptibility chi=0 and some problems are found in the case with mq different from 0. We also discuss the relation proposed by Son and Y…
In this paper, minimal coupling constants of meson-$Δ$ baryon and meson-nucleon to $Δ$ baryon transition have been investigated in the AdS/QCD soft-wall model at finite temperature limits. Initially, the right and left profile functions of $Δ$ baryons have been calculated using the Rarita-Schwinger field in this model. After this, coupling constants have been written by taking into account the profile functions of thermal hadrons according to the zero-temperature case. Then, the temperature dependence graphs are plotted for strong couplings $g_{ρΔΔ}(T)$, $g_{a_{1} ΔΔ}(T)$ and $g_{ρN Δ}(T)$. As…
We consider a classical source, moving on the 4-D boundary of a 5-D ADS space, that is coupled to quantum fields residing in the bulk. Bremsstrahlung-like radiation of the corresponding quanta is shown to occur and the S-matrix is derived assuming that the source is sufficiently massive so that recoil effects are negligible. As an illustrative example, using the ADS hard-wall model, we consider vector mesons coupled to a heavy nucleus that is moved around at high speed in an accelerator ring. The meson radiation rate is found to be finite but small. Much higher accelerations, such as when a pa…
We explicitly demonstrate how to correctly define the hadronic parton distributions (PDFs, TMDs, and GPDs) in the soft-wall AdS/QCD approach, based on the use of a quadratic dilaton field, providing confinement and spontaneous breaking of conformal and chiral symmetries. The power behavior of parton distributions at large values of the light-cone variable is consistent with quark counting rules and Drell-Yan-West duality. All parton distributions are defined in terms of profile functions, which depend on the light-cone coordinate and are fixed from PDFs and electromagnetic form factors.
Meson spectroscopy within the frame of the soft-wall AdS/QCD, became one of the most interesting topics of particle physics in the last six years. In this work we attempt a generalized parametric analysis of the background dilaton gauge field which previous studied by K.M.Keita and Y.H.Dicko. Aim is that using a positive z-depended dilaton gauge field and setting the appropriate parameters on it, we are able to reproduce the full rho vector meson mass spectrum. To reinforce the results, we compare the proposed parametric model with the experimental data. This comparison, returns in some cases …
We study the axial-vector form factor of the nucleons at constant and homogenous isospin chemical potential using holographic QCD. Nucleon mass splitting in such isospin medium is taken into account. According to AdS/CFT correspondence, the critical value of the isospin chemical potential μ_I equals to UV- boundary value of the time component of the bulk gauge field. We calculate the axial-vector form factor of the proton and neutron in such background in the framework of the hard-wall model and plot the form factors for the isospin chemical potential critical value μ_I=m_π.
This note focuses on the large-N behaviour of the Hard Wall model of QCD and clarifies the AdS/QCD dictionary formulated on the basis of the AdS/CFT correspondence. It is shown how short-distance studies performed in the framework of the AdS/QCD Soft Wall model allow one to determine unambiguously the chiral symmetry breaking function in the Hard Wall model. Especially, the different forms of the field/operator prescription are emphasized. The large-N behaviour of the Hard Wall model is then checked considering the vector and gravitational form factors of the pion in the chiral limit.
Mesons and baryons are considered in soft-wall holographic approach based on the correspondence of string theory in AdS space and conformal field theory in physical space-time. The model generates Regge trajectories linear in n and J (L) for the hadronic mass spectrum. Results obtained for heavy-light meson masses and decay constants are consistent with predictions of HQET. In the baryon sector applications to the nucleon electromagnetic form factors and generalized parton distributions are discussed.
We present a numerical analysis of helicity independent nucleon generalized parton distributions (GPDs) using the known formalism based on inclusion of higher Fock states in the soft-wall approach of the anti-de Sitter/QCD model. We calculate the momentum space GPDs by matching the electromagnetic form factors in the AdS model to the sum rules in QCD. We investigate their Mellin moments, transverse impact parameter GPDs, transverse mean square radius, and transverse width. We further extend this work to investigate the charge and anomalous magnetization densities for both unpolarized and trans…
We study the chiral phase transition with 2 + 1 quark flavors in an improved soft-wall AdS/QCD model, which can produce the light meson spectrum and many other low-energy quantities consistent with experiments in the two-flavor case. The chiral transition behaviors of the quark condensates at different quark masses are analysed in detail, and the (m_{u,d}, m_s) phase diagram for the quark sector has been obtained from the improved soft-wall model. We find that the features of the calculated phase diagram are completely consistent with the standard scenario, which is supported by lattice simula…
We investigate in detail the chiral thermal transition of QCD in an improved soft-wall AdS/QCD model with a simply modified 5D conformal mass of the bulk scalar field. We also present a calculation in this model for the light meson spectra and other low-energy characteristic quantities including the pion form factor, the pi-rho coupling constant and the decay constants of pi, rho, a_1, which are shown to result in a good agreement with experimental data except for the pion decay constant. The thermal behavior of chiral condensate is studied. It is found that such a simply improved soft-wall mo…
We propose a unified approach to study meson, nucleon and $Δ$-baryon properties at zero and finite temperatures in the context of hard-wall AdS/QCD model. We first combine some previous works dealing with mesons and baryons separately, and introduce a new parameter~$ξ$ so that the model could give a universal description of spectrum and couplings of both sectors in a self-consistent way. All observables calculated numerically show reasonable agreement with experimental data. We then study these observables at nonzero temperature by modifying the AdS space-time into AdS-Schwartzchild space-time…
We use QCD light-cone sum rules (LCSR) with holographic anti de Sitter/Chromodynamics (AdS/QCD) Distribution Amplitudes (DAs) for the $ρ$ meson to predict the form factors that govern the leading amplitudes of the rare radiative $B -> ργ$ decay and the semileptonic decay $B -> ρl ν$. We test the Isgur-Wise relation between the radiative and semileptonic form factors. We also compute the total width (in units of $|V_{ub}|^2$) for the semileptonic decay $B -> ρl ν$ as well as ratios of partial decay widths which are independent of $|V_{ub}|$.
The scalar glueball is investigated in a soft-wall model of AdS/QCD. Constraints of the mass of the scalar glueball are given through an analysis of a relation between the bulk mass and the anomalous dimension. The mass of the ground scalar glueball is located at $0.96^{+0.04}_{-0.07} \rm{GeV}<m_G<1.36^{+0.05}_{-0.10}\rm{GeV}$. In terms of a background dilaton field $Φ(z)=cz^2$, the two-point correlation function for the scalar gluon operator is obtained. The two-point correlation function at $Δ=4$ gives a different behavior compared with the one in QCD.
We use an anti-de Sitter/Quantum Chromodynamics (AdS/QCD) holographic light-front wavefunction for the $ρ$ and $ϕ$ mesons, in conjunction with the Color Glass Condensate (CGC) dipole cross-section whose parameters are fitted to the most recent 2015 high precision HERA data on inclusive Deep Inelastic Scattering (DIS), in order to predict the cross-sections for diffractive $ρ$ and $ϕ$ electroproduction. Our results suggest that the holographic meson light-front wavefunction is able to give a simultaneous description of the $ρ$ and $ϕ$ production data provided we use a set of light quark masses …
We give a further study on chiral phase diagram in the improved soft-wall AdS/QCD model with $2+1$ flavors. The equations of motion for the octet pseudoscalar, vector and axial-vector mesons are derived to compute the octet meson spectra and relevant decay constants, by which the model parameters are determined. The chemical potential effects on thermal transition of chiral condensate are investigated, which enables us to obtain the chiral phase diagram in the $μ-T$ plane. We find that the critical end point linking the crossover transition with the first-order phase transition still exists an…
We study the gluon parton densities [parton distribution functions (PDFs), transverse momentum distributions (TMDs), generalized parton distributions (GPDs)] and form factors in soft-wall AdS/QCD. We show that the power behavior of gluon parton distributions and form factors at large values of the light-cone variable and large values of square momentum is consistent with quark counting rules. We also show that the transverse momentum distributions derived in our approach obey the model-independent Mulders-Rodrigues inequalities without referring to specific model parameters. All gluon parton d…
By using gauge/gravity duality, we calculate the spectral function of the heavy vector mesons with the presence of an intense magnetic field in a hot and dense medium. The results show that, a general conclusion, as the increases of magnetic field, chemical potential and temperature, the height of the peak of the spectral function decreases and the width increases. A nontrivial result is the change from the peak position of spectral function. We explain this non-trivial behavior by the interplay of the interaction between the two heavy quarks and the interaction between the medium with each of…
The AdS/CFT correspondence may offer new and useful insights into the non-perturbative regime of strongly coupled gauge theories such as Quantum Chromodynamics. Soft-wall AdS/QCD models have reproduced the linear trajectories of meson spectra by including background dilaton and chiral condensate fields. Efforts to derive these background fields from a scalar potential have so far been unsuccessful in satisfying the UV boundary conditions set by the AdS/CFT dictionary while reproducing the IR behavior needed to obtain the correct chiral symmetry breaking and meson spectra. We present a three-fi…
We present a high-quality description of the deuteron electromagnetic form factors in a soft-wall AdS/QCD approach. We first propose an effective action describing the dynamics of the deuteron in the presence of an external vector field. Based on this action the deuteron electromagnetic form factors are calculated, displaying the correct 1/Q^10 power scaling for large Q^2 values. This finding is consistent with quark counting rules and the earlier observation that this result holds in confining gauge/gravity duals. The Q^2 dependence of the deuteron form factors is defined by a single and univ…
