We calculate the stress tensor, or energy-momentum tensor, form factors of the pion and of axial vector mesons in the chiral limit of a hard wall AdS/CFT model of QCD. One (of the two) pion gravitational form factors is directly related to the second moment of the pion generalized parton distribution, thus providing a sum rule for the latter. As was also the case for vector mesons, both the pion and the axial vector mesons appear strikingly more compact measured by the gravitational form factor than by the electromagnetic form factor.
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.
We study light pseudoscalar and axial states using a soft wall model that is modified by introducing two extra parameters: an UV-cutoff and an anomalous term in the conformal dimension of the fields involved such that meson fields with different parities are easily distinguishable. We find that 23 of these light mesonic states, including the scalars and vector states analyzed with one of our previous results, are fitted within the RMS error bounds given for this model, whose parameters are given by the quadratic dilaton profile, the UV locus $z_{0}$ and the anomalous term $Δ_{P}$. Our results …
The axial-vector form factor of the nucleons is considered in the framework of hard-wall model of holographic QCD. A new interaction term between the bulk gauge and matter fields was included into the interaction Lagrangian. We obtain the axial-vector form factor of nucleons in the boundary QCD from the bulk action using AdS/CFT correspondence. The momentum square dependence of the axial-vector form factor is analysed numerically.
A SU(4) flavor symmetrical Lagrangian is constructed for the interaction of the pseudo-scalar mesons with the vector mesons. SU(4) symmetry is broken to SU(3) by suppression of terms in the Lagrangian where the interaction should be driven by charmed mesons. Chiral symmetry can be restored by setting this new SU(4) symmetry breaking parameters to zero. Unitarization in coupled channels leads to the dynamical generation of resonances. Many known axial resonances can be identified including the new controversial X(3872) and the structure found recently by Belle around 3875 MeV in the hidden char…
Solution of the boundary problem for the axial-vector field in the hard-wall AdS/QCD model
Baku State University（巴库国立大学）；Institute for Applied Mathematics, Baku State University（巴库国立大学应用数学研究所）；Institute for Physical Problems, Baku State University（巴库国立大学物理问题研究所）；Institute of Physics, Ministry of Science and Education（科学与教育部物理研究所）；Khazar University（哈扎尔大学）
We study the decays of the lightest axial-vector and pseudovector mesons, interpreted as quark-antiquark states, into a vector and a pseudoscalar meson. We show that the quarkonium assignment delivers a good description of the decays and allows also to make further testable predictions. In the kaonic sector, the physical resonances $K_{1}(1270)$ and $K_{1}(1400)$ emerge as mixed objects of an axial vector state $K_{1,A}$ and a pseudovector state $K_{1,B}$. We determine the mixing angle as $\left\vert θ_{K}\right\vert=\left(33.6\pm4.3\right) ^{\circ}$, a value compatible with previous studies b…
Recent reports of the observation of the decay $τ\rarrow ν_τ + K + π+ π$ raise interesting questions. The $u-s$ quark mass difference can induce an effective second-class current in the strange sector and enhance decays to helicity-suppressed scalar states. This suggests searches for scalar strange mesons in the $τ\rarrow ν_τ + K + η' $ and $τ\rarrow ν_τ + K + π$ decay modes. $τ$ decays to axial vector final states may clarify strange meson spectroscopy by analogy with the clarification of the $a_1$ problem in the nonstrange sector. Open questions include mixing effects in the strange axial ve…
The $Z'$-portal is one of most popular and well-explored scenarios of dark matter (DM). To avoid the strong constraints coming from dilepton resonance searches at the LHC and direct detection of DM, it is usually required that in addition to being leptophobic, the $Z'$ is axially coupled to either the (fermionic) DM or the standard model (SM) quarks. The first possibility has been extensively studied both in the context of simplified model and UV complete scenarios. However, the studies on the second possibiliy are largely confined to simplified models only. Here, we construct the minimal UV c…
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 extend the predictive soft-wall AdS/QCD model to a thermodynamic model by considering the black hole metric. A modified bulk vacuum expectation value and a modified coefficient for the quartic term in the bulk scalar potential are introduced to obtain a smooth dilaton solution for computing the spectral functions of the vector and axial-vector mesons. It is demonstrated that the peaks appearing in the spectral functions characterize the thermal mass spectra of vector and axial-vector mesons, where the location of the peak moves to a lower value and the width of the peak becomes wider when i…
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.
In this paper we explore the chiral phase transition in QCD within the three-flavor Nambu-Jona-Lasinio (NJL) model with a negative coupling constant in the isoscalar axial-vector channel, which is associated with a polarized instanton--anti-instanton molecule background. The QCD phase diagram described in this scenario shows a new first order phase transition around the transition temperature $T_c$ toward a phase without chiral condensates, but with nontrivial dynamic chiral chemical potentials for the light quarks, spontaneously giving rise to local $\mathcal {CP}$ violation and local chirali…
We study the two-body decays of mesons using the covariant helicity formalism. In particular, we show how the partial wave analysis of decays constrains the interacting terms entering the Lagrangian describing the decays of mesons with $J=1$ and $J=2$. We use available information on partial wave analysis to study specific mesonic decays and to make predictions for not yet measured quantities as well as to investigate the isoscalar mixing angle in the axial-vector, pseudovector and pseudotensor sectors. In particular, in the axial-vector sector our result agrees with the LHCb one, and in the p…
The singlet pseudoscalar sector of light mesons is investigated in the soft-wall model, a bottom-up approach to the AdS/QCD correspondence. The $η^\prime$ mass results from the mixing among the fields dual to the axial current, pseudoscalar current and the $G\tilde G$ operator. The topological susceptibility is computed for any quark mass, and the Witten-Veneziano relation is obtained in the large $N_c$ limit.
We study the effects of dimension six terms on the predictions of the holographic model for the vector meson form factors and determine the corrections to the electric radius, the magnetic and the quadrupole moments of the rho-meson. We show that the only dimension six terms which contribute nontrivially to the vector meson form factors are X^2F^2 and F^3. It appears that the effect from the former term is equivalent to the metric deformation and can change only masses, decay constants and charge radii of vector mesons, leaving the magnetic and the quadrupole moments intact. The latter term gi…
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.
Chiral perturbation theory (ChPT) is the effective field theory of the strong interactions at low energies. We will address the issue of a consistent power counting scheme in a manifestly Lorentz-invariant formulation of baryon ChPT. As applications we show how the inclusion of vector and axial-vector mesons in the calculation of the nucleon electromagnetic and axial form factors, respectively, lead to an improved description of the empirical data. Finally, we will outline a systematic implementation of the Delta(1232) resonance into the effective field theory program.
Recent advances in the development of a chiral linear $σ$-model with (axial-)vector mesons are presented. The model is based on the basic requirements of global chiral symmetry and dilatation invariance. The role of (axial-)vector states turns out to be crucial both in the meson and the baryon sectors. First results at nonzero temperature and density are discussed.
The phenomenology at future hadron colliders of a model with strong interacting vector and axial vector bosons possessing a discrete symmetry demanding mass degeneracy is presented.
We calculate the $a_1$ meson-nucleon coupling constant in the framework of soft-wall and hard-wall AdS/QCD models. In the bulk of AdS space were written bulk interaction Lagrangians for a minimal gauge coupling, a magnetic gauge coupling and a triple coupling. To use AdS/CFT correspondence and these bulk interaction Lagrangians we calculate the $a_1$ axial-vector meson-nucleon coupling constant in the boundary of AdS space within both models. We observe that the numerical values for the $g_{a_1 NN}$ coupling constant in the framework of both models are more close to the experimental value than…
If a new massive vector boson with nonzero axial couplings to fermions will be observed at LHC, then an upper limit on the scale of new physics could be derived from unitarity of $\mathcal{S}$-matrix. The new physics will involve either new massive fermions, or scalars, or even a strongly coupled sector. We derive a model independent bound on the scale of new physics. If $M_{G}/ g_{A} < 3$ TeV and the fermion is a top quark, the upper limit is 78 TeV.
We derive the O(p6) Chiral Perturbation Theory Lagrangian in the massless quark limit for a class of gravity dual models of Quantum Chromodynamics with the chiral symmetry broken through boundary conditions. The odd O(p6) couplings are related to the O(p4) low-energy constants (LEC's) in the even-parity sector. Some combinations of even O(p6) couplings are found to be universal and independent of the peculiarities of the model. These relations turn out to be the manifestation at low energies of a broader relation between anomalous and even-parity amplitudes.
We consider the axial-vector mesons $K_1(1270)$ and $K_1(1400)$ as a mixture of two $|^3P_1\rangle$ and $|^1P_1\rangle$ states with the mixing angle $θ$ that equal to $(-34\pm 13)^\circ$. We calculate the light-front distribution amplitudes (LFDAs) and decay constant formulas for both the axial-vector mesons $K_1$ in the AdS/QCD correspondence. The transition form factors of the semileptonic $B\to K_1$ decays are derived in terms of the LFDAs for $K_1$ mesons. Using these form factors and decay constant values, the differential branching ratios of $B\to K_1 (1270, 1400) \ell^+ \ell^-$,~$\ell=μ…
We discuss how to calculate form factors using a holographic model of QCD, mainly focusing on vector, axial, and pseudoscalar mesons. We illustrate the techniques on gravitational form factors (which are useful for constraining the generalized parton distributions) as well as quoting the results for electromagnetic form factors. One striking outcome, comparing the several types of calculated form factors, is that mesons appear noticeably more compact when measured by the gravitational form factors than when measured by the charge form factor.
In this paper, we revisit a scale-invariant extension of the standard model (SM) with a strongly interacting hidden sector within AdS/QCD approach. Using the AdS/QCD, we reduce the number of input parameters to three, {\it i.e.} hidden pion decay constant, hidden pion mass and $\tanβ$ that is defined as the ratio of the vacuum expectation values (VEV) of the singlet scalar field and the SM Higgs boson. As a result, our model has sharp predictability. We perform the phenomenological analysis of the hidden pions which is one of the dark matter (DM) candidates in this model. With various theoreti…
Whilst the prospect of new $Z'$ gauge bosons with only axial couplings to the Standard Model (SM) fermions is widely discussed, examples of anomaly-free renormalisable models are lacking in the literature. We look to remedy this by constructing several motivated examples. Specifically, we consider axial vectors which couple universally to all SM fermions, as well as those which are generation-specific, leptophilic, and leptophobic. Anomaly cancellation typically requires the presence of new coloured and charged chiral fermions, and we argue that in a large class of models masses of these new s…
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.
Compactified 2HDM under the Non-SUSY AdS instability conjecture
Faculty of Sciences, Mohammed V University（穆罕默德五世大学理学院）；Centre of Physics and Mathematics, CPM-Morocco（摩洛哥物理与数学中心）；Hassan II Academy of Science and Technology, Kingdom of Morocco（摩洛哥王国哈桑二世科学技术学院）
Axial-vector transitions of decuplet to octet baryons are parametrized at low energies guided by a complete and minimal chiral Lagrangian up to next-to-leading order. It is pointed out that beyond the well-known leading-order term, there is only one contribution at next-to-leading order. This contribution is flavor symmetric. Therefore the corresponding low-energy constant can be determined in any strangeness sector. As functions of this low-energy constant, we calculate the decay widths and Dalitz distributions for the decays of decuplet baryons to octet baryons, pions, and photons and for th…
We use QCD sum rules to study the possible existence of a $D_s\bar{D}^*+ D_s^*\bar{D}$ molecule with the quantum number $J^P=1^+$. We consider the contributions of condensates up to dimension eight and work at leading order in $α_s$. We obtain $m_{D_sD^*}=(3.96\pm0.10) \GeV$ around 100 MeV above the mass of the meson X(3872). The proposed state is a natural generalized state to the strangeness sector of the X(3872), which was also found to be consistent with a multiquark state from a previous QCD sum rule analysis.
Whereas the theoretical results for the dominant contributions to hadronic light-by-light scattering coming from pseudoscalar meson exchange have converged over the past years, the various published estimates of the contribution due to axial vector meson exchange differ wildly. Since holographic AdS/QCD models have proved to provide rather good models of singly and doubly virtual pion transition form factors, which reproduce remarkably well the known low-energy data and also the asymptotic leading-order pQCD behavior, it is of interest to consider their predictions for axial vector transition …
In this paper a model incorporating chiral symmetry breaking and dynamical soft-wall AdS/QCD is established. The AdS/QCD background is introduced dynamically as suggested by Wayne de Paula etc al and chiral symmetry breaking is discussed by using a bulk scalar field including a cubic term. The mass spectrum of scalar, vector and axial vector mesons are obtained and a comparison with experimental data is presented.
We present simulation results employing overlap fermions for the axial correlation functions in the epsilon-regime of chiral perturbation theory. In this regime, finite size effects and topology play a dominant role. Their description by quenched chiral perturbation theory is compared to our numerical results in quenched QCD. We show that lattices with a linear extent L > 1.1 fm are necessary to interpret the numerical data obtained in distinct topological sectors in terms of the epsilon-expansion. Such lattices are, however, still substantially smaller than the ones needed in standard chiral …
We derive the general 5-dimension metric structure of the $Dp-Dq$ system in type II superstring theory, and demonstrate the physical meaning of the parameters characterizing the 5-dimension metric structure of the \textit{holographic} QCD model by relating them to the parameters describing Regge trajectories. By matching the spectra of vector mesons $ρ_1$ with deformed $Dp-Dq$ soft-wall model, we find that the spectra of vector mesons $ρ_1$ can be described very well in the soft-wall $D3-Dq$ model, i.e, $AdS_5$ soft-wall model. We then investigate how well the $AdS_5$ soft-wall model can descr…
We consider chiral symmetry breaking AdS / QCD models with cubic and quartic potentials in the scalar sector and a z dependent mass for scalars in the bulk. In these models it is possible to get good mesonic spectra using current quark masses.
We show that holographic models of QCD predict the presence of a Chern-Simons coupling between vector and axial-vector mesons at finite baryon density. In the AdS/CFT dictionary, the coefficient of this coupling is proportional to the baryon number density, and is fixed uniquely in the five-dimensional holographic dual by anomalies in the flavor currents. For the lightest mesons, the coupling mixes transverse $ρ$ and $a_1$ polarization states. At sufficiently large baryon number densities, it produces an instability, which causes the $ρ$ and $a_1$ mesons to condense in a state breaking both ro…
We study the equilibrium instability of chiral quarkonia in a plasma in the presence of constant magnetic and electric field and at finite axial chemical potential using AdS/CFT duality. The model in use is a supersymmetric QCD at large 't$\,$Hooft coupling and number of colors. We show that the presence of the magnetic field and the axial chemical potential even in the absence of the electric field make the system unstable. In a gapped system, a stable/unstable equilibrium state phase transition is observed and the initial transition amplitude of the equilibrium state to the non-equilibrium s…
We calculate matrix elements of the axial current for static-light mesons and baryons in lattice QCD with dynamical domain wall fermions. We use partially quenched heavy hadron chiral perturbation theory in a finite volume to extract the axial couplings g_1, g_2, and g_3 from the data. These axial couplings allow the prediction of strong decay rates and enter chiral extrapolations of most lattice results in the b sector. Our calculations are performed with two lattice spacings and with pion masses down to 227 MeV.
Axial charge in a QCD plasma is P- and CP-odd. We propose and study P- and CP-odd observables in photon and di-lepton emissions from an axially charged QCD plasma, which may provide possible experimental evidences of axial charge fluctuation and triangle anomaly in the plasma created in heavy-ion collisions. Our observables measure spin alignments of the emitted photons and di-leptons, and are shown to be related to the imaginary part of chiral magnetic conductivity at finite frequency-momentum, which ultimately arises from the underlying triangle anomaly of the QCD plasma with a finite axial …
A soft-wall anti-de Sitter/QCD model with a modified five-dimensional metric at the infrared region is constructed to obtain a nontrivial dilaton solution, which incorporates the chiral symmetry breaking and linear confinement. By taking the pion mass and decay constant as two input mass scales, the resulting predictions for the resonance states of pseudoscalar, scalar, vector and axial-vector mesons agree remarkably with the experimentally confirmed resonance states. The effects of the quartic interaction term are investigated by taking an appropriate sign and magnitude for maintaining the st…
We discuss a minimal holographic model for the description of heavy-light and light mesons with chiral symmetry, defined in a slab of AdS space. The model consists of a pair of chiral Yang-Mills and tachyon fields with specific boundary conditions that break spontaneously chiral symmetry in the infrared. The heavy-light spectrum and decay constants are evaluated explicitly. In the heavy mass limit the model exhibits both heavy-quark and chiral symmetry and allows for the explicit derivation of the one-pion axial couplings to the heavy-light mesons.
We show how to incorporate chiral symmetry breaking in the 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. Moreover our 5D model automatically incorporates linear trajectories and non chiral-symmetry restoration for highly excited radial states. We compare our resulting mass spectra in the scalar, vector and axial-vector sectors with the respective QCD resonances and find reasonable agreement using the known values for the …
We construct and investigate an infrared-improved soft-wall AdS/QCD model for mesons. Both linear confinement and chiral symmetry breaking of low energy QCD are well characterized in such an infrared-improved soft-wall AdS/QCD model. The model enables us to obtain a more consistent numerical prediction for the mass spectra of resonance scalar, pseudoscalar, vector and axial-vector mesons. In particular, the predicted mass for the lightest ground state scalar meson shows a good agreement with the experimental data. The model also provides a remarkable check for the Gell-Mann-Oakes-Renner relati…
We study the complete set of flavor changing hyperon axial current matrix elements at small momentum transfer. Using partially quenched heavy baryon chiral perturbation theory, we derive the chiral and momentum behavior of the axial and induced pseudoscalar form factors. The meson pole contributions to the latter posses a striking signal for chiral physics. We argue that the study of hyperon axial matrix elements enables a systematic lattice investigation of the efficacy of three flavor chiral expansions in the baryon sector. This can be achieved by considering chiral corrections to SU(3) symm…
According to the conjecture of the gauge/gravity duality a strongly coupled 4D field theory may be described by a dual 5D theory which is a free field theory in the first approximation. The usual description of the axial-vector sector in the bottom-up AdS/QCD models includes, however, the quartic interaction with a bulk scalar field. The question appears whether it is possible to describe some aspects of the chiral symmetry breaking in a way more consistent with the original proposal, i.e. within a free 5D theory? We suggest that a natural candidate for this purpose is the soft-wall model with…
We study multidimensional gravitational models with scalar curvature nonlinearities of the type 1/R and R^4. It is assumed that the corresponding higher dimensional spacetime manifolds undergo a spontaneous compactification to manifolds with warped product structure. Special attention is paid to the stability of the extra-dimensional factor spaces. It is shown that for certain parameter regions the systems allow for a freezing stabilization of these spaces. In particular, we find for the 1/R model that configurations with stabilized extra dimensions do not provide a late-time acceleration (the…
Based on the IR-improved bulk holographic AdS/QCD model which provides a consistent prediction for the mass spectra of resonance scalar, pseudoscalar, vector and axial vector mesons, we investigate its finite temperature behavior. By analyzing the spectral function of mesons and fitting it with a Breit-Wigner form, we perform an analysis for the critical temperature of mesons. The back-reaction effects of bulk vacuum are considered, the thermal mass spectral function of resonance mesons is calculated based on the back-reaction improved action. A reasonable melting temperature is found to be $T…
Bulk mesons propagating in chiral and gluon condensates, in a gravity background, are scrutinized in holographic soft wall AdS/QCD models, involving deformed dilatonic backgrounds. The configurational entropy of the $a_1$ axial vector, the $ρ$ vector, and the $f_0$ scalar meson families is then computed. Two types of informational entropic Regge trajectories are then obtained, where the logarithm of the mesons configurational entropy is expressed in terms of both the experimental meson mass spectra and their excitation number as well. Therefore the mass spectra of the next generation of elemen…
In this work, we consider a non-quadratic dilaton $Φ(z)=(κ\,z)^{2-α}$ in the context of the static soft wall model to describe the mass spectrum of a wide range of vector mesons from the light up to the heavy sectors. The effect of this non-quadratic approach is translated into non-linear Regge trajectories with the generic form $M^2=a\,(n+b)^ν$. We apply this sort of fits for the isovector states of $ω$, $ϕ$, $J/ψ$ and $Υ$ mesons and compare with the corresponding holographic duals. We also extend these ideas to the heavy-light sector by using the isovector set of parameters to extrapolate th…
Axial-Vector Lattice Benchmarks Reveal a Common Medium Response of Meson Screening in Hot QCD
University of Science and Technology of China（中国科学技术大学）；Peng Huanwu Center for Fundamental Theory（彭桓武理论研究中心）；Beijing Institute of Technology（北京理工大学）；Chongqing University（重庆大学）
The AdS/CFT correspondence defines a sector with universal strongly coupled dynamics in the field theory as the dual of pure gravity in AdS described by Einstein's equation with a negative cosmological constant. We explain here, from the field-theoretic viewpoint how the dynamics in this sector gets determined by the expectation value of the energy-momentum tensor \emph{alone}. We first show that the Boltzmann equation has very special solutions which could be \textit{functionally} completely determined in terms of the energy-momentum tensor alone. We call these solutions \textit{conservative …
Beta-decay and muon-capture experiments in nuclei are reviewed. The conserved vector current hypothesis is confirmed through the observed constancy of the vector coupling constant determined from the superallowed Fermi transitions and from the measurement of the weak-magnetism term in mirror Gamow-Teller transitions. The axial-vector and pseudoscalar coupling constants in the nucleon are determined from neutron decay and muon capture on the proton respectively. In finite nuclei, evidence for these coupling constants being reduced relative to their free-nucleon values is discussed. Meson-exchan…
The structure of the scalar mesons has been a subject of debate for many decades. In this work we look for $\bar{q}q$ states among the physical resonances using an extended Linear Sigma Model that contains scalar, pseudoscalar, vector, and axial-vector mesons both in the non-strange and strange sectors. We perform global fits of meson masses, decay widths and amplitudes in order to ascertain whether the scalar $\bar{q}q$ states are below or above 1 GeV. We find the scalar states above 1 GeV to be preferred as $\bar{q}q$ states.
