arXiv subjects

Hao-qian Li

Publications and source records attributed to Hao-qian Li.

7 recordsLinked to original sources

arXiv2025

Holographic spectroscopy of fermion with instantons

Using the gauge-gravity duality, we investigate the fermionic spectroscopy in the D(-1)-D3 brane system. The background geometry of this system described by IIB supergravity includes a black (deconfined) and bubble (confined) D3-brane which corresponds respectively to a deconfined and a confined gauge theory in holography. The charge of the D(-1) brane as the D-instanton gives the gluon condensate in this model. To simplify the holographic setup, we first reduce briefly the ten-dimensional supergravity background produced by D(-1)-D3-branes to an equivalently five-dimensional background. Then the fermionic spectrum in the confined case is obtained by decomposing the fermion with dimensional reduction. In addition, by using the standard method for computing the Green function in the AdS/CFT dictionary, we derive the equations for the fermionic correlation functions and solve them numerically with the infalling boundary condition. Our numerical results in the deconfined case illustrate that the fermionic correlation function as spectral function includes two branches of the dispersion curves whose behavior is very close to the results obtained from the method of hard thermal loop. And the effective mass generated by the medium effect of fermion splits into two values due to the spin-dependent interactions induced by instantons. In the confined case, the holographic correlation function indicates several separated dispersion curves which illustrates consistently the onset mass in the fermionic spectrum we obtained. Therefore, this work in holography demonstrates the instantonic configuration is very influential to the fermion in QCD.

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arXiv2024

The worldvolume fermion as baryon in holographic QCD with instanton

In this work, we investigate the worldvolume fermion on the flavor brane in the D0-D4/D8 model which is holographically equivalent to the four-dimensional QCD with instantons, or equivalently with a theta angle. The action for the worldvolume fermion is obtained by the T-duality rules in string theory and we accordingly derive its effectively five-dimensional, canonical four-dimensional forms by using the systematical dimensional reduction and decomposition of spinor. Afterwards, we employ the AdS/CFT dictionary in order to evaluate the two-point correlation function as the spectral function for the worldvolume fermion and interpret the fermion as baryon by analyzing its quantum number with the baryon vertex in holography. In this sense, the interacted action involving the worldvolume fermion and gauge field on the flavor brane are finally derived in holography which describes the various interaction of meson and baryon with instantons in large-N limit. Therefore, this work provides a holographic picture to describe baryon and its interactions based on string theory, in particular, in the presence of instantons or a theta angle.

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arXiv2024

Out-of-time-order correlator as a detector of baryonic phase structure in holographic QCD with instanton

We study the out-of-time-order correlators (OTOC) of Skyrmion as baryon in the D0-D4/D8 model which is expected to be holographically dual to QCD with instantons as D0-branes or with a non-zero theta angle. Baryon states are identified to the excitations of the Skyrmion which are described by a holographic quantum mechanical system in this model. By employing the definition of OTOC in quantum mechanics, we derive the formulas and demonstrate explicitly the numerical calculations of the OTOC. Our calculation illustrates the quantum OTOC with imaginary Lyapunov coefficient indicates the possibly metastable baryonic status in the presence of the instanton while the classical OTOC can not, thus it reveals the instantonic or theta-dependent features of QCD are dominated basically by its quantum properties. Furthermore, the OTOC also implies the baryonic phase becomes really chaotic with real Lyapunov exponent if the instanton charge increases sufficiently which agrees with the unstable baryon spectrum presented in this model. In this sense, we believe the OTOC may be treated as a tool to detect the baryonic phase structure of QCD.

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arXiv2024

Correlation function of flavored fermion in holographic QCD

By using the gauge-gravity duality, we investigate the correlation function of flavored fermion in the \mathrm{D}_{p}/\mathrm{D}_{p+4} model as top-down approaches of holographic QCD for p=4,3. The bulk spinor, as the source of the flavored fermion in QCD, is identified to the worldvolume fermion on the flavor \mathrm{D}_{p+4}-branes and the standard form of its action can be therefore obtained by the T-duality rules in string theory. Keeping this in hand, we afterwards generalize the prescription for two-point correlation function in AdS/CFT dictionary into general D-brane backgrounds and apply it to the case of p=4,3, i.e. the D4/D8 and D3/D7 approach respectively. Resultantly, our numerical calculation with the bubble background always displays discrete peaks in the correlation functions which imply the bound states created by the flavored fermions as the confinement in QCD. With the black brane background, the onshell condition illustrated by the correlation function covers basically the dispersion curves of fermion obtained by the hard thermal loop approximation in the hot medium. Finally, we interpret the flavored fermions in the bubble background as baryons by taking into account a baryon vertex, then find the two-point correlation function is able to fit the lowest baryon spectrum. In this sense, we conclude remarkably that our top-down approach in this work could reveal the fundamental properties of QCD both in the confined and deconfined phase.

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arXiv2024

Out-of-time-order correlators of Skyrmion as baryon in holographic QCD

As the out-of-time-order correlator (OTOC) is a measure of quantum chaos and an important observable in the context of AdS/CFT, we investigate the OTOC of holographic Skyrmion which is described by an analytical quantum mechanical system from the D4/D8 model (as the holographic QCD). By employing the OTOC defined in quantum mechanics, we derive the formulas and demonstrate the numerical calculations of the OTOC explicitly which is also available for the general case with central force field. Our numerical evaluation illustrates the behaviors of the OTOC with large $N_{c}$, however the expected exponential growth of OTOC is not obtained. Besides, we also take a look at the classical limit of the OTOC and analyze the associated behaviors. At the end of this work, we additionally study the OTOC with three-dimensional Coulomb potential, as another example for the central force field, to support our analyses of the general properties of quantum OTOC.

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arXiv2022

Corrections to the instanton configuration as baryon in holographic QCD

In this work, we first derive the corrections to the instanton configuration of the flavored gauge field in the D4-D8 model with generic flavor numbers. Then, as the instanton configuration on the D8-branes represents equivalently baryon in this model, keeping our corrections in hand, we systemically study the spectrum of baryon, heavy-light baryon or heavy-light meson and find it is possible to fit the experimental data with the meson data in this model. Besides, we briefly outline how to include the interaction of glueball and heavy-light meson or baryon with our corrections, evaluate numerically the decay rate of the heavy-light meson or baryonic matter involving glueball. Since it is possible to fit all the spectra with same choice of the parameters to the experimental data, we believe our corrections improve the framework of D4-D8 model and the corrected instanton configuration is also useful to investigate other properties of baryon in holography.

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arXiv2022

Holographic Schwinger effect and electric instability with anisotropy

According to the gauge-gravity duality, we systematically study the Schwinger effect and electric instability with anisotropy in a top-down holographic approach. The anisotropic black brane and bubble (soliton) background in IIB supergravity are employed and the dual theories in these backgrounds are expected to be anisotropic theory at finite temperature and anisotropic theory with confinement respectively. Then performing the potential analysis, we find due to the anisotropy, the potential barrier behaves oppositely with parallel and perpendicular electric fields, and this behavior agrees with the previous study about the quark potential with anisotropy in this system. Afterwards, we evaluate the pair production rate by solving the equation of motion for a fundamental string numerically which reveals the consistent behavior with the potential analysis. Furthermore, the probe D7-brane as flavor is introduced into the bulk in order to investigate the electric instability. The vacuum decay rate can be obtained by evaluating the imaginary part of the D7-brane action which again agrees with our potential analysis. Solving the associated constraint of gauge field strength on the flavor brane, we finally obtain the V-A curve displaying the distinct behavior of the conductivity in parallel and perpendicular direction which is in agreement with some bottom-up and phenomenologically holographic approaches in anisotropic fluid. Accordingly, we believe this work may be remarkable to study the electric features in strongly coupled anisotropic system.

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