Background Dilaton Field Research Articles

Celestial Liouville theory for Yang-Mills amplitudes

We consider Yang-Mills theory with the coupling constant and theta angle determined by the vacuum expectation values of a dynamical (complex, zero mass) dilaton field. We discuss the tree-level N-gluon MHV scattering amplitudes in the presence of a nontrivial background dilaton field and construct the corresponding celestial amplitudes by taking Mellin transforms with respect to the light cone frame energies. In this way, we obtain two-dimensional CFT correlators of primary fields on the celestial sphere. We show that the celestial Yang-Mills amplitudes evaluated in the presence of a spherical dilaton shockwave are given by the correlation functions of primary field operators factorized into the holomorphic current operators times the “light” Liouville operators. They are evaluated in the semiclassical limit of Liouville theory (the limit of infinite central charge) and are determined by the classical Liouville field describing metrics on the celestial sphere.

Elements of celestial conformal field theory

In celestial holography, four-dimensional scattering amplitudes are considered as two-dimensional conformal correlators of a putative two-dimensional celestial conformal field theory (CCFT). The simplest way of converting momentum space amplitudes into CCFT correlators is by taking their Mellin transforms with respect to light-cone energies. For massless particles, like gluons, however, such a construction leads to three-point and four-point correlators that vanish everywhere except for a measure zero hypersurface of celestial coordinates. This is due to the four-dimensional momentum conservation law that constrains the insertion points of the operators associated with massless particles. These correlators are reminiscent of Coulomb gas correlators that, in the absence of background charges, vanish due to charge conservation. We supply the background momentum by coupling Yang-Mills theory to a background dilaton field, with the (complex) dilaton source localized on the celestial sphere. This picture emerges from the physical interpretation of the solutions of the system of differential equations discovered by Banerjee and Ghosh. We show that the solutions can be written as Mellin transforms of the amplitudes evaluated in such a dilaton background. The resultant three-gluon and four-gluon amplitudes are single-valued functions of celestial coordinates enjoying crossing symmetry and all other properties expected from standard CFT correlators. We use them to extract OPEs and compare them with the OPEs extracted from multi-gluon celestial amplitudes without a dilaton background. We perform the conformal block decomposition of the four-gluon single-valued correlator and determine the dimensions, spin and group representations of the entire primary field spectrum of the Yang-Mills sector of CCFT.

Dual D-brane actions in nonrelativistic string theory

We study worldvolume actions for D-branes coupled to the worldvolume U(1) gauge field and Ramond-Ramond (RR) potentials in nonrelativistic string theory. This theory is a self-contained corner of relativistic string theory and has a string spectrum with a Galilean-invariant dispersion relation. We therefore refer to such D-branes in nonrelativistic string theory as nonrelativistic D-branes. We focus on the bosonic fields in spacetime and also couple the D-branes to general closed string geometry, Kalb-Ramond, and dilaton background fields. We dualize nonrelativistic D-branes by performing a duality transformation on the worldvolume U(1) gauge field and uncover novel dual D-brane actions. This generalizes familiar properties, such as the SL(2, ℤ) duality in Type IIB superstring theory and the relation between Type IIA superstring and M-theory, to nonrelativistic string and M-theory. Moreover, we generalize the limit of string theory, in which nonrelativistic string theory arises, to include RR potentials. This stringy limit induces a codimension-two foliation structure in spacetime. This spacetime geometry is non-Riemannian and known as string Newton-Cartan geometry. In contrast, nonrelativistic M-theory that we probe by dualizing D2- and D4-branes in nonrelativistic string theory arises as a membrane limit of M-theory, and it is coupled to a membrane Newton-Cartan geometry with a codimension-three foliation structure. We also discuss T-duality in nonrelativistic string theory and generalize Buscher rules from earlier work to include RR potentials.

Hadron Structure in Holographic Quantum Chromodynamics

Hadrons and multiquark states are discussed within the context of holographic quantum chromodynamics. This approach is based on an action that describes the hadron structure with breaking of conformal and chiral symmetry and includes confinement through the presence of a background dilaton field. According to gauge/gravity duality, five-dimensional boson and fermion fields, moving in AdS space, are dual to the four-dimensional fields on the surface of the AdS sphere, which correspond to hadrons. In this framework, the hadron wave functions – the building blocks of the hadron properties – are dual to the profiles of the AdS fields in the fifth (holographic) dimension, which is identified with a scale. As applications, we consider the properties of hadrons and multiquark states.

Strongly interacting matter from holographic QCD model

We introduce the 5-dimension dynamical holographic QCD model, which is constructed in the graviton-dilaton-scalar framework with the dilaton background field $\Phi$ and the scalar field $X$ responsible for the gluodynamics and chiral dynamics, respectively. We review our results on the hadron spectra including the glueball and light meson spectra, QCD phase transitions and transport properties in the framework of the dynamical holographic QCD model.

Generalized Parton Distributions for Nucleon in the Impact Parameter Space

We investigate the generalized parton distributions (GPDs) for the proton and neutron in both momentum and position space in the soft-wall approach of anti-de Sitter/QCD model. The soft-wall model is based upon an action which incorporates confinement through the presence of a background dilaton field and the contribution of higher Fock states are holographically incorporated via studying the dynamics of 5D fermion fields of different scaling dimension. Our results are comparable with the other phenomenological models of the nucleon GPDs.

Dynamical three-field AdS/QCD model

The Anti-de Sitter Space/Conformal Field Theory (AdS/CFT) correspondence may offer new and useful insights into the non-perturbative regime of strongly coupled gauge theories such as Quantum Chromodynamics (QCD). We present an AdS/CFT-inspired model that describes the spectra of light mesons. The conformal symmetry is broken by a background dilaton field, and chiral symmetry breaking and linear confinement are described by a chiral condensate field. These background fields, along with a background glueball condensate field, are derived from a potential. We describe the construction of the potential, and the calculation of the meson spectra, which match experimental data well. We argue that the presence of the third background field is necessary to properly describe the meson spectra.

Dynamical holographic QCD model

We develop a dynamical holographic QCD model, which resembles the renormalization group from ultraviolet (UV) to infrared (IR). The dynamical holographic model is constructed in the graviton-dilaton-scalar framework with the dilaton background field $\Phi$ and scalar field $X$ responsible for the gluodynamics and chiral dynamics, respectively. We summarize our results on hadron spectra, QCD phase transition and transport properties including the jet quenching parameter and the shear/bulk viscosity in the framework of the dynamical holographic QCD model.

Scalar glueball in a soft-wall model of AdS/QCD

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 GeV <mG < 1.36+0.05−0.10 GeV. In terms of a background dilaton field Φ(z) = cz2, 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.

Dynamical holographic QCD model for glueball and light meson spectra

In this work, we offer a dynamical soft-wall model to describe the gluodynamics and chiral dynamics in one systematical framework. We firstly construct a quenched dynamical holographic QCD (hQCD) model in the graviton-dilaton framework for the pure gluon system, then develop a dynamical hQCD model for the two flavor system in the graviton-dilaton-scalar framework by adding light flavors on the gluodynamical background. For two forms of dilaton background field $\Phi=\mu_G^2z^2$ and $\Phi=\mu_G^2z^2\tanh(\mu_{G^2}^4z^2/\mu_G^2)$, the quadratic correction to dilaton background field at infrared encodes important non-perturbative gluodynamics and naturally induces a deformed warp factor of the metric. By self-consistently solving the deformed metric induced by the dilaton background field, we find that the scalar glueball spectra in the quenched dynamical model is in very well agreement with lattice data. For two flavor system in the graviton-dilaton-scalar framework, the deformed metric is self-consistently solved by considering both the chiral condensate and nonperturbative gluodynamics in the vacuum, which are responsible for the chiral symmetry breaking and linear confinement, respectively. It is found that the mixing between the chiral condensate and gluon condensate is important to produce the correct light flavor meson spectra. The pion form factor and the vector couplings are also investigated in the dynamical hQCD model. Besides, we give the criteria for the existence of linear quark potential from the metric structure, and show a negative quadratic dilaton background field is not favored in the graviton-dilaton framework.

Dilaton in a soft-wall holographic approach to mesons and baryons

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 show that in the case of the bound-state problem (hadronic mass spectrum) two versions of the model with a positive and negative dilaton profile are equivalent to each other by a special transformation of the bulk field. We also comment on recent works which discuss the dilaton sign in the context of soft-wall approaches.

Hadron properties in AdS/QCD

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. Results obtained for heavy-light meson masses and decay constants are consistent with predictions of HQET. In the baryon sector, applications to the baryon masses, nucleon electromagnetic form factors and generalized parton distributions are discussed.

Mesons and Baryons in a Soft-wall Holographic Approach

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.

S-wave scattering of fermion revisited

A model where a Dirac fermion is coupled to background dilaton field is considered to study s-wave scattering of fermion by a back ground dilaton black hole. It is found that an uncomfortable situation towards information loss scenario arises when one loop correction gets involved during bosonization.

Glueballs at finite temperature from AdS/QCD

Inspired in the AdS/CFT correspondence, a variety of holographic phenomenological models have been proposed in the last years to describe non-perturbative aspects of strong interactions. These models are denominated as AdS/QCD. In this work we review the use of the AdS/QCD soft-wall model to investigate the spectrum of scalar glueballs at finite temperature. The scalar glueball states are identified as the poles of the retarded correlation function of the glueball operator. In the gauge/gravity duality, these poles are determined by the quasinormal spectrum of a massless scalar field propagating in the bulk geometry that consists on an AdS5 black hole with a background dilaton field. We discuss some results for masses and decay widths of scalar glueballs in the plasma phase and analyze how these quantities evolve with temperature and momentum.

INVESTIGATING AdS/QCD DUALITY THROUGH THE SCALAR GLUEBALL CORRELATOR

We investigate AdS/QCD duality for the two-point correlation function of the lowest dimension scalar glueball operator, in the case of the IR soft wall model. We point out the role of the boundary conditions for the bulk-to-boundary propagator in determining the gluon condensates. We show how a low energy QCD theorem can be obtained within the AdS approach, together with a gluon condensate close to the commonly accepted value and robust against perturbation of the background dilaton field.

DOES CHIRAL FERMION COUPLED TO A BACKGROUND DILATON FIELD PRESERVE INFORMATION?

A model where chiral boson is coupled to a background dilaton field is considered to study the s-wave scattering of fermion by a background dilaton black hole. It is found that the scattering process of chiral fermion does not violate unitarity and information remains preserved. Faddevian anomaly plays a crucial role on the information scenario.

Nucleon electromagnetic and gravitational form factors from holography

The electromagnetic form factors of nucleons are calculated using an anti--de Sitter (AdS)/QCD model by considering a Dirac field coupled to a vector field in the five-dimensional AdS space. We also calculate a gravitational or energy-momentum form factor by perturbing the metric from the static AdS solution. We consider both the hard-wall model where the AdS geometry is cut off at ${z}_{0}$ and the soft-wall model where the geometry is smoothly cut off by a background dilaton field.

Proper acceleration, the geometric tachyon and the dynamics of a fundamental string near Dp branes

We present a detailed analysis of our recent observation that the origin of the geometric tachyon, which arises when a Dp brane propagates in the vicinity of a stack of coincident NS5 branes, is due to the proper acceleration generated by the background dilaton field. We show that when a fundamental string (F-string), described by the Nambu–Goto action, is moving in the background of a stack of coincident Dp branes, the geometric tachyon mode can also appear since the overall conformal mode of the induced metric for the string can act as a source for proper acceleration. We also studied the detailed dynamics of the F-string as well as the instability by mapping the Nambu–Goto action of the F-string to the tachyon effective action of the non-BPS D-string. We qualitatively argue that the condensation of the geometric tachyon is responsible for the (F,Dp) bound state formation.

Light scalar mesons in the soft-wall model of AdS/QCD

We study light scalar mesons in the holographic QCD soft-wall model with a background dilaton field. The masses and decay constants are compatible with experiment and QCD determinations if a{sub 0}(980) and f{sub 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 derived on the anti-de Sitter side and in 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: we discuss how this discrepancy is related to the description of chiral symmetry breaking in this model, and the possible solutions.