arXiv subjects

Amir H. Fariborz

Publications and source records attributed to Amir H. Fariborz.

At least 19 recordsLinked to original sources

arXiv2025

Strengthening the Bridge Between Chiral Lagrangians and QCD Sum-Rules

Previous work has shown that mesonic fields in chiral Lagrangians can be systematically connected to quark-level operators in QCD sum rules through chiral-symmetry constrained and energy-independent scale factor matrices. This framework yields universal scale factors associated with each chiral nonet, whether composed of quark-antiquark ($q\bar{q}$) or four-quark ($qq\bar{q}\bar{q}$) operators. Building on the demonstrated scale-factor universality for the $K_0^*$ isodoublet and $a_0$ isotriplet scalar mesons, we develop a revised Gaussian QCD sum-rule methodology that extends the analysis to higher-dimensional isospin sectors. To access nonperturbative information about resonances arising from final-state interactions, we introduce a background-resonance interference approximation. This approximation successfully reproduces both $πK$ scattering amplitude data and $πη$ scattering predictions. It also motivates new resonance models that enhance the scale-factor analysis linking chiral Lagrangians to QCD sum rules. Within this refined framework, we explore the scale factors for the $K_0^*$ and $a_0$ mesons across a sequence of increasingly detailed resonance models.

hep-ph↗

arXiv2025

Spinless glueballs in generalized linear sigma model

Within the framework of the generalized linear sigma model, a comprehensive analysis of scalar and pseudoscalar glueballs and their mixing with mesons is presented. The Lagrangian of the model contains two chiral nonets, a quark-antiquark type and a two-quark two-antiquark type. The pseudoscalar and scalar glueballs are introduced through their connections with the axial and the trace anomalies of QCD, respectively. It is found that in order to satisfy the axial anomaly and at the same time accurately generate all seven eta masses, it is necessary to include at least two pseudoscalar glueballs, a physical one and an unphysical one that gets integrated out and yields an effective instanton-type term which is needed in generation of the eta masses. At the leading order, which corresponds to keeping effective terms in the Lagrangian that contain no more than eight underlying quarks and antiquarks, the mass spectrum of the model is worked out and shown to be in complete agreement with experiment. The quark and glue contents of the isosinglet scalars below 2 GeV, and of the isosinglet pseudoscalars up to around 2.2 GeV, are analyzed in detail and their correlations with the scalar glueball condensate are examined. Decay widths of isosinglet scalars as well as different self consistencies within this framework are used to probe the glueball condensate and thereby estimate the quark and glue contents of these states. In the pseudoscalar sector, the state that is dominantly made of glue is clearly a state with mass above 2 GeV. In the scalar sector, the identification of glue contents is less certain and in principle the three isosinglets in the 1.5-2.0 GeV can contain substantial glue. These glue contents are determined as functions of the scalar glueball condensate which is the key quantity in this analysis.

hep-ph↗

arXiv2025

Extending the Bridge Connecting Chiral Lagrangians and QCD Gaussian Sum-Rules for Low-Energy Hadronic Physics

It has previously been demonstrated that the mesonic fields in chiral Lagrangians can be related to the quark-level operators of QCD sum-rules via energy-independent (constant) scale factor matrices constrained by chiral symmetry. This leads to universal scale factors for each type of chiral nonet related to quark-antiquark ($q\bar q$) operators and four-quark ($qq\bar q\bar q$) operators. Motivated by these successful demonstrations of scale-factor universality for the $K_0^*$ isodoublet and $a_0$ isotriplet scalar mesons, a revised Gaussian QCD sum-rule methodology is developed that enables the extension to higher-dimensional isospin sectors, including the possibility of mixing with glueball components. Moreover, to extract non-perturbative information about a resonance stemming from the final state interactions of its decay products, a background-resonance interference approximation is developed and shown to provide an excellent description of both $πK$ scattering amplitude data and $πη$ scattering calculations. This background-resonance interference approximation inspires new resonance models as ingredients in the scale-factor analysis connecting chiral Lagrangians and QCD Gaussian sum-rules. Using the revised Gaussian QCD sum-rule methodology, key properties of the scale factors are examined for the $K_0^*$ isodoublet and $a_0$ isotriplet scalar mesons for a sequence of increasingly sophisticated resonance models. Gaussian sum-rules are demonstrated to have sufficient resolution to distinguish between different resonance models, and it is shown that the background-resonance interference approximation not only describes $\{πK,πη\}$ scattering, but leads to the best universality and energy-independence properties of the scale factors.

hep-ph↗

arXiv2022

Chiral Nonet Mixing in $πη$ Scattering

The generalized linear sigma model for mixing among two- and four-quark components of scalar (and psedudosclar) mesons below and above 1 GeV is applied to the $πη$ channel in which the isovector scalars $a_0(980)$ and $a_0(1450)$ are probed. In the leading order, the model parameters have been previously fixed by various low-energy experimental data, and then applied to $ππ$ and $πK$ channels in which the properties of the light and broad $σ$ and $κ$ mesons are extracted in agreement with estimates reported in the literature. With the same parameters fixed in the leading order, in the present work the prediction of the model for the $πη$ scattering amplitude in the elastic region is given and unitarized with the K-matrix method. The poles of the unitarized scattering amplitude, which determine the mass and decay width of $a_0(980)$ and $a_0(1450)$ are computed. It is found that the model predicts an isovector scalar state below 1 GeV, with mass 984 $\pm$ 6 MeV and decay width 108 $\pm$ 30 MeV which is a clear signal for the $a_0(980)$. The $a_0$ pole extracted in this work, further supports the plausibility of the mixing patterns for scalar mesons predicted by this model according to which there is a significant underlying mixing among scalars below and above 1 GeV, with those below 1 GeV being generally of four-quark nature while those above 1 GeV being overall closer to quark-antiquark states. Predictions for various scattering lengths as well as for properties of $a_0(1450)$ are also presented.

hep-ph↗

arXiv2022

Non-inertial torques and the Euler equation

The fundamental equation describing the rotational dynamics of a rigid body is ${\vec τ}=d{\vec L} / dt$ which is a straightforward consequence of the Newton's second law of motion and is only valid in an inertial coordinate system. While this equation is written down by an inertial observer, for practical purposes, it is worked out within a non-inertial ancillary coordinate system which is typically fixed in the rigid body. This results in the famous Euler equation for rotation of the rigid bodies. We show that it is also possible to describe the rotational dynamics of a rigid body from the point of view of a non-inertial observer (rotating with the ancillary coordinate system fixed in the rigid body), provided that the non-inertial torques are taken into account. We explicitly calculate the non-inertial torques and express them in terms of physical characteristics of the rigid body. We show that the resulting dynamical equations exactly recover the Euler equation.

physics.class-ph↗

arXiv2021

Spinless mesons and glueballs mixing patterns in SU(3) flavor limit

We present a detailed study of the interactions among scalar and pseudoscalar mesons and glueballs within the framework of the generalized linear sigma model in the SU(3) flavor limit. The basis of our approach is to develop a global understanding of light scalar and pseudoscalar mesons (up to around 2 GeV) and thereby explore the underlying mixings among composite quark matter fields and glueballs. The chiral sector of the Lagrangian is formulated in terms of two chiral nonets representing quark-antiquarks and tetraquarks (in the leading order, this sector contains terms with eight or fewer number of quak or antiquark lines). The Lagrangian also contains a sector that represents scalar and pseudoscalar glueballs and their interactions with the matter chiral fields, in a manner that the axial and trace anomalies of QCD are exactly realized. In this construct, the model has two scalar octets and two pdeudoscalar octets (each a linear combination of two- and four-quark components), as well as three scalar SU(3) singlets and three pseudoscalar SU(3) singlets (each a linear combination of two- and four-quark components as well as a glueball component). With the inputs of the experimental masses of $a_0(980)$, $a_0(1450)$, and the masses of $π(137)$, $π(1300)$ and their decay constants, we perform an extensive numerical simulation to determine the boundaries of the parameter space of the model. We further incorporate experimental data on the mass spectrum of eta states as well as on several decay widths and decay ratios of $f_0$ states to zoom in on the parameter space and make predictions for the substructure of pseudoscalar and scalar SU(3) octets and singlets as well as for the pseudoscalar and scalar glueball masses. We find the scalar and pseudoscalar glueball masses around 1.6 and 2.0 GeV, respectively.

hep-ph↗

arXiv2020

Universal Scale Factors: A Bridge Between Chiral Lagrangians and QCD Sum-Rules

Chiral Lagrangian mesonic fields can be connected to QCD quark operators via matrix operators containing scale factors. These scale factor matrices are shown to be constrained by chiral symmetry, resulting in a universal scale factor for each Chiral Lagrangian nonet. QCD sum-rules, combined with mixing angles from Chiral Lagrangian analyses, are used to determine the scale factors for the $a_0$ isotriplet and $K_0^*$ isodoublet scalar mesons. The resulting scale factors verify the universality property, providing a validation of the scale factor matrices connecting Chiral Lagrangian mesonic fields and quark operators.

hep-ph↗

arXiv2020

Universal scale factors relating mesonic fields and quark operators

Scale factor matrices relating mesonic fields in chiral Lagrangians and quark-level operators of QCD sum-rules are shown to be constrained by chiral symmetry, resulting in universal scale factors for each chiral nonet. Built upon this interplay between chiral Lagrangians and QCD sum-rules, the scale factors relating the $a_0$ isotriplet scalar mesons to their underlying quark composite field were recently determined. It is shown that the same technique when applied to $K_0^*$ isodoublet scalars reproduces the same scale factors, confirming the universality property and further validating this connection between chiral Lagrangians and QCD sum-rules which can have nontrivial impacts on our understanding of the low-energy QCD, in general, and the physics of scalar mesons in particular.

hep-ph↗

arXiv2019

The Bridge Between Chiral Lagrangians and QCD Sum-Rules

Properties of the scale-factor matrices forming a bridge between the mesonic fields of chiral Lagrangians and quark-level structures of QCD sum-rules are reviewed. The scale-factor matrices combined with mixing angles provide a physical projection of a QCD correlation function matrix that disentangles the mesonic states. This methodology is illustrated for the isotriplet $a_0(980)$-$a_0(1450)$ system, and the scale factors are determined from the combined inputs of QCD sum-rules and chiral Lagrangians. The resulting scale factors are shown to be in good agreement with the vacuum expectation values in the chiral Lagrangian framework. The sensitivity of the scale factors on the gluon condensate QCD sum-rule parameter is explored.

hep-ph↗

arXiv2018

Generalized linear sigma model with two glueballs

We present a generalized linear sigma model that includes both scalar and pseudoscalar glueballs in addition to a quark-antiquark as well as a four-quark chiral nonet. Utilizing the axial and trace anomalies of QCD (at the effective mesonic level), we aim to develope the most general structure of the Lagrangian which can be used to study the interaction of quarkonia with glueballs. We then study the effect of scalar glueball on the vacuum of the model by considering a decoupling limit in which the glueball fields are decoupled from quarkonia. This determines the properties of the pure scalar glueball and builds a practical foundation for determining the model parameters when the interactions are turned on.

hep-ph↗

arXiv2018

Quark and glue spectroscopy of scalars and pseudoscalars in SU(3) flavor limit

Within the framework of the generalized linear sigma model with glueballs recently proposed [1,2], we study the schematic spectroscopy of scalar and pseudoscalar mesons in the SU(3) flavor limit and explore their quark and glue contents. In this framework, for both scalars and pseudoscalars, the two octet physical states are admixtures of quark-antiquark and four-quark components, and the three singlet states contain quark-antiquark, four-quark and glue components. We identify the two scalar octets with $a_0(980)$ and $a_0(1450)$ and the two pseudoscalar octets with $π(137)$ and $π(1300)$. We show that, as expected, the light pseudoscalar octet is made dominantly of quark-antiquarks whereas the light scalar octet has a reversed substructure with a dominant four-quark component. The case of singlets is more complex due to surplus of states up to around 2 GeV. We consider all 35 permutations for identifying the three pseudoscalar singlets of our model with three of the seven experimental candidates. Our numerical simulation unambiguously identifies the lightest and the heaviest pseudoscalar singlets with $η(547)$ and $η(2225)$, respectively, and favors the identification of the middle singlet with either $η(1295)$ or $η(1405)$ [or, to a lesser extent, with $η(1475)$] and thereby allows a probe of their substructures. We then estimate the quark and glue components and find that the three pseudoscalar singlets (from lightest to heaviest) are mainly of quark-antiquark, four-quark and glue substructure, while the corresponding three scalar singlets (from lightest to heaviest) are of four-quark, quark antiquark and glue contents. The masses of pure pseudoscalar and scalar glueballs are estimated around 2.0 and 1.6 GeV, respectively.

hep-ph↗

arXiv2018

Comment on scalar glueball mass

We study the interaction of scalar glueball with quark-antiquark and four-quark spinless meson fields within the framework of a generalized linear sigma model in which the trace anomaly of QCD is exactly realized. To determine the pure scalar glueball mass ($m_h$), we consider the decoupling limit in which the scalar glueball decouples from the meson fields. We find the exact relationship $m_h = 2\, h_0$ where $h_0$ is the vacuum expectation value of the scalar glueball field independent of the properties of the framework used.

hep-ph↗

arXiv2017

Electromagnetic trace anomaly in a generalized linear sigma model

We build the electromagnetic trace anomaly effective term for a generalized linear sigma model with two chiral nonets, one with a quark-antiquark structure, the other one with a four quark content. In the leading order of this framework, we study the decays into two photons of the lowest isosinglet scalar mesons. We find that the direct inclusion of underlying mixing among two- and four-quark components in the trace anomaly term is essential in order for the model prediction to agree with the available experimental data on decay width of $f_0(980)$ to two photons. Consequently, this sets a lower bound of 0.5 KeV on the decay with of $f_0(500)$ to two photons.

hep-ph↗

arXiv2017

A solution to the naturalness problem

We present a solution to the naturalness problem of the electroweak scale based on a change of variable in the Fourier space of non supersymmetric nature that transforms a boson into a fermion and viceversa. This is exemplified for that part of the standard model Lagrangian that contains a Dirac fermion coupled with the Higgs field. The full Lagrangian which contains both the initial particles and the partners obtained through this method is invariant under the symmetry associated to this change of variables and is free of quadratic divergences to the scalar particles present in the Lagrangian. The partners appear mostly as "off-shell" states thus explaining their experimental absence at any particle accelerators.

hep-ph↗

arXiv2017

Generalized fermion symmetry, its currents algebra and Ward-Takahashi identities

We introduce a new local symmetry into the fermion sector of a gauge invariant Lagrangian which may or may not contain a scalar or spontaneous symmetry breaking. The Standard Model in the unitary gauge and QCD are particular cases where this symmetry may apply. We determine the associated vector and axial vector currents and their conservation laws. We show that a single current conservation law may lead to multiple Ward-Takahashi identities. Our results can potentially have important consequences for effective models of low-energy QCD and hadron structure. As an specific example, we discuss the construction of tetraquark states within a generalized linear sigma model and show that this new symmetry probes the tetraquarks in a manner that is consistent with the large $N_c$ limit of QCD.

hep-ph↗

arXiv2017

Electromagnetic axial anomaly in a generalized linear sigma model

We construct the electromagnetic anomaly effective term for a generalized linear sigma model with two chiral nonets, one with a quark-antiquark structure, the other one with a four quark content. We compute in the leading order of this framework the decays into two photons of six pseudoscalars: $π_0(137)$, $π_0(1300)$, $η(547)$, $η(958)$, $η(1295)$ and $η(1760)$. Our results agree well with the available experimental data.

hep-ph↗

arXiv2016

Examining a possible cascade effect in chiral symmetry breaking

We examine a toy model and a cascade effect for confinement and chiral symmetry breaking which consists in several phase transitions corresponding to the formation of bound states and chiral condensates with different number of fermions for a strong group. We analyze two examples: regular QCD where we calculate the "four quark" vacuum condensate and a preon composite model based on QCD at higher scales. In this context we also determine the number of flavors at which the second chiral and confinement phase transitions occur and discuss the consequences.

hep-ph↗

arXiv2016

Mass Ansatze for the standard model fermions from a composite perspective

We consider a composite model in which the standard model fermions are bound states of elementary spin $\frac{1}{2}$ particles, the preons, situated in the conjugate product representation of the color group. In this framework we propose and analyze two mass Ansatze one for the leptons, the other one for the quarks, based on mass formulae of the Gell-Mann Okubo type. We find that these mass Ansatze can give an adequate description of the known standard model fermion masses.

hep-ph↗