arXiv subjects

Jose L. Goity

Publications and source records attributed to Jose L. Goity.

13 recordsLinked to original sources

arXiv2024

Target normal single-spin asymmetry in inclusive electron-nucleon scattering in the 1/Nc expansion

The target normal single-spin asymmetry in electron nucleon scattering is studied in the framework of the 1/Nc expansion of QCD, which allows for a rigorous description in the energy range that includes the Delta resonance and below the second baryon resonance region. The asymmetry is driven by the absorptive part of the two-photon exchange component of the scattering amplitude, being therefore the most unambiguous two-photon exchange effect. Such amplitude is shown to be described up to the next to leading order in the 1/Nc expansion only in terms of the charge and magnetic form factors of the nucleons, consequence of the approximate $SU(4)$ spin flavor symmetry valid in the large Nc limit for baryons. A discussion is provided of the 1/Nc expansion framework along with the results for the asymmetries in elastic, inelastic, and inclusive electron-nucleon scattering.

hep-ph↗

arXiv2023

QCD angular momentum in $N \rightarrow Δ$ transitions

$N \rightarrow Δ$ transitions offer new possibilities for exploring the isovector component of the QCD quark angular momentum (AM) operator causing the $J^{u - d}$ flavor asymmetry in the nucleon. We extend the concept of QCD AM to transitions between baryon states, using light-front densities of the energy-momentum tensor in transversely localized states. We calculate the $N \rightarrow Δ$ transition AM in the $1/N_c$ expansion, connect it with the $J^{u - d}$ flavor asymmetry in the nucleon, and estimate the values using lattice QCD results. In the same setup we connect the transition AM to the transition GPDs sampled in hard exclusive electroproduction processes with $N \rightarrow Δ$ transitions, enabling experimental study of the transition AM.

hep-ph↗

arXiv2023

Target normal single-spin asymmetry in inclusive electron-nucleon scattering in the 1/Nc expansion

The target normal single-spin asymmetry in inclusive electron-nucleon scattering is studied in the low-energy regime that includes the $Δ$ resonance. The particular interest in the asymmetry resides in that it is driven by two-photon exchange effects. It probes the spin-dependent absorptive part of the two-photon exchange amplitude, which is free of infrared and collinear singularities and represents the most pristine expression of two-photon exchange dynamics. The study presented here uses the 1/Nc expansion of QCD, which combines the $N$ and $Δ$ through the emergent SU(4) spin-flavor symmetry in the baryon sector and allows for a systematic construction of the transition EM currents. The analysis includes the first subleading corrections in the 1/Nc expansion and presents results for elastic and inelastic final states. The asymmetry is found to be in the range $10^{-3}-10^{-2}$. The $Δ$ resonance plays an important role as an intermediate state in the elastic asymmetry and as a final state in the inclusive asymmetry.

hep-ph↗

arXiv2019

The SU(3) Vector Currents in BChPT x 1/Nc

Baryon Chiral Perturbation Theory (BChPT) combined with the 1/Nc expansion is applied to the SU(3) vector currents. In terms of the xi power counting linking the low energy and 1/Nc expansions according to O(xi) = O(p) = O(1/Nc), the study is carried out to next-to-next-to-leading order, and it includes SU(3) breaking corrections to the |Delta S|= 1 vector charges, charge radii, and magnetic moments and radii. The results are obtained for generic Nc, allowing for investigating the various scalings in Nc.

hep-ph↗

arXiv2019

Baryon sigma terms in SU(3) BChPT x 1/Nc

ChPT and the $1/N_c$ expansion provide systematic frameworks for the strong interactions at low energy. A combined framework of both expansions has been developed and applied for baryons with three light-quark-flavors. The small scale expansion of the combined approach is identified as the $ξ$-expansion, in which the power counting of the expansions is linked according to $O(p)=O(1/N_c)=O(ξ)$. The physical baryon masses as well as lattice QCD baryon masses for different quark mass masses are analyzed to $O(ξ^3)$ in that framework. $σ$ terms are addressed using the Feynman Hellmann theorem. For the nucleon, a useful connection between the deviation of the Gell-Mann-Okubo relation and the $σ$ term $σ_{8N}$ associated with the scalar density $\bar u u+\bar d d-2\bar s s$ is identified. In particular, the deviation from the tree level relation $σ_{8N}=\frac 13(2 m_N-m_Σ-m_Ξ)$, which gives rise to the so called $σ$-term puzzle, is studied in the $ξ$-expansion. A large correction non-analytic in $ξ$ results for that relation, making plausible the resolution of the puzzle. Issues with the determination of the strangeness $σ$ terms are discussed, emphasizing the need for lattice calculations at smaller $m_s$ for better understanding the range of validity of the effective theory. The analysis presented here leads to $σ_{πN}=69(10)$~MeV and $σ_{πΔ}=60(10)$~MeV.

hep-ph↗

arXiv2019

BChPT$\times 1/{\rm N_c}$ in SU(3): a more effective theory

The chiral and $1/N_c$ expansions are combined in the description of low energy baryons. The combination furnishes a better behaved expansion, consequence of exactly eliminating large terms that violate the $1/N_c$ expansion and which are typical of formulations of BChPT where consistency with the large $N_c$ limit is disregarded. The improvements are particularly dramatic in the case of SU(3). The general framework is outlined and applications to the vector charges and axial couplings are presented along with a comparison with Lattice QCD results with three quark flavors.

hep-ph↗

arXiv2018

Baryon Chiral Perturbation Theory combined with the ${\mathbf{1/N_c}}$ Expansion in SU(3) I: Framework

Baryon Chiral Perturbation Theory combined with the $1/N_c$ expansion is implemented for three flavors. Baryon masses, vector charges and axial vector couplings are studied to one-loop and organized according to the $ξ$-expansion, in which the $1/N_c$ and the low energy power countings are linked according to $1/N_c={\cal{O}}(ξ)={\cal{O}}(p)$. The renormalization to ${\cal{O}}(ξ^3)$ necessary for the mentioned observables is provided, along with applications to the baryon masses and axial couplings as obtained in lattice QCD calculations.

nucl-th↗

arXiv2014

Baryon spin-flavor structure from an analysis of lattice QCD results of the baryon spectrum

The excited baryon masses are analyzed in the framework of the $1/N_c$ expansion using the available physical masses and also the masses obtained in lattice QCD for different quark masses. The baryon states are organized into irreducible representations of $SU(6)\times O(3)$, where the $[{\bf{56}},\ell^P=0^+]$ ground state and excited baryons, and the $[{\bf{56}},2^+]$ and $[{\bf{70}},1^-]$ excited states are analyzed. The analyses are carried out to order 1/Nc and first order in the quark masses. The issue of state identifications is discussed. Numerous parameter independent mass relations result at those orders, among them the well known Gell-Mann-Okubo and Equal Spacing relations, as well as additional relations involving baryons with different spins. It is observed that such relations are satisfied at the expected level of precision. From the quark mass dependence of the coefficients in the baryon mass formulas an increasingly simpler picture of the spin-flavor composition of the baryons is observed with increasing quark masses, as measured by the number of significant mass operators.

hep-ph↗

arXiv2014

The baryon vector current in the combined chiral and 1/Nc expansions

The baryon vector current is computed at one-loop order in large-Nc baryon chiral perturbation theory, where Nc is the number of colors. Loop graphs with octet and decuplet intermediate states are systematically incorporated into the analysis and the effects of the decuplet-octet mass difference and SU(3) flavor symmetry breaking are accounted for. There are large-Nc cancellations between different one-loop graphs as a consequence of the large-Nc spin-flavor symmetry of QCD baryons. The results are compared against the available experimental data through several fits in order to extract information about the unknown parameters. The large-Nc baryon chiral perturbation theory predictions are in very good agreement both with the expectations from the 1/Nc expansion and with the experimental data. The effect of SU(3) flavor symmetry breaking for the |Delta S|=1 vector current form factors f1(0) results in a reduction by a few percent with respect to the corresponding SU(3) symmetric values.

hep-ph↗

arXiv2012

Holographic models and the QCD trace anomaly

Five dimensional dilaton models are considered as possible holographic duals of the pure gauge QCD vacuum. In the framework of these models, the QCD trace anomaly equation is considered. Each quantity appearing in that equation is computed by holographic means. Two exact solutions for different dilaton potentials corresponding to perturbative and non-perturbative beta-functions are studied. It is shown that in the perturbative case, where the beta-function is the QCD one at leading order, the resulting space is not asymptotically AdS. In the non-perturbative case, the model considered presents confinement of static quarks and leads to a non-vanishing gluon condensate, although it does not correspond to an asymptotically free theory. In both cases analyses based on the trace anomaly and on Wilson loops are carried out.

hep-ph↗

arXiv2007

Strong and Electromagnetic Mass Splittings in Heavy Mesons

The contributions to heavy meson mass differences by the strong hyperfine interaction, the light quark masses and the electromagnetic interaction are obtained from the empirical values of the $D$, $D^*$, $B$ and $B^*$ masses by means of a mass formula based on the heavy quark mass expansion. The three different types of contributions are determined with significant accuracy to next to leading order in that expansion.

hep-ph↗

arXiv2004

1/Nc Countings in Baryons

The $1/N_c$ power countings for baryon decays and configuration mixings are determined by means of a non-relativistic quark picture. Such countings are expected to be robust under changes in the quark masses, and therefore valid as these become light. It is shown that excited baryons have natural widths of ${\cal{O}}(N_c^0)$. These dominant widths are due to the decays that proceed directly to the ground state baryons, with cascade decays being suppressed to ${\cal{O}}(1/N_c)$. Configuration mixings, defined as mixings between states belonging to different $O(3)\times SU(2 N_f)$ multiplets, are shown to be sub-leading in an expansion in $1/\sqrt{N_c}$ when they involve the ground state baryons, while the mixings between excited states can be ${\cal{O}}(N_c^0)$.

hep-ph↗

arXiv1998

Operator Analysis of L=1 Baryon Masses in Large N_c QCD

We consider in detail the mass operator analysis for the nonstrange L=1 excited baryons in large N_c QCD. We present a straightforward procedure for constructing the large N_c baryon wavefunctions, and provide complete analytic expressions for the matrix elements of all the independent isosinglet mass operators. We discuss the relationship between the old-fashioned operator analyses based on nonrelativistic SU(6) symmetry and the modern large N_c approach, which has a firmer theoretical foundation. We then suggest a possible dynamical interpretation for the subset of operators preferred strongly by the data.

hep-ph↗