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A. Calle Cordon

Publications and source records attributed to A. Calle Cordon.

17 recordsLinked to original sources
arXiv2014

The Nc dependencies of baryon masses: Analysis with Lattice QCD and Effective Theory

Baryon masses at varying values of Nc and light quark masses are studied with Lattice QCD and the results are analyzed in a low energy effective theory based on a combined framework of the 1/Nc and Heavy Baryon Chiral Perturbation Theory expansions. Lattice QCD results for Nc = 3, 5 and 7 obtained in quenched calculations, as well as results for unquenched calculations for Nc = 3, are used for the analysis. The results are consistent with a previous analysis of Nc = 3 Lattice QCD results, and in addition permit the determination of sub-leading in 1/Nc effects in the spin-flavor singlet component of the baryon masses as well as in the hyperfine splittings.

hep-ph↗
arXiv2013

Nucleon and Delta axial-vector couplings in 1/Nc - Baryon Chiral Perturbation Theory

In this contribution, baryon axial-vector couplings are studied in the framework of the combined 1/Nc and chiral expansions. This framework is implemented on the basis of the emergent spin-flavor symmetry in baryons at large Nc and HBChPT, and linking both expansions (ξ-expansion), where 1/Nc is taken to be a quantity O(p). The study is carried out including one-loop contributions, which corresponds to O(ξ^3) for baryon masses and O(ξ^2) for the axial couplings. An analysis of the Lattice QCD results for the axial couplings of both N and Δis presented.

nucl-th↗
arXiv2013

Baryon Masses and Axial Couplings in the Combined 1/Nc and Chiral Expansions

The effective theory for baryons with combined 1/Nc and chiral expansions is analyzed for non-strange baryons. Results for baryon masses and axial couplings are obtained in the small scale expansion, to be coined as the ξ-expansion, in which the 1/Nc and the low energy power countings are linked according to 1/Nc=O(ξ)=O(p). Masses and axial couplings are analyzed to O(ξ^3) and O(ξ^2) respectively, which correspond to next-to-next to leading order evaluations, and require one-loop contributions in the effective theory. The role of the spin-flavor approximate symmetry in baryons, consequence of the large Nc limit, is manifested in the physical world with Nc=3 in a significant way, as the analysis of its breaking in the masses and the axial couplings shows. Applications to the recent lattice QCD results on baryon masses and the nucleon's axial coupling are presented. It is shown that those results are naturally described within the effective theory at the order considered in the ξ-expansion.

nucl-th↗
arXiv2012

Baryon masses and axial charges in 1/Nc - ChPT

An analysis is presented of the ground state baryon's (N and Δ) masses and axial couplings in the combined 1/Nc and chiral expansions. Renormalization and alternative power counting schemes are discussed to one loop (NNLO). An application is made to lattice QCD results for non-strange baryon masses and the nucleon axial coupling as functions of the pion mass. This work represents a brief summary of a more extensive analysis to be presented elsewhere.

hep-ph↗
arXiv2011

Spin-Flavor van der Waals Forces and NN interaction

We study the Nucleon-Nucleon interaction in the Born-Oppenheimer approximation at second order in perturbation theory including the Δ resonance as an intermediate state. The potential resembles strongly chiral potentials computed either via soliton models or chiral perturbation theory and has a van der Waals like singularity at short distances which is handled by means of renormalization techniques. Results for the deuteron are discussed.

nucl-th↗
arXiv2010

Universal low energy features of two-body systems

We apply renormalization ideas to study low-energy interactions in two-body systems. As we will see this method highlights a model-independent description of a broad variety of systems ranging from ultra-could atoms to NN and Lambda-Lambda interactions.

nucl-th↗
arXiv2010

Effective interactions and long distance symmetries in the Nucleon-Nucleon system

Effective interactions, when defined in a coarse grained sense, such as Vlowk at the scale 450 MeV, display a remarkable symmetry pattern. Serber symmetry works with high accuracy for spin triplet states. Wigner SU(4) spin-isospin symmetry with nucleons in the fundamental representation works only for even partial waves exactly as predicted by large Nc limit of QCD with accuracy O(1/Nc^2). This suggests tailoring the very definition of effective interactions to provide a best possible fulfillment of long distance symmetries. With the Vlowk definition Wigner symmetry requires that chiral potentials have low cut-offs (450 MeV). Perturbative saturation of heavy mesonic resonances does not faithfully display the Serber symmetry pattern.

nucl-th↗
arXiv2010

Nucleon-Nucleon interaction, charge symmetry breaking and renormalization

We study the interplay between charge symmetry breaking and renormalization in the NN system for s-waves. We find a set of universality relations which disentangle explicitly the known long distance dynamics from low energy parameters and extend them to the Coulomb case. We analyze within such an approach the One-Boson-Exchange potential and the theoretical conditions which allow to relate the proton-neutron, proton-proton and neutron-neutron scattering observables without the introduction of extra new parameters and providing good phenomenological success.

nucl-th↗
arXiv2010

Renormalization of One Meson Exchange Potentials and Their Currents

The Nucleon-Nucleon One Meson Exchange Potential, its wave functions and related Meson Exchange Currents are analyzed for point-like nucleons. The leading Nc contributions generate a local and energy independent potential which presents 1/r^3 singularities, requiring renormalization. We show how invoking suitable boundary conditions, neutron-proton phase shifts and deuteron properties become largely insensitive to the nucleon substructure and to the vector mesons. Actually, reasonable agreement with low energy data for realistic values of the coupling constants (e.g. SU(3) values) is found. The analysis along similar lines for the Meson Exchange Currents suggests that this renormalization scheme implies tremendous simplifications while complying with exact gauge invariance at any stage of the calculation.

nucl-th↗
arXiv2009

Renormalization and Universality of Van der Waals forces

Renormalization ideas can profitably be exploited in conjunction with the superposition principle of boundary conditions in the description of model independent and universal scaling features of the singular and long range Van der Waals force between neutral atoms. The dominance of the leading power law is highlighted both in the scattering as well as in the bound state problem. The role of off-shell two-body unitarity and causality within the Effective Field Theory framework on the light of universality and scaling at low energies is analyzed.

cond-mat.other↗
arXiv2009

Low energy universality and scaling of Van der Waals forces

At long distances interactions between neutral ground state atoms can be described by the Van der Waals potential V(r) =-C6/r^6-C8/r^8 - ... . In the ultra-cold regime atom-atom scattering is dominated by s-waves phase shifts given by an effective range expansion p cot d0 (p) = -1/a0 + r0 p^2/2 + ... in terms of the scattering length a0 and the effective range r0. We show that while for these potentials the scattering length cannot be predicted, the effective range is given by the universal low energy theorem r0 = A + B/a0+ C/a0^2 where A,B and C depend on the dispersion coefficients Cn and the reduced di-atom mass. We confront this formula to about a hundred determinations of r0 and a0 and show why the result is dominated by the leading dispersion coefficient C6. Universality and scaling extends much beyond naive dimensional analysis estimates.

cond-mat.other↗
arXiv2009

Renormalization and Universality of NN interactions in Chiral Quark and Soliton Models

We use renormalization as a tool to extract universal features of the NN interaction in quark and soliton nucleon models, having the same long distance behaviour but different short distance components. While fine tuning conditions in the models make difficult to fit NN data, the introduction of suitable renormalization conditions supresses the short distance sensitivity. Departures from universality are equivalent to extracting information on the model nucleon structure.

hep-ph↗
arXiv2009

Renormalization vs Strong Form Factors for One Boson Exchange Potentials

We analyze the One Boson Exchange Potential from the point of view of Renormalization theory. We show that the nucleon-meson Lagrangean while predicting the NN force does not predict the NN scattering matrix nor the deuteron properties unambiguously due to the appearance of short distance singularities. While the problem has traditionally been circumvented by introducing vertex functions via phenomenological strong form factors, we propose to impose physical renormalization conditions on the scattering amplitude at low energies. Working in the large Nc approximation with pi,sigma,rho and omega mesons, we show that, once these conditions are applied, results for low energy phases of proton-neutron scattering as well as deuteron properties become largely insensitive to the form factors and to the vector mesons and yield a reasonable agreement with the data, for realistic values of the coupling constants.

nucl-th↗
arXiv2009

Serber symmetry, Large Nc and Yukawa-like One Boson Exchange Potentials

The Serber force has relative orbital parity symmetry and requires vanishing NN interactions in partial waves with odd angular momentum. We illustrate how this property is well fulfilled for spin triplet states with odd angular momentum and violated for odd singlet states for realistic potentials but fails for chiral potentials. We analyze how Serber symmetry can be accommodated within a large Nc perspective when interpreted as a long distance symmetry. A prerequisite for this is the numerical similarity of the scalar and vector meson resonance masses. The conditions under which the resonance exchange potential can be approximated by a Yukawa form are also discussed. While these masses arise as poles on the Second Riemann in pi-pi scattering, we find that within the large Nc expansion the corresponding Yukawa masses correspond instead to a well defined large Nc approximation to the pole which cannot be distinguished from their location as Breit-Wigner resonances.

nucl-th↗
arXiv2008

Wigner symmetry, Large Nc and Renormalized One Boson Exchange Potential

Wigner symmetry in Nuclear Physics provides a unique example of a non-perturbative long distance symmetry, a symmetry strongly broken at short distances. We analyse the consequences of such a concept within the framework of One Boson Exchange Potentials in NN scattering and keeping the leading Nc contributions. Phenomenologically successful relations between singlet 1S0 and triplet 3S1 scattering phase shifts are provided in the entire elastic region. We establish symmetry breaking relations among non-central phase shifts which are successfully fulfilled by even-L partial waves and strongly violated by odd-L partial waves, in full agreement with large Nc requirements.

nucl-th↗
arXiv2008

Scalar meson mass from renormalized One Boson Exchange Potential

We determine the mass and strength of the scalar meson from NN scattering data by renormalizing the One Boson Exchange Potential. This procedure provides a great insensitivity to the unknown short distance interaction making the vector mesons marginally important and allowing for SU(3) couplings in the 1S0 channel. The scalar meson parameters are tightly constrained by low energy np. We discuss whether this scalar should be compared to the recent findings based on the Roy equations analysis of pipi scattering.

nucl-th↗