@article{general_llanes-estrada_cotanch_2007, title={Coulomb gauge approach to (qqg)over-bar hybrid mesons}, volume={51}, ISSN={["1434-6052"]}, DOI={10.1140/epjc/s10052-007-0298-3}, abstractNote={An effective Coulomb gauge Hamiltonian, Heff, is used to calculate the light (uūg), strange (ss̄g) and charmed (cc̄g) hybrid meson spectra. For the same two parameter Heff providing glueball masses consistent with lattice results and a good description of the observed u,d,s and c quark mesons, a large-scale variational treatment predicts that the lightest hybrid has JPC=0++ and mass 2.1 GeV. The lightest exotic 1-+ state is just above 2.2 GeV, near the upper limit of lattice and flux tube predictions. These theoretical formulations all indicate that the observed 1-+ π1(1600) and, more clearly, π1(1400) are not hybrid states. The Coulomb gauge approach further predicts that in the strange and charmed sectors, respectively, the ground state hybrids have 1+- with masses 2.1 and 3.8 GeV, while the first exotic 1-+ states are at 2.4 and 4.0 GeV. Finally, using our hybrid wavefunctions and the Franck–Condon principle, a novel experimental signature is presented to assist heavy hybrid meson searches.}, number={2}, journal={EUROPEAN PHYSICAL JOURNAL C}, author={General, I. J. and Llanes-Estrada, F. J. and Cotanch, S. R.}, year={2007}, month={Jul}, pages={347–358} }
 @article{general_wang_cotanch_llanes-estrada_2007, title={Light 1(-+) exotics: Molecular resonances}, volume={653}, ISSN={["1873-2445"]}, DOI={10.1016/j.physletb.2007.08.015}, abstractNote={Highlights in the search for nonconventional (non-qq¯) meson states are the π1(1400) and π1(1600) exotic candidates. Should they exist, mounting theoretical arguments suggest that they are tetraquark molecular resonances excitable by meson rescattering. We report a new tetraquark calculation within a model field theory approximation to Quantum Chromodynamics in the Coulomb gauge supporting this conjecture. We also strengthen this claim by consistently contrasting results with exotic state predictions for hybrid (qq¯g) mesons within the same theoretical framework. Our findings confirm that molecular-like configurations involving two color singlets (a resonance, not a bound state) are clearly favored over hybrid or color-exotic tetraquark meson (qq¯qq¯ atoms) formation. Finally, to assist needed further experimental searches we document a useful off-plane correlator for establishing the structure of these exotic systems along with similar, but anticipated much narrower, states that should exist in the charmonium and bottomonium spectra.}, number={2-4}, journal={PHYSICS LETTERS B}, author={General, Ignacio J. and Wang, Ping and Cotanch, Stephen R. and Llanes-Estrada, Felipe J.}, year={2007}, month={Sep}, pages={216–223} }
 @article{llanes-estrada_cotanch_szczepaniak_swanson_2004, title={Hyperfine meson splittings: chiral symmetry versus transverse gluon exchange}, volume={70}, ISSN={["1089-490X"]}, DOI={10.1103/physrevc.70.035202}, abstractNote={Meson spin splittings are examined within an effective Coulomb gauge QCD Hamiltonian incorporating chiral symmetry and a transverse hyperfine interaction necessary for heavy quarks. For light and heavy quarkonium systems the pseudoscalar-vector meson spectrum is generated by approximate Bardeen-Cooper- Schrieffer, random-phase approximation diagonalizations. This relativistic formulation includes both S and D waves for the vector mesons which generates a set of coupled integral equations. A smooth transition from the heavy to the light quark regime is found with chiral symmetry dominating the p-r mass difference. A reasonable description of the observed meson spin splittings and chiral quantities, such as the quark condensate and the p mass, is obtained. Similar comparisons with Tamm-Dancoff diagonalizations, which violate chiral symmetry, are deficient for light pseudoscalar mesons, indicating the need to simultaneously include both chiral symmetry and a hyperfine interaction. The hb mass is predicted to be around 9400 MeV, consistent with other theoretical expectations and above the unconfirmed 9300 MeV candidate. Finally, for comparison with lattice results, the J reliability parameter is also evaluated.}, number={3}, journal={PHYSICAL REVIEW C}, author={Llanes-Estrada, FJ and Cotanch, SR and Szczepaniak, AP and Swanson, ES}, year={2004}, month={Sep} }
 @article{llanes-estrada_cotanch_bicudo_ribeiro_szczepaniak_2002, title={QCD glueball Regge trajectory and the pomeron}, volume={710}, ISSN={["1873-1554"]}, DOI={10.1016/S0375-9474(02)01090-4}, abstractNote={Implementing many-body techniques successful in other fields, we report a glueball Regge trajectory emerging from diagonalizing a confining Coulomb gauge Hamiltonian for constituent gluons. Through a BCS vacuum ansatz and gap equation, the dressed gluons acquire a dynamic mass, of order 0.8 GeV, providing the quasiparticle degrees of freedom for a TDA glueball formulation. The TDA eigenstates for two constituent gluons have orbital, L, excitations with a characteristic energy of 0.4 GeV revealing a clear Regge trajectory. In particular, the JPC=2++ glueball coincides with the pomeron given by αP(t)=1.08+(0.25GeV−2)t. We also ascertain that lattice data supports our result. Finally, we conjecture on the odderon puzzle.}, number={1-2}, journal={NUCLEAR PHYSICS A}, author={Llanes-Estrada, FJ and Cotanch, SR and Bicudo, PJD and Ribeiro, JEFT and Szczepaniak, A}, year={2002}, month={Nov}, pages={45–54} }
 @article{llanes-estrada_cotanch_2002, title={Relativistic many-body Hamiltonian approach to mesons}, volume={697}, ISSN={["1873-1554"]}, DOI={10.1016/S0375-9474(01)01237-4}, abstractNote={We represent QCD at the hadronic scale by means of an effective Hamiltonian, H, formulated in the Coulomb gauge. As in the Nambu–Jona-Lasinio model, chiral symmetry is explicitly broken, however our approach is renormalizable and also includes confinement through a linear potential with slope specified by lattice gauge theory. This interaction generates an infrared integrable singularity and we detail the computationally intensive procedure necessary for numerical solution. We focus upon applications for the u,d,s and c quark flavors and compute the mass spectrum for the pseudoscalar, scalar and vector mesons. We also perform a comparative study of alternative many-body techniques for approximately diagonalizing H: BCS for the vacuum ground state; TDA and RPA for the excited hadron states. The Dirac structure of the field theoretical Hamiltonian naturally generates spin-dependent interactions, including tensor, spin–orbit and hyperfine, and we clarify the degree of level splitting due to both spin and chiral symmetry effects. Significantly, we find that roughly two-thirds of the π–ρ mass difference is due to chiral symmetry and that only the RPA preserves chiral symmetry. We also document how hadronic mass scales are generated by chiral symmetry breaking in the model vacuum. In addition to the vacuum condensates, we compute meson decay constants and detail the Nambu–Goldstone realization of chiral symmetry by numerically verifying the Gell-Mann–Oakes–Renner relation.}, number={1-2}, journal={NUCLEAR PHYSICS A}, author={Llanes-Estrada, FJ and Cotanch, SR}, year={2002}, month={Jan}, pages={303–337} }
 @article{llanes-estrada_cotanch_2001, title={Many-body Coulomb gauge exotic and charmed hybrids}, volume={504}, ISSN={["0370-2693"]}, DOI={10.1016/S0370-2693(01)00290-8}, abstractNote={Utilizing an effective QCD Coulomb gauge Hamiltonian with linear confinement specified by lattice, we report a relativistic many-body calculation for the light exotic and charmed hybrid mesons. The Hamiltonian successfully describes both quark and gluon sectors, with vacuum and quasiparticle properties generated by a BCS transformation and more elaborate TDA and RPA diagonalizations for the meson (qq̄) and glueball (gg) masses. Hybrids entail a computationally intense relativistic three quasiparticle (qq̄g) calculation with the 9-dimensional Hamiltonian matrix elements evaluated variationally by Monte Carlo techniques. Our new TDA (RPA) spectrum for the nonexotic 1−− charmed (cc̄ and cc̄g) system provides an explanation for the overpopulation of the observed J/ψ states. For the important 1−+ light exotic channel we obtain hybrid masses above 2 GeV, in broad agreement with lattice and flux tube models, indicating that the recently observed resonances at 1.4 and 1.6 GeV are of different, perhaps four quark, structure.}, number={1-2}, journal={PHYSICS LETTERS B}, author={Llanes-Estrada, FJ and Cotanch, SR}, year={2001}, month={Apr}, pages={15–20} }
 @article{cotanch_llanes-estrada_2001, title={Relativistic many-body approach to exotic and charmed hybrid mesons}, volume={689}, DOI={10.1016/s0375-9474(01)00886-7}, abstractNote={A relativistic many-body calculation for an effective QCD Hamiltonians reported for exotic and charmed hybrid mesons. The nonexotic J(PC) = 1(--) charmonium spectrum now resolves the anonymous overpopulation of observed J/psi states. The exotic hybrid states are near but above 2 GeV, in agreement with lattice and flux-tube calculations, indicating the recently observed J(PC) = 1(+-) resonances at 1.4 and 1.6 GeV are not hybrids.}, number={1-2}, journal={Nuclear Physics. A}, author={Cotanch, Stephen and Llanes-Estrada, F. J.}, year={2001}, pages={481C–484} }
 @article{llanes-estrada_cotanch_2000, title={Coulomb gauge hybrid mason calculation}, volume={90}, ISSN={["0920-5632"]}, DOI={10.1016/S0920-5632(00)00883-5}, abstractNote={We report a relativistic many-body calculation for the hybrid meson spectrum utilizing a QCD inspired Coulomb gauge Hamiltonian.Our approach is comprehensive and unifies the quark and gluon sectors.The vacuum and quasiparticle properties are generated by a BCS transformation, whereas the meson and glueball spectra are described by the TDA and RPA approximations.Using the quark and gluon gap solutions, we formulate hybrid mesons as states composed of three quasiparticles (quark, antiquark and gluon) and compute the mass spectrum variationally with trial wavefunctions.We predict the important exotic 1 -+ states to have masses above 2 GeV in rough agreement with lattice and flux tube models, implying the recently observed resonances are not hybrids.}, number={2000 Dec.}, journal={NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS}, author={Llanes-Estrada, FJ and Cotanch, SR}, year={2000}, month={Dec}, pages={117–119} }
 @article{llanes-estrada_cotanch_2000, title={Meson structure in a relativistic many-body approach}, volume={84}, ISSN={["1079-7114"]}, DOI={10.1103/PhysRevLett.84.1102}, abstractNote={Results from an extensive relativistic many-body analysis utilizing a realistic effective QCD Hamiltonian are presented for the meson spectrum. A comparative numerical study of the BCS, Tamm-Dancoff (TDA), and RPA treatments provides new, significant insight into the condensate structure of the vacuum, the chiral symmetry governance of the pion, and the meson spin, orbital, and flavor mass splitting contributions. In contrast to a previous glueball application, substantial quantitative differences are computed between TDA and RPA for the light quark sector with the pion emerging as a Goldstone boson only in the RPA.}, number={6}, journal={PHYSICAL REVIEW LETTERS}, author={Llanes-Estrada, FJ and Cotanch, SR}, year={2000}, month={Feb}, pages={1102–1105} }