Infrared regularization for spin-1 fields

We extend the method of infrared regularization to spin-1 fields. As applications, we discuss the chiral extrapolation of the rho meson mass from lattice QCD data and the pion-rho sigma term.Comment: 22 pp, 5 fig

J/ψ(ηc)NJ/\psi (\eta_c) N and Υ(ηb)N\Upsilon (\eta_b) N cross sections

Inspired by the recent findings of the two $P_c^+$ states in the $J/\psi p$ mass spectrum at LHCb, we investigate the elastic and inelastic cross sections of the $J/\psi N$, $\eta_c N$, $\Upsilon N$ and $\eta_b N$ channels within the constraints from heavy quark spin and flavour symmetry. The $\bar{D}^{(*)} \Sigma_c^{(*)}$ ($B^{(*)} \Sigma_b^{(*)}$) bound states predicted in earlier works should be accessible in elastic and/or inelastic processes of the $J/\psi N$ and/or $\eta_c N$ ($\Upsilon N$ and/or $\eta_b N$) interactions.Comment: Minor correction

Model-independent approach to eta -> pi+ pi- gamma and eta' -> pi+ pi- gamma

We present a new, model-independent method to analyze radiative decays of mesons to a vector, isovector pair of pions of invariant mass square below the first significant pion-pion threshold in the vector channel. It is based on a combination of chiral perturbation theory and dispersion theory. This allows for a controlled inclusion of resonance physics without the necessity to involve vector meson dominance explicitly. As an example, the method is applied to an analysis of the reactions eta -> pi+ pi- gamma and eta'->pi+ pi- gamma.Comment: 16 pages, 4 figure

Lattice effective field theory calculations for A = 3,4,6,12 nuclei

We present lattice results for the ground state energies of tritium, helium-3, helium-4, lithium-6, and carbon-12 nuclei. Our analysis includes isospin-breaking, Coulomb effects, and interactions up to next-to-next-to-leading order in chiral effective field theory.Comment: 4 pages, 4 figures, published version to appear in Phys. Rev. Lett

Dispersive and absorptive corrections to the pion-deuteron scattering length

We present a parameter--free calculation of the dispersive and absorptive contributions to the pion--deuteron scattering length based on chiral perturbation theory. We show that once all diagrams contributing to leading order to this process are included, their net effect provides a small correction to the real part of the pion--deuteron scattering length. At the same time the sizable imaginary part of the pion--deuteron scattering length is reproduced accurately.Comment: Numerical error corrected. Results for dispersive corrections changed - conclusions unchanged. Version as accepted by Phys. Lett.

Gauge invariance in two-particle scattering

It is shown how gauge invariance is obtained for the coupling of a photon to a two-body state described by the solution of the Bethe-Salpeter equation. This is illustrated both for a complex scalar field theory and for interaction kernels derived from chiral effective Lagrangians.Comment: 16 pages, 2 figures, references added and commented o

Ab initio calculation of the Hoyle state

The Hoyle state plays a crucial role in the hydrogen burning of stars heavier than our sun and in the production of carbon and other elements necessary for life. This excited state of the carbon-12 nucleus was postulated by Hoyle [1] as a necessary ingredient for the fusion of three alpha particles to produce carbon at stellar temperatures. Although the Hoyle state was seen experimentally more than a half century ago [2,3], nuclear theorists have not yet uncovered the nature of this state from first principles. In this letter we report the first ab initio calculation of the low-lying states of carbon-12 using supercomputer lattice simulations and a theoretical framework known as effective field theory. In addition to the ground state and excited spin-2 state, we find a resonance at -85(3) MeV with all of the properties of the Hoyle state and in agreement with the experimentally observed energy. These lattice simulations provide insight into the structure of this unique state and new clues as to the amount of fine-tuning needed in nature for the production of carbon in stars.Comment: 4 pp, 3 eps figs, version accepted for publication in Physical Review Letter

Partonic Pole Matrix Elements for Fragmentation

A model-independent analysis of collinear three-parton correlation functions for fragmentation is performed. By investigating their support properties it is shown, in particular, that the so-called partonic pole matrix elements vanish. This sheds new light on the understanding of transverse single spin asymmetries in various hard semi-inclusive reactions. Moreover, it gives additional strong evidence for the universality of transverse-momentum-dependent fragmentation functions.Comment: 4 pages, 2 figures; minor changes, matches journal versio

Chiral dynamics in few-nucleon systems

We report on recent progress achieved in calculating various few-nucleon low-energy observables from effective field theory. Our discussion includes scattering and bound states in the 2N, 3N and 4N systems and isospin violating effects in the 2N system. We also establish a link between the nucleon-nucleon potential derived in chiral effective field theory and various modern high-precision potentials.Comment: 12 pp, uses aipproc style files, 4 figures, contribution to the conference on "Mesons and Light Nuclei", Prag, July 2001, to appear in the proceeding

Towards an improved understanding of eta --> gamma^* gamma^*

We argue that high-quality data on the reaction $e^+e^-\to \pi^+\pi^-\eta$ will allow one to determine the double off-shell form factor $\eta \to \gamma^*\gamma^*$ in a model-independent way with controlled accuracy. This is an important step towards a reliable evaluation of the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon. When analyzing the existing data for $e^+e^- \to \pi^+\pi^-\eta$ in the range of total energies $1\text{GeV}^2<Q_2^2<(4.5\text{GeV})^2$, we demonstrate that the double off-shell form factor $F_{\eta\gamma^*\gamma^*}(Q_1^2,Q_2^2)$ is consistent with the commonly employed factorization ansatz at least for $Q_1^2<1\text{GeV}^2$, if the effect of the $a_2$ meson is taken into account. However, better data are needed to draw firm conclusions.Comment: 7 pages, 3 figure