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We work out details of defining the spatial densities corresponding to the gravitational form factors of spin-0 and spin-1/2 systems using spherically symmetric sharply localized wave packets. The expressions for the spatial densities are provided in the frames with both zero and non-zero expectation values of the momentum operator. [ABSTRACT FROM AUTHOR]

The leading one-loop corrections to the gravitational form factors of the delta resonance are calculated in the framework of chiral effective field theory. Various contributions to the energy–momentum tensor and the renormalization of the low-energy constants are worked out. Using the small scale expansion, expressions for static quantities are obtained and the real and imaginary parts of the gravitational form factors are calculated numerically. [ABSTRACT FROM AUTHOR]

We argue that high-quality data on the reaction e + e - → π + π - η will allow one to determine the doubly-virtual form factor η → γ ∗ γ ∗ 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 - → π + π - η for total energies squared k 2 > 1 GeV 2 , we demonstrate that the effect of the a 2 meson provides a natural breaking mechanism for the commonly employed factorization ansatz in the doubly-virtual form factor F η γ ∗ γ ∗ (q 2 , k 2) . However, better data are needed to draw firm conclusions. [ABSTRACT FROM AUTHOR]

We study the unitarized meson–baryon scattering amplitude at leading order in the strangeness S = - 1 sector using time-ordered perturbation theory for a manifestly Lorentz-invariant formulation of chiral effective field theory. By solving the coupled-channel integral equations with the full off-shell dependence of the effective potential and applying subtractive renormalization, we analyze the renormalized scattering amplitudes and obtain the two-pole structure of the Λ (1405) resonance. We also point out the necessity of including higher-order terms. [ABSTRACT FROM AUTHOR]

The generalization of the Feynman-Hellmann theorem for resonance states in quantum field theory is derived. On the basis of this theorem, a criterion is proposed to study the possible exotic nature of certain hadronic states emerging in QCD. It is shown that this proposal is supported by explicit calculations in chiral perturbation theory and by large- $$N_c$$ arguments. Analyzing recent lattice data on the quark mass dependence in the pseudoscalar, vector meson, baryon octet and baryon decuplet sectors, we conclude that, as expected, these are predominately quark-model states, albeit the corrections are non-negligible. [ABSTRACT FROM AUTHOR]

We analyze vector meson-vector meson scattering in a unitarized chiral theory based on a chiral covariant framework restricted to $$\rho \rho $$ intermediate states. We show that a pole assigned to the scalar meson $$f_0(1370)$$ can be dynamically generated from the $$\rho \rho $$ interaction, while this is not the case for the tensor meson $$f_2(1270)$$ as found in earlier work. We show that the generation of the tensor state is untenable due to the extreme non-relativistic kinematics used before. We further consider the effects arising from the coupling of channels with different orbital angular momenta which are also important. We suggest to use the formalism outlined here to obtain more reliable results for the dynamical generation of resonances in the vector-vector interaction. [ABSTRACT FROM AUTHOR]

A dispersion integral is derived that connects data on η→ π π γ to the η→ γγ transition form factor. A detailed analysis of the uncertainties is provided. We find for the slope of the η transition form factor at the origin $b_{\eta}= (2.05 \ \mbox{}^{+0.22}_{-0.10} )~\mathrm{GeV}^{-2}$. Using an additional, plausible assumption, one finds for the corresponding slope of the η′ transition form factor, $b_{\eta'} = (1.53\ \mbox{}^{+0.15}_{-0.08} )~\mathrm{GeV}^{-2}$. Both values are consistent with all recent data, but differ from some previous theoretical analyses. [ABSTRACT FROM AUTHOR]

We extend the method of infrared regularization to spin-1 fields coupled to baryons. As an application, we discuss the axial form factor of the nucleon. [ABSTRACT FROM AUTHOR]

The charged kaon decay channel K+ ℓ3γ allows for studies of direct CP violation, possibly due to non-standard mechanisms, with the help of T-odd correlation variables. In order to be able to extract a CP-violating signal from experiment, it is necessary to understand all possible standard model phases that also produce T-odd asymmetries. We complement earlier studies by considering strong interaction phases in hadronic structure functions that appear at higher orders in chiral perturbation theory, and we compare our findings to other potential sources of asymmetries. [ABSTRACT FROM AUTHOR]

We present a detailed study of the recently conjectured infrared renormalization group limit cycle in QCD using chiral effective field theory. It was conjectured that small increases in the up and down quark masses can move QCD to the critical trajectory for an infrared limit cycle in the three-nucleon system. At the critical quark masses, the binding energies of the deuteron and its spin-singlet partner are tuned to zero and the triton has infinitely many excited states with an accumulation point at the three-nucleon threshold. We exemplify three parameter sets where this effect occurs at next-to-leading order in the chiral counting. For one of them, we study the structure of the three-nucleon system in detail using both chiral and contact effective field theories. Furthermore, we investigate the matching of the chiral and contact theories in the critical region and calculate the influence of the limit cycle on three-nucleon scattering observables. [ABSTRACT FROM AUTHOR]

The extraction of the S-wave kaon–nucleon scattering lengths a0 and a1 from a combined analysis of existing kaonic hydrogen and synthetic deuterium data has been carried out within the framework of a low-energy effective field theory. It turns out that with the present DEAR central values for the kaonic hydrogen ground-state energy and width, a solution for a0 and a1 exists only in a restricted domain of input values for the kaon–deuteron scattering length. Consequently, measuring this scattering length imposes stringent constraints on the theoretical description of the kaon–deuteron interactions at low energies, if supplemented with DEAR data on kaonic hydrogen. [ABSTRACT FROM AUTHOR]

We use the framework of effective field theories to discuss the determination of the S-wave scattering lengths from the recent high-precision measurements of pionic deuterium observables. The theoretical analysis proceeds in several steps. Initially, the precise value of the pion-deuteron scattering length is extracted from the data. Next, is related to the S-wave scattering lengths a + and a-. We discuss the use of this information for constraining the values of these scattering lengths in the full analysis, which also includes the input from the pionic hydrogen energy shift and width measurements, and thoroughly investigate the accuracy limits for this procedure. In this paper, we also give a detailed comparison to other effective field theory approaches, as well as to the earlier work on the subject, carried out within the potential model and multiple scattering framework. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

By using the non-relativistic effective Lagrangian approach to bound states, a complete expression for the isospin-breaking correction to the energy levels and the decay widths of kaonic hydrogen is obtained up-to-and-including (Oα,md-mu) in QCD. It is demonstrated that, although the leading-order corrections at O(α½,(md-mu)½) emerging due to the unitarity cusp are huge, they can be expressed solely in terms of the K N S-wave scattering lengths. Consequently, at leading order, it is possible to derive parameter-free modified. Deser-type relations, which can be used to extract the scattering lengths from the hadronic atom data. [ABSTRACT FROM AUTHOR]

We calculate the one-loop contributions to the difference $\Delta_\pi K$ between the isoscalar on-shell pion-kaon scattering amplitude at the Cheng-Dashen point and the scalar form factor $\Gamma_K (2M_\pi_2)$ in the framework of three flavor chiral perturbation theory. These corrections turn out to be small. This is further sharpened by treating the kaons as heavy fields (two flavor chiral perturbation theory). We also analyze the two-loop corrections to the kaon scalar form factor based on a dispersive technique. We find that these corrections are smaller than in the comparable case of the scalar form factor of the pion. This is related to the weaker final state interactions in the pion-kaon channel. [ABSTRACT FROM AUTHOR]

We analyze the electromagnetic form factors of the ground state baryon octet to fourth order in relativistic baryon chiral perturbation theory. Predictions for the $\Sigma^-$ charge radius and the $\Lambda$– $\Sigma^0$ transition moment are found to be in excellent agreement with the available experimental information. Furthermore, the convergence behavior of the hyperon charge radii is shown to be more than satisfactory. [ABSTRACT FROM AUTHOR]

The possibility for a common effective field theory for hadronic molecules with different heavy-quark flavours is examined critically. It is argued that such a theory does not allow one to draw definite conclusions for doubly heavy molecules. In particular, it does not allow one to relate binding energies for the molecules in the c-quark and b-quark sectors with controlled uncertainties. Therefore, while this kind of reasoning does not preclude from employing heavy-quark spin symmetry for charmonium- and bottomonium-like states separately within a well established effective field theory framework, relations between different heavy-quark sectors can only be obtained using phenomenological approaches with uncontrolled uncertainties. [ABSTRACT FROM AUTHOR]

A correction to the article "The pion-nucleon scattering lengths from pionic deuterium" that was published in April 8, 2005 is presented.