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We use the feature that the gravitational Compton scattering amplitude factorizes in terms of Abelian QED amplitudes to evaluate various gravitational Compton processes. We examine both the QED and gravitational Compton scattering from a massive spin-1 system by the use of helicity amplitude methods. In the case of gravitational Compton scattering we show how the massless limit can be used to evaluate the cross section for graviton-photon scattering and discuss the difference between photon interactions and the zero mass spin-1 limit. We show that the forward scattering cross section for graviton photoproduction has a very peculiar behavior, differing from the standard Thomson and Rutherford cross sections for a Coulomb-like potential., LaTeX, 33 pages, 5 figures; v2 typos corrected, version to be published in PRD

We determine the $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\eta}}^{\ensuremath{'}}$ mixing angle via a procedure relatively independent of theoretical assumptions by simultaneously fitting $\ensuremath{\eta},{\ensuremath{\eta}}^{\ensuremath{'}}$ reactions involving the anomaly $\ensuremath{\eta},{\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma},$ ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\gamma}.$ We extract reasonably precise renormalized values of the octet and singlet pseudoscalar decay constants ${F}_{8},$ ${F}_{0},$ as well as the mixing angle \ensuremath{\theta}.

We show that recent calculations of \Delta I=3/2 effects in nonleptonic hyperon decay induced by m_d-m_u\neq 0 are subject to significant model dependence., Comment: 8 page standard Latex file

We investigate the spin-independent part of the virtual Compton scattering (VCS) amplitude off the nucleon within the framework of chiral perturbation theory. We perform a consistent calculation to third order in external momenta according to Weinberg's power counting. With this calculation we can determine the second- and fourth-order structure-dependent coefficients of the general low-energy expansion of the spin-averaged VCS amplitude based on gauge invariance, crossing symmetry and the discrete symmetries. We discuss the kinematical regime to which our calculation can be applied and compare our expansion with the multipole expansion by Guichon, Liu and Thomas. We establish the connection of our calculation with the generalized polarizabilities of the nucleon where it is possible., Comment: 26 pages, 2 Postscript figures, RevTex using epsfig

We examine mass-corrected SU(6) symmetry predictions in the quark model relating vector, axial-vector, and strong [ital NN] and [ital N][Delta] couplings, and demonstrate that the experimental [ital N][Delta] value is significantly higher than predicted in each case. Nevertheless the Goldberger-Treiman relation is satisfied in both sectors. Possible origins of the discrepancy of the quark model predictions with experiments are discussed.

Agreement between the experimental value {Gamma}({ital K}{sub {ital S}}{r_arrow}{gamma}{gamma}) and the number predicted via a one-loop chiral perturbation theory calculation has been cited as a success for the latter. On the other hand, the one-loop prediction for the closely related process {ital K}{sub {ital L}}{r_arrow}{pi}{sup 0}{gamma}{gamma} has been found to be a factor 3 below the experimental value. Using the inputs of unitarity and dispersion relations, we demonstrate the importance of higher order loop effects to both of these processes.

We present the results of a systematic leading-order calculation of hyperon Compton scattering and extract the forward spin polarizability--{gamma}{sub 0}--of hyperons within the framework of SU(3) heavy baryon chiral perturbation theory (HBChPT). The results obtained for {gamma}{sub 0} in the case of nucleons agree with that of the known results of SU(2) HBChPT when kaon loops are not considered.

One of the coefficients that parametrizes the chiral Lagrangian of QCD is expressible in terms of a sum rule for which the integrand is known from experiment. We confront two model calculations of this coefficient with the behavior of the data. The model related to vector dominance reproduces the sumrule behavior very well, whereas a one-loop chiral quark model calculation fails badly. The sum rule allows one to identify those ingredients which are needed to make the quark method more realistic

The properties of the neutrino charge radius (NCR) and anapole moments (AM's) of elementary fermions, nucleons, and nuclei are discussed. The dependence of these off-shell electromagnetic couplings on the weak gauge parameter is explicitly demonstrated by a calculation performed in the ${R}_{\ensuremath{\xi}}$ gauge. The gauge dependence of the AM's and NCR implies that they cannot be observed in isolation from other second-order, electroweak effects. It is shown, however, that the AM's of various hadronic systems having an $\mathrm{SU}{(2)}_{L}$ quantum number ${T}_{3}^{L}=0$ can be considered "observables" in certain formal, though unphysical, limits. It is argued that, apart from these special limits, the AM is a physically meaningful entity only for heavy and/or nearly degenerate nuclei.

The treatment of kaon decays using chiral symmetry yields predictions for th\`e form factors in $K\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}e\ensuremath{\nu}$. In addition, the large-${N}_{c}$ limit of QCD implies that a particular combination of low-energy constants should be suppressed. We present the chiral predictions for ${K}_{l4}$ decays at next-to-leading order in the energy expansion. By combining the phenomenologies of ${K}_{l4}$ and $\ensuremath{\pi}\ensuremath{\pi}$ scattering, we test these predictions and provide a determination of the parameters in the chiral Lagrangian of QCD.

We calculate the semileptonic baryon octet-octet transition form factors using a manifestly Lorentz covariant quark model approach based on the factorization of the contribution of valence quarks and chiral effects. We perform a detailed analysis of SU(3)-breaking corrections to the hyperon semileptonic decay form factors. We present complete results on decay rates and asymmetry parameters including lepton mass effects for the rates.

We calculate chiral corrections to the semileptonic vector and axial quark coupling constants using a manifestly Lorentz covariant chiral quark approach up to order O(p4) in the two- and tree-flavor picture. These couplings are then used in the evaluation of the corresponding couplings which govern the semileptonic transitions between octet baryon states. In the calculation of baryon matrix elements we use a general ansatz for the spatial form of the quark wave function, without referring to a specific realization of hadronization and confinement of quarks in baryons. Matching the physical amplitudes calculated within our approach to the model-independent predictions of baryon chiral perturbation theory (ChPT) allows one to deduce the connection between our parameters and those of baryon ChPT., 28 pages, 4 figures

Chiral perturbation theory is used in order to analyze the {ital K}{sub {ital l}3{gamma}} process and results are compared with the PCAC (partial conservation of axial-vector current) and Low-theorem analyses of Fearing, Fischbach, and Smith. These predictions are found to be consistent with but much stronger than those of the earlier analysis, and verification of these results can be used as a test of chiral symmetry.

We use results by Kirilin to comment that in general relativity the nonleading terms in the energy-momentum tensor of a particle depends on the parameterization of the gravitational field. The classical observables are parameterization independent after a change in coordinates. The quantum effects that emerge within the same calculation of the metric also depend on the parameterization and a full quantum calculation requires the inclusion of further diagrams. However, within a given parameterization the quantum effects calculated by us in a previous paper are well defined. Flaws of Kirilin's proposed alternate metric definition are described and we explain why the diagrams that we calculated are the appropriate ones.

Previous evaluations of long range one-photon and one-graviton-loop corrections to the energy-momentum tensor and the metric tensor describing spacetime in the vicinity of massive spinless and spin $1/2$ systems have been extended to particles with unit spin and speculations are confirmed concerning universal properties of such forms.

We calculate magnetic moments of light baryons and N{yields}{delta}{gamma} transition characteristics using a manifestly Lorentz covariant chiral quark approach for the study of baryons as bound states of constituent quarks dressed by a cloud of pseudoscalar mesons.

Measurement of the {gamma}3{pi} process has revealed a possible conflict with what should be a solid prediction generated by the chiral anomaly. We show that inclusion of appropriate energy-momentum dependence in the matrix element reduces the discrepancy. {copyright} {ital 1996 The American Physical Society.}

We examine the corrections to the lowest order gravitational interactions of massive particles arising from gravitational radiative corrections. We show how the masslessness of the graviton and the gravitational self interactions imply the presence of nonanalytic pieces sqrt{-q^2}, ln-q^2, etc. in the form factors of the energy-momentum tensor and that these correspond to long range modifications of the metric tensor g_{\mu\nu} of the form G^2m^2/r^2, G^2m\hbar/r^3, etc. The former coincide with well known solutions from classical general relativity, while the latter represent new quantum mechanical effects, whose strength and form is necessitated by the low energy quantum nature of the general relativity. We use these results to define a running gravitational charge., Comment: 30 pages, 4 figures

The two photon decay width of the neutral pion is analyzed within the combined framework of Chiral Perturbation Theory and the 1/Nc expansion up to order p^6 and p^4 times 1/Nc in the decay amplitude. The eta' is explicitly included in the analysis. It is found that the decay width is enhanced by about 4.5% due to the isospin-breaking induced mixing of the pure U(3) states. This effect, which is of leading order in the low energy expansion, is shown to persist nearly unchanged at next to leading order. The chief prediction for the width with its estimated uncertainty is 8.10+-0.08 eV. This prediction at the 1% level makes the upcomming precision measurement of the decay width even more urgent. Observations on the eta and eta' can also be made, especially about their mixing, which is shown to be significantly affected by next to leading order corrections.

We construct the complete SU(2) parity-violating (PV) $\pi, N, \Delta$ interaction Lagrangian with one derivative, and calculate the chiral corrections to the PV Yukawa $NN\pi$ coupling constant $h_\pi$ through ${\cal O}(1/\Lambda_\chi^3)$ in the leading order of heavy baryon expansion. We discuss the relationship between the renormalized $\hpi$, the measured value of $\hpi$, and the corresponding quantity calculated microscopically from the Standard Model four-quark PV interaction., Comment: RevTex, 26 pages + 5 PS figures

Parity-violating (PV) interactions among quarks in the nucleon induce a PV $\gamma NN$ coupling, or anapole moment (AM). We compute electroweak gauge-independent contributions to the AM through ${\cal O}(1/\lamchis)$ in chiral perturbation theory. We estimate short-distance PV effects using resonance saturation. The AM contributions to PV electron-proton scattering slightly enhance the axial vector radiative corrections, R_A^p, over the scale implied by the Standard Model when weak quark-quark interactions are neglected. We estimate the theoretical uncertainty associated with the AM contributions to R_A^p to be large, and discuss the implications for the interpretation PV of ep scattering., Comment: RevTex 29 pages + 8 PS figures, references and discussions added, to appear in Phys. Rev. D

Using the techniques of chiral effective field theories we evaluate the so called generalized polarizabilities of the nucleon, which characterize the structure dependent components in virtual Compton scattering (VCS) as probed in the electron scattering reaction e N \to e' N gamma. Results are given for both spin-dependent and spin-independent structure effects to O(p^3) in SU(2) Heavy Baryon Chiral Perturbation Theory and to O(epsilon^3) in the SU(2) Small Scale Expansion. Finally we compare our calculations with results from the pioneering VCS experiment on the proton from Mainz., Comment: 39 pages, 12 figures, revtex

We examine the problem of hadronic atom energy shifts using the technique of effective interactions and demonstrate equivalence with the conventional quantum mechanical approach., 22 page latex file with 2 figures

We examine the importance of J^P = 1/2^+, 1/2^- resonances for weak nonleptonic Omega^- decays within the framework of chiral perturbation theory. The spin-1/2 resonances are included into an effective theory and tree contributions to the Omega^- decays are calculated. We find significant contributions to the decay amplitudes and satisfactory agreement with experiment. This confirms and extends previous results wherein such spin-1/2 resonances were included in nonleptonic and radiative-nonleptonic hyperon decays.