Roxanne P. Springer

Strong Interaction Effects in Weak Radiative

Abstract Strong-interaction corrections to the effective hamiltonian for weak radiative B - meson decay (i.e., B → X s γ , where Xs denotes a strange hadronic final state) are calculated using the leading logarithmic approximation. The inclusive rate for decays B → X s γ , where the energy of the photon is large, is computed in the standard model with minimal particle content and in extensions of the minimal standard model with two Higgs doublets.

\bar{B}

Abstract The inclusive rate for decay of a B-meson to a hard photon and strange hadronic final states (i.e., B→γXs with X s = K ∗ , etc.), is likely to be dominated by short-distance physics which gives rise to an effective hamiltonian that is a magnetic-moment-type operator. Strong interaction corrections to this hamiltonian are computed in the leading logarithmic approximation.

Meson Decay

Abstract To explore further the role that QCD symmetries play on hadron dynamics, we discuss the radiative decay of the baryon decuplet to the baryon octet and compute the leading non-analytic SU(3) violating corrections induced at the one-loop level. In the limit of exact flavour SU(3) symmetry two of the possible decay modes are forbidden and the rates for these two decays are dominated by loop corrections. There is only one SU(3) conserving contact term at leading order in chiral perturbation theory for the radiative decays. We determine its coefficient from the observed branching ratio for Δ → Nγ and from the present upper limit on Ξ ∗0 → Ξ 0 γ . We then predict the branching fractions for Σ ∗− → Σ − γ, Σ ∗0 → Λγ, Σ ∗0 → Σ 0 γ, Σ ∗+ → Σ + γ, Ξ ∗0 γ → Ξ 0 γ and Ξ ∗− → Ξ − γ . Some of the decay modes are predicted to have branching fractions near the current experimental upper limit and could possibly be observed in the near future. The leading corrections to the octet-decuplet-meson strong coupling constant, C , are computed at one-loop and the strong decay rates of the Δ, Σ ∗ and Ξ ∗ allow us to determine | C | = 1.2 ± 0.1 and H = −2.2 ± 0.6 , in remarkable agreement with predictions based on spin-flavour symmetry. We calculate the Δ pole graph contribution to the polarisability of the nucleon to order 1 Λ χ 2 in chiral perturbation theory.

Effective hamiltonian for weak radiative B-meson decay☆

Abstract Weak interactions are expected to induce a parity violating pion–nucleon coupling, hπNN(1). This coupling should be measurable in a proposed experiment to study the parity violating asymmetry Aγ in the process n → +p→d+γ . We compute the leading dependence of Aγ on the coupling hπNN(1) using recently developed effective field theory techniques and find an asymmetry of A γ =+0.17 h πNN (1) at leading order. This asymmetry has the opposite sign to that given by Desplanques and Missimer.

Strong and electromagnetic decays of the baryon decuplet

Abstract The scalar and tensor polarizabilities of the deuteron are calculated using the recently developed effective field theory that describes nucleon-nucleon interactions. Leading and next-to-leading order contributions in the perturbative expansion predict a scalar electric polarizability of α e0 = 0.595 fm 3 . The tensor electric polarizability receives contributions starting at next-to-leading order from the exchange of a single potential pion and is found to be α e2 = −0.062 fm 3 . We compute the leading contributions to the scalar and tensor magnetic polarizabilities, finding β m0 = 0.067 fm 3 and β m2 = 0.195 fm 3 .

An effective field theory calculation of the parity violating asymmetry in

Abstract Effective field theory, including pions, provides a consistent and systematic description of nucleon-nucleon strong interactions up to center-of-mass momentum p ∼ 300 MeV per nucleon. We describe the inclusion of hadronic parity violation into this effective field theory and find an analytic form for the deuteron anapole moment at leading order in the expansion.

THE POLARIZABILITY OF THE DEUTERON

Abstract We analyze parity-violating nucleon–nucleon scattering at energies E m π 2 / M using the effective field theory appropriate for this regime. The minimal Lagrangian for short-range parity-violating NN interactions is written in an operator basis that encodes the five partial-wave transitions that dominate at these energies. We calculate the leading-order relationships between parity-violating NN asymmetries and the coefficients in the Lagrangian and also discuss the size of sub-leading corrections. We conclude with a discussion of further observables needed to completely determine the leading-order Lagrangian.

Parity violation in effective field theory and the deuteron anapole moment

We compute the leading contributions to the magnetic dipole and electric quadrupole moments of the baryon decuplet in chiral perturbation theory. The measured value for the magnetic moment of the [Omega][sup [minus]] is used to determine the local counterterm for the magnetic moments. We compare the chiral perturbation theory predictions for the magnetic moments of the decuplet with those of the baryon octet and find reasonable agreement with the predictions of the large-[ital N][sub [ital c]] limit of QCD. The leading contribution to the quadrupole moment of the [Delta] and other members of the decuplet comes from one-loop graphs. The pionic contribution is shown to be proportional to [ital I][sub [ital z]] (and so will not contribute to the quadrupole moment of [ital I]=0 nuclei), while the contribution from kaons has both isovector and isoscalar components. The chiral logarithmic enhancement of both pion and kaon loops has a coefficient that vanishes in the SU(6) limit. The third allowed moment, the magnetic octupole, is shown to be dominated by a local counterterm with corrections arising at two loops. We briefly mention the strange counterparts of these moments.

An effective-field-theory analysis of low-energy parity-violation in nucleon–nucleon scattering

Abstract The differential cross section for γ-deuteron Compton scattering is computed to next-to-leading order (NLO) in an effective field theory that describes nucleon-nucleon interactions below the pion production threshold. Contributions at NLO include the nucleon isoscalar electric polarizability from its 1 m π behavior in the chiral limit. The parameter-free prediction of the γ-deuteron differential cross section at NLO is in good agreement with data.

Electromagnetic moments of the baryon decuplet.

Abstract We complete the leading contribution to the E 2 M 1 mixing ratio of the decay Δ → Nγ in heavy baryon chiral perturbation theory. We find the mixing ratio to be 4%⪅|δ E 2 M 1 |⪅11% , much larger than estimates based on the quark model and other hadronic models. We also compute the mixing ratio for the radiative decay of the hyperon resonances. The decays ⩞ ∗+ →⩞ + γ and Ξ ∗− →Ξ − γ provide a particularly sensitive probe of deviations from heavy baryon spin-flavour SU(6).