arXiv subjects

M. J. Ramsey-Musolf

Publications and source records attributed to M. J. Ramsey-Musolf.

54 records · Page 3Linked to original sources

arXiv2000

Recoil Order Chiral Corrections to Baryon Octet Axial Currents

We calculate chiral corrections to the octet axial currents through ${\cal O}(p^3)$ using baryon chiral perturbation theory (BCPT). The relativistic BCPT framework allows one to sum an infinite series of recoil corrections at a given order in the chiral expansion. We also include SU(3)-breaking operators occuring at ${\cal O}(p^2)$ not previously considered. We determine the corresponding low-energy constants (LEC's) from hyperon semileptonic decay data using a variety of infrared regularization schemes. We find that the chiral expansion of the axial currents does not display the proper convergence behavior, regardless of which scheme is chosen. We explore the implications of our analysis for determinations of the strange quark contribution to the nucleon spin, $Δs$.

hep-ph↗

arXiv2000

Octet Baryon Charge Radii, Chiral Symmetry and Decuplet Intermediate States

We compute the octet baryon charge radii to O(1/Heavy^3) in heavy baryon chiral perturbation theory. We examine the effect of including the decuplet of spin-3/2 baryons explicitly. We find that it does no t improve the level of agreement between the HBchiPT and experimental values for the Sigma^- charge radius.

hep-ph↗

arXiv2000

Chiral Symmetry and the Parity-Violating $NNπ$ Yukawa Coupling

We construct the complete SU(2) parity-violating (PV) $π, N, Δ$ interaction Lagrangian with one derivative, and calculate the chiral corrections to the PV Yukawa $NNπ$ coupling constant $h_π$ through ${\cal O}(1/Λ_χ^3)$ 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.

hep-ph↗

arXiv2000

The Nucleon Anapole Moment and Parity-Violating ep Scattering

Parity-violating (PV) interactions among quarks in the nucleon induce a PV $γNN$ 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.

hep-ph↗

arXiv2000

Nuclear beta-decay, Atomic Parity Violation, and New Physics

Determinations of vuds with super-allowed Fermi beta-decay in nuclei and of the weak charge of the cesium in atomic parity-violation deviate from the Standard Model predicitions by 2 sigma or more. In both cases, the Standard Model over-predicts the magnitudes of the relevant observables. I discuss the implications of these results for R-parity violating (RPV) extensions of the minimal supersymmetric Standard Model. I also explore the possible consequences for RPV supersymmetry of prospective future low-energy electroweak measurements.

hep-ph↗

arXiv2000

Electrons, New Physics, and the Future of Parity-Violation

The study of parity-violation in semi-leptonic processes has yielded important insights into the structure of the Standard Model and the substructure of the nucleon. I discuss the future of semi-leptonic parity-violation and the role it might play in uncovering physics beyond the Standard Model.

hep-ph↗

arXiv1999

Baryon Octet magnetic moments in $χ$PT: More on the importance of the Decuplet

We address the impact of treating the decuplet of spin-3/2 baryons as an explicit degree of freedom in the chiral expansion of the magnetic moments of the octet of spin-1/2 baryons. We carry out a complete calculation of the octet moments to O(1/\lamchic), including decuplet contributions to the chiral loops. In contrast to results of previous analyses, we find that inclusion of the decuplet preserves the convergence behavior of the chiral expansion implied by power counting arguments.

hep-ph↗

arXiv1999

Electric Dipole Moments and the Mass Scale of New T-Violating, P-Conserving Interactions

We consider the implications of experimental limits on the permanent electric dipole moment (EDM) of the electron and neutron for possible new parity-conserving (PC) time-reversal violating (TV) interactions. We show that the constraints derived from one-loop contributions to the EDM exceed previously reported two-loop limits by more than an order of magnitude and imply a lower bound on the new TVPC mass scale $\lamtv$ of 100 TeV for new TVPC strong interactions. These results imply a value of $10^{-15}$ or smaller for the ratio of low-energy TVPC matrix elements to those of the residual strong interaction.

hep-ph↗

arXiv1999

Spectral Content of Isoscalar Nucleon Form Factors

The nucleon strange vector and isoscalar electromagnetic form factors are studied using a spectral decomposition. The K\bar{K} contribution to the electric and magnetic radii as well as the magnetic moment is evaluated to all orders in the strong interaction using an analytic continuation of experimental KN scattering amplitudes and bounds from unitarity. The relationship between non-resonant and resonant K\bar{K} contributions to the form factors is demonstrated, and values for the vector and tensor ϕN\bar{N} couplings are derived. The K\bar{K} spectral functions are used to evaluate the credibility of model calculations for the strange quark vector current form factors.

hep-ph↗

arXiv1999

Low-Energy Parity-Violation and New Physics

The new physics sensitivity of a variety of low-energy parity-violating (PV) observables is analyzed. A comparison is made between atomic PV for a single isotope, atomic PV using isotope ratios, and PV electron-hadron and electron-electron scattering. The complementarity among these observables, as well as with high-energy processes, is emphasized. Theoretical uncertainties entering the interpretation of low-energy measurements are discussed.

hep-ph↗

arXiv1999

K\bar{K}-Continuum and Isoscalar Nucleon Form Factors

We analyse the isoscalar vector current form factors of the nucleon using dispersion relations. In addition to the usual vector meson poles, we account for the K\bar{K}-continuum contribution by drawing upon a recent analytic continuation of KN scattering amplitudes. For the Pauli form factor all strength in the ϕregion is already given by the continuum contribution, whereas for the Dirac form factor additional strength in the ϕregion is required. The pertinent implications for the leading strangeness moments are demonstrated as well. We derive a reasonable range for the leading moments which is free of assumptions about the asymptotic behavior of the form factors. We also determine the \phiNN coupling constants from the form factor fits and directly from the K\bar{K} -> N\bar{N} partial waves and compare the resulting values.

hep-ph↗

arXiv1999

Sensitivity of Low-Energy Parity-Violation To New Physics

I review the new physics sensitivity of low-energy parity-violating (PV) observables. I concentrate on signatures of new tree-level physics in atomic PV with a single isotope, ratios of atomic PV observables, and PV electron scattering. In addition to comparing the new physics sensitivities of these observables with those of high-energy colliders, I also discuss the theoretical issues involved in the extraction of new physics limits from low-energy PV observables.

hep-ph↗

arXiv1998

K^* Mesons and Nucleon Strangeness

We study contributions to the nucleon strange quark vector current form factors from intermediate states containing K^* mesons. We show how these contributions may be comparable in magnitude to those made by K mesons, using methods complementary to those employed in quark model studies. We also analyze the degree of theoretical uncertainty associated with K^* contributions.

hep-ph↗

arXiv1998

Parity-Violating Excitation of the Δ(1232): Hadron Structure and New Physics

We consider prospects for studying the parity-violating (PV) electroweak excitation of the Δ(1232) resonance with polarized electron scattering. Given present knowledge of Standard Model parameters, such PV experiments could allow a determination of the N -> Δelectroweak helicity amplitudes. We discuss the experimental feasibility and theoretical interpretability of such a determination as well as the prospective implications for hadron structure theory. We also analyze the extent to which a PV N -> Δmeasurement could constrain various extensions of the Standard Model.

nucl-th↗

arXiv1998

KN Scattering and the Nucleon Strangeness Radius

The leading non-zero electric moment of the nucleon strange-quark vector current is the mean square strangeness radius, $ $. We evaluate the lightest OZI-allowed contribution to $ $, arising from the kaon cloud, using dispersion relations. Drawing upon unitarity constraints as well as $K^{+}N$ scattering and $e^+e^-\to K\bar{K}$ cross section data, we find the structure of this contribution differs significantly from that suggested by a variety of QCD-inspired model calculations. In particular, we find evidence for a strong $ϕ$-meson resonance which may enhance the scale of kaon cloud contribution to an observable level.

hep-ph↗

arXiv1997

Nucleon Strangeness: Theory

The status of theoretical calculations of the strange quark vector current form factors of the nucleon is reviewed.

hep-ph↗

arXiv1997

Strange Mesonic Transition Form Factor in the Chiral Constituent Quark Model

The form factor $g_{ρπ}^{(S)}(Q^{2})$ of the strange vector current transition matrix element $<ρ| \bar{s}γ_\mus|π>$ is calculated within the chiral quark model. A strange vector current of the constituent $U$- and D-quarks is induced by kaon radiative corrections and this mechanism yields the nonvanishing values of $g_{ρπ}^{(S)}(0)$. The numerical result at the photon point is consistent with the one given by the $ϕ$-meson dominance model, but the fall-off in the $Q^{2}$-dependence is faster than the monopole form factor. Mesonic radiative corrections are also examined for the electromagnetic $ρ$-to-$π$ and $K^{*}$-to-$K$ transition amplitudes.

nucl-th↗

arXiv1997

Nucleon Vector Strangeness Form Factors: Multi-pion Continuum and the OZI Rule

We estimate the 3 πcontinuum contribution to the nucleon strange quark vector current form factors, including the effect of a 3 π<----> ρπresonance. We find the magnitude of this OZI-violating contribution to be comparable to that of typical OZI-allowed contributions. We also study the isoscalar electromagnetic form factors, and find that the presence of a ρπresonance in the multi-pion continuum may generate an appreciable contribution.

hep-ph↗