arXiv subjects

Kim Maltman

Publications and source records attributed to Kim Maltman.

98 records · Page 6Linked to original sources

arXiv1995

Two Model-Independent Results for the Momentum Dependence of Rho-Omega Mixing

Two model-independent results on the momentum-dependence of $ρ$-$ω$ mixing are described. First, an explicit choice of interpolating fields for the vector mesons is displayed for which both the mixing in the propagator and the isospin-breaking at the nucleon-vector meson vertices (and hence also the one-vector-meson-exchange contribution to NN charge symmetry breaking) vanish identically at $q^2=0$. Second, it is shown, using the constraints of unitarity and analyticity on the spectral function of the vector meson propagator, that there is no possible choice of interpolating fields for the $ρ^0$, $ω^0$ mesons such that, with the $ρω$ element of the propagator defined by $Δ^{ρω}_{μν}(q^2)= (g_{μν}-q_μq_ν/q^2)$$θ(q^2)/(q^2-m^2_ρ)(q^2- m^2_ω)$, $θ(q^2)$ is independent of momentum. It follows that the standard treatment of charge symmetry breaking in few-body systems cannot be interpreted as arising from any realizable effective meson-baryon Lagrangian and must, therefore, be considered purely phenomenological in content.

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arXiv1995

The Mixed Vector Current Correlator <0|T(V^3_μV^8_ν)|0> To Two Loops in Chiral Perturbation Theory

The isospin-breaking correlator of the product of flavor octet vector currents, $V^3_μ$ and $V^8_ν$, $Π^{38}_{μν}(q^2)$ is computed to next-to-next- to-leading (two-loop) order in Chiral Perturbation Theory. Large corrections to both the magnitude and $q^2$-dependence of the one-loop result are found, and the reasons for the slow convergence of the chiral series for the correlator given. The two-loop expression involves a single ${\cal O}(q^6)$ counterterm, present also in the two-loop expressions for $Π^{33}_{μν}(q^2)$ and $Π^{88}_{μν}(q^2)$, which counterterm contributes a constant to the scalar correlator $Π^{38}(q^2)$. The feasibility of extracting the value of this counterterm from other sources is discussed. Analysis of the slope of the correlator with respect to $q^2$ using QCD sum rules is shown to suggest that, even to two-loop order, the chiral series for the correlator may not yet be well-converged.

hep-ph↗

arXiv1995

Strong Isospin Mixing Effects on the Extraction of $ΔI=3/2$ Non-Leptonic Hyperon Decay Amplitudes

The existence of isospin admixtures in the physical $Λ$, $π^o$ complicates the extraction of Delta I=3/2 non-leptonic hyperon decay amplitudes from experimental data, allowing contributions associated with large Delta I=1/2 amplitudes to appear in the (nominally) Delta I=3/2 amplitudes obtained ignoring these admixtures. We show how to correct for this effect to leading order in $(m_d-m_u)$ and extract the true Delta I=3/2 amplitudes. The resulting corrections are modest ($<25\%$) for s-waves, but extremely large, $\simeq 100\%$ and $\simeq 400\%$ for $Λ$ and $Ξ$ p-waves, respectively.

hep-ph↗

arXiv1995

Comparison of Chiral Perturbation Theory and QCD Sum Rule Results for Pseudoscalar Isoscalar-Isovector Mixing

The forms of the neutral, non-strange pseudoscalar propagator matrix and mixed axial current correlator, $\lngle0|T(A_μ^3 A_ν^8)|0\rangle$, are discussed at next-to-leading (one-loop) order in chiral perturbation theory, and the results compared to those obtained using QCD sum rules. This comparison provides a check of the truncations employed in the sum rule treatment of the current correlator. Values for the slope of the correlator with $q^2$ in the two approaches are found to differ by more than an order of magnitude and the source of this discrepancy is shown to be the incorrect chiral behavior of the sum rule result.

hep-ph↗

arXiv1995

Factorization Contributions and the Breaking of the $ΔI=1/2$ Rule in Weak $ΛNρ$ and $ΣNρ$ Couplings

We compute the modified factorization contributions to the $Λ\rightarrow Nρ$ and $Σ\rightarrow Nρ$ couplings and demonstrate that these contributions naturally include $ΔI=3/2$ terms which are comparable ($\simeq 0.4$ to $-0.8$ times) in magnitude to the corresponding $ΔI=1/2$ terms. As a consequence, we conclude that models which treat vector meson exchange contributions to the weak conversion process $ΛN\rightarrow NN$ assuming such weak couplings to satisfy the $ΔI=1/2$ rule are unlikely to be reliable.

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arXiv1995

The Mixed-Isospin Vector Current Correlator in Chiral Perturbation Theory and QCD Sum Rules

The mixed-isospin vector current correlator, $\langle 0\vert T(V^ρ_μV^ω_ν)\vert 0\rangle$ is evaluated using both QCD sum rules and Chiral Perturbation Theory (ChPT) to one-loop order. The sum rule treatment is a modification of previous analyses necessitated by the observation that those analyses produce forms of the correlator that fail to be dominated, near $q^2=0$, by the most nearby singularities. Inclusion of contributions associated with the $ϕ$ meson rectify this problem. The resulting sum rule fit provides evidence for a significant direct $ω\rightarrowππ$ coupling contribution in $e^+e^-\rightarrowπ^+π^-$. It is also pointed out that results for the $q^2$-dependence of the correlator cannot be used to provide information about the (off-shell) $q^2$-dependence of the off-diagonal element of the vector meson propagator unless a very specific choice of interpolating fields for the vector mesons is made. The results for the value of the correlator near $q^2=0$ in ChPT are shown to be more than an order of magnitude smaller than those extracted from the sum rule analysis and the reasons why this suggests slow convergence of the chiral series for the correlator given.

hep-ph↗

arXiv1992

$q^2$-Dependence of Meson Mixing in Few-Body Charge Symmetry Breaking: $π^o-η$ Mixing to One Loop in Chiral Perturbation Theory

It is pointed out that the meson mixing matrix elements usually considered responsible for the bulk of the observed few-body charge symmetry breaking are naturally $q^2$-dependent in QCD. For $π^o-η$ mixing, using the usual representation of the pseudoscalar fields, the leading $q^2$ dependence can be explicitly calculated using chiral perturbation theory to one loop, the result being a significant decrease in the magnitude of the matrix element in going from timelike to spacelike values of $q^2$. Since it is the latter range of $q^2$ which is relevant to NN scattering and the few-body bound state, this result calls into serious question the standard treatment of few-body charge symmetry breaking contributions associated with $π^o-η$ and $ρ-ω$ mixing.

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arXiv1992

Modelling the Off-Shell Dependence of $π^{o}- η$ Mixing with Quark Loops

It is shown that including form factors for the quark-pseudoscalar meson couplings of the Georgi-Manohar chiral quark model allows one to obtain the leading off-shell dependence of $π^{o}- η$ mixing (as predicted by chiral perturbation theory) from the effect of quark loops on the meson propagators. Implications for $ρ^{o} - ω$ mixing and for the effects on meson mixing contributions to few body charge symmetry breaking observables are also discussed.

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