Tim Ledwig

Tensor charges and form factors of SU(3) baryons in the self-consistent SU(3) chiral quark-soliton model

We investigate the tensor form factors of the baryon octet within the framework of the chiral quark-soliton model, emphasizing those of the nucleon, taking linear 1/N{sub c} rotational as well as linear m{sub s} corrections into account, and applying the symmetry-conserving quantization. We explicitly calculate the tensor form factors H{sub T}{sup q}(Q{sup 2}) corresponding to the generalized parton distributions H{sub T}(x,{xi},t). The tensor form factors are obtained for the momentum transfer up to Q{sup 2{<=}}1 GeV{sup 2} and at a renormalization scale of 0.36 GeV{sup 2}. We find for the tensor charges {delta}u=1.08, {delta}d=-0.32, and {delta}s=-0.01 and discuss their physical consequences, comparing them with those from other models. Results for tensor charges for the baryon octet are also given.

Octet-baryon axial-vector charges and SU(3)-breaking effects in the semileptonic hyperon decays

The octet-baryon axial-vector charges and the g1/f1 ratios measured in the semileptonic hyperon decays are studied up to O(p^3) using the covariant baryon chiral perturbation theory with explicit decuplet contributions. We clarify the role of different low-energy constants and find a good convergence for the chiral expansion of the axial-vector charges of the baryon octet, g1(0), with O(p^3) corrections typically around 20% of the leading ones. This is a consequence of strong cancellations between different next-to-leading order terms. We show that considering only non-analytic terms is not enough and that analytic terms appearing at the same chiral order play an important role in this description. The same effects still hold for the chiral extrapolation of the axial-vector charges and result in a rather mild quark-mass dependence. As a result, we report a determination of the leading order chiral couplings, D=0.623(61)(17) and F=0.441(47)(2), as obtained from a completely consistent chiral analysis up to O(p^3). Furthermore, we note that the appearance of an unknown low-energy constant precludes the extraction of the proton octet-charge from semileptonic decay data alone, which is relevant for an analysis of the composition of the proton spin.

The Nucleon and

An expansion of the electromagnetic form factors of the nucleon and Delta(1232) in small momentum transfer and pion mass is performed in a manifestly-covariant EFT framework consistent with chiral symmetry and analyticity. We present the expressions for the nucleon and Delta(1232) electromagnetic form factors, charge radii, and electromagnetic moments in the framework of SU(2) baryon chiral perturbation theory, with nucleon and Delta(1232)-isobar degrees of freedom, to next-to-leading order. Motivated by the results for the proton electric radius obtained from the muonic-hydrogen atom and electron-scattering process, we extract values for the second derivative of the electric form factor which is a genuine prediction of the p^3 BChPT. The chiral behavior of radii and moments is studied and compared to that obtained in the heavy-baryon framework and lattice QCD. The chiral behavior of Delta(1232)-isobar properties exhibits cusps and singularities at the threshold of Delta->pi N decay, and their physical significance is discussed.

\Delta

We investigate the form factors of the chiral-odd nucleon matrix element of the tensor current. In particular, we aim at the anomalous tensor magnetic form factors of the nucleon within the framework of the SU(3) and SU(2) chiral quark-soliton model. We consider 1/N{sub c} rotational corrections and linear effects of SU(3) symmetry breaking with the symmetry-conserving quantization employed. We first obtain the results of the anomalous tensor magnetic moments for the up and down quarks: {kappa}{sub T}{sup u}=3.56 and {kappa}{sub T}{sup d}=1.83, respectively. The strange anomalous tensor magnetic moment is yielded to be {kappa}{sub T}{sup s}=0.2{approx}-0.2, that is compatible with zero. We also calculate the corresponding form factors {kappa}{sub T}{sup q}(Q{sup 2}) up to a momentum transfer Q{sup 2{<=}}1 GeV{sup 2} at a renormalization scale of 0.36 GeV{sup 2}.

(1232) form factors at low momentum-transfer and small pion masses

We examine the electromagnetic properties of the �(1232) resonance within the self-consistent chiral quark-soliton model. In particular we present theform factors of the vector-current GE0(Q 2 ), GE2(Q 2 ) and GM1(Q 2 ) for a momentum-transfer range of 0 � Q 2 � 1GeV 2 . We ap- ply the symmetry-conserving quantization of the soliton and take 1/Nc rotational corrections into account. Values for the magnetic moments of all decuplet baryons as well as for the Ntransition are given. Special interest is also given to the electric quadrupole moment of the �. I. INTRODUCTION

Anomalous tensor magnetic moments and form factors of the proton in the self-consistent chiral quark-soliton model

We deal with the problem of assigning electromagnetic moments to a quasi-stable particle (i.e., a particle with mass located at particles decay threshold). In this case, an application of a small external electromagnetic field changes the energy in a non-analytic way, which makes it difficult to assign definitive moments. On the example of a spin-1/2 field with mass Minteracting with two fields of masses M and m, we show how a conventionally defined magnetic dipole moment diverges at M� = M +m. We then show that the conventional definition makes sense only when the values of the applied magnetic field B satisfy jeBj/2M� � j M� −M −mj. We discuss implications of these results to existing studies in electroweak theory, chiral effective-field theory, and lattice QCD. Electromagnetic (e.m.) moments of a particle are de- termined through observations of the particles behavior in an applied electromagnetic field. For example, the magnetic moment is measured by observing the spin pre- cession in a magnetic field. In doing so, one assumes that the uniform magnetic field ~ B induces a linear response in the energy: �E = −~ � ~

Electromagnetic properties of the Delta(1232) and decuplet baryons in the self-consistent SU(3) chiral quark-soliton model

We investigate the axial-vector transition constants of the baryon antidecuplet to the octet and decuplet within the framework of the self-consistent SU(3) chiral quark-soliton model. Taking into account rotational 1/N{sub c} and linear m{sub s} corrections and using the symmetry-conserving quantization, we calculate the axial-vector transition constants. It is found that the leading-order contributions are generally almost canceled by the rotational 1/N{sub c} corrections. Thus, the m{sub s} corrections turn out to be essential contributions to the axial-vector constants. The decay width of the {theta}{sup +}{yields}NK transition is determined to be {gamma}({theta}{yields}NK)=0.71 MeV, based on the result of the axial-vector transition constant g{sub A}*({theta}{yields}NK)=0.05. In addition, other strong decays of the baryon antidecuplet are investigated. The forbidden decays from the baryon antidecuplet to the decuplet are also studied.

Electromagnetic moments of quasistable particle

We investigate the semileptonic hyperon decays within the framework of the self-consistent SU(3) chiral quark-soliton model (χQSM). We take linear 1/Nc rotational as well as linear ms corrections into account and apply the symmetry conserving quantization. We present the results for the form factors f1(Q2), f2(Q2) and g1(Q2) in addition to the semileptonic decay constants of hyperons. We also have calculated the radii and dipole masses of these form factors for all relevant strangeness-conserving and strangeness-changing transitions.

Axial-vector transitions and strong decays of the baryon antidecuplet in the self-consistent SU(3) chiral quark-soliton model

Abstract We investigate the vector transition form factors of the nucleon and vector meson K ∗ to the pentaquark baryon Θ + within the framework of the SU ( 3 ) chiral quark–soliton model. We take into account the rotational 1 / N c and linear m s corrections, assuming isospin symmetry and employing the symmetry-conserving quantization. It turns out that the leading-order contributions to the form factors are almost cancelled by the rotational corrections. Because of this, the flavor SU ( 3 ) symmetry-breaking terms yield sizeable effects on the vector transition form factors. In particular, the main contribution to the electric-like transition form factor comes from the wave-function corrections, which is a consequence of the generalized Ademollo–Gatto theorem derived in the present work. We estimate with the help of the vector meson dominance the K ∗ vector and tensor coupling constants for the Θ + : g K ∗ N Θ = 0.74 – 0.87 and f K ∗ N Θ = 0.53 – 1.16 . We argue that the outcome of the present work is consistent with the null results of the CLAS experiments in the reactions γ n → K − Θ + and γ p → K ¯ 0 Θ + . The results of the present work are also consistent with the recent experiments at KEK. In addition, we present the results of the Σ 10 ¯ → N K ¯ ∗ transition form factors and its K ¯ ∗ N Σ 10 ¯ coupling constants.

Semileptonic hyperon decays in the self-consistent SU(3) chiral quark-soliton model

Fits of the p4 covariant SU(2) baryon chiral perturbation theory to lattice QCD nucleon mass data from several collaborations for 2 and 2+1 flavors are presented. We consider contributions from explicit Δ(1232) degrees of freedom, finite volume and finite spacing corrections. We emphasize here on our Nf = 2 + 1 study. We obtain low-energy constants of natural size that are compatible with the rather linear pion-mass dependence of the nucleon mass observed in lattice QCD. We report a value of σπN = 41(5)(4) MeV in the 2 flavor case and σπN = 52(3)(8) MeV for 2+1 flavors.