arXiv subjects

M. Wakamatsu

Publications and source records attributed to M. Wakamatsu.

40 records · Page 3Linked to original sources

arXiv1999

On the Chiral Quark Soliton Model with Pauli-Villars Regularization

The Pauli-Villars regularization scheme is often used for evaluating parton distributions within the framework of the chiral quark soliton model with inclusion of the vacuum polarization effects. Its simplest version with a single subtraction term should however be taken with some caution, since it does not fully get rid of divergences contained in scalar and psuedoscalar quark densities appearing in the soliton equation of motion. To remedy this shortcoming, we propose here its natural extention, i.e. the Pauli-Villars regularization scheme with multi-subtraction terms. We also carry out a comparative analysis of the Pauli-Villars regularization scheme and more popular proper-time one. It turns out that some isovector observables like the isovector magnetic moment of the nucleon is rather sensitive to the choice of the regularization scheme. In the process of tracing the origin of this sensitivity, a noticeable difference of the two regularization scheme is revealed.

hep-ph↗

arXiv1998

Chiral Symmetry and the Nucleon Spin Structure Functions

We carry out a systematic investigation of twist-two spin dependent structure functions of the nucleon within the framework of the chiral quark soliton model (CQSM) by paying special attention to the role of chiral symmetry of QCD. We observe a substantial difference between the predictions of the longitudinally polarized distribution functions and the transversity distribution ones. That the chiral symmetry is responsible for this difference can most clearly be seen in the isospin dependence of the corresponding first moments, i.e. the axial and tensor charges. The CQSM predicts $g_A^{(0)} / g_A^{(3)} \simeq 0.25$ for the ratio of the isoscalar to isovector axial charges, and $g_T^{(0)} / g_T^{(3)} \simeq 0.46$ for the ratio of the isoscalar to isovector tensor charges, which should be compared with the prediction of the naive (non-chiral) MIT bag model, $g_A^{(0)} / g_A^{(3)} = g_T^{(0)} / g_T^{(3)} = 3 / 5$.

hep-ph↗

arXiv1996

The Extended Nambu-Jona-Lasinio Model and Hidden Local Symmetry of Low Energy QCD

Using the standard auxiliary field method, we derive from the extended Nambu-Jona-Lasinio model an effective meson action containing vector and axial-vector mesons in addition to Goldstone bosons. The vector and axial-vector mesons in this effective action transform as gauge fields of hidden local symmetry $G_{local} = {[U(n)_L \times U(n)_R]}_{local}$. Here, the realization of enlarged hidden local symmetry is accomplished via the introduction of two kinds of ``compensating'' fields. For obtaining the intrinsic-parity violating part of the action, we generalize the standard gauged Wess-Zumino-Witten action such that it also contains two kinds of ``compensators'' in addition to the usual Goldstone bosons as well as the vector and axial-vector mesons. This generalized gauged Wess-Zumino-Witten action turns out to have $G_{globa} \times G_{local}$ symmetry, where $G_{global}$ being the usual $U(n)_L \times U(n)_R$ global chiral symmetry while $G_{local}$ being the $U(n)_L \times U(n)_R$ hidden local symmetry. This means that $G_{local}$ has no gauge anomaly and its associated vector and axial-vector mesons can be regarded as gauge bosons of $G_{local}$. The introduction of the coupling with the external electroweak fields requires us to gauge some appropriate subgroup of $G_{global}$. To perform it in consistent with the anomaly structure of QCD is a nontrivial problem. We explain how this can be done, following the recent suggestion by several authors.

hep-ph↗

arXiv1993

$1/N_c$ Rotational Corrections to $g_A$ and Isovector Magnetic Moment of the Nucleon

The $1/N_c$ rotational corrections to the axial vector constant and the isovector magnetic moment of the nucleon are studied in the Nambu -- Jona-Lasinio model. We follow a semiclassical quantization procedure in terms of path integrals in which we can include perturbatively corrections in powers of angular velocity $Ω\sim \frac 1{N_c}$. We find non-zero $1/N_c$ order corrections from both the valence and the Dirac sea quarks. These corrections are large enough to resolve the long-standing problem of a strong underestimation of both $g_A$ and $μ^{IV}$ in the leading order. The axial constant $g_A$ is well reproduced, whereas the isovector magnetic moment $μ^{IV}$ is still underestimated by 25 \%.

hep-ph↗