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K. Goeke

Publications and source records attributed to K. Goeke.

At least 91 records · Page 5Linked to original sources
arXiv1997

Self-consistent calculation of parton distributions at low normalization point in the chiral quark-soliton model

We calculate the isosinglet unpolarized quark-- and antiquark distributions at a low normalization point in the large--$N_c$ limit. The nucleon is described as a self-consistent soliton solution of the effective chiral theory. The ultraviolet cutoff is implemented by a Pauli-Villars subtraction. The quark and antiquark distributions satisfy the momentum as well as the baryon number sum rule, corresponding to ``constituent'' quarks whose structure is not yet resolved at the low scale. Already at this level a sizable number of antiquarks is present.

hep-ph↗
arXiv1997

Off-forward quark distributions of the nucleon in the large N_c limit

We study the off-forward quark distributions (OFQD's) in the chiral quark-soliton model of the nucleon. This model is based on the large-N_c picture of the nucleon as a soliton of the effective chiral lagrangian and allows to calculate the leading twist quark- and antiquark distributions at a low normalization point. We demonstrate the consistency of the approach by checking various sum rules for the OFQD's. We present numerical estimates of the isosinglet distribution H(x,ξ,Δ^2). In contrast to other approaches we find a strong qualitative dependence on the longitudinal momentum transfer, ξ. In particular, H(x,ξ,Δ^2) as a function of x exhibits fast crossovers at |x| = ξ/2. Such behaviour could lead to a considerable enhancement of the deeply-virtual Compton scattering cross section.

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arXiv1996

Meson loops in the Nambu-Jona-Lasinio model

The effects of meson loops in the vacuum sector of the Nambu--Jona-Lasinio model are calculated. Using the effective action formalism we take consistently all next-to-leading-order $1 \over \Nc$ terms into account. This leads to a symmetry-conserving approach, in which all features of spontaneously broken chiral symmetry, such as the Goldstone theorem, the Gold\-ber\-ger--Treiman and the Gell-Mann--Oakes--Renner relations are preserved. Contributions to $\langle \overline{q}q \rangle$ and $F_π$ are calculated, and are shown to be substantial, at the level of $\sim 30\%$, consistent with the $1 \over \Nc$ expansion. The leading nonanalytic terms in the chiral expansion of $\langle \overline{q}q \rangle$, $F_π$ and $m_π$ agree have the same form as the one-loop results of chiral perturbation theory.

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arXiv1996

Analytic structure of meson propagators in the proper-time regularized Nambu--Jona-Lasinio model

We analyze the analytic structure of meson propagators in the Nambu--Jona-Lasinio model with a proper-time regulator. We show that the regulator produces unphysical complex singularities. As a result the naive use of the Wick rotation is no longer allowed. Formulas involving integration over mesonic momenta, such as meson-loop contributions or dispersion relations for meson Green's functions, cannot be written in usual forms.

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arXiv1996

A Top Quark Soliton and its Anomalous Chromomagnetic Moment

We show that under the assumption of dynamical symmetry breaking of electro weak interactions by a top quark condensate, motivated by the Top Mode Standard Model, the top quark in this effective theory can be considered then as chiral color soliton (qualiton). This is realized in an effective four-fermion interaction with chiral $SU(3)_c$ as well as $SU(2)_L\otimes U_Y(1)$ symmetry. In the pure top sector the qualiton consists of a top valence quark and a Dirac sea of top and anti-top quark coupled to a color octet of Goldstone pions. The mass spectra, isoscalar quadratic radii and the anomalous chromomagnetic moment due to a non-trivial color form factor are calculated with zero and finite current top masses and effects at the Hadron Colliders are discussed. The anomalous chromomagnetic moment turns out to have a value consistent with the top production rates of the D0- and CDF-measurements.

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arXiv1996

Baryons as non-topological chiral solitons

The present review gives a survey of recent developments and applications of the Nambu--Jona-Lasinio model with $N_f=2$ and $N_f=3$ quark flavors for the structure of baryons. The model is an effective chiral quark theory which incorporates the SU(N$_f$)$_L\otimes$SU(N$_f$)$_R\otimes$U(1)$_V$ approximate symmetry of Quantum chromodynamics. The approach describes the spontaneous chiral symmetry breaking and dynamical quark mass generation. Mesons appear as quark-antiquark excitations and baryons arise as non-topological solitons with three valence quarks and a polarized Dirac sea. For the evaluation of the baryon properties the present review concentrates on the non-linear Nambu--Jona-Lasinio model with quark and Goldstone degrees of freedom which is identical to the Chiral quark soliton model obtained from the instanton liquid model of the QCD vacuum. In this non-linear model, a wide variety of observables of baryons of the octet and decuplet is considered. These include, in particular, electromagnetic, axial, pseudoscalar and pion nucleon form factors and the related static properties like magnetic moments, radii and coupling constants of the nucleon as well as the mass splittings and electromagnetic form factors of hyperons. Predictions are given for the strange form factors, the scalar form factor and the tensor charge of the nucleon.

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arXiv1995

Nucleon Tensor Charges in the Chiral Quark--Soliton Model

We investigate the singlet $g_T^{(0)}$ and isovector $g_T^{(3)}$ tensor charges of the nucleon, which are deeply related to the first moment of the leading twist transversity quark distribution $h_1(x)$, in the chiral quark-soliton model. With rotational $O(1/N_c) $ corrections taken into account, we obtain $g_T^{(0)}=0.69$ and $g_T^{(3)}=1.45$ at a low normalization poin of several hundreds MeV. Within the same approximation and parameters the model yields $g_A^{(0)}=0.36$, $g_A^{(3)}=1.21$ for axial charges and correct octet--decuplet mass splitting. We show how the chiral quark-soliton model interpolates between the nonrelativistic quark model and the Skyrme model.

hep-ph↗
arXiv1995

Magnetic Moments of the SU(3) Octet Baryons in the semibosonized SU(3) Nambu-Jona-Lasinio Model

We investigate the magnetic moments of the SU(3) octet baryons in the framework of the $SU(3)$ semibosonized Nambu--Jona--Lasinio model. The rotational $1/N_c$ corrections and strange quark mass in linear order are taken into account. We derive general relations between magnetic moments of the SU(3) octet baryons, based on the symmetry of our model. These relations indicate that higher order corrections such as $O(m_s/N_c)$ and $O(m^{2}_{s})$ are relatively small. The magnetic moments of the octet baryons predicted by our model are quantitatively in a good agreement with experimental results within about 15$\%$.

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arXiv1995

Sphaleron transitions in the Minimal Standard Model and the upper bound for the Higgs Mass

We calculate the dissipation of the baryon number after the electroweak phase transition due to thermal fluctuations above the sphaleron barrier. We consider not only the classical Boltzmann factor but also fermionic and bosonic one-loop contributions. We find that both bosonic and especially fermionic fluctuations can considerably suppress the transition rate. Assuming the Langer--Affleck formalism for this rate, the condition that an initial baryon asymmetry must not be washed out by sphaleron transitions leads, in the Minimal Standard Model ($\sinθ_W=0$), to an upper bound for the Higgs mass in the range 60 to 75 GeV.

hep-ph↗
arXiv1995

Electromagnetic form factors of the nucleon in the chiral quark soliton model

In this paper we present the derivation as well as the numerical results for the electromagnetic form factors of the nucleon within the chiral quark soliton model in the semiclassical quantization scheme. The model is based on semibosonized SU(2) Nambu -- Jona-Lasinio lagrangean, where the boson fields are treated as classical ones. Other observables, namely the nucleon mean squared radii, the magnetic moments, and the nucleon--$Δ$ splitting are calculated as well. The calculations have been done taking into account the quark sea polarization effects. The final results, including rotational $1/N_c$ corrections, are compared with the existing experimental data, and they are found to be in a good agreement for the constituent quark mass of about 420 MeV. The only exception is the neutron electric form factor which is overestimated.

hep-ph↗
arXiv1995

Axial form factor in the chiral quark soliton model

We calculate the axial form factor in the chiral quark soliton (semibosonized Nambu - Jona-Lasinio) model using the semiclassical quantization scheme in the next to leading order in angular velocity. The obtained axial form factor is in a good absolute (without additional scaling) agreement with the experimental data. Both the value at the origin and the $q$-dependence of the form factor as well as the axial m.s.radius are fairly well reproduced.

hep-ph↗
arXiv1995

The Constituent Quark Limit and the Skyrmion Limit of the Chiral Quark Soliton Model

We calculate $g_A^3$ and $g_A^0$ in the Chiral Quark-Soliton Model (or equivalently in semibosonized Nambu--Jona-Lasinio model) in the limit of small and large soliton size. In small soliton limit we recover the results of the Constituent Quark Model. The agreement between the two models is achieved due to the recently calculated $1/\Nc$ contributions to $g_A^3$ and to $g_A^0$. In the case of $g_A^3$ these terms arise from the {\it time-ordering} of the collective operators. For large solitons simple scaling arguments show that the $1/\Nc$ contributions vanish with the inverse power of the soliton size.

hep-ph↗
arXiv1995

$E2/M1$ Ratio for the $γN\rightarrow Δ$ Transition in the Chiral Quark Soliton Model

We calculate the electric quadrupole to magnetic dipole transition ratio $E2/M1$ for the reaction $γN \ra Δ(1232)$ in the chiral quark soliton model. The calculated $E2/M1$ ratio is in a good agreement with the very new experimental data. We obtain non-zero negative value for the electric quadrupole $N-Δ$ transition moment, which suggests an oblate deformed charge structure of the nucleon or/and the delta isobar. Other observables related to this quantity, namely the $N-Δ$ mass splitting, the isovector charge radius, and isovector magnetic moment, are properly reproduced as well.

hep-ph↗
arXiv1995

NJL model with vector couplings vs. phenomenology

We study the pseudoscalar, vector and axial current correlation functions in SU(2)-NJL model with scalar and vector couplings. The correlation functions are evaluated in leading order in number of colors $N_c$. As it is expected in the pseudoscalar channel pions appear as Goldstone bosons, and after fixing the cutoff to reproduce the physical pion decay constant, we obtain well-known current-algebra results. For the vector and axial channels we use essentially that at spacelike momenta the correlation functions can be related to the experimentally known spectral density via dispersion relations. We show that the latter imposes strong bounds on the strength of the vector coupling in the model. We find that the commonly used on-shell treatment of the vector and axial mesons (identified as poles at large timelike momenta) fails to reproduce the behavior of the corresponding correlation functions at small spacelike momenta extracted from the physical spectral density. The parameters of the NJL model fixed by the correlation functions at small spacelike momenta differ noticeably from those of the on-shell treatment.

hep-ph↗
arXiv1994

Isospin Mass Splittings and the $\ms$ Corrections in the Semibosonized SU(3)-NJL-Model

The mass splittings of hyperons including the isospin splittings are calculated with $O(\ms^2)$ and $O(\ms \dm)$ accuracy respectively within the semibosonized SU(3)-NJL model. The pattern of the isospin splittings is not spoiled by the terms of the order $O(\ms \dm)$, and both splittings between the different isospin multiplets and within the same multiplet are well reproduced for acceptable values of $\ms$ and $\dm$.

hep-ph↗
arXiv1994

Hyperon in Chiral Effective Quark Models

Baryonic correlation functions are calculated within an effective chiral quark model motivated by the instanton liquid model of QCD. Using a flavour SU(3) symmetry for the local four-quark interaction and taking rotational zero modes for the quantization into account low-energy hadronic observables are in surprising agreement with experimental data. (Talk presented at the Conference on Hypernuclear and Strange Particle Physics (HYP94), Vancouver, B.C., Canada, 4.-8- Juli 1994)

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