arXiv subjects
Publications and source records attributed to M. A. Ivanov.
Exclusive nonleptonic decays of bottom and charm baryons are studied within a relativistic quark model. We include factorizing as well as nonfactorizing contributions to the decay amplitudes.
Bethe-Salpeter approach has been applied to the study of b --> c transitions both for heavy mesons and heavy baryons. Meson and baryon IW functions are calculated on the equal footing. A reasonable agreement with the experimental data for heavy to heavy semileptonic transitions has been obtained.
We report on a confined quark model calculation of the transition form factors for the radiative decays of η(η')->γl^+l^- and η(η')->γπ^+π^-. The η-η' mixing angle θ_P is determined from the set of data on the electromagnetic η(η') decays. It is found that θ_P\sim -16.5. The analysis of the dipionic mass distribution in the decay η'->γπ^+π^- confirms the existence of a non-resonant contribution which is the box anomaly.
A heavy-quark limit of the Dyson-Schwinger equations is introduced and used in an exploratory study of leptonic and semileptonic decays of heavy mesons. The application of this framework to heavy-to-light semileptonic decays, which require a good knowledge of light-quark propagation characteristics and light-meson bound state amplitudes, is illustrated.
The gamma(*) pi(0) -> gamma form factor is obtained within the Lagrangian quark model with separable interaction known to provide a good description of the pion observables at low energies. The pion-quarks vertex is chosen in a Gaussian form. The form factor obtained is close to the available experimental data and reaches smoothly the Brodsky-Lepage limit at Q2 = 10 GeV2.
The semileptonic and leptonic decays of heavy mesons are studied as a phenomenological application and exploration of a heavy-quark limit of Dyson-Schwinger equations. The single form factor, $ξ(w)$, which characterises the semileptonic decay in this limit, is calculated and compares well with recent experimental extractions. We obtain a lower bound of 1/3 on the slope-parameter $ρ^2 \equiv -ξ^\prime(1)$, which, in calculations with realistic input, is exceeded by a great deal: agreement with experimental data requiring $ρ^2 \sim 1.2 - 1.6$. The flavour and momentum dependence of the light-quark propagators has observable consequences.
We report the calculation of electromagnetic form factors of nucleons within a relativistic three-quark model with Gaussian shape for the nucleon-quark vertex. The allowed region for two adjustable parameters, the range parameter $Λ_N$ in the Gaussian and the constituent quark mass $m_q$, is obtained from fitting the data for magnetic moments and electromagnetic radii of nucleons. It is found that their values calculated with $m_q$=420 MeV and $Λ_N$=1.25 GeV agree very well with the experimental data. It is turned out that the electric proton and magnetic nucleon form factors fall faster than the dipole fit of the experimental data for momentum transfers $0\le Q^2\le 1$ GeV$^2$.
Exclusive semileptonic decays of bottom and charm baryons are considered within a relativistic three-quark model with a Gaussian shape for the baryon-three-quark vertex and standard quark propagators. We calculate the baryonic Isgur-Wise functions, decay rates and asymmetry parameters.
Semileptonic decays of bottom and charm baryons are considered within a relativistic three-quark model with the Gaussian shape for the baryon-three-quark vertex and standard quark propagators.
We report the calculation of electromagnetic form factors of nucleons within a relativistic three-quark model with Gaussian shape for the nucleon-quark vertex. The allowed region for two adjustable parameters, the range parameter $Λ_N$ in the Gaussian and the constituent quark mass $m_q$, is obtained from fitting the data for magnetic moments and electromagnetic radii of nucleons. The shapes of electric and magnetic nucleon form factors calculated in this approach with the central parameters $m_q$=420 MeV and $Λ_N$=1.25 GeV are close to the data for momentum transfers $0\le Q^2\le 1$ GeV$^2$
A confined quark model study in a couple of chirally anomalous processes is presented in comparison with effective meson Lagrangian approaches of various kind. The processes considered are π^0 \to γγand γ\to π^+ π^- π^0 (or the equivalent πγ\to ππ) for which there is a well-known low energy theorem relating the latter amplitude with the former one by a very simple algebraic relation in the zero energy (or chiral, or soft pion) limit. Our quark model naturally generates the so-called contact term in the amplitude for the second process, but with the opposite sign to what effective chiral meson models indicate. A reinterpretation of our vector pole contribution restores the consistency, however. While the first reaction is observed to serve in it calibrating various models, it is found difficult, based upon the quality of the existing data in the second reaction, to single out the best model, which appears indispensable for testing the validity of the above low energy theorem. Thus the proposed experiments and their analyses should aim at attaining an optimal accuracy.
The results for observables of semileptonic decays of bottom and charm baryons (Isgur-Wise functions, decay rates, distributions, asymmetry parameters) are given within relativistic quark model. A comparison with recent experimental data (CLEO Collaboration) is made.
In connection with planned experiments devoted to investigation of semileptonic decays of beauty baryons Isgur-Wise function and observables of $Λ_b$ baryon (decay rates and distributions, leptonic spectra and asymmetry parameters) are calculated in the framework of diquark model with taking into account of infrared regime for heavy quark.
We demonstrate that to calculate the self-energy of a heavy quark in the heavy quark limit (or the heavy fermion limit in what is called the Baryon Chiral Perturbation Theory), the use of standard dimensional regularization provides only the quantum limit: opposite to the heavy quark (or classical) limit that one wishes to obtain. We thus devised a standard ultraviolet/infrared regularization procedure in calculating the one- and two-loop contributions to the heavy quark self-energy in this limit. Then the one-loop result is shown to provide the standard classical Coulomb self-energy of a static colour source that is linearly proportional to the untraviolet cutoff $Λ$. All the two-loop contributions are found to be proportional to $Λ\ln(Λ/λ)$ where $λ$ is the infrared cutoff. Often only the contribution from the bubble (light quarks, gluon and ghost) insertion to the gluon propagator has been considered as the $O(α_s)$ correction to the Coulomb energy to this order. Our result shows that other contributions are of the same magnitude, thus have to be taken into account.
We have studied the weak decay constants and the Isgur-Wise form factor of the B and D mesons in the heavy quark limit, by employing a relativistic quark confinement model. It is an attempt to improve our previous work within the same line of thinking, but by incorporating a couple of novel aspects. First, the infrared behavior of the heavy quark is considered by modifying its conventional propagator in terms of a single parameter $ν$. Second, the mass difference of the heavy meson and heavy quark: $E=m_H-M_Q$ has been included. It is found that the weak decay constants depend strongly on the mass difference E with a relatively mild $ν$ dependence. As for the Isgur-Wise function it is controlled more sensitively by the infrared parameter $ν$, leading to its suppression at maximum meson recoil.