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A. V. Lanyov

Publications and source records attributed to A. V. Lanyov.

16 recordsLinked to original sources
arXiv2003

What we have learned from direct CP violation studies in kaon decays

A self-consistent analysis of K --> 2pi and K --> 3pi decays within a unique framework of chiral dynamics applied to the QCD-corrected weak nonleptonic quark lagrangian has been performed. The results on K --> 2pi amplitudes at O(p^6), including the value for epsilon'/epsilon, are compared with experiment to fix phenomenological B-factors for mesonic matrix elements of nonpenguin and penguin four-quark operators. The dependence of these B-factors on different theoretical uncertainties and experimental errors of various input parameters is investigated. Finally, we present our estimates at O(p^6) for the CP asymmetry of linear slope parameters in the K+- --> 3pi Dalitz plot.

hep-ph↗
arXiv2000

Direct CP Violation in Nonleptonic Kaon Decays by an Effective Chiral Lagrangian Approach at O(p^6)

A self-consistent analysis of K->2pi and K->3pi decays within a unique framework of chiral dynamics applied to the QCD-corrected weak nonleptonic quark lagrangian has been performed. The results on K->2pi amplitudes at O(p^6), including the value for epsilon'/epsilon, are compared with the experiment to fix phenomenological B-factors for mesonic matrix elements of nonpenguin and penguin four-quark operators. The dependence of B-factors on different theoretical uncertainties and experimental errors of various input parameters is investigated. Finally, we present our estimates at O(p^6) for the CP-asymmetry of linear slope parameters in the K(+-)->3pi Dalitz plot.

hep-ph↗
arXiv1999

Phenomenological analysis of epsilon'/epsilon within an effective chiral lagrangian approach at O(p^6)

We have combined a new systematic calculation of mesonic matrix elements at O(p^6) from an effective chiral lagrangian approach with Wilson coefficients taken from paper by G.Buchalla et al. Rev.Mod.Phys. 68 (1996) 1125, derived in the framework of perturbative QCD, and restricted partly by experimental data. We derive complete expressions for K-->2pi amplitudes and compare the results for epsilon'/epsilon with experiment.

hep-ph↗
arXiv1997

Results on K --> 2pi decays at O(p^6) and epsilon'/epsilon from an effective chiral lagrangian approach

We have combined a new systematic calculation of mesonic matrix elements at O(p^6) from an effective chiral lagrangian approach using Wilson coefficients taken from [G.Buchalla, A.J.Buras, M.E.Lautenbacher, Rev.Mod.Phys. 68 (1996) 1125], derived in the framework of perturbative QCD, and restricted partly by experimental data. We derive complete expressions for K --> 2pi amplitudes and give new estimates for epsilon'/epsilon.

hep-ph↗
arXiv1997

Photoproduction of neutral pion pairs in the Coulomb field of the nucleus

The total cross section for Coulomb photoproduction of neutral pion pairs in the reaction gamma A --> pi0 pi0 A is estimated within the effective chiral lagrangian approach. The amplitude of gamma gamma* --> pi0 pi0 with one off-shell photon is calculated at O(p^6) in the momentum expansion; in addition, nuclear absorption is taken into account. Besides its experimental feasibility, the results of the calculation demonstrate that the reaction gamma A --> pi0 pi0 A is a powerful source of information on the process gamma gamma --> pi0 pi0 close to threshold.

hep-ph↗
arXiv1995

$γγ\toπ^0π^0$ and $η\toπ^0γγ$ at $O(p^6)$ in the NJL model

We discuss the processes $γγ\toπ^0π^0$ and $η\toπ^0 γγ$ at $O(p^6)$ in the momentum expansion. The calculation involves tree--level, one--loop and two--loop diagrams of a chiral effective lagrangian which is obtained by a bosonization of the NJL model. The importance of integrating out meson resonances (reduction) is pointed out. Our final results for the total cross section of $γγ\toπ^0π^0$ are in good agreement with the experimental data of the Crystal Ball Collaboration. For the width of the $η\toπ^0γγ$ decay we obtain the value $0.11$ eV which has to be compared with the experimental value of $(0.84 \pm 0.18)$ eV. Alternatively, taking empirical parameters from a vector--meson--dominance model the prediction for the decay width is $0.35$ eV. We present a prediction for the differential decay probability as a function of $m_{γγ}^2/m_η^2$.

hep-ph↗
arXiv1995

Calculation of Heat-Kernel Coefficients and Usage of Computer Algebra

The calculation of heat-kernel coefficients with the classical DeWitt algorithm has been discussed. We present the explicit form of the coefficients up to $h_5$ in the general case and up to $h_7^{min}$ for the minimal parts. The results are compared with the expressions in other papers. A method to optimize the usage of memory for working with large expressions on universal computer algebra systems has been proposed.

hep-ph↗
arXiv1994

An Effective Chiral Meson Lagrangian at $O(P^6)$ from the NJL Model

In this work we present a strong chiral meson Lagrangian up to and including $O(p^6)$ in the momentum expansion. It is derived from the Nambu--Jona-Lasinio (NJL) model using the heat-kernel method. Identities related to the properties of covariant derivatives of the chiral matrix $U$ as well as field transformations have been used to obtain a minimal set of linearly independent terms.

hep-ph↗
arXiv1994

Chiral Meson Lagrangians from the QCD Based NJL Model Modified by Nonlocal Effects

Starting from a QCD inspired bilocal quark interaction we obtain a local effective meson lagrangian. In contrast to previous local (NJL-like) approaches, we include nonlocal corrections related to the finite meson size which we characterize by a small parameter. After bosonization using the heat-kernel method we predict the structure coefficients of the Gasser-Leutwyler $p^4$-lagrangian up to first order in this parameter. The modifications for the $L_i$ coefficients are typically of the order 10-20\%, except for $L_5$, where we find a stronger nonlocal influence.

hep-ph↗
arXiv1993

What can we learn from new measurements of Dalitz plot parameters for K $\rightarrow 3 π$ decays ?

We give a simple expression in linear and quadratic Dalitz--plot slopes which does not depend on the charge combination of the $3π$ state $(K^\pm \to π^{\pm}π^{+}π^{-}$ or $π^{\pm}π^{0}π^{0}$ and $K_L^{0} \to π^{+}π^{-}π^{0}$ or $π^{0}π^{0}π^{0})$, if all phases between final states are negligible. After investigating the influence of radiative corrections, it is shown how new measurements, especially of quadratic slopes in the $π^{\pm} π^{0} π^{0}$ channel, could help to test theoretical predictions more stringently. A FORTRAN code for the radiatiative corrections is available on request.

hep-ph↗
arXiv1993

On the $p^4$--corrections to $K \to 3π$ decay amplitudes in nonlinear and linear chiral models

The calculations of isotopic amplitudes and their results for the direct $CP$--violating charge asymmetry in $K^\pm \to 3π$ decays within the nonlinear and linear ($σ$--model) chiral Lagrangian approach are compared with each other. It is shown, that the latter, taking into account intermediate scalar resonances, does not reproduce the $p^4$--corrections of the nonlinear approach introduced by Gasser and Leutwyler, being saturated mainly by vector resonance exchange. The resulting differences concerning the $CP$ violation effect are traced in some detail.

hep-ph↗
arXiv1993

Radiative Kaon Decays and $CP$ Violation

The amplitudes of $K \rightarrow πγ^* \rightarrow πe^+e^-$ and $K \rightarrow ππγ$ decays have been calculated within chiral Lagrangian approach including higher-order derivative terms and meson loops. The selfconsistency of the simultaneous description of the experimental data on the nonleptonic and radiative kaon decays have been demonstrated. We estimate the effects of ``indirect'' and ``direct'' $CP$-violation in $K^0_L \rightarrow π^0 e^+e^-$ decays and discuss $CP$-violating charge asymmetries in $K^{\pm} \rightarrow π^{\pm} π^0 γ$ decays.

hep-ph↗
arXiv1993

On the Origin of the Enhancementof CP-violating Charge Asymmetries in $K \rightarrow 3π$ Decays Predicted from Chiral Theory

We present an analysis of the enhancement of CP-violating charge asymmetries in $K \rightarrow 3π$ decays. Calculations of decay amplitudes are performed on the basis of bosonized strong and weak Lagrangians derived from QCD-motivated quark Lagrangians. We show that the interplay of fourth-order contributions of chiral Lagrangians for strong interactions and penguin operators in weak interactions significantly enhances the charge asymmetries.

hep-ph↗
arXiv1993

Heat-Kernel Calculation of Quark Determinant and Computer Algebra

In this paper there we describe the calculational background of deriving a strong meson Lagrangian from the Nambu--Jona-Lasinio quark model using the computer algebra systems FORM and REDUCE in recursive algorithms, based on the heat-kernel method for the calculation of the quark determinant.

hep-ph↗