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A. A. Penin

Publications and source records attributed to A. A. Penin.

48 records · Page 3Linked to original sources
arXiv1998

Next-to-next-to-leading order relation between $R(e^+e^-\to b\bar b)$ and $Γ_{\rm sl}(b\to clν_l)$ and precise determination of $|V_{cb}|$

We present the next-to-next-to-leading order relation between the moments of the $Υ$ system spectral density and the inclusive $B$-meson semileptonic width. The perturbative series for the width as an explicit function of the moments is well convergent in three consequent orders in the strong coupling constant that provides solid and accurate theoretical estimate. As a result, the uncertainty of the value of $|V_{cb}|$ Cabibbo-Kobayashi-Maskawa matrix element is reduced.

hep-ph↗
arXiv1998

Instantons and Non-Perturbative Dynamics of N=2 Supersymmetric Abelian Gauge Theories in Two Dimensions

We study N=2 supersymmetric Abelian gauge model with the Fayet-Iliopoulos term and an arbitrary number of chiral matter multiplets in two dimensions. By analyzing the instanton contribution we compute the non-perturbative corrections to the mass spectrum of the theory and the quantum deformation of the classical vacua space. In contrast to known examples the non-perturbative bosonic potential is saturated by the one-instanton contribution and can be directly found within the semiclassical expansion around the one-instanton saddle point.

hep-th↗
arXiv1998

Next-to-next-to-leading order vacuum polarization function of heavy quark near threshold and sum rules for $b \bar b$ system

A correlator of the vector current of a heavy quark is computed analytically near threshold in the next-to-next-to-leading order in perturbative and relativistic expansion that includes $\al_s^2$, $\al_sv$ and $v^2$ corrections in the coupling constant and velocity of the heavy quark to the nonrelativistic Coulomb approximation. Based on this result, the numerical values of the $b$-quark pole mass and the strong coupling constant are determined from the analysis of sum rules for the $Υ$ system. The next-to-next-to-leading corrections are found to be of order of next-to-leading ones.

hep-ph↗
arXiv1998

Coulomb resummation for $b \bar b$ system near threshold and precision determination of $\al_s$ and $m_b$.

We analyze sum rules for the $Υ$ system with resummation of threshold effects on the basis of the nonrelativistic Coulomb approximation. We find for the pole mass of the bottom quark $m_b=4.75\pm 0.04 GeV$ and for the strong coupling constant $\al_s(M_Z)=0.118\pm 0.006$. The origin of the contradiction between two recent estimates obtained within the same formal framework is clarified.

hep-ph↗
arXiv1997

Quark-hadron duality for $K^0-\bar{K^0}$ mixing

Long distance contribution to the $K^0-\bar K^0$ mixing is taken into account consistently and the corrections to the naive duality result represented by the famous box diagram are found to be small. Estimates are given in the leading order of the chiral perturbation theory.

hep-ph↗
arXiv1997

Practical techniques of QCD vs exact results of solvable models

We check quantitatively the validity of some popular phenomenological approaches of QCD in simple models. Dispersion sum rules are considered within the ladder approximation of a field-theoretic model with OPE given by ordinary loop diagrams which are computable for any number of loops. A correlator of two currents within the model complies with all requirements of standard QCD sum rules approach for fitting low-lying resonances such as fast convergence and good stability while the exact spectrum contains no resonance. Optimized PT as it is inspired by the principle of minimal sensitivity is analyzed within a quantum mechanical model and is shown to work well as compared to pure asymptotic expansion in the coupling constant or Padé approximation. Renormalon technique is tested within another quantum mechanical model and is found to fail to detect its low-energy structure.

hep-ph↗
arXiv1997

Numerical analysis of renormalon technique in quantum mechanics

We discuss the ways of extracting a low energy scale of an underlying theory using high energy scattering data. Within an exactly solvable model of quantum mechanics we analyze a technique based on introduction of nonperturbative power corrections accounting for asymptotically small terms and an alternative approach exploiting a modified running coupling constant of the model and nonperturbative continuation of evolution equations into an infrared region. Numerical estimates show that the latter is more efficient in approximating low-energy data of the model.

hep-ph↗
arXiv1996

What Becomes of Vortices in Theories with Flat Directions

In many theories with flat directions of scalar potential, static vortex solutions do not exist for a generic choice of vacuum. In two Euclidean dimensions, we find their substitutes --- constrained instantons consisting of compact core formed by Abrikosov--Nielsen--Olesen vortex and long-ranged cloud of modulus field. In (3+1) dimensions, an initial compact configuration of string topology evolves in such a way that at every point in space the modulus relaxes, in a universal manner, to one and the same value characteristic to the theory.

hep-ph↗
arXiv1995

A scalar gluonium contribution to $K\rightarrowππ$ decay

We study a new $K\rightarrowππ$ decay channel with gluons in intermediate state which is normally neglected within the factorization framework. Both short-distance and long-distance parts of the amplitude are calculated. The chiral Lagrangian approach is used for obtaining the long-distance contribution. The nonperturbative contribution gives an additional enhancement to $K\rightarrowππ$ decay amplitude with $ΔI=1/2$. A sizable violation of factorization in the $p^4$ order of chiral perturbation theory is found.

hep-ph↗
arXiv1995

On a subtle point of sum rules calculations: toy model

We consider a two-point correlator in massless $ϕ^3$ model within the ladder approximation . The spectral density of the correlator is known explicitly and does not contain any resonances. Meanwhile making use of the standard sum rules technique with a simple "resonance + continuum" model of the spectrum allows to predict parameters of the "resonance" very accurately in the sense that all necessary criteria of stability are perfectly satisfied.

hep-ph↗
arXiv1995

Extended analysis of the "penguin" part of $K\toππ$ amplitude

We make an attempt to clarify the role of the annihilation or "penguin" mode in the description of the $K\rightarrowππ$ decay within the Standard Model. The attention is concentrated on new operators in the effective $ΔS=1$ Hamiltonian and the violation of factorization for mesonic matrix elements of the local four-quark operators. We propose a regular method to evaluate the mesonic matrix elements of $K\rightarrowππ$ transitions based on studying three-point correlators via {\it QCD} sum rules using the chiral effective theory as an underlying low-energy model for strong interaction. Matrix elements of the {\it QCD} penguin operator are calculated within this approach. The total "penguin" contribution is found to be relatively large that improves the theoretical description of the $ΔI=1/2$ rule in non-leptonic kaon decays.

hep-ph↗