arXiv subjects

O. I. Yakovlev

Publications and source records attributed to O. I. Yakovlev.

9 recordsLinked to original sources

arXiv1999

Baryonic currents and their correlators in the Heavy Quark Effective Theory

HQET currents with the quantum numbers of the ground-state baryons are discussed. One-loop anomalous dimensions are calculated, and exact one-loop matching to QCD currents is found. Two-point correlators of these currents are calculated taking into account $d\le9$ terms of the OPE. Sum rules for heavy baryons Lambda_Q and Sigma^(*)_Q are analyzed. Three-point correlators of two baryonic currents and a heavy-heavy velocity changing current are calculated with the same accuracy. The baryonic Isgur-Wise form factors are estimated from the corresponding sum rules.

hep-ph↗

arXiv1997

On the resummation of double logarithms in the process Higgs --> two photons

The decay of the Higgs boson into two photons is discussed. Using Sudakov technicue, we study a new type of double logarithms in the case of the light quark loop. First, we examine the origin of such logarithms at the one loop level. Then we perform a two-loop analysis, and finally we present an explicit result of the resummation of double logarithms in all order in QCD. The phenomenological applications are discussed.

hep-ph↗

arXiv1997

Couplings of heavy hadrons with soft pions from QCD sum rules

We estimate the couplings in the Heavy Hadron Chiral Theory (HHCT) lagrangian from the QCD sum rules in an external axial field. We take into account the perturbative correction to the meson correlator in the infinite mass limit. With the perturbative correction and three successive power corrections, the meson correlator in an axial field becomes one of the best known correlators. In spite of this, the corresponding sum rule is not very stable. It yields the result g_1 F^2/(380MeV)^3 = 0.1 - 0.2, where F^2 = f_M^2 m/4 = (380MeV)^3 is the central value of the heavy meson decay constant with the perturbative correction. This result is surprisingly low as compared with the constituent quark model estimate g_1 = 0.75. The sum rules for g_{2,3} following from nondiagonal Sigma-Sigma and diagonal Lambda-Sigma baryon correlators in an external axial field suggest g_{2,3} = 0.4 - 0.7, while diagonal Sigma-Sigma and nondiagonal Lambda-Sigma baryon sum rules have too large uncertainties.

hep-ph↗

arXiv1997

An Analysis of Diagonal and Non-diagonal QCD Sum Rules for Heavy Baryons at Next-to-Leading Order in α_S

We consider diagonal and non-diagonal QCD sum rules for the ground state heavy baryons to leading order in $1/m_Q$ and at next-to-leading order in $α_S$. In the non-diagonal case we evaluate the eight different two-loop diagrams which determine the perturbative $α_S$-corrections to the Wilson coefficient of the quark condensate in the Operator Product Expansion. The QCD corrections to the non-diagonal sum rules are moderate compared to the QCD corrections in the diagonal case. We also consider constituent type sum rules using constituent type interpolating currents. The obtained results are in reasonable agreement with the corresponding results obtained in the diagonal case. As central values for the bound state energies we find $m(Λ_Q)-m_Q = 760 MeV$ and $m(Σ_Q)-m_Q = 940 MeV$. The central values for the residues are given by $F(Λ_Q) = 0.030 GeV^3$ and $F(Σ_Q) = 0.038 GeV^3$.

hep-ph↗

arXiv1996

QCD Sum Rules for Heavy Baryons at Next-to-Leading Order in alpha_s

We derive QCD sum rules for heavy baryons at leading order in $1/m_Q$ and at next-to-leading order in $α_s$. The calculation involves the evaluation of four different perturbative three-loop diagrams which determine the $α_s$-corrections to the Wilson coefficients of the leading term in the Operator Product Expansion (OPE). From the sum rules we obtain estimates for the masses and the residues of the heavy baryons $Λ_Q$ and $Σ_Q$. The perturbative $O(α_s)$ corrections to the leading order spectral function amount to about $100%$, and they shift the calculated values for the baryon masses slightly upward. The residues are shifted upward by about $20-50%$. For the bound state energy $\barΛ$ given by the difference of the heavy baryon mass and the pole mass of the heavy quark $m_Q$ we obtain $m_{Λ_Q}-m_Q=780 MeV$ and $m_{Σ_Q}-m_Q=950 MeV$. For the residues we find $|F_Λ|=0.028 GeV^3$ and $|F_Σ|=0.039 GeV^3$.

hep-ph↗

arXiv1996

Heavy Baryons and QCD Sum Rules

We discuss an application of QCD sum rules to the heavy baryons $Λ_Q$ and $Σ_Q$. The predictions for the masses of heavy baryons, residues and Isgur-Wise function are presented. The new results on two loop anomalous dimensions of baryonic currents and QCD radiative corrections (two- and three- loop contributions) to the first two Wilson coefficients in OPE are explicitly presented.

hep-ph↗

arXiv1996

Two-loop Anomalous Dimensions of Heavy Baryon Currents in Heavy Quark Effective Theory

We present results on the two-loop anomalous dimensions of the heavy baryon HQET currents $J=(q^TCΓτq)Γ'Q$ with arbitrary Dirac matrices $Γ$ and $Γ'$. From our general result we obtain the two-loop anomalous dimensions for currents with quantum numbers of the ground state heavy baryons $Λ_Q$, $Σ_Q$ and $Σ_Q^*$. As a by-product of our calculation and as an additional check we rederive the known two-loop anomalous dimensions of mesonic scalar, pseudoscalar, vector, axial vector and tensor currents $(J=\bar qΓq)$ in massless QCD as well as in HQET.

hep-ph↗

arXiv1995

Two -loop $O(G_F{M_H}^2)$ radiative corrections to the Higgs decay width $H \to γγ$ for large Higgs boson masses

This note is devoted to the calculation of the two-loop $O(G_F {M_H}^2)$ radiative corrections to the Higgs decay width $H \to γγ$ for large values of the Higgs boson mass $M_H$ within the Minimal Standard Model. The use of the Equivalence Theorem makes it possible to reduce the problem to the consideration of the physical Higgs boson field and the Goldstone bosons $w^{+},w^{-},z$. We present analytical results for the various two- and three-particle absorptive parts of two-loop contributions, using dispersive techniques, analytic results for all but one of the dispersive contributions. The typical size of the correction is $\sim ~30 $ percent for a Higgs boson mass of order $1~TeV$.

hep-ph↗

arXiv1994

Couplings of heavy hadrons with soft pions from QCD sum rules

We estimate the couplings in the Heavy Hadron Chiral Theory (HHCT) lagrangian from the QCD sum rules in an external axial field. Stability of the sum rules at moderate values of the Borel parameter is poor that probably signals a slow convergence of the OPE series. At large values of the Borel parameter they stabilize, and yield the couplings much lower than the constituent quark model expectations. This region is not trustworthy for baryons, but in the meson case only unexpectedly large contributions of a few lowest excitations could invalidate the prediction $g_1\approx0.2$.

hep-ph↗