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A. Khodjamirian

Publications and source records attributed to A. Khodjamirian.

At least 37 records · Page 2Linked to original sources
arXiv2004

Kaon Distribution Amplitude from QCD Sum Rules

We present a new calculation of the first Gegenbauer moment $a_1^K$ of the kaon light-cone distribution amplitude. This moment is determined by the difference between the average momenta of strange and nonstrange valence quarks in the kaon. To calculate $a_1^K$, QCD sum rule for the diagonal correlation function of local and nonlocal axial-vector currents is used. Contributions of condensates up to dimension six are taken into account, including $O(α_s)$-corrections to the quark-condensate term. We obtain $a_1^K=0.05\pm 0.02$, differing by the sign and magnitude from the recent sum-rule estimate from the nondiagonal correlation function of pseudoscalar and axial-vector currents. We argue that the nondiagonal sum rule is numerically not reliable. Furthermore, an independent indication for a positive $a_1^K$ is given, based on the matching of two different light-cone sum rules for the $K\toπ$ form factor. With the new interval of $a_1^K$ we update our previous numerical predictions for SU(3)-violating effects in $B_{(s)}\to K$ form factors and charmless (B) decays.

hep-ph↗
arXiv2003

QCD Light-Cone Sum Rule Estimate of Charming Penguin Contributions in B -> pi pi

Employing the QCD light-cone sum rule approach we calculate the B -> pi pi hadronic matrix element of the current-current operator with c quarks in the penguin topology (``charming penguin''). The dominant contribution to the sum rule is due to the c-quark loop at short distances and is of O(alpha_s) with respect to the factorizable B -> pi pi amplitude. The effects of soft gluons are suppressed at least by O(alpha_s m_b^{-2}). Our result indicates that sizable nonperturbative effects generated by charming penguins at finite m_b are absent. The same is valid for the penguin contractions of the current-current operators with light quarks.

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arXiv2000

Predictions on $B \to π\bar{l} ν_l$, $D \to π\bar{l} ν_l$ and $D\to K \bar{l} ν_l$ from QCD Light-Cone Sum Rules

The $f^+$ form factors of the $B\to π$, $D\to π$ and $D\to K$ transitions are calculated from QCD light-cone sum rules (LCSR) and used to predict the widths and differential distributions of the exclusive semileptonic decays $B\to π\bar{l}ν_l$, $D \toπ\bar{l}ν_l$ and $D \to K \bar{l}ν_l$, where $l=e,μ$. The current theoretical uncertainties are estimated. The LCSR results are found to agree with the results of lattice QCD calculations and with experimental data on exclusive semileptonic D decays. Comparison of the LCSR prediction on $B\to π\bar{l} ν_l$ with the CLEO measurement yields a value of |V_{ub}| in agreement with other determinations.

hep-ph↗
arXiv1999

Pion Form Factor in QCD at Intermediate Momentum Transfers

We present a quantitative analysis of the electromagnetic pion form factor in the light-cone sum rule approach, including radiative corrections and higher-twist effects. The comparison to the existing data favors the asymptotic profile of the pion distribution amplitude and allows to estimate the deviation: $(\int du/u ϕ_π(u))/ (\int du/u ϕ^{\rm as}_π(u))=$ 1.1$\pm$ 0.1 at the scale 1 GeV. Special attention is payed to the precise definition and interplay of soft and hard contributions at intermediate momentum transfer, and to matching of the sum rule to the perturbative QCD prediction. We observe a strong numerical cancellation between the soft (end point) contribution and power suppressed hard contributions of higher twist, so that the total nonperturbative correction to the usual pQCD result turns out to be of order 30% for $Q^2\sim 1$ GeV$^2$.

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arXiv1999

Pion Form Factors from QCD Light-Cone Sum Rules

Light-cone sum rules have proved to be very useful in calculating hadronic matrix elements for exclusive processes. I present recent applications of this method to the pion electromagnetic form factor and to the form factors of $γ^* ρ\to π$ and $γ^*γ\to π^0$ transitions.

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arXiv1999

Perturbative QCD Correction to the Light-Cone Sum Rule for the $B^*Bπ$ and $D^*Dπ$ Couplings

The $B^*Bπ$ and $D^*Dπ$ couplings have previously been derived from a QCD light-cone sum rule in leading order. Here, we describe the calculation of the $O(α_s)$ correction to the twist 2 term of this sum rule. The result is used for a first next-to-leading order analysis. We obtain $g_{B^*Bπ}= 22\pm 7$ and $g_{D^*Dπ}=10.5\pm 3$, where the error indicates the remaining theoretical uncertainty.

hep-ph↗
arXiv1998

Exclusive Nonleptonic Decays of Heavy Mesons in QCD

We use operator product expansion and QCD light-cone sum rules to estimate the amplitude of the decay $B \to J/ψK $ taking into account leading nonfactorizable contributions. The result is very similar to the estimate obtained earlier from a four-point QCD sum rule. We discuss applications of this method to other nonleptonic $B$ decay modes.

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arXiv1998

The Scalar $B\to π$ and $D \to π$ Form Factors in QCD

QCD sum rules on the light-cone are derived for the sum $f^+ + f^-$ of the $B\to π$ and $D\to π$ form factors taking into account contributions up to twist four. Combining the results with the corresponding $f^+$ form factors calculated previously by the same method, we obtain the scalar form factors $f^0$. Our sum rule predictions are compared with lattice results, current-algebra constraints, and quark-model calculations. Furthermore, we calculate decay distributions and the integrated width for the semileptonic decay $B \to π\barτν_τ$ which is sensitive to $f^0$. Finally, the dependence of the sum rules on the heavy quark mass and the asymptotic scaling laws are discussed.

hep-ph↗
arXiv1998

QCD Sum Rules for Exclusive Decays of Heavy Mesons

Applications of QCD sum rules to exclusive decays of heavy mesons are reviewed. In detail, we discuss the calculations of the B and $D$ decay constants, the heavy-to-light form factors $f^+(p^2)$ and $f^0(p^2)$, and the strong couplings $g_{B^*Bπ}$ and $g_{D^*Dπ}$. Predictions are presented for the semileptonic weak decays $B \to π\bar{l} ν_l$ and $B \to ρ\bar{l} ν_l$, and used to extract $V_{ub}$ from the measured decay widths. Results are also shown on $D \to π\bar{l} ν_l$ and $D^* \to D π$. Furthermore, we reconsider the factorization hypothesis in nonleptonic two-body decays, and describe a sum rule estimate of the nonfactorizable contribution to the amplitude of $B \to J/ψK$.

hep-ph↗
arXiv1997

Perturbative QCD Correction to the $B\toπ$ Transition Form Factor

We report on the perturbative $O(α_s)$ correction to the light-cone QCD sum rule for the $B\to π$ transition form factor $f^+$. The correction to the product $f_Bf^+$ in leading twist approximation is found to be about 30%, that is similar in magnitude to the corresponding $O(α_s)$ correction in the two-point sum rule for $f_B$. The resulting cancellation of large QCD corrections in $f^+$ eliminates one important uncertainty in the sum-rule prediction for this form factor.

hep-ph↗
arXiv1997

QCD estimate of the long-distance effect in $B \to K^* γ$

We suggest to use operator product expansion and QCD sum rule techniques to estimate the long-distance contribution to the amplitude of the exclusive rare decay $B\to K^* γ$. In contrast to a phenomenological description in terms of $ψ$ resonances converting into a photon, the virtual charm quark loop interacting with soft gluons is represented by a new quark-gluon-photon operator. The matrix element of this operator is calculated in the same approximation as the matrix element of the leading magnetic penguin operator. The overall correction is found to be small, not more than about 5%.

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arXiv1996

Sum-Rule Results on Exclusive Decays of Heavy Mesons

We review QCD sum rule applications to hadronic matrix elements of exclusive $B$ and $D$ decays. Results are presented for the form factors $f^+$ and $F_0$ of $B \rightarrow π$ and $D\rightarrow π$ transitions. The predictions are used to compute the width of $D^* \rightarrow D π$, and to extract the CKM parameter $V_{ub}$ from the measured $B \rightarrow πe ν$ width. Furthermore, we comment on weak annihilation in $B \rightarrow ργ$, as well as on the radiative decays $D \rightarrow ργ$, $D \rightarrow K^* γ$, and $B \rightarrow μνγ$.

hep-ph↗
arXiv1996

Calculation of the $B \to π$ Transition Matrix Element in QCD

We describe the calculation of the $B\rightarrow π$ hadronic matrix element from operator product expansion near the light-cone in QCD. In the resulting sum rules, the form factors $f^+$ and $F_0$ determining this matrix element are expressed in terms of pion light-cone wave functions. We present predictions for $f^+$ and $F_0$ in the region of momentum transfer $0 \leq p^2 < m_b^2 - {\cal O}(\mbox{1 GeV}^2)$ taking into account the wave functions up to twist 4. We also discuss the extrapolation of the form factors to higher $p^2$ and their asymptotic dependence on the heavy quark mass.

hep-ph↗
arXiv1995

B Meson Form Factors and Exclusive Decays

We present results for the $B \rightarrow π$ and $D\rightarrow π$ form factors derived from QCD sum rules on the light-cone. Our predictions are compared with experiment and used to extract the quark mixing parameter $|V_{ub}|$ from a recent CLEO measurement of $B \ra πl^+ ν$. Furthermore, we discuss the factorization approximation for exclusive nonleptonic matrix elements, and describe a first QCD estimate of the nonfactorizable contribution to the amplitude of $B \rightarrow J/ψK $.

hep-ph↗
arXiv1995

Calculation of Long-Distance Effects in Exclusive Weak Radiative Decays of B-Mesons

We calculate the contribution of the weak annihilation to the $B\rightarrow ργ$ decay amplitude by means of QCD sum rules using the photon light-cone wave function. We find that this long-distance contribution amounts to about 10\% of the leading short-distance effect in $B^-\rightarrow ρ^-γ$. On the other hand, weak annihilation is the dominant source of the corresponding $D$ meson decays and according to our estimates, yields branching ratios of $O(10^{-4})$ for $D^0\rightarrow \bar{K}^{*0}γ$, $O(10^{-5})$ for $D_s\rightarrow ρ^+γ$, and $O(10^{-6})$ for $D^-\rightarrow ρ^-γ$ and for $D^0\rightarrow ρ^0γ$.

hep-ph↗
arXiv1995

Heavy Meson Exclusive Decays in the Framework of QCD Sum Rules

We discuss applications of QCD sum rules on the light-cone to the form factors of the exclusive transitions $B \rightarrow π$ and $D\rightarrow π$, and to the $B^*B π$ and $D^*D π$ coupling constants. In the light of our results we examine the pole dominance model for these form factors. A first estimate is given on the nonfactorizable amplitude of the decay $ B \ra J/ψK$.

hep-ph↗
arXiv1994

$D^*Dπ$ and $B^*Bπ$ couplings in QCD

We calculate the $D^*Dπ$ and $B^*Bπ$ couplings using QCD sum rules on the light-cone. In this approach, the large-distance dynamics is incorporated in a set of pion wave functions. We take into account two-particle and three-particle wave functions of twist 2, 3 and 4. The resulting values of the coupling constants are $g_{D^*Dπ}= 12.5\pm 1$ and $g_{B^*Bπ}= 29\pm 3 $. From this we predict the partial width $ Γ(D^{*+} \ra D^0 π^+ )=32 \pm 5~ keV $. We also discuss the soft-pion limit of the sum rules which is equivalent to the external axial field approach employed in earlier calculations. Furthermore, using $g_{B^*Bπ}$ and $g_{D^*Dπ}$ the pole dominance model for the $ B \ra π$ and $D\ra π$ semileptonic form factors is compared with the direct calculation of these form factors in the same framework of light-cone sum rules.

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