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O. Yakovlev

Publications and source records attributed to O. Yakovlev.

14 recordsLinked to original sources
arXiv2002

On the Resummation of Large QCD Corrections to photon photon to b anti-b

We study the resummation of large QCD radiative corrections up to the next to leading logarithmic accuracy to the process photon photon to b anti-b; i.e., we resum logarithms of the type alpha_s^p log^{2p}{m^2/s} and alpha_s^p log^{2p-1}{m^2/s} (m is the quark mass). The only source of all the logarithms to this accuracy is the off-shell Sudakov form factor included into the triangle topologies of the one-loop box diagram. We prove that any other configurations of diagrams to this accuracy, either cancel in subgroups or develop a universal on-shell Sudakov exponent due to the final quark anti-quark lines. We study the mechanism of cancellations between the different diagrams, which leads to the simple resummed results. We show the cancellation explicitly at three loops for the leading and at two loops for the next-to-leading logarithms. We also point out the general mechanism responsible for it, and discuss how it can be extended to higher orders.

hep-ph↗
arXiv2001

On the Resummation of Large QCD Logarithms in Higgs -> 2 Photons Decay

We study the strong corrections to the Higgs coupling to two photons. This coupling is the dominant mechanism for Higgs production in photon-photon collisions. In addition, the two photon decay mode of the Higgs is an important and relatively background free channel of relevance at the LHC and the Tevatron. We develop a method for the resummation of large QCD corrections in the form of Sudakov-like logarithms of the type α_s^n\ln^{2n}(m/m_H) and α_s^n\ln^{2n-1}(m/m_H) (where m is the light quark mass) which can contribute to this process in certain models (for example, the MSSM for large tan β) up to next-to-leading-logarithmic (NLL) accuracy. The NLL correction is moderate, the substantial part of which comes from terms not related to running coupling effects.

hep-ph↗
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↗
arXiv2000

QCD Sum Rules for Heavy Flavors

We give a short review of QCD sum rule results for B and D mesons and Lambda_Q and Sigma_Q baryons. We focus mainly on recent developments concerning semileptonic B->pion and D->pion transitions, pion couplings to heavy hadrons, decay constants and estimates of the b quark mass from a baryonic sum rule, and the extraction of the pion distribution amplitude from CLEO data.

hep-ph↗
arXiv2000

Top-Antitop Pair Production close to Threshold: Synopsis of recent NNLO Results

Using non-relativistic effective theories, new next-to-next-to-leading order (NNLO) QCD corrections to the total $t\bar t$ production cross section at the Linear Collider have been calculated recently. In this article the NNLO calculations of several groups are compared and the remaining uncertainties are discussed. The theoretical prospects for an accurate determination of top quark mass parameters are discussed in detail. An outlook on possible future improvements is given.

hep-ph↗
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↗
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↗
arXiv1996

Final state interaction in the production of heavy unstable particles

We make an attempt to discuss in detail the effects originating from the final state interaction in the processes involving production of unstable elementary particles and their subsequent decay. Two complementary scenarios are considered: the single resonance production and the production of two resonances. We argue that part of the corrections due to the final state interaction can be connected with the Coulomb phases of the involved charge particles; the presence of the unstable particle in the problem makes the Coulomb phase ``visible''. It is shown how corrections due to the final state interaction disappear when one proceeds to the total cross-sections. We derive one-loop non-factorizable radiative corrections to the lowest order matrix element of both single and double resonance production. We discuss how the infrared limit of the theories with the unstable particles is modified. In conclusion we briefly discuss our results in the context of the forthcoming experiments on the $W^+W^-$ and the $t\bar t$ production at LEP $2$ and NLC.

hep-ph↗
arXiv1995

QCD Radiative Correction to Zero Recoil Sum Rules for Heavy Flavor Transitions in the Small Velocity Limit.

We consider the small velocity sum rules for heavy flavour semileptonic transitions that are used to estimate the zero recoil values of semileptonic heavy flavour form factors. We analyze the complete O($α_S$) radiative correction to these sum rules. The corrections are universal and influence all "model-independent" bounds previously derived for semileptonic form factors at zero recoil.

hep-ph↗
arXiv1993

Top Near Threshold: All QCD Radiative Corrections are Trivial

We have calculated part of O($α_{S}$) QCD radiative correction to the total cross-section of top's threshold production in $ e^{+}e^{-} \to t\bar t \to W^{-} b W^{+} \bar b$ reaction. We found out a curious fact: there is no O($α_{S}$) correction to the total cross-section, originated from $b \bar b , t \bar b ,\bar t b $ gluon exchange and corresponding gluon emission. Thus, all O($α_{S}$) corrections which are non-zero, can be classified as: 1) corrections to $t \bar t$ nonrelativistic potential 2) corrections to the top's width 3) hard gluon correction to $γt \bar t$-vertex. These corrections are well-known and were described in the previous papers. We can conclude that similar situation takes place for all unstable particles threshold production. This result can be expressed in the form of a general statment: There is no O($α_{QED}$ or $α_{QCD}$) corrections for the total cross-section , originated from the "jet-jet" interection.

hep-ph↗
arXiv1993

Higgs - Two Photon Decay: QCD radiative correction

QCD radiative correction to Higgs $\rightarrow$ two photons decay rate is calculated. Below the threshold we found negligible correction, thus supporting results obtained earlier by Djouadi et all [7]. Above the threshold radiative correction appears to be large for both real and imaginary part of H $γγ$ vertex. This leads to radiative correction for $Γ$(H $\rightarrow γγ$) to be of order 20--100 percents at $m_{t}=150 GeV$. Possible applications of our results for Higgs search at Next Linear Colliders (NLC) are briefly discussed.

hep-ph↗