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S. S. Agaev

Publications and source records attributed to S. S. Agaev.

At least 91 records · Page 5Linked to original sources
arXiv2016

Exploring $X(5568)$ as a meson molecule

The parameters, i.e. the mass and current coupling of the exotic $X(5568)$ state observed by the D0 Collaboration as well as the decay width of the process $X \to B_s^{0}π^{+}$ are explored using $B\bar{K}$ molecule assumption on its structure. Employed computational methods include QCD two-point and light-cone sum rules, latter being considered in the soft-meson approximation. The obtained results are compared with the data of the D0 Collaboration as well as with the predictions of the diquark-antidiquark model. This comparison strengthens a diquark-antidiquark picture for the $X(5568)$ state rather than a meson molecule structure.

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arXiv2016

Width of the exotic $X_b(5568)$ state through its strong decay to $B_s^{0} π^{+}$

The width of the newly observed exotic state $X_b(5568)$ is calculated via its dominant strong decay to $% B_s^{0} π^{+}$ using the QCD sum rule method on the light-cone in conjunction with the soft-meson approximation. To this end, the vertex $X_{b}B_{s}π$ is studied and the strong coupling $g_{X_{b}B_{s}π}$ is computed employing for $X_b(5568)$ state the interpolating diquark-antidiquark current of the $[su][\overline{b}\overline{d}]$ type. The obtained prediction for the decay width of $X_b(5568)$ is confronted and a nice agreement found with the experimental data of the D0 Collaboration.

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arXiv2016

Mass and decay constant of the newly observed exotic $X(5568)$ state

The mass and decay constant of the $X(5568)$ state newly observed by D0 Collaboration are computed within the two-point sum rule method using the diquark-antidiquark interpolating current. In calculations, the vacuum condensates up to eight dimensions are taken into account. The obtained result for the mass of the $X(5568)$ state is in a nice agreement with the experimental data.

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arXiv2016

Charmed partner of the exotic $X(5568)$ state and its properties

The mass, decay constant and width of a hypothetical charmed partner $X_c$ of the newly observed exotic $X_b(5568)$ state are calculated using a technique of QCD sum rule method. The $X_c=[su][\overline{c}\overline{d}]$ state with $J^{P}=0^{+}$ is described employing two types of the diquark-antidiquark interpolating currents. The evaluation of the mass $m_{X_c}$ and decay constant $f_{X_c}$ is carried out utilizing the two-point sum rule method by including vacuum condensates up to eight dimensions. The widths of the decay channels $X_c \to D_s^{-} π^{+}$ and $X_c \to D^{0} K^{0}$ are also found. To this end, the strong couplings $g_{X_{c}D_{s}π}$ and $g_{X_{c}D K}$ are computed by means of QCD sum rules on the light-cone and soft-meson approximation.

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arXiv2016

Strong $Z_c^{+}(3900)\rightarrow J/ψπ^{+}; η_{c} ρ^{+}$ decays in QCD

The widths of the strong decays $Z_c^{+}(3900)\to J/ψπ^{+}$ and $Z_c^{+}(3900)\to η_{c} ρ^{+}$ are calculated. To this end, the mass and decay constant of the exotic $Z_c^{+}(3900)$ state are computed by means of a two-point sum rule. The obtained results are then used to calculate the strong couplings $g_{Z_{c}J/ψπ}$ and $g_{Z_{c}η_{c} ρ}$ employing QCD sum rules on the light-cone supplied by a technique of the soft-meson approximation. We compare our predictions on the mass and decay widths with available experimental data and other theoretical results.

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arXiv2015

Strong $D^{*}_sD_{s}η^{(\prime)}$ and $B^{*}_sB_{s}η^{(\prime)}$ vertices from QCD light-cone sum rules

The strong $D^{*}_sD_{s}η^{(\prime)}$ and $B^{*}_sB_{s}η^{(\prime)}$ vertices are studied and the relevant couplings are calculated in the context of the light-cone QCD sum rule method with twist-4 accuracy by including the next-to-leading order corrections. In the analysis, both the quark and gluon components of the $η$ and $η^{\prime}$ mesons and the axial anomaly corrected higher twist distributions are included.

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arXiv2014

Transition form factors $γ^*γ\toη$ and $γ^*γ\toη'$ in QCD

We update the theoretical framework for the QCD calculation of transition form factors $γ^*γ\toη$ and $γ^*γ\toη'$ at large photon virtualities including full next-to-leading order analysis of perturbative corrections, the charm quark contribution, and taking into account SU(3)-flavor breaking effects and the axial anomaly contributions to the power-suppressed twist-four distribution amplitudes. The numerical analysis of the existing experimental data is performed with these improvements.

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arXiv2010

Light Cone Sum Rules for the pi0-gamma*-gamma Form Factor Revisited

We provide a theoretical update of the calculations of the pi0-gamma*-gamma form factor in the LCSR framework, including up to six polynomials in the conformal expansion of the pion distribution amplitude and taking into account twist-six corrections related to the photon emission at large distances. The results are compared with the calculations of the B-> pi l nu decay and pion electromagnetic form factors in the same framework. Our conclusion is that the recent BaBar measurements of the pi0-gamma*-gamma form factor at large momentum transfers are consistent with QCD, although they do suggest that the pion DA may have more structure than usually assumed.

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arXiv2010

Comments on "Single meson production in photon-photon collisions and infrared renormalons" [arXiv:0911.5226v1]

This paper contains our comments on the work of the authors A. I. Ahmadov \textit{et al.} "Single meson production in photon-photon collisions and infrared renormalons" [arXiv:0911.5226v1 27 Nov 2009]. We draw attention to errors made in this work in calculation of the subprocess cross sections within the frozen and running coupling approaches, in deriving the Borel transforms and Borel resummed expressions for the cross sections in the running coupling approach. We show that the same fatal errors were made by these authors also in their work published in Phys. Rev. D80, 016003 (2009).

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arXiv2008

Soft end-point and mass corrections to the eta' g*g* vertex function

Power-suppressed corrections arising from end-point integration regions to the space-like vertex function of the massive eta'-meson virtual gluon transition eta' - g*g* are computed. Calculations are performed within the standard hard-scattering approach (HSA) and the running coupling method supplemented by the infrared renormalon calculus. Contributions to the vertex function from the quark and gluon contents of the eta' -meson are taken into account and the Borel resummed expressions for F_{eta' g*g*}(Q2,ω,η), as well as for F_{eta' g g*}}(Q^{2},ω=\pm 1,η) and F_{eta' g*g*}(Q^{2},ω=0,η) are obtained. It is demonstrated that the power-suppressed corrections \sim (Λ^{2}/Q^{2})^{n}, in the explored range of the total gluon virtuality 1 <Q2 < 25 GeV2, considerably enhance the vertex function relative to the results found in the framework of the standard HSA with a fixed coupling. Modifications generated by the eta ' -meson mass effects are discussed.

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arXiv2008

Pion distribution amplitude from holographic QCD and the electromagnetic form factor F_pi(Q2)

The holographic QCD prediction for the pion distribution amplitude (DA) $ϕ_{hol}(u)$ is used to compute the pion spacelike electromagnetic form factor $F_π(Q^2)$ within the QCD light-cone sum rule method. In calculations the pion's renormalon-based model twist-4 DA, as well as the asymptotic twist-4 DA are employed. Obtained theoretical predictions are compared with experimental data and with results of the holographic QCD.

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arXiv2006

Impact of the higher twist effects on the $γγ^{*} \to π^{0}$ transition form factor

We reanalyze the $γγ^{*} \to π^{0}$ transition form factor $F_{πγ}(Q^2)$ within the QCD light-cone sum rules method with the twist-4 accuracy. In computations the pion leading twist distribution amplitude (DA) with two nonasymptotic terms, and the renormalon method-inspired twist-4 DAs are used. The latters allow us to estimate impact of effects due to higher conformal spin components in the pion twist-4 DAs on the form factor $F_{πγ}(Q^2)$. Obtained theoretical predictions are employed to deduce constraints on the pion DAs from CELLO and CLEO data.

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arXiv2005

Higher twist distribution amplitudes of the pion and electromagnetic form factor $F_π(Q^2)$

The pion electromagnetic form factor is calculated within the QCD light-cone sum rule method and using a renormalon model for the higher twist distribution amplitudes (DAs). The theoretical predictions are compared with the experimental data and constraints on the pion leading and twist-4 DAs are extracted. An upper bound on the twist-4 contribution to the form factor and estimates of effects due to higher conformal spins in the pion twist-4 DAs are obtained.

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arXiv2004

Power corrections to the process $γ^{*}γ\to ππ$ in the running coupling method

Power-suppressed corrections coming from the end-point integration regions in the amplitude of the process $γ^{*}γ\to ππ$ at large $Q^2$ and small squared center-of-mass energy $W^2$ are calculated in the QCD hard-scattering approach where the amplitudes factorize in a hard perturbatively calculable part and a generalized distribution amplitude. The running coupling method and the technique of infrared renormalon calculus are applied to obtain Borel resummed expressions for the two main components of the process amplitude. Numerical estimates for these power corrections are presented. They are sizeable when $Q^2 < 10 GeV^2$.

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arXiv2004

The gluon content of the $η$ and $η^{\prime}$ mesons and the $ηγ$, $η^{\prime}γ$ electromagnetic transition form factors

We compute power-suppressed corrections to the ηγand η^{\prime}γtransition form factors Q^2F_{η(η^{\prime})γ}(Q^2) arising from the end point regions x \to 0,1 by employing the infrared-renormalon approach. The contribution to the form factors from the quark and gluon content of the η,η^{\prime} mesons is taken into account using for the η-η^{\prime} mixing the SU_f(3) singlet η_1 and octet η_8 basis. The theoretical predictions obtained this way are compared with the corresponding CLEO data and restrictions on the input parameters (Gegenbauer coefficients) B_2^q(η_1), B_2^g(η_1), and B_2^q(η_8) in the distribution amplitudes for the η_1,η_8 states with one nonasymptotic term are deduced. Comparison is made with the results from QCD perturbation theory.

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arXiv2004

The gluon content of the $η$ and $η^{\prime}$ mesons

We analyze power-suppressed contributions to singlet pseudoscalar $η$ and $η^{\prime}$ meson transition form factors. These corrections stem from endpoint singularities and help improve the agreement between QCD theory and the experimental data, in particular, at low-momentum transfers. Using the CLEO data, we extract information on the profile of the $η_1$ and $η_8$ distribution amplitudes in the $SU(3)_{F}$ octet-singlet basis employing both the one-angle and the two-angle mixing schemes. In the former scheme, we find good agreement with the CLEO data, while in the second case, our approach requires non-asymptotic profiles for these mesons.

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arXiv2004

Power corrections to the $π^0γ$ transition form factor and pion distribution amplitudes

Employing the standard hard-scattering approach and the running coupling method we calculate a class of power-suppressed corrections $\sim 1/Q^{2n},n=1,2,3,...$ to the electromagnetic $π^0γ$ transition form factor (FF) $Q^2F_{πγ}(Q^2)$ arising from the end-point $x \to 0,1$ integration regions. In the investigations we use a hard-scattering amplitude of the subprocess $γ+γ^{*} \to q +\bar{q}$, symmetrized under exchange $μ_R^2 \leftrightarrow \barμ_R^2$ important for exclusive processes containing two external photons. In the computations the pion model distribution amplitudes (DA's) with one and two non-asymptotic terms are employed. The obtained predictions are compared with the CLEO data and constraints on the DA parameters $b_2(μ_0^2)$ and $b_4(μ_0^2)$ at the normalization point $μ_0^2=1 GeV^2$ are extracted. Further restrictions on the pion DA's are deduced from the experimental data on the electromagnetic FF $F_π(Q^2)$.

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