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A. Ya. Parkhomenko

Publications and source records attributed to A. Ya. Parkhomenko.

At least 19 recordsLinked to original sources
arXiv2012

Light-Cone Distribution Amplitudes of the Ground State Bottom Baryons in HQET

We provide the definition of the complete set of light-cone distribution amplitudes (LCDAs) for the ground state heavy bottom baryons with the spin-parities J^P = 1/2^+ and J^P = 3/2^+ in the heavy quark limit. We present the renormalization effects on the twist-2 light-cone distribution amplitudes and use the QCD sum rules to compute the moments of twist-2, twist-3, and twist-4 LCDAs. Simple models for the heavy baryon distribution amplitudes are analyzed with account of their scale dependence.

hep-ph↗
arXiv2005

Branching Ratios for $B \to K^* γ$ and $B \to ργ$ Decays in Next-to-Leading Order in the Large Eneregy Effective Theory

We calculate the so-called hard spectator corrections in ${\cal O} (α_s)$ in the leading-twist approximation to the decay widths for $B \to K^{*} γ$ and $B \to ργ$ decays and their charge conjugates, using the Large Energy Effective Theory (LEET) techniques. Combined with the hard vertex and annihilation contributions, they are used to compute the branching ratios for these decays in the next-to-leading order (NLO) in the strong coupling $α_s$ and in leading power in $Λ_{\rm QCD}/M_B$. These corrections are found to be large, leading to the inference that the theoretical branching ratios for the decays $B \to K^* γ$ in the LEET approach can be reconciled with current data only for significantly lower values of the form factors than their estimates in the QCD sum rule and Lattice QCD approaches. However, the form factor related uncertainties mostly cancel in the ratios ${\cal B}(B \to ργ)/{\cal B}(B \to K^* γ)$ and $Δ= (Δ^{+0}+ Δ^{-0})/2$, where $Δ^{\pm 0} = Γ(B^\pm \to ρ^\pm γ)/ [2 Γ(B^0 (\bar B^0)\to ρ^0 γ)] - 1$, and hence their measurements will provide quantitative information on the standard model parameters, in particular the ratio of the CKM matrix elements $| V_{td}/V_{ts}|$ and the inner angle $α$ of the CKM-unitarity triangle. We also calculate direct CP asymmetries for the decays $B^\pm \to ρ^\pm γ$ and $B^0/\bar B^0 \to ρ^0 γ$ and find, in conformity with the observations made in the existing literature, that the hard spectator contributions significantly reduce the asymmetries arising from the vertex corrections.

hep-ph↗
arXiv2004

Isospin Amplitude Analysis of $B \to ππ$ Decays within the Standard Model

Taking into account the recent measurements of the branching ratios and CP asymmetries in the $B \to ππ$ decays by the BABAR and BELLE collaborations, an amplitude analysis based on the isospin symmetry is reported. These data allow to get an independent determination of the CKM unitarity-triangle angle $γ$. One of the best-fit solutions gives the range $γ= (65 \pm 5)^\circ$, in excellent agreement with the global CKM fit within the Standard Model. The other parameters from this fit confirm the earlier analyses that the data on $B \to ππ$ decays require various topological amplitudes (neglecting the electroweak ones) to be of comparable magnitude with large strong-phase differences.

hep-ph↗
arXiv2004

Implication of the $B \to (ρ, ω) γ$ Branching Ratios for the CKM Phenomenology

We study the implication of the recent measurement by the BELLE collaboration of the averaged branching fraction $\bar B_{exp} [B \to (ρ, ω) γ] = (1.8^{+0.6}_{-0.5} \pm 0.1) \times 10^{-6}$ for the CKM phenomenology. Combined with the averaged branching fraction $\bar B_{exp} (B \to K^* γ) = (4.06 \pm 0.26) \times 10^{-5}$ measured earlier, this yields $\bar R_{exp} [(ρ, ω) γ/K^* γ] = (4.2 \pm 1.3)%$ for the ratio of the two branching fractions. Updating earlier theoretical analysis of these decays based on the QCD factorization framework, and constraining the CKM-Wolfenstein parameters from the unitarity fits, our results yield $\bar B_{th} [B \to (ρ, ω) γ] = (1.38 \pm 0.42) \times 10^{-6}$ and $\bar R_{th} [(ρ, ω) γ/K^* γ] = (3.3 \pm 1.0)%$, in agreement with the BELLE data. Leaving instead the CKM-Wolfenstein parameters free, our analysis gives (at 68% C.L.) $0.16\leq |V_{td}/V_{ts}| \leq 0.29$, which is in agreement with but less precise than the indirect CKM-unitarity fit of the same, $0.18 \leq |V_{td}/V_{ts}| \leq 0.22$. The isospin-violating ratio in the $B \to ργ$ decays and the SU(3)-violating ratio in the $B_d^0 \to (ρ^0, ω) γ$ decays are presented together with estimates of the direct and mixing-induced CP-asymmetries in the $B \to (ρ,ω) γ$ decays within the SM. Their measurements will overconstrain the angle $α$ of the CKM-unitarity triangle.

hep-ph↗
arXiv2003

The $η^\prime g^* g^{(*)}$ Vertex Function in Perturbative QCD and $η^\prime$-Meson Mass Effects

The $η^\prime g^* g^{(*)}$ effective vertex function (EVF) is calculated in the QCD hard-scattering approach, taking into account the $η^\prime$-meson mass. We work in the approximation in which only one non-leading Gegenbauer moment in both the quark-antiquark and gluonic light-cone distribution amplitude for the $η^\prime$-meson is kept. The EVF with one off-shell gluon is shown to have the form $F_{η^\prime g^* g} (q_1^2, 0, m_{η^\prime}^2) = m_{η^\prime}^2 H(q_1^2)/(q_1^2 - m_{η^\prime}^2)$, valid for $|q_1^2| > m_{η^\prime}^2$. An interpolating formulae for the EVF in the space-like region of the virtuality $q_1^2$, which satisfies the QCD-anomaly normalization for on-shell gluons and the perturbative-QCD result for the gluon virtuality $|q_1^2| \gtrsim 2 GeV^2$, is also presented.

hep-ph↗
arXiv2003

Improved $η^\prime$-Meson Distribution Amplitudes from Inclusive $Υ(1S) \to η^\prime X$ Decay

We calculate the $η^\prime$-meson energy spectrum in the $Υ(1S) \to η^\prime g g g \to η^\prime X$ decay in the leading-order perturbative QCD in the static-quark limit for the orthoquarkonium.Our principal result is the extraction of parameters of the $η^\prime g^* g$ effective vertex function (EVF) involving a virtual and a real gluon from the available data on the hard part of the $η^\prime$-meson energy spectrum. The perturbative-QCD based framework provides a good description of the available CLEO data, allowing one to constrain the lowest Gegenbauer coefficients $B^{(q)}_2$ and $B^{(g)}_2$ of the quark-antiquark and gluonic distribution amplitudes of the $η^\prime$-meson. The resulting constraints are combined with the existing ones on these coefficients from an analysis of the $η^\prime - γ$ transition form factor and the requirement of positivity of the EVF, yielding $B^{(q)}_2 (μ_0^2) = -0.008 \pm 0.054$ and $B^{(g)}_2 (μ_0^2) = 4.6 \pm 2.5$ for $μ_0^2 = 2 GeV^2$. This reduces significantly the current uncertainty on these coefficients.

hep-ph↗
arXiv2003

The $η^\prime g^* g^{(*)}$ Vertex Including the $η^\prime$-Meson Mass

The $η^\prime g^* g^{(*)}$ effective vertex function is calculated in the QCD hard-scattering approach, taking into account the $η^\prime$-meson mass. We work in the approximation in which only one non-leading Gegenbauer moment for both the quark-antiquark and the gluonic light-cone distribution amplitudes for the $η^\prime$-meson is kept. The vertex function with one off-shell gluon is shown to have the form (valid for $| q_1^2 | > m_{η^\prime}^2$) $F_{η^\prime g^* g} (q_1^2, 0, m_{η^\prime}^2) = m_{η^\prime}^2 H(q_1^2)/(q_1^2 - m_{η^\prime}^2)$, where $H(q_1^2)$ is a slowly varying function, derived analytically in this paper. The resulting vertex function is in agreement with the phenomenologically inferred form of this vertex obtained from an analysis of the CLEO data on the $η^\prime$-meson energy spectrum in the decay $Υ(1S) \to η^\prime X$. We also present an interpolating formula for the vertex function $F_{η^\prime g^* g} (q_1^2, 0, m_{η^\prime}^2)$ for the space-like region of the virtuality $q_1^2$, which satisfies the QCD anomaly normalization for on-shell gluons and the perturbative-QCD result for the gluon virtuality $| q_1^2| \gtrsim 2$ GeV$^2$.

hep-ph↗
arXiv2003

An Analysis of the Inclusive Decay $Υ(1S) \to η^\prime X$ and Constraints on the $η^\prime$-Meson Distribution Amplitudes

We calculate the $η^\prime$-meson energy spectrum in the decay $Υ(1S) \to η^\prime g g g \to η^\prime X$ in the leading-order perturbative QCD in the static quark limit for the Orthoquarkonium. Our principal result is the extraction of parameters of the $η^\prime g^* g$ effective vertex function (EVF) involving a virtual and a real gluon from the available data on the hard part of the $η^\prime$-meson energy spectrum. The perturbative QCD based framework provides a good description of the available CLEO data, allowing to constrain the lowest Gegenbauer coefficients $B^{(q)}_2$ and $B^{(g)}_2$ of the quark-antiquark and gluonic distribution amplitudes of the $η^\prime$-meson. The resulting constraints are combined with the existing ones on these coefficients from an analysis of the $η-γ$ and $η^\prime-γ$ transition form factors and the requirement of positivity of the EVF, yielding $B^{(q)}_2(μ_0^2) = -0.008 \pm 0.054$ and $B^{(g)}_2(μ_0^2) = 4.6 \pm 2.5$ for $μ_0^2 = 2$ GeV$^2$. This reduces significantly the current uncertainty on these coefficients. The resulting EFV $F_{η^\prime g^* g} (p^2, 0, m_{η^\prime}^2)$, including the $η^\prime$-meson mass effects, is presented.

hep-ph↗
arXiv2001

The Effective $η^\prime g^* g^*$ Vertex at Arbitrary Gluon Virtualities

The effective $η^\prime g^* g^*$ vertex is studied in the standard (Brodsky-Lepage) and modified hard scattering approaches for arbitrary gluon virtualities in the time-like and space-like regions. The contribution of the gluons in the $η^\prime$-meson is taken into account, and the wave-function is constrained using data on the electromagnetic transition form factor of the $η^\prime$ meson. Our results have implications for the inclusive decay $B \to η^\prime X$ and exclusive decays, such as $B \to η^\prime (K, K^*)$, and in hadronic production processes $N + N (\bar N) \to η^\prime X$.

hep-ph↗
arXiv2001

The $η^\prime g^* g^*$ vertex with arbitrary gluon virtualities in the perturbative QCD hard scattering approach

We study the $η^\prime g^* g^*$ vertex for arbitrary gluon virtualities in the time-like and space-like regions, using the perturbative QCD hard scattering approach and an input wave-function of the $η^\prime$-meson consistent with the measured $η^\prime γ^* γ$ transition form factor. The contribution of the gluonic content of the $η^\prime$-meson is taken into account, enhancing the form factor over the entire virtuality considered. However, data on the electromagnetic transition form factor of the $η^\prime$-meson is not sufficient to quantify the gluonic enhancement. We also study the effect of the transverse momenta of the partons in the $η^\prime$-meson on the $η^\prime g^* g^*$ vertex, using the modified hard scattering approach based on Sudakov formalism. Analytic expressions for the $η^\prime g^* g^*$ vertex are presented in limiting kinematic regions and parametrizations are given satisfying the QCD anomaly, for real gluons, and perturbative QCD behavior for large gluon virtualities, in both the time-like and space-like regions. Our results have implications for the inclusive decay $B \to η^\prime X$ and exclusive decays, such as $B \to η^\prime (K,K^*)$, and in hadronic production processes $N + N (\bar N) \to η^\prime X$.

hep-ph↗
arXiv2000

Mass Shift of Axion in Magnetic Field

A mass-shift of the axion propagating in an external constant homogenious magnetic field is calculated. The contributions via an electron loop and a virtual photon are examined. It is shown that the virtual photon contribution dominates substantially over the electron-loop one. Under the conditions of the early Universe the electron-loop contribution to the massless axion mass-shift is equal to zero while the virtual photon contribution is finite and can be of order of the recent restrictions on the axion mass.

hep-ph↗
arXiv1999

Axion in an External Electromagnetic Field

We investigate the effective interaction of a pseudoscalar particle with two photons in an external electromagnetic field in the general case of all external particles being off the mass shell. This interaction is used to study the radiative decay $a \to γγ$ of the axion, a pseudoscalar particle associated with the Peccei-Quinn symmetry, and the crossing channel of photon splitting $γ\to γa$. It is shown that the external field removes the suppression associated with the smallness of the axion mass and so leads to the strong catalysis of these processes. The field-induced axion emission by photon is analyzed as one more possible source of energy losses by astrophysical objects.

hep-ph↗
arXiv1999

Axion Decay of a Photon in an External Electromagnetic Field

An interaction of a pseudoscalar particle with two photons induced by an external electromagnetic field is used to study the photon decay $γ\to γa$ where a is a pseudoscalar particle associated with the Peccei-Quinn U(1) symmetry. The field-induced axion emission by photon is analyzed as a possible source of energy losses by astrophysical objects.

hep-ph↗
arXiv1999

Field-induced axion decay $a \to e^+ e^-$ in plasma

The axion decay $a \to e^+ e^-$ is investigated in the presence of a plasma and an external magnetic field. The results demonstrate a strong catalyzing influence of medium. The axion lifetime in the magnetic field of order $10^{15}$ G and at the temperature of order 10 MeV is reduced to $10^4$ s.

hep-ph↗
arXiv1998

Mass effects in the quark-gluon decays of heavy paraquarkonia

Quark-gluon decays of heavy paraquarkonia $^1 S_0(\bar Q Q) \to \bar q q g$ are investigated with account of the masses of final quarks. The decay widths and the energy distributions of the final quarks and gluons are calculated in dependence on the relative quark masses. The strong collinear enhancement of the gluon energy distribution at the end of the spectrum is shown to take place in all such decays of $η_c$ and $η_b$ mesons except the decay $η_b \to \bar c c g$. The total decay width is shown to have an essential dependence on the final quark masses. The corresponding branching ratios of $η_c$ and $η_b$ mesons are numerically estimated with a good agreement of $Br(η_c \to \bar s s g)$ with experimental data on $η_c$ decays.

hep-ph↗
arXiv1998

Field-induced axion decay $a \to e^+ e^-$ via plasmon

The axion decay $a \to e^+ e^-$ via a plasmon is investigated in an external magnetic field. The results we have obtained demonstrate a strong catalyzing influence of the field as the axion lifetime in the magnetic field of order $10^{15}$ G and at temperature of order 10 MeV is reduced to $10^4$ sec.

hep-ph↗
arXiv1998

Field-induced axion emission via process $e^+ e^- \to a$ in plasma

The annihilation into axion $e^+ e^- \to a$ is investigated in a plasma and an external magnetic field. This process via a plasmon intermediate state has a resonant character at a particular energy of the emitted axion. The emissivity by $e^+ e^- \to a$ is compared with the axion cyclotron emissivity.

hep-ph↗