An interplay between static potential and Reggeon trajectory for QCD string

I consider two cases where QCD string is described by an effective theory of long strings: the static potential and meson scattering amplitudes in the Regge regime. I show how they can be solved in the mean-field approximation, justified by the large number of space–time dimensions, and argue that it turns out to be exact. I compare contributions from QCD string and perturbative QCD and discuss experimental consequences for the scattering amplitudes.     

Scattering amplitudes of QCD string in the worldline formalism

I review the derivation of large-N QCD meson scattering amplitudes in the Regge regime, where the effective theory of long strings applies in d = 4. A special attention is payed to the reparametrization path integral which plays a crucial role in the consistency of off-shell amplitudes. I show how the linear Reggeon trajectory is obtained for QCD string in the mean-field approximation, which turns out to be exact for the Nambu-Goto string, and discuss the interrelation with perturbative QCD.     

DiffractiveJ/Ψ electroproduction in LLA QCD

Cross section of diffractiveJ/ψ production in deep inelastic scattering in the Born and the leading-log approximations of perturbative QCD are calculated.     

Theoretical Description and Measurement of the Pion–Photon Transition Form Factor

Detailed predictions for the scaled pion–photon transition form factor are given, derived with the method of light-cone sum rules and using pion distribution amplitudes with two and three Gegenbauer coefficients obtained from QCD sum rules with nonlocal condensates. These predictions agree well with all experimental data that are compatible with QCD scaling (and collinear factorization), but disagree with the high-Q ² data of the BaBar Collaboration that grow with the momentum. A good agreement of our predictions with results obtained from AdS/QCD models and Dyson–Schwinger computations is found.     

TheJ/ψ→η c γ decay in QCD sum rules

In QCD sum rules, including power correction ≈G ², the amplitudes and decay rates of “magnetic-dipole” (M1) types radiative transition in charmonium are obtained.     

Two-body nonleptonic decays ofD mesons

The amplitudes for two-body Cabibbo allowed nonleptonic decays ofD mesons are evaluated within the factorization approximation from the effective Hamiltonian including short distance QCD corrections to next-to-leading order. Annihilation andW-exchange contributions as well as final state interaction effects have been included and are in fact crucial to obtain agreement with the experimental data.     

Radiative corrections to QCD amplitudes in quasi-multi-Regge kinematics

Radiative corrections to QCD amplitudes in the quasi-multi-Regge kinematics are interesting, in particular, since the Reggeized form of these amplitudes is used in the derivation of the NLO BFKL. This form is a hypothesis which must be at least carefully checked, if not proved. We calculate the radiative corrections in the one-loop approximation using the s-channel unitarity. Compatibility of the Reggeized form of the amplitudes with the s-channel unitarity requires fulfillment of the set of nonlinear equations for the Reggeon vertices. We show that these equations are satisfied.     

QCD corrections to b→sγγ and exclusive Bs→γγ decay

The short distance QCD corrections to b→sγγ are calculated in the leading logarithmic approximation. The equivalence of operator basis reduction for S-matrix elements by using the equations of motion or by proving a low energy theorem is discussed. We apply the above results to the exclusive B_s→γγ decay. The branching ratio of this decay is found to be 5×10⁻⁷ in the Standard Model. We also found that QCD corrections modify considerably the ratio between CP-even and CP-odd two-photon amplitudes.     

Conserved currents of the three-reggeon interaction

We consider an extension of Lipatov's conjecture about the deep relation between amplitudes in the high-energy limit of QCD (gluodynamics) and XXX Heisenberg chains with noncompact spins to the case of presence fermions (quarks).     

Leading logarithmic approximation in QCD

The leading logarithmic approximation (LLA) for the scattering amplitudes in QCD is reviewed. The double-logarithmic asymptotics of scattering amplitudes is obtained as a solution to nonlinear evolution equations in the infrared cutoff. The DGLAP equation describes an evolution of parton distributions with increasing parton virtuality. The evolution of the amplitudes with respect to the scale in the longitudinal subspace is given by the BFKL equation. The gluon and quarks in QCD lie on the Regge trajectories calculable in perturbation theory. Mesons and baryons are composite states of Reggeized quarks. Similarly the Pomeron and Odderon are colorless ground states of Reggeized gluons. In the case of multicolor QCD, the Reggeon field theory in LLA is completely integrable. The Reggeon interactions in QCD are derived from a gauge-invariant effective action. In particular, next-to-leading corrections to the BFKL equation in QCD and in supersymmetric gauge models are obtained in this way.     

The QCD scattering amplitude from area behaved Wilson loops

We explicitly construct the dominant saddle-point trajectory in the sum-over-path representation of meson scattering amplitudes in large N QCD for area-behaved Wilson loops and show that it dominates in the Regge regime. The graphic representation of the leading trajectory is very similar to the diagrams widely used to illustrate meson scattering.     

Analytic proton-nucleus scattering amplitudes

Analytic expressions for the elastic nucleon-nucleus amplitudes F(q) and G(q) are derived. They are based on analytic approximations of the nuclear profile functions in the Glauber formulation. Our amplitudes are sums of terms with a familiar structure, black-sphere Bessel functions multiplied by form factors accounting for the diffuseness of the nuclear surface. Their accuracy is tested with the Woods-Saxon density and found to be excellent for momentum transfers q? 5fm^?1.     

On AdS/QCD correspondence and the partonic picture of deep inelastic scattering

We critically examine the question of scaling of the Deep Inelastic Scattering process in the medium Bjorken x region on a scalar boson in the framework of the AdS/QCD correspondence. To get the right polarization structure of the forward electroproduction amplitude, we show that one needs to add (at least) the scalar to scalar and scalar to vector hadronic amplitudes. This illustrates how the partonic picture may emerge from a simple scenario based on the AdS/QCD correspondence, provided one allows the conformal dimension of the hadronic field to equal 1 and use the concept of “hadron–parton duality”.     

Isolation of definite naturality exchanges: The general solution

For an arbitrary 2→2 scattering process we show how to isolate exactly the various contributions of definite naturality from the helicity amplitudes. For a Bosonict-channel this exact separation requires knowledge of a finite number of energy-derivatives of the amplitudes. If thet-channel is Fermionic our exact separation scheme is difficult to implement; however, it can be approximated to arbitrary accuracy in terms of a finite number of energy-derivatives of the amplitudes. Taking just a single energy-derivative we obtain a single approximate isolation scheme forall 2→2 processes. We show that this approximation is likely to be good, while more conventional approximations are likely to be poor.     

Radiative B* meson decays in QCD sum rules

The decay constant g _B* of the B* mesons and the transition amplitudes of the radiative decays $B_{a}^{?t}?ghtarrow B_{a}αmma$are calculated in the frame-work of QCD sum rules. It is shown that the decay rates B* → Bγ are one order smaller than the corresponding D* meson decays.     

Vector meson electroproduction at next-to-leading order

The process of light neutral vector meson electroproduction is studied in the framework of QCD factorization in which the amplitude factorizes in a convolution of the nonperturbative meson distribution amplitude and generalized parton densities with perturbatively calculable hard-scattering amplitudes. We derive a complete set of hard-scattering amplitudes at next-to-leading order (NLO) for the production of vector mesons, V=ρ⁰, ω, ?.     

推导赝标Goldstone玻色子有效拉氏量

从QCD出发,未作近似推导出了赝标量Goldstone玻色子的有效手征拉氏量(ECL)理论.并以QCD中格林函数的形式给出了直到p⁴阶的ECL的系数的定义.     

A soluble realistic model for low energy ππ scattering

Using analyticity, crossing and unitarity and making a few approximations, we predict the ππ scattering amplitudes in terms of the S-wave scattering lengths from threshold up to 800 MeV.     

Perturbative expansions in QCD and analytic properties of α s

It is shown that analytic properties of standard QCD perturbation theory contradict known spectral properties and contain, in particular, infrared-generated Landau ghost poles and cuts. As an outcome, a rigorous background perturbation theory is developed and its analytic properties are shown to be in agreement with general requirements. In the limiting case of large N _c, where QCD amplitudes contain only pole singularities, the strong coupling constant α _s(Q ²) is shown to be a meromorphic function of external momenta as well. Some simple models and examples are given where nonperturbative β function and α _s(Q ²) can be written explicitly. The general form of amplitudes at large N _c is given in the framework of background perturbation theory, and its correspondence with standard perturbation theory at highmomenta is demonstrated in the example of e ⁺ e ^? annihilation. For timelike momenta, the background coupling constant differs drastically from the standard one, but the background series averaged over energy intervals has the same (AF) behavior at high momenta in the Euclidean and in the Minkowskian region.