M. A. Braun, S. S. Pozdnyakov, M. Yu. Salykin, M. I. Vyazovsky
Gluon production on two scattering centers is studied in the formalism of reggeized gluons. Different contributions to the inclusive cross-section are derived with the help of the Lipatov effective action. The AGK relations between these contributions are established. The found inclusive cross-section is compared to the one in the dipole picture and demonstrated to be the same.
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The one-loop diffractive amplitude for emission of two real gluons with widely different rapidities is studied in the Lipatov effective action formalism. It is shown that after integration over longitudinal momenta in the loop the resulting expression coincides with the one obtained by the Lipatov-Bartels formalism in transversal space provided the same prescription is used to exclude divergent contributions as previously proposed for emission of a single real gluon.
In the Regge kinematics the amplitude for gluon production off three scattering centers is found in the Lipatov effective action technique. The vertex for gluon emission with the reggeon splitting in three reggeons is calculated and its transversality is demonstrated. It is shown that in the sum of all contributions terms containing principal value singularities are cancelled and substituted by the standard Feynman poles. These results may be used for calculation of the inclusive cross-section for gluon production on two nucleons in the nucleus.
The process of gluon production in quark-nucleus collisions is studied in the framework of Lipatov's effective action formalism. The relevant simplifications and rules for longitudinal integrations are discussed in detail. The results obtained with the help of these rules correspond to the purely transversal formalism based on effective vertices in the transversal space.
Lipatov's high-energy effective action is a useful tool for computations in the Regge limit beyond leading order. Recently, a regularisation/subtraction prescription has been proposed that allows to apply this formalism to calculate next-to-leading order corrections in a consistent way. We illustrate this procedure with the computation of the gluon Regge trajectory at two loops.
We discuss aspects of our recent derivation of the gluon Regge trajectory at two loop from Lipatov's high energy effective action. We show how the gluon Regge trajectory can be rigorously defined through renormalization of the high energy divergence of the reggeized gluon propagator. We furthermore provide some details on the determination of the two-loop reggeized gluon self-energy.
We discuss computational details of our recent result, namely, the first derivation of the two-loop gluon Regge trajectory within the framework of Lipatov's high energy effective action. In particular, we elaborate on the direct evaluation of Feynman two-loop diagrams by using the Mellin-Barnes representations technique. Our result is in precise agreement with previous computations in the literature, providing this way a highly non-trivial test of the effective action and the proposed subtraction and renormalization scheme combined with our approach for the treatment of the loop diagrams.
We consider the formalism of small-x effective action for reggeized gluons, Gribov (Sov Phys JETP 26:414, 1968), Lipatov (Nucl Phys B 452:369, 1995; Phys Rep 286:131, 1997; Subnucl Ser 49:131, 2013, Int J Mod Phys Conf Ser 39:1560082, 2015; Int J Mod Phys A 31(28/29):1645011, 2016; EPJ Web Conf 125:01010, 2016) and Lipatov et al. (Sov J Nucl Phys 23:338, 1976; Sov Phys JETP 45:199, 1977; Sov J Nucl Phys 28:822, 1978), and, following to the approach developed in Bondarenko et al. (Eur Phys J C 77(8):527, 2017, Eur Phys J C 77(9):630, 2017), calculate the classical gluon field to NNLO precision …
We show that the recently derived renormalization group improved Yennie-Frautschi-Suura (YFS) exponentiation of soft $(k_o\to 0)$ gluons in QCD is fully compatible with the usual Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution of the structure functions of hadrons in the respective hadron-hadron hard interactions. We show how to implement the YFS exponentiation without double or over counting effects already implied by the DGLAP equation. In this way, we arrive at a theory which allows for the development of realistic, multiple gluon Monte Carlo event generators for hard hadron-ha…
We present particular and unique solutions of singlet and non-singlet Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations in leading order (LO) and next-to-leading order (NLO) and gluon, sea and valence quark Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations in leading order (LO) by applying Taylor expansion method at small-x. We obtain t-evolutions of deuteron, proton, neutron, difference and ratio of proton and neutron, gluon, light sea and valence quark structure functions and x-evolution of deuteron,gluon and light sea quark structure functions at sm…
The vertex for gluon emission during the splitting of a reggeized gluon into two is constructed in the framework of Lipatov effective action formalism. Its reduction to a pure transverse form for the diffractive amplitude gives the standard Bartels vertex plus an additional contribution corresponding to the emission from a pointlike splitting vertex. This additional contribution turns out to be given by a longitudinal integral divergent both in the ultraviolet and infrared. A certain specific recipe for this part, including the principal value prescription for the integration, allows to elimin…
We investigate the question whether Lipatov's high energy effective action is capable to reproduce quark and gluon propagators which resum interaction with a strong background field within high energy factorization. Such propagators are frequently employed in calculations within the Color Glass Condensate formalism, in particular when considering scattering of a dilute projectile on a dense target nucleus or nucleon. We find that such propagators can be obtained from the high energy effective action, if a special parametrization of the gluonic field is used, first proposed by Lipatov in the or…
We present the derivation of the two-loop gluon Regge trajectory using Lipatov's high energy effective action and a direct evaluation of Feynman diagrams. Using a gauge invariant regularization of high energy divergences by deforming the light-cone vectors of the effective action, we determine the two-loop self-energy of the reggeized gluon, after computing the master integrals involved using the Mellin-Barnes representations technique. The self-energy is further matched to QCD through a recently proposed subtraction prescription. The Regge trajectory of the gluon is then defined through renor…
We review Lipatov's high energy effective action and show that it is a useful computational tool to calculate scattering amplitudes in (quasi)-multi-Regge kinematics. We explain in some detail our recent work where a novel regularization and subtraction procedure has been proposed that allows to extend the use of this effective action beyond tree level. Two examples are calculated at next-to-leading order: forward jet vertices and the gluon Regge trajectory.
We investigate the gluon Green's function in the high energy limit of QCD using a recently proposed iterative solution of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation at next-to-leading logarithmic (NLL) accuracy. To establish the applicability of this method in the NLL approximation we solve the BFKL equation as originally written by Fadin and Lipatov, and compare the results with previous studies in the leading logarithmic (LL) approximation.
We derive a generalized Balitskii-Fadin-Kuraev-Lipatov equation, which applies directly to the perturbative QCD component of total cross section. With the gluon correlation radius $R_{c} \sim 0.4$f we reproduce the empirical rate of growth of the hadron-nucleon total cross sections. The simultaneous estimate of the triple-pomeron coupling also agrees with the experiment.
We calculate the transverse momentum dependent gluon-to-gluon splitting function within $k_T$-factorization, generalizing the framework employed in the calculation of the quark splitting functions in [1-3] and demonstrate at the same time the consistency of the extended formalism with previous results. While existing versions of $k_T$ factorized evolution equations contain already a gluon-to-gluon splitting function i.e. the leading order Balitsky-Fadin-Kuraev-Lipatov (BFKL) kernel or the Ciafaloni-Catani-Fiore-Marchesini (CCFM) kernel, the obtained splitting function has the important propert…
In this contribution we briefly review some aspects of Lipatov's gauge invariant QCD high energy effective action. The high energy effective provides a field theory framework to systematically factorize QCD scattering amplitudes and related theories in the limit of high center of mass energies. After a short review of the underlying concepts, we address the question how the high energy effective action can be used for actual calculations. As an explicit example we review the derivation of the gluon Regge trajectory up to 2 loop. We then review two topics of current interest: automatic amplitud…
In this note we discuss a generalization of the Lipatov's effective action approach, \cite{LipatovEff,LipatovEff1}, for the case of description of gluon and quark production amplitudes in the quasi-multi-Regge kinematics. Following to \cite{Faddeev}, we define the S-matrix elements of high energy QCD processes in this kinematics and discuss applications of the obtained results.
We consider the twist-3 gluon contribution to the transverse spin structure function $g_2$.We find that the Burkhardt-Cottingham sum rule is satisfied. The additional {\it nonlocal} operators appear in the moments of g2 which were absent in previous analysis of Bukhvostov, Kuraev and Lipatov.
We propose a new unified evolution equation for parton distribution functions appropriate for both large and small Bjorken variables $x$, which is an improved version of the Ciafaloni-Catani-Fiorani-Marchesini equation. In this new equation the cancellation of soft divergences between virtual and real gluon emissions is explicit without introducing infrared cutoffs, next-to-leading contributions to the Sudakov resummation can be included systematically. It is shown that the new equation reduces to the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equation at large $x$, to the Balitsky-Fadin-Kurae…
We discuss the high energy scattering of hadrons with the multi - Regge kinematics. The effective $2D$ model for the interaction between the produced hard gluons appears as a result of the dimensional reduction, which is similar to the dimensional reduction $3+1$ D $\to 3$ D of the high temperature gauge theory. It is demonstrated that being supplemented by the exchange by virtual $3+1$ D gluons this $2D$ model gives rise to the hermitian version of the effective action of Lipatov for the interaction between the ordinary and the reggeized gluons.
We recently derived explicit solutions of the leading-order Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) equations for the $Q^2$ evolution of the singlet structure function $F_s(x,Q^2)$ and the gluon distribution $G(x,Q^2)$ using very efficient Laplace transform techniques. We apply our results here to a study of the HERA data on deep inelastic $ep$ scattering as recently combined by the H1 and ZEUS groups. We use initial distributions $F_2^{γp}(x,Q_0^2)$ and $G(x,Q_0^2)$ fixed by a global fit to the HERA data. From $F_2^{γp}(x,Q_0^2)$ we obtain the singlet quark distribution $F_s(x,Q_0^…
The two loop (NLO) diagrams with quark content contributing to the gluon Regge trajectory are computed within the framework of Lipatov's effective action for QCD, using the regularization procedure for longitudinal divergencies recently proposed by two of us in http://arXiv.org/abs/arXiv:1110.6741. Perfect agreement with previous results in the literature is found, providing a robust check of the regularization prescription and showing that the high energy effective action is a very useful computational tool in the quasi-multi-Regge limit.
The Two-Loop Lipatov Vertex in QCD
本文将QCD高能因子化框架从2到2扩展到2到3过程，通过计算多Reggeon交换并从非平面双圈QCD振幅中匹配，首次确定了维度正规化下双圈Lipatov顶点，并以单值广义多重对数函数基给出紧凑解析结果。
Gravitational wave double copy of radiation from gluon shockwave collisions
本文证明通过将经典色-动力学对偶性应用于胶子激波碰撞的辐射谱，可直接推导出跨普朗克激波散射中引力波谱的双拷贝结果。
We determine both real and virtual next-to-leading order corrections to the gluon induced forward jet vertex, from the high energy effective action proposed by Lipatov. For these calculations we employ the same regularization and subtraction formalism developed in our previous work on the quark-initiated vertex. We find agreement with previous results in the literature.
We investigate photo-production of vector mesons J/Psi and Upsilon measured both at HERA and LHC, using 2 particular fits of inclusive unintegrated gluon distributions, based on non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and next-to-leading order Balitsky-Fadin-Kuraev-Lipatov evolution (Hentschinski-Sabio Vera-Salas gluon; HSS). We find that linear next-to-leading order evolution can only describe production at highest energies, if perturbative corrections are increased to unnaturally large values; rendering this corrections to a perturbative size, the growth with energy …
We propose a modified Balitskii-Fadin-Kuraev-Lipatov equation from the viewpoint of the resummation technique, which satisfies the unitarity bound. The idea is to relax the strong rapidity ordering and to restrict phase space for real gluon emissions in the evaluation of the BFKL kernel. It is found that the gluon distribution function rises as a power of the Bjorken variable $x$, and then saturates at $x\to 0$. We estimate that the saturation begins to occur for $x< 10^{-4}$.
The Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach for the cross sections at high energy $\sqrt s$ in perturbative QCD is briefly reviewed. The role of gluon Reggeization in the derivation of the BFKL equation and its compatibility with $s$-channel unitarity (``bootstrap'') are discussed.
We propose a modified Balitsky-Fadin-Kuraev-Lipatov equation from the viewpoint of the resummation technique, which contains an intrinsic dependence on momentum transfer Q, and satisfies the unitarity bound. The idea is to relax the strong rapidity ordering and to restrict phase space for real gluon emissions in the evaluation of the BFKL kernel. It is shown that the power-law rise of the gluon distribution function with the small Bjorken variable x turns into a logarithmic rise, and that the predictions for the proton structure function $F_2(x,Q^2)$ are consistent with the HERA data.
In the Catani-Ciafaloni-Hautmann high-energy factorization approach a cross section is expressed as a convolution of unintegrated gluon densities and a gauge-invariant hard process, in which two incoming gluons are off-shell with momenta satisfying certain high-energy kinematics. We present two methods of evaluating the tree-level hard process with multiple final states. The first one assumes that only one of the gluons is off-shell and relies on the Slavnov-Taylor identities. Such asymmetric configuration of incoming gluons is phenomenologically important in small x probing by forward process…
Differential cross section of processes with high energy $p(\bar p)p$ collisions in frames of QED: creation of scalar, pseudoscalar and lepton pair - are considered in Weizsäcker - Williams approximation. In frames of QCD processes with conversion of initial proton (antiproton) to fermionic jets accompanied with one gluon jet as well as the state of two gluons and quark-antiquark pair (with out rapidity gap) are considered in frames of effective Reggion action of theory of Lipatov. Process of creation of a Higgs boson accompanied with two fermionic jets is considered. The azimuthal correlation…
The high energy limit of scattering amplitudes in the N=4 supersymmetric Yang-Mills theory is studied by solving the corresponding BFKL equation in the next-to-leading approximation. The gluon Green's function is analysed using a newly proposed method suitable for investigating the contribution from higher conformal spins. From this new approach complete agreement is obtained with the results of Kotikov and Lipatov on conformal spins and angular dependence.
We discuss application of formalism of small-$x$ effective action for reggeized gluons, \cite{Gribov,LipatovEff,BFKL}, for the calculation of classical gluon field of relativistic color charge, similarly to that done in CGC approach of \cite{Venug,Kovner}. The equations of motion with the reggeon fields are solved in LO and NLO approximations and new solutions are found. The results are compared to the calculations performed in the CGC framework and it is demonstrated that the LO CGC results for the classical field are reproduced in our calculations. Possible applications of the NLO solution i…
In this talk we examine how one-loop soft and collinear splitting functions occur in the calculation of next-to-next-to-leading order (NNLO) corrections to production rates, and we present the one-loop gluon soft and splitting functions, computed to all orders in the dimensional regularization parameter $ε$. We apply the one-loop gluon soft function to the calculation of the next-to-leading logarithmic corrections to the Lipatov vertex to all orders in $ε$.
We use the hard (Lipatov) pomeron for the low-x gluon distribution and provide a compact formula for the ratio $R^{c} =F_{L}^{c}/F_{2}^{c}$ that is useful to extract the charm structure function from the reduced charm cross-section, in particular at DESY HERA. Our results show that this ratio is independent of x and independent of the DGLAP evolution of the gluon PDF. As a result, we show that the charm structure function and the reduced charm cross-section exponents do not have the same behaviour at very low x. This difference is independent of the input gluon distribution functions and predi…
We consider central exclusive production of $gg$ dijets in proton-proton (proton-antiproton) collisions at LHC and Tevatron for different intermediate and final gluon polarisations. The amplitude for the process is derived within the $k_\perp$-factorization approach (with both the standard QCD and the Lipatov's effective three-gluon verticies) and is considered in various kinematical asymptotia, in particular, in the important limit of high-$p_\perp$ jets. Compared to earlier works we include emissions of gluons from different gluonic $t$-channel lines as well as emission of quark-antiquark di…
We compute the pole mass of the gluon in QCD from the local composite operator formalism at two loops in the MSbar renormalization scheme. For Yang-Mills theory an estimate of the mass at two loops is 2.13 Lambda_MSbar.
We investigate photo-production of vector mesons J/Psi and Psi(2s), based on both HERA and LHC data, using 2 fits of unintegrated gluon distributions. The latter are subject to non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and linear next-to-leading order Balitsky-Kuraev-Fadin-Lipatov evolution (Hentschinski-Sabio Vera-Salas; HSS gluon) respectively. Apart from extending previous studies to the case of radially excited charmonium Psi(2s), we further use an improved set of charmonium wave functions and provide an estimate of the uncertainties associated with the HSS gluon. Wh…
We investigate the energy dependence of the photo-production cross-section of vector mesons $J/Ψ$ and $Υ$, measured by both HERA experiments H1 and ZEUS in electron-proton collisions and by LHC experiments ALICE, CMS and LHCb in ultra-peripheral proton-proton and ultra-peripheral proton-lead collisions. Our study uses 2 particular fits of inclusive unintegrated gluon distribution, based on non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and next-to-leading order Balitsky-Fadin-Kuraev-Lipatov evolution (Hentschinski-Sabio Vera-Salas gluon; HSS). We find that linear next-to-lead…
We compute the one loop corrections to the pole mass of the gluon in the MSbar scheme in the Landau gauge in both the Curci-Ferrari model and the local composite operator formalism with Nf flavours of massless quarks. For the latter we determine an estimate for the gluon mass using the effective potential of a local dimension two composite operator and find, for example, m_{gluon} = 2.10 Lambda_MSbar in Yang-Mills theory.
We derive the medium-induced, coherent gluon radiation spectrum associated with the hard forward scattering of an energetic parton off a nucleus, in the saturation formalism and within the Gaussian approximation for the relevant correlators of Wilson lines. The calculation reproduces the simple expression for the spectrum previously obtained in the opacity expansion formalism, and rigorously specifies its validity range. The connection between the calculations in the opacity expansion and saturation formalisms is made apparent. This study may serve as a first step in order to implement consist…
We study the structure functions $F_{k}^{b}(x,Q^{2})$ ($k=2, L$) and the reduced cross section $σ_{r}^{b}(x,Q^{2})$ for small values of Bjorken$^{,}$s $x$ variable with respect to the hard (Lipatov) pomeron for the gluon distribution and provide a compact formula for the ratio $R^{b}$ that is useful to extract the beauty structure function from the beauty reduced cross section, in particular at DESY HERA. Also we show that the effects of the nonlinear corrections to the gluon distribution tame the behavior of the beauty structure function and the beauty reduced cross section at low $x$.
Employing the so-called hybrid formalism, we calculate the cross section of inclusive hadron production in proton-proton collisions at forward rapidity in small-$x$ formalism at one-loop order. For the case of hadron production at forward rapidity, we can uses collinear parton distributions for projectile proton and $k_\perp$ dependent gluon distribution for target proton. We show that collinear divergences associated with initial and final state parton radiations are renormalized into parton distributions and fragmentation functions in terms of the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi e…
Inclusive as well as exclusive emissions in forward and central directions of rapidity are widely recognized as excellent channels to access the proton structure at small-x. In this regime, to describe nucleons structure, it is necessary to use kT-unintegrated distributions. In particular, at large transverse momenta, the x-evolution of the so-called unintegrated gluon distribution is driven by the Balitsky-Fadin-Kuraev-Lipatov equation, within the framework of the high-energy factorization (HEF). Recent analyses on the diffractive electroproduction of ρmesons have corroborated the underlying …
Two- and Three-gluon Glueballs within the Helicity Formalism
该研究采用组分胶子方法，基于螺旋度形式构建两、三胶子胶球全对称波函数，首次推导两种三粒子态耦合方案的关系，所得能谱与格点QCD模拟整体吻合，且三胶子谱预测了额外低能态。
We review the currently available formalisms for radiative energy loss of a high-momentum parton in a dense strongly interacting medium. The underlying theoretical framework of the four commonly used formalisms is discussed and the differences and commonalities between the formalisms are highlighted. A quantitative comparison of the single gluon emission spectra as well as the energy loss distributions is given for a model system consisting of a uniform medium with a fixed length of L=2 fm and L=5 fm (the `Brick'). Sizable quantitative differences are found. The largest differences can be attr…
We derive inclusive and diffractive forward-gluon production in the scattering of a $q\bar{q}$ dipole off an arbitrary target in the high-energy eikonal approximation, suitable to study the saturation regime. We show how the inclusive cross-section is related to the total cross-section for the scattering of a colorless pair of gluons on the target: the gluon-production cross-section can be expressed as a convolution between this $gg$ dipole total cross-section and a dipole distribution. We then consider as an application the forward-jet production from an incident hadron and describe forward-j…
The modification and amplification of the gluon angular distribution produced along with hard jets in nuclear collisions is computed. We consider the limit of a thin quark-gluon plasma, where the number of rescatterings of the jet and gluons is small. The focus is on jet quenching associated with the formation of highly off-shell partons in hard scattering events involving nuclei. The interference between the initial hard radiation amplitude, the multiple induced Gunion-Bertsch radiation amplitudes, and gluon rescattering amplitudes leads to an angular distribution that differs considerably fr…
Universal features of $ 2\to N$ scattering in QCD and gravity from shockwave collisions
该研究构建了QCD胶子冲击波碰撞辐射的半经典杨-米尔斯框架与广义相对论对应框架的定量对应，证明了稀疏-稀疏近似下的Lipatov双重拷贝，并提出该对应关系的多类扩展方向。
We compute next to eikonal (NE) and next to next to eikonal (NNE) corrections to the Lipatov vertex due to a finite target thickness. These arise from electric field insertions into the eikonal Wilson lines. We then derive a $k_T$-factorization formula for single inclusive gluon production at NNE accuracy and find that nuclear effects are absent. We also analyze NNE corrections to two-gluon production where some of the contributions are found to exhibit corrections proportional to $A^{2/3}$.
We compute multi-gluon production in the Color Glass Condensate approach in dilute-dense collisions, p$A$, extending previous calculations up to four gluons. We include the contributions that are leading in the overlap area of the collision but keep all orders in the expansion in the number of colors. We develop a diagrammatic technique to write the numerous color contractions and exploit the symmetries to group the diagrams and simplify the expressions. To proceed further, we use the McLerran-Venugopalan and Golec-Biernat-Wüsthoff models for the projectile and target averages, respectively. W…
Deep inelastic scattering (DIS) samples a part of the wave function of a hadron in the vicinity of the light cone. Lipatov constructed a spin chain which describes the amplitude of DIS in leading logarithmic approximation. Kharzeev and Levin proposed the entanglement entropy as an observable in DIS [Phys. Rev. D 95, 114008 (2017)], and suggested a relation between the entanglement entropy and parton distributions. Here we represent the DIS process as a local quench in the Lipatov's spin chain, and study the time evolution of the produced entanglement entropy. We show that the resulting entangl…
We propose a formalism for calculating the event cross-section of parton interactions. In this formalism, we use the light-front bound-state wave function to expand scattering initial state. This leads to an expression of the cross-section in terms of square of wave functions which can be used to define the parton distribution functions. The probability interpretation of the partonic interactions among hadron-hadron scattering is naturally achieved. We apply this formalism to calculate the 4-particle final state cross-section for single parton, double parton and gluon splitting interactions. W…
We present a new formalism for parton shower simulation of QCD jets, which incorporates the following features: invariance under boosts along jet axes, improved treatment of heavy quark fragmentation, angular-ordered evolution with soft gluon coherence, more accurate soft gluon angular distributions, and better coverage of phase space. It is implemented in the new HERWIG++ event generator.
The quark scalar, axial and tensor charges of nucleon are calculated in the Schwinger-Dyson formalism. We first calculate these charges in the rainbow-ladder truncation using the IR cut quark-gluon vertex, and show that the result is in agreement with the known data. We then perform the same calculation with the phenomenological IR singular quark-gluon vertex. In this case, the Schwinger-Dyson equation does not converge. We show that this result suggests the requirement of additional corrections to the rainbow-ladder truncation, due to the interaction between quark and gluons in the deep IR re…
We study the inclusive DbarD and DD pair production in proton-proton collisions at the LHC at lead- ing order of the parton Reggeization approach endowed with universal scale-depended fragmen- tation functions for c-quark to D-meson and for gluon to D-meson transitions. We have described DbarD and DD distributions in azimuthal angle, as well as transverse momentum, rapidity distance, and invariant mass measured in the region of large rapidity 2 < y < 4 by the LHCb Collabora- tion at the LHC without free parameters. We have used Reggeized amplitudes for the processes RR - gg and RR - c barc whi…
We calculate single parton distributions inside quark and gluon jets within the coherent branching formalism, which resums leading and next-to-leading logarithmic contributions. This formalism is at the basis of the modified leading logarithmic approximation (MLLA), and it conserves energy exactly. For a wide preasymptotic range of the evolution variable Y=ln[Eθ/Q_0], we find marked differences in the shape and norm of single parton distributions calculated in the MLLA or in the coherent branching formalism, respectively. For asymptotically large values Y>5-10, the difference in norm persists,…
In the last decade, lattice QCD has been able to compute the low-lying glueball spectrum with accuracy. Like other effective approaches of QCD, potential models still have difficulties to cope with gluonic hadrons. Assuming that glueballs are bound states of valence gluons with zero current mass, it is readily understood that the use of a potential model, intrinsically non covariant, could be problematic in this case. The main challenge for this kind of model is actually to find a way to introduce properly the more relevant degree of freedom of the gluon: spin or helicity. In this work, we use…
The formalism for treating the leading-twist contributions of the two-gluon Fock components occurring in hard exclusive processes that involve eta and eta' mesons is reviewed. The calculation of the eta, eta'--photon transition form factor in next-to-leading order in alpha_s, as well as, the analysis of the g* g* eta' vertex and the electro- and photoproduction of eta, eta' mesons are presented. Applications of this formalism to other relevant quantities such as glueballs are also discussed.
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