Search

We study the role of $1\rightarrow2$ and $1\rightarrow3$ processes in triple charmonium production. We see that the ratio of effective cross sections of TPS and DPS only moderately depends on charmonium transverse momenta, but the total DPS and TPS cross sections each separately may have rather strong dependence on charmonia transverse momenta in the central kinematics that can be studied experimentally., Comment: 15 pages, 7 figures

We calculate the rate of double parton scattering (DPS) in proton - proton collisions in the framework of the recently proposed hot spot model of the nucleon structure. The resulting rate, especially for the case of three hot spots, appears to be in tension with the current experimental data on DPS at the LHC., Comment: 12 pages 2 figures 1 table

We study the contribution of color correlations to Double Parton Scattering (DPS). We show that there is a specific class of Feynman diagrams related to so called 1 \textrightarrow{} 2 processes when the contribution of these color correlations is not Sudakov suppressed with the transverse scales. The split scale increases with the transverse scale Q, with color correlations being up to 5-10 percent of singlet ones. The effective absence of Sudakov suppression gives hope that although they are small relative to color singlet correlations, they eventually can be observed., Comment: 60 pages 25 figures,6 tables

We study the influence of quantum interference and colour flow on three point correlations described by asymmetric cumulants in high multiplicity events in pp collisions. We use the model previously developed for the study of the collectivity in symmetric cumulants. We show that the resulting three point asymmetric cumulant is in qualitative agreement with the experimental data for the same parameters of the model as it was with the symmetric cumulants. Our results show that the initial state correlations must play a major role and may be even dominant in the explanation of the correlations in high multiplicity pp events., Comment: 29 pages, 14 figures, we extended comparison with experimental data, added a figure, streamlined the discussion and added references

We study the effects of adding the Coulomb interactions to the harmonic oscillator (HO) approximation of the heavy parton propagating through the quark-gluon plasma (the extension to QCD of the Molliere theory). We explicitly find the expression for the transverse momentum distribution of the gluon radiation of the heavy quark propagating in the quark gluon plasma in the framework of the Moliere theory, taking into account the BDMPSZ radiation in the harmonic oscillator (HO) approximation, and the Coulomb logarithms described by the additional logarithmic terms in the effective potential. We show that these Coulomb logarithms significantly influence the HO distribution, derived in the BDMPSZ works, especially for the small transverse momenta, filling the dead cone, and reducing the dead cone suppression of the heavy quark radiation (dead cone effect). In addition we study the effect of the phase space constraints on the heavy quark energy loss, and argue that taking into account of both the phase space constraints and of the Coulomb gluons reduces the dependence of the heavy quark energy loss on its mas in the HO approximation., Comment: 26 pages, 7 figures 2 tables. arXiv admin note: text overlap with arXiv:2002.11233, references added,a mistake in the numerical code for angular distributions leading to unphysical oscillations corrected

We present results on Zjj production via double parton scattering in pA collisions at the LHC. We perform the analysis at leading and next-leading order accuracy with different sets of cuts on jet transverse momenta and accounting for the single parton scattering background. By exploiting the experimental capability to measure the centrality dependence of the cross section, we discuss the feasibility of DPS observation in already collected data at the LHC and in future runs., Comment: 10 pages, 4 figures, 4 tables. arXiv admin note: text overlap with arXiv:1912.02508, arXiv:2003.10880 New version includes a QCD NL0 calculation of DPS , 2 tables nd 2 figures are added

We present predictions for the double parton scattering (DPS) four-jet production cross sections in $pA$ collisions at the LHC. Relying on the experimental capabilities to correlate centrality with impact parameter $B$ of the proton-nucleus collision, we discuss a strategy to extract the double parton scattering contributions in $pA$ collisions, which gives direct access to double parton distribution in the nucleon. We show that the production cross sections via DPS of four jets, out of which two may be light- or heavy-quark jets, are large enough to allow the method to be used already with data accumulated in 2016 $pA$ run., Comment: 11 pages, 5 figures, 3 tables. arXiv admin note: substantial text overlap with arXiv:1912.02508

We study the energy loss of a heavy quark propagating in the Quark-Gluon Plasma (QGP) in the framework of the Moller theory, including possible large Coulomb logarithms as a perturbation to BDMPSZ bremsstrahlung, described in the Harmonic Oscillator (HO) approximation. We derive the analytical expression that describes the energy loss in the entire emitted gluon frequency region. In the small frequencies region, for angles larger than the dead cone angle, the energy loss is controlled by the BDMPSZ mechanism, while for larger frequencies it is described by N=1 term in the GLV opacity expansion. We estimate corresponding quenching rates for different values of the heavy quark path and different $m/E$ ratios., Comment: 20 pages, 4 figures

We consider the production of $W$-boson plus dijet, $W$-boson plus b-jets and same sign $WW$ via double parton scattering (DPS) in $pA$ collisions at the LHC and evaluate the corresponding cross sections. The impact of a novel DPS contribution pertinent to $pA$ collisions is quantified. Exploiting the experimental capability of performing measurements differential in the impact parameter in $pA$ collisions, we discuss a method to single out this novel DPS contribution. The method allows the subtraction of the leading twist (LT) single parton scattering background and it gives access in a very clean way to double parton distribution functions in the proton. We calculate leading twist and DPS cross sections and study the dependence of the observables on the cuts in the jets phase space. In the $Wjj$ channel the observation of DPS is possible with data already accumulated in $pA$ runs and the situation will greatly improve for the next high luminosity runs. For the $Wb\bar{b}$ final state, the statistics within the current data is too low, but there is possibility to observe DPS in this channel in future runs, albeit with much reduced sensitivity than in $Wjj$ final state. Finally the DPS observation in the same sign $WW$ channel will require either significant increase of integrated luminosity beyond that foreseen in next $pA$ runs or improved methods for $W$ reconstruction, along with its charge, in hadronic decay channels., Comment: 15 pages,8 figures and 3 tables; significant changes are made, in particular basic observables where changed to minimize systematic errors, leading twist contributions were calculated, and systematic error in DPS determination was estimated, permitting to find at what kinematic constraints DPS contribution to W jj ,Wbb ,WW final states can be separated

We derive expressions for the cross section of the multiparton interactions based on the analysis of the relevant Feynman diagrams. We express the cross sections through the double (triple, ...) generalized parton distributions (GPDs). In the mean field approximation for the double GPDs the answer is expressed through the integral over two gluon form factor which was measured in the exclusive DIS vector meson production.We explain under what conditions the derived expressions correspond to an intuitive picture of hard interactions in the impact parameter representation. The mean field approximation in which correlations of the partons are neglected fail to explain the data, while pQCD induced correlation enhance large $p_\perp$ and $ 0.001 < x < 0.1$ typically enhance the cross section by a factor of 1.5 -- 2 explaining the current data. We argue that in the small x kinematics ($10^{-4} \le x \le 10^{-3}$) where effects of perturbative correlations diminish, the nonperturbative mechanism kicks in and generates positive correlations comparable in magnitude with the perturbative ones. We explain how our technique can be used for calculations of MPI in the proton - nucleus scattering. The interplay of hard interactions and underlying event is discussed, as well as different geometric pictures for each of MPI mechanisms-pQCD, nonperturbative correlations and mean field. Predictions for value of \effs for various processes and a wide range of kinematics are given. We show that together different MPI mechanisms give good description of experimental data, both at Tvatron, and LHC, including the central kinematics studied by ATLAS and CMS detectors, and forward (heavy flavors) kinematics studied by LHCb., Comment: 40 pages, 16 figures, To be published in "Multiple parton Interactions at the LHC", P. Bartalini and J. Gaunt eds, World Scientific}. arXiv admin note: text overlap with arXiv:1306.3763

It is shown that $\alpha_s(E)$, the strong coupling constant, can be determined in the non-perturbative regime from Bose-Einstein correlations (BEC). The obtained $\alpha_s(E)$ is in agreement with the prescriptions dealt with in the Analytic Perturbative Theory approach. It also extrapolates smoothly to the standard perturbative $\alpha_s(E)$ at higher energies. Our results indicate that BEC dimension can be considered as an alternative approach to the short range measure between hadrons., Comment: 7 pages, 4 figures

Analytical study of the rapidity distribution of the final state particles in deep inelastic scattering at small x is presented. We separate and analyse three sources of particle production: fragmentation of the quark-antiquark pair, accompanying coherent soft gluon radiation due to octet color exchange in the t-channel, and fragmentation of gluons that form parton distribution functions. Connection to Catani-Ciafaloni-Fiorani-Marchesini (CCFM) equations and the role of gluon reggezation are also discussed., Comment: 14 pages, 6 Figures. Abstract extended, minor misprints corrected, derivations improved and explanations are streamlined. Published in Physics Letters, B/

We study the role of soft/nonperturbative correlations in the multi parton interactions in the central kinematics relevant for double parton scattering (DPS) and underlying event (UE) measurements at ATLAS and CMS. We show that the effect of soft correlations is negligible for DPS regime (typical transverse momenta larger than 10-20 GeV), but may be important for UE (several GeV scale). The characteristic scale where soft correlations become important increases with decrease of $x$ (energy increase) leading to approximately constant \effs at small x., Comment: 14 pages,11 figures, we added 5 additional pictures to illustrate our results for LHC at 13 TeV, for the sigma eff as a function of c.m.s energy for UE, and dependence of the scale where soft correlations become irrelevant on c.m.s. energy

We calculate the rate of double open charm production in the forward kinematics studied recently in the LHCb experiment. We find that the mean field approximation for the double parton GPD (Generalized parton distributions), which neglects parton - parton correlations, underestimates the rate by a factor of two. The enhancement due to the perturbative QCD correlation \12 mechanism which explains the rate of double parton interactions at the central rapidities is found to explain 60 $\div$ 80 \% of the discrepancy. We argue that the nonperturbative fluctuations leading to non-factorized (correlated) contributions to the initial conditions for the DGLAP collinear evolution of the double parton GPD play an important role in this kinematics. Combined, the two correlation mechanisms provide a good description of the rate of double charm production reported by the LHCb. We also give predictions for the variation of the \effs (i.e. the ratio of double and square of single inclusive rates) in the discussed kinematics as a function of $p_t$. The account for two correlation mechanisms strongly reduces sensitivity of the results to the starting point of the QCD evolution., Comment: 9 figures, 19 pages. Several misprints were eliminated, to be published in Eur. J. of Physics, C

The new numerical approach that includes 1 to 2 mechanism is applied to double parton scattering (DPS) in W+dijet and Z+dijet final state production in proton-proton collisions at LHC. By using the underlying event (UE) simulation from a pythia 8 tune extracted in hadronic events, we show that, like in the case of a four-jet final state, the inclusion of 1 to 2 mechanism improves the description of experimental data measured at 7 TeV. In addition, predictions for proton-proton collisions at a center-of-mass energy of 14 TeV are shown for DPS- and UE-sensitive observables., Comment: 24 pages 10 figures. arXiv admin note: text overlap with arXiv:1503.08246

Multiple Partonic Interactions are often crucial for interpreting results obtained at the Large Hadron Collider (LHC). The quest for a sound understanding of the dynamics behind MPI - particularly at this time when the LHC is due to start its "Run II" operations - has focused the aim of this workshop. MPI@LHC2014 concentrated mainly on the phenomenology of LHC measurements whilst keeping in perspective those results obtained at previous hadron colliders. The workshop has also debated some of the state-of-the-art theoretical considerations and the modeling of MPI in Monte Carlo event generators. The topics debated in the workshop included: Phenomenology of MPI processes and multiparton distributions; Considerations for the description of MPI in Quantum Chromodynamics (QCD); Measuring multiple partonic interactions; Experimental results on inelastic hadronic collisions: underlying event, minimum bias, forward energy flow; Monte Carlo generator development and tuning; Connections with low-x phenomena, diffraction, heavy-ion physics and cosmic rays. In a total of 57 plenary talks the workshop covered a wide range of experimental results, Monte Carlo development and tuning, phenomenology and dedicated measurements of MPI which were produced with data from the LHC's Run I. Recent progress of theoretical understanding of MPI in pp, pA and AA collisions as well as the role of MPI in diffraction and small-x physics were also covered. The workshop forstered close contact between the experimental and theoretical communities. It provided a setting to discuss many of the different aspects of MPI, eventually identifying them as a unifying concept between apparently different lines of research and evaluating their impact on the LHC physics programme., Comment: MPI@LHC 2014, 3 - 7 November 2014, Krakow, Poland, 81 pages

We improve the treatment of Multiple Parton Interactions (MPI) in \textsc{Pythia} by including the \12 mechanism and treating the \22 mechanism in a model-independent way. The \22 mechanism is calculated within the mean field approximation, and its parameters are expressed through Generalized Parton Distributions extracted from HERA data. The parameters related to the transverse parton distribution inside the proton are thus independent of the performed fit. The \12 mechanism is included along the lines of the recently developed perturbative QCD formalism. A unified description of MPI at moderate and hard transverse momenta is obtained within a consistent framework, in good agreement with experimental data measured at 7 TeV. Predictions are shown for the considered observables at 14 TeV. The corresponding code implementing the new MPI approach is available., Comment: 24 pages, 12 figures, An additional chapter"Comparison with recent HERWIG Tunes" is added,1 figure added

We derive expressions for the differential distributions and the total cross section of double- parton interaction in direct photon interaction with proton and nuclei. We demonstrate that in this case the cross section is more directly related to the nucleon generalized parton distribution than in the case of double parton interactions in the proton - proton collisions. We focus on the production of two dijets each containing charm (anticharm) quarks and carrying $x_1,x_2>0.2$ fractions of the photon momentum. Numerical results are presented for the case of $\gamma p$ collisions at LHeC, HERA and in the ultraperipheral $AA$ and $pA$ collisions at the LHC. We find that the events of this kind would be abundantly produced at the LHeC. For $\sqrt{s}=1.3$ TeV the expected rate is $2\cdot 10^8$ events for the luminosity $10^{34}$ cm$^{-2}s^{-1}$, the running time of $10^6$ s and the transverse cutoff of $p_t>5$ GeV. This would make it feasible to use these processes for the model independent determination of two parton GPDs in nucleon and in nuclei. For HERA the total accumulated number of the events is also high, but efficiency of the detection of charm seems too low to study the process. We also find that a significant number of such double parton interactions should be produced in $p - Pb$ and $Pb- Pb$ collisions at the LHC: $\sim 6\cdot 10^4$ for $Pb-Pb$, and $\sim 7 \cdot 10^3$ for $p-Pb$ collisions for the same transverse momentum cutoff., Comment: 19 pages, 11 figures

We study the screening effect for the multiparton interactions (MPI) for proton--deuteron collisions in the kinematics where one parton belonging to the deuteron has small $x_1$ so the leading twist shadowing is present while the second parton ($x_2$) is involved in the interaction %%ms in the kinematics where shadowing effects are small. We find that the ratio of the shadowing and the impulse approximation terms is approximately factor of two larger for MPI than for the single parton distributions. We also calculate the double parton antishadowing (DPA) contribution to the cross section due to the independent interactions of the partons ofthe projectile proton with two nucleons of the deuteron and find that shadowing leads to a strong reduction ofthe DPA effect.For example, for the resolution scale $Q_1^2 \sim 4$~$\mbox{GeV}^2$ of the interaction with parton $x_1$ we find that shadowing reduces the DPA effect by $\sim$ 30%. It is argued that in the discussed kinematics the contribution of interference diagrams, which correspond to the interchange ofpartonsbetween the proton and neutron, constitutes only a small correction to the shadowing contributions., Comment: 24 pages, 7 figures; we added a section discussing the role of the interference mechanism in MPI in pd collisions

We examine the role played in double parton interactions (DPI) by the parton--parton correlations originating from perturbative QCD parton splittings. Also presented are the results of the numerical analysis of the integrated DPI cross sections at Tevatron and LHC energies. To obtain the numerical results the knowledge of the single-parton GPDs gained by the HERA experiments was used to construct the non-perturbative input for generalized double parton distributions. The perturbative two-parton correlations induced by three-parton interactions contribute significantly to resolution of the longstanding puzzle of an excess of multi-jet production events in the back-to-back kinematics observed at the Tevatron., Comment: 16 pages, 13 figures

We demonstrate that perturbative QCD leads to positive 3D parton--parton correlations inside nucleon explaining a factor two enhancement of the cross section of multi-parton interactions observed at Tevatron at $x_i\ge 0.01$ as compared to the predictions of the independent parton approximation. We also find that though perturbative correlations decrease with $x$ decreasing, the nonperturbative mechanism kicks in and should generate correlation which, at $x$ below $10^{-3}$, is comparable in magnitude with the perturbative one for $x\sim 0.01$., Comment: 4 pages, 5 figures

We review the recent progress in the theoretical description and experimental observation of multiple parton interactions. Subjects covered include experimental measurements of minimum bias interactions and of the underlying event, models of soft physics implemented in Monte Carlo generators, developments in the theoretical description of multiple parton interactions and phenomenological studies of double parton scattering. This article stems from contributions presented at the Helmholtz Alliance workshop on "Multi-Parton Interactions at the LHC", DESY Hamburg, 13-15 September 2010., Comment: 68 pages

We study production of two pairs of jets in %hard hadron--hadron collisions in view of extracting contribution of {\em double hard interactions} of three and four partons ($3\to4$, $4\to4$). Such interactions, in spite of being power suppressed at the level of the total cross section, become comparable with the standard hard collisions of two partons, $2\to4$, in the {\em back-to-back kinematics} when the transverse momentum imbalances of two pairing jets are relatively small. We express differential and total cross sections for two-dijet production in double parton collisions through the generalized two-parton distributions, $_2$GPDs \cite{BDFS1}, that contain large-distance two-parton correlations of non-perturbative origin as well as small-distance correlations due to parton evolution. We find that these large- and small-distance correlations participate in different manner in 4-jet production, and treat them in the leading logarithmic approximation of pQCD that resums collinear logarithms in all orders. A special emphasis is given to $3\to4$ double hard interaction processes that occur as an interplay between large- and short-distance parton correlations and were not taken into consideration by approaches inspired by the parton model picture. We demonstrate that the $3\to4$ mechanism, being of the same order in $\as$ as the $4\to4$ process, turns out to be {\em geometrically enhanced} compared to the latter and should contribute significantly to 4-jet production. The framework developed here takes into systematic consideration perturbative $Q^2$ evolution of $_2$GPDs. It can be used as a basis for future analysis of NLO corrections to multi-parton interactions (MPI) at LHC and Tevatron colliders, in particular for improving evaluation of QCD backgrounds to new physics searches., Comment: 16 pages,4 figures Improved presentation; list of references reworked; qualitative estimate of the magnitude of different contributions in the beck-to- back region corrected

We demonstrate that in the back-to-back kinematics the production of four jets in the collision of two partons is suppressed in the leading log approximation of pQCD, compared to the hard processes involving the collision of four partons. We derive the basic equation for four-jet production in QCD in terms of the convolution of generalized two-parton distributions of colliding hadrons in the momentum space representation. Our derivation leads to geometrical approach in the impact parameter space close to that suggested within the parton model and used before to describe the four-jet production. We develop the independent parton approximation to the light-cone wave function of the proton. Comparison with the CDF and D0 data shows that the independent parton approximation to the light-cone wave function of the proton is insufficient to explain the data. We argue that the data indicate the presence of significant multiparton correlations in the light-cone wave functions of colliding protons., Comment: 5 pages, 2 figures, final version published in Phys.Rev.D, rapid communications

The objective of this first workshop on Multiple Partonic Interactions (MPI) at the LHC is to raise the profile of MPI studies, summarizing the legacy from the older phenomenology at hadronic colliders and favouring further specific contacts between the theory and experimental communities. The MPI are experiencing a growing popularity and are currently widely invoked to account for observations that would not be explained otherwise: the activity of the Underlying Event, the cross sections for multiple heavy flavour production, the survival probability of large rapidity gaps in hard diffraction, etc. At the same time, the implementation of the MPI effects in the Monte Carlo models is quickly proceeding through an increasing level of sophistication and complexity that in perspective achieves deep general implications for the LHC physics. The ultimate ambition of this workshop is to promote the MPI as unification concept between seemingly heterogeneous research lines and to profit of the complete experimental picture in order to constrain their implementation in the models, evaluating the spin offs on the LHC physics program., Comment: MPI'08 international workshop has been held in October 27-31, 2008, Perugia, Italy - 349 pages

We evaluate within the LO DGLAP approximation the dependence on energy of the cross section of the photo(electro)production of vector meson V ($V=J/\psi,...$) in the hard elastic processes off a parton $\gamma^*+g\to V=J/\psi+g$ as the function of momentum transfer $t=(q_{\gamma}-p_V)^2$. We demonstrate that in the limit $-t \ge m_V^2 +Q^2$ the cross section does not contain double logarithmic terms in any order of the DGLAP approximation leading to the energy independent cross section. Thus the energy dependence of cross section $\gamma^*+p\to J/\psi+{\rm rapidity ~gap} +X$ is governed at large $t$ by the gluon distribution within a proton, i.e. it is unambiguously predicted within the DGLAP approximation including the stronger $W_{\gamma N}$ dependence at larger $-t$ . This prediction explains recent HERA data. The calculations which follow perturbative Pomeron logic predict opposite trend of a weaker $W_{\gamma N}$ dependence at larger $t$. We explain that at the HERA energies double logarithmic terms characteristic for DGLAP approximation dominate in the hard processes as the consequence of constraints due to energy-momentum conservation. We give predictions for ultraperipheral hard diffractive processes at the LHC and show that these processes are well suited for looking for the contribution of the single logarithmic terms due to the gluon emission in the multiRegge kinematics. We also comment on the interrelation between energy and $t$ dependence of the cross sections of the hard exclusive processes., Comment: 12 pages, 3 figures

We predict the dependence on energy of photo(electro) production processes: $\gamma(\gamma^*)+p\to V+ X$ with large rapidity gap at small x and large momentum $-t$ transferred to $V$ in pQCD. Here V is a heavy quarkonium ($J/\psi, \Upsilon$) or longitudinally polarized light vector meson (in the electroproduction processes), etc. In the kinematics of HERA we calculate the dependence on energy of cross sections of these processes as the function of momentum transfer $t$, photon virtuality $Q^2$ and/or quarkonium mass. In the kinematical region $Q_0^2\le -t\ll Q^2+M^2_V$ the nontrivial energy dependence of the cross section for the vector meson production due to the photon scattering off a parton follows within QCD from the summing of the double logarithmic terms. In the second regime $-t\ge Q^2+M^2_V$ within DGLAP approximation in all orders of perturbation theory the $q\bar q - {\rm parton}$ elastic cross section is energy independent. We show that the correct account of the double logarithmic terms and of the gluon radiation including kinematical constraints removes the disagreement between pQCD calculations and recent HERA experimental data. The explicit formula for the dependence of the differential cross section$\displaystyle{\frac{d^2\sigma}{dtdx_J}}$ of these processes on $s_{\gamma^*N}$ is obtained. We show that perturbative Pomeron type behavior may reveal itself only at energies significantly larger than those available at HERA. In addition we evaluate the energy dependence of DCVS processes., Comment: 22 pages, 4 figures

The dipole and the DGLAP approximations are combined with the $k_t$ factorization theorem to demonstrate the fundamental property of pQCD: smaller is the size of the colorless quark-gluon configurations in the fragmentation region, more rapid is the increase of its interaction with the target as a function of energy. First, we show that the transverse momenta of the quark(antiquark) within the $q\bar{q}$ pair, produced in the fragmentation region by the strongly virtual photon, increase with the decrease of x for fixed $Q^2$. As practical consequence of these effects we show that the cross sections of DIS and DVCS. We predict that the ratio of DVCS to DIS amplitudes should very slowly approach one from above at very large collision energies. Second, we study a closely related phenomenon of the increase of the transverse momenta with the energy of the characteristic transverse momenta of the gluon/quark configurations responsible for the transition to the black disk regime. We discuss the impact of this phenomenona on the slowing of the dependence on the initial energy of the coherence length. We demonstrate that a rapid projectile has the biconcave shape, which is different from the expectations of the preQCD parton model where a fast hadron has a pancake shape. We show that the increase of the transverse momenta leads to a new expression for the total cross section of a DIS scattering at very large energies, relevant to LHeC and LHC. We discuss the impact of the discovered phenomena on the hard processes in pp collisions, and on the dominance ofdifferent phases of chiral and conformal symmetries in the central and peripheral pp, pA, and AA collisions., Comment: 37 pages, 6 figures, uses file pdfsync.sty some typos and misspellings are eliminated

We visualize the fundamental property of pQCD: the smaller size of the colorless quark-gluon configurations leads to a more rapid increase of its interaction with energy. Within the frame of dipole model we use the $k_t$ factorization theorem to generalize the DGLAP approximation and/or leading $\ln(x_0/x)$ approximation and evaluate the interaction of quark dipole with a target. In the limit of fixed $Q^2$ and $x\to 0$ we found the increase with energy of transverse momenta of quark(antiquark) within q$\bar q$ pair produced by strongly virtual photon. The average $p^2_t$ is evaluated analytically within the double logarithmic approximation. We demonstrate that the invariant mass$^2$ of the q$\bar q$ pair increases with the energy as $M^2_0(x_0/x)^{\lambda}$, where $\lambda\sim 0.4\alpha_sN_c/\pi$ for transverse photons, and as $\sim M^2_0 \exp{0.17[(4\alpha_sN_c/\pi)\log(x_0/x)]^{1/2}}$ for longitudinal photons, where $M^2_0 \approx 0.7Q^2$ at the energies of the order $s_0\sim 10^4$ GeV$^2$ ($x_0\sim 10^{-2}$). The magnitude of the effect depends strongly on the small $x$ behavior of the gluon distribution. Similar pattern of the energy dependence of $M^2$ is found in the LO DGLAP approximation generalized to account for $k_t$ factorization. We discuss the impact of the found phenomenon on the dependence of the coherence length on the initial energy and demonstrate that the shape of final hadron state in DIS has biconcave form instead of pancake. Some implications of the found phenomena for the hard processes in pp collisions are discussed., Comment: 14 pages, 2 figures, uses epstopdf.sty typos corrected

We find, within the pQCD dipole model for DIS processes, a rapid increase with energy of the scale of parton momenta in the current fragmentation region in the limit $s\to \infty$ and fixed $Q^2$ . We explain the equivalence between the dispersion representation over $Q^2$ for LT pQCD zero angle amplitude of $\gamma^*+T\to \gamma^*+T$ scattering at large energies and the $k_t$ factorization, and use it to evaluate the scales of the hard processes in the current fragmentation region. We derive within the black disc (BD) regime the modified Gribov formula for the total cross-section of the DIS. We evaluate the coherence length of the processes relevant for the BD regime and find that it increases with energy as $\sim s^{0.6}$ i.e. significantly slower than in the parton model ($1/2m_Nx$ - the Ioffe length) as well as in pQCD. In the BD regime we estimate the gluon densities, local in the coordinate space, and find that they do not decrease with the energy. We discuss briefly how the new pQCD phenomena may reveal itself in the proton-proton collisions at LHC, Comment: 14 pages, 5 tables, a talk given by B.Blok at the small x conference at Columpari, Crete, 2008

The causality and/or the energy-momentum constraints on the amplitudes of high energy processes are generalized to QCD. The constraints imply that the energetic parton may experience at most one inelastic collision only and that the number of the constituents in the light cone wave function of the projectile is increasing with the collision energy and the atomic number., Comment: 24 pages,8 figures. The paper is streamlined, some references are changed and misprints are eliminated

We investigate the effective field theory (EFT) which gives the approximate description of the scattering of the two hard small dipoles in the small $x$ processes in QCD near the black disc limit(BDL). We argue that the perturbative QCD approaches predict the existence of tachyon and visualize it in the approximation where $\alpha'_P=0$ . We demonstrate that the high energy behavior of the cross-section depends strongly on the diffusion law in the impact parameter plane. On the other hand, almost threshold behavior of the cross section of the hard processes and multiplicities, i.e. fast increase of cross sections (color inflation), melting of ladders into color network and softening of the longitudinal distributions of hadrons are qualitatively insensitive to the value of diffusion in the impact parameter space. We evaluate $\alpha'_P$ near the black disk limit and find significant $\alpha'_P$ as the consequence of the probability conservation., Comment: 11 pages, 2 figures

At sufficiently small $x$ where pQCD methods become insufficient we rewrote sum of dominant Feynman diagrams for single-scale hard processes in the form of the effective field theory where a quasiparticle corresponds to pQCD ladder. We explain that pQCD series are divergent at small $x$ since pQCD produces tachyon in effective field theory and because of degeneracy of vacua . Within the WKB approximation we found the hierarchy among quasiparticle interactions due to smallness of the QCD coupling constant which justifies restriction by the triple quasiparticle interaction in the Lagrangean of effective field theory. Degeneracy of vacua is removed by accounting for the classical solutions -kinks which cannot be decomposed into series over powers f $\alpha_s$ but describe color inflation, Bose-Einstein condensation of quasiparticles. Quantum fluctuations around the WKB solution lead to the spontaneous violation of two-dimensional translation symmetry and the appearance of zero modes- ``phonons'' which are relevant for the black disc behaviour of small x processes. Account of gluon exchanges between overlapping ladders neglected in the first approximation produces a color network occupying a "macroscopic" longitudinal volume. We discuss briefly possible role of new QCD phenomena in the two-scale hard processes ., Comment: 9 pages, Talk given by B.Blok at the second conference: QCD at cosmic energies, Skopelos, Greece, September 2005

We argue that at sufficiently small Bjorken $x$ where pQCD amplitude rapidly increases with energy and violates probability conservation the shadowing effects in the single-scale small $x$ hard QCD processes can be described by an effective quantum field theory of interacting quasiparticles. The quasiparticles are the perturbative QCD ladders. We find, within the WKB approximation, that the smallness of the QCD coupling constant ensures the hierarchy among many-quasiparticle interactions evaluated within physical vacuum and in particular, the dominance in the Lagrangian of the triple quasiparticle interaction. It is explained that the effective field theory considered near the perturbative QCD vacuum contains a tachyon relevant for the divergency of the perturbative QCD series at sufficiently small $x$. We solve the equations of motion of the effective field theory within the WKB approximation and find the physical vacuum and the transitions between the false (perturbative) and physical vacua. Classical solutions which dominate transitions between the false and physical vacua are kinks that cannot be decomposed into perturbative series over the powers of $\alpha_s$. These kinks lead to color inflation and the Bose-Einstein condensation of quasiparticles. The account of the quantum fluctuations around the WKB solution reveals the appearance of the "massless" particles-- "phonons". It is explained that "phonons" are relevant for the black disc behaviour of small $x$ processes, leading to a Froissart rise of the cross-section. The condensation of the ladders produces a color network occupying a "macroscopic" longitudinal volume. We discuss briefly the possible detection of new QCD effects., Comment: 24 pages, 1 Figure. References added, and several misprints eliminated

We show that in QCD in the leading twist approximation flavor singlet light cone current-current correlators increase with distances rapidly similar to the correlator of velocities in turbulence and argue that this property is precursor of phase transitions in high energy processes . It is shown that absence of spatial oscillations of current-current correlators follows from asymptotic freedom in QCD. We discuss also influence of this new long-range interaction on the wave function of dipole in high energy DIS processes near the black disc limit., Comment: 10 pages, several misprints eliminated, detailed explanation is added on the change of dipole size, wave function and coherence length near the unitarity limit

We evaluate the coordinate space dependence of the matrix elements of the commutator of the electromagnetic and gluon currents in the vicinity of the light-cone but at large distances within the parton model, DGLAP, the resummation approaches to the small x behaviour of DIS processes, and for the Unitarity Bound. We find that an increase of the commutator with relative distance $py$ as $\propto (py)f(py,y^2=t^2-r^2)$ is the generic property of QCD at small but fixed space-time interval $y^2=t^2-r^2$ in perturbative and nonperturbative QCD regimes. We explain that the factor $py$ follows within the dipole model (QCD factorization theorem) from the properties of Lorents transformation. The increase of $f(r)$ disappeares at central impact parameters if cross section of DIS may achieve the Unitarity Limit. We argue that such long range forces are hardly consistent with thermodynamic equilibrium while a Unitarity Limit may signal equilibration. Possible implications of this new long range interaction are briefly discussed., Comment: 23 pages

We calculate the total scattering cross-section of a dynamical quantum electrically neutral dipole in QED of the infinitely heavy charge and of the infinitely heavy dipole in the leading order in electromagnetic coupling constant., Comment: 7 pages, no figures

We discuss space-time evolution of ultrarelativistic quantum dipole in QED. We show that the space-time evolution can be described, in a certain approximation, by means of a regularized wave function, whose parameters are determined by the process of the dipole creation by a local current. We derive using these wave functions the dipole expansion law, that is found to coincide parametrically in the leading order with the one suggested by Farrar, Frankfurt,Liu and Strikman., Comment: 15 pages

We study in the quasiclassical approximation the radiation reaction and its influence on the space-time evolution for the small relativistic dipole moving in a constant external electromagnetic field in QED., Comment: 41 pages, 20 eps figures

We study the quantum-mechanical evolution of the nonrelativistic oscillator, rapidly moving in the media with the random vector fields. We calculate the evolution of the level probability distribution as a function of time, and obtain rapid level diffusion over the energy levels. Our results imply a new mechanism of charmonium dissociation in QCD media., Comment: 32 pages, 13 figures

We discuss the issue of the local quark-hadron duality at high energies in two- and four-dimensional QCD. A mechanism of the dynamical realization of the quark-hadron duality in two- dimensional QCD in the limit of large number of colors, N_c -> \infty, (the 't Hooft model) is considered. A similar mechanism of dynamical smearing may be relevant in four-dimensional QCD. Although particular details of our results are model-dependent, the general features of the duality implementation conjectured previously get further support., Comment: LATEX, epsfig.sty, 22 pages, 6 figures

We pursue the issue of the local quark-hadron duality at high energies in two- and four-dimensional QCD. A mechanism of the dynamical realization of the quark-hadron duality in two-dimensional QCD in the limit of large number of colors, $N_c \to \infty$, (the ' t Hooft model) is investigated. We argue that a similar mechanism of dynamical smearing may be relevant in four-dimensional QCD. Although particular details of our results are model-dependent (especially in the latter case), the general features of the duality implementation conjectured previously get further support., Comment: Talk at QCD-97 Euroconference, Montpellier,France, July 1997. Technion preprint, 18 pp

Motivated by recent work on three-point QCD sum rules in heavy quark physics, we use the simple quantum mechanical models to study the basic issue of duality in three-point sum rules. We show that while in all of these models the duality in two-point sum rules works fine, the duality in three-point sum rules may be 100%- violated, leading to completely unreliable predictions for the matrix elements in question. The implications for three-point QCD sum rules are discussed. A new estimate for the parameter $\lambda_1$ of HQET is given., Comment: 31 pages, 19 figures. Several references are added. Several typos and minor numerical mistakes are corrected. None of new changes alters any result of the paper