arXiv subjects
Publications and source records attributed to Carlo Ewerz.
I give a brief description of Gribov's light quark confinement scenario and of the Gribov--Dyson--Schwinger equation for light quarks. It is shown that the Green function obtained from this equation exhibits chiral symmetry breaking.
We study the Odderon contribution to elastic pp and ppbar scattering at high energies. Different models for the Odderon-proton coupling are considered and their effects on the differential cross section in the dip region are investigated. We use a Regge fit by Donnachie and Landshoff as a framework and replace its Odderon contribution by the different models. We consider two models for the Odderon-proton impact factor proposed by Fukugita and Kwiecinski and by Levin and Ryskin. In addition we construct a geometric model of the proton which allows us to put limits on the size of a possible diquark cluster in the proton. All models are able to describe the data well. The two models for the impact factor require the strong coupling constant to be fixed rather precisely. In the geometric model a relatively small diquark size is required to describe the data.
We study perturbative unitarity corrections in the generalized leading logarithmic approximation in high energy QCD. It is shown that the corresponding amplitudes with up to six gluons in the t-channel are conformally invariant in impact parameter space. In particular we give a new representation for the two-to-six reggeized gluon vertex in terms of conformally invariant functions. With the help of this representation an interesting regularity in the structure of the two-to-four and the two-to-six transition vertices is found.
We study QCD in the regime of high parton density arising in hadronic collisions at large center-of-mass energy. The n-gluon amplitudes of the generalized leading logarithmic approximation are investigated. We find identities relating amplitudes with different numbers of gluons in the t-channel. These identities constrain the reggeization of the gluon in high energy QCD. The tensors describing the reggeization of a gluon in color space are identified.
Hadronic final states at the LHC will be an interesting testing ground for QCD. A good understanding of QCD radiation will also be important for the discovery of new physics at the LHC. I discuss some aspects of this subject and give a few examples.
I give a brief account of Gribov's scenario of supercritical charges in QCD. Gribov's equation for the Green function of light quarks and its derivation from the corresponding Dyson-Schwinger equation are described. The resulting Green function is shown to exhibit chiral symmetry breaking.
We perform a numerical study of various improvements of the LO BFKL prediction for the gamma^* gamma^* total cross section in the kinematical region of the L3 detector at LEP. In particular, we study the effects of a massive charm quark and of different photon polarizations. The variation of the BFKL prediction under changes of alpha_s is investigated.
Gribov's scenario of supercritical charges in QCD is investigated. We perform a numerical study of the corresponding equation for the Green function of light quarks. This is done in an approximation which neglects all pion contributions. Different types of solutions in the Euclidean region are discussed and the mass function of the quark is calculated. The solutions of the equation are shown to have a qualitatively different behaviour if the strong coupling constant alpha_s exceeds a critical value alpha_c = 0.43 in the infrared region. Chiral symmetry breaking is found to occur at supercritical coupling. The analytic structure of the solutions is investigated. Earlier results obtained by Gribov are confirmed and extended.
Hadron colliders can provide important tests of BFKL `small-x' dynamics. We discuss two examples of such tests, the inclusive dijet jet cross section at large rapidity separation and the number of associated `mini-jets' in Higgs boson production.
A new representation for the two-to-four gluon vertex arising in the context of unitarity corrections is derived which involves only BFKL kernels. We discuss possible implications of this representation, including the possibility of finding the NLO corrections to the vertex.
The high energy limit of QCD is investigated in the generalized leading logarithmic approximation. We study unitarity corrections to the BFKL Pomeron containing t-channel states with up to six gluons. Special attention is given to the field theory structure of the corresponding multi-gluon amplitudes. We discuss the transition from two to six gluons in the t-channel.
We derive closed expressions for the mean and variance of the (mini-)jet multiplicity distribution in hard scattering processes at low x. Here (mini-)jets are defined as those due to initial-state radiation of gluons with transverse momenta greater than some resolution scale m_R, where Lambda^2 << m_R^2 << Q^2, Lambda being the intrinsic QCD scale and Q the momentum transfer scale of the hard scattering. Our results are valid to leading order in log(1/x) but include all sub-leading logarithms of Q^2/m_R^2. As an illustration, we predict the mini-jet multiplicity in Higgs boson production at the Large Hadron Collider.
I explain the motivation for investigating the high energy limit of QCD and give a brief presentation of recent progress in the understanding of unitarity corrections in this kinematic regime. Special emphasis is given to the conformal field theory structure discovered in these unitarity corrections.
We present predictions of jet rates in deep inelastic scattering at small x to leading-logarithmic order in x, including all sub-leading logarithms of Q^2/m_R^2 where m_R is the transverse momentum scale at which jets are resolved. We give explicit results for up to three jets, and a perturbative expansion for multi-jet rates and jet multiplicities.