Browsing by Subject "QCD"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Gluon propagator in classical color field of colliding hadrons and its implications for hadronic cross sections(2011-08) Cheung, Man-Fung; Chiu, Charles; Dicus, Duane; Gonzalez, Oscar; Markert, Christina; Sudarshan, E. C. GeorgeWe review the Regge theory and the minijet model for pp and pp collisions. We show that, in the conventional minijet approach, the asymptotic behavior of the total cross section calculated using currently accepted gluon distribution function and perturbative QCD rises too rapidly when compared with the data and fails to satisfy Froissart bound. To tame the rise, we have developed a new formalism for the interaction between QCD gluon and the classical color field of the colliding nucleons, and show how the gluon propagator is modified. The corresponding gauge invariance condition of the propagator is derived and shown to be satisfied. The modified gluon propagator leads to a suppression of the minijet cross section due to the gg [rightwards arrow] gg sub-process in the small-x region. We show that the pp and pp total cross section from [square root]s = 5 GeV to 30 TeV can be described as a sum of a hard component contributed by the classical field modified minijet model and a soft component due to the exchange of the Pomeron and the I=0 exchange-degenerate [omega] and f Regge trajectories. The soft-component model is motivated by the notion of duality. The predicted total cross section has a ln s asymptotic behavior.Item Phase transitions in holographic QCD and instanton crystals(2014-08) Alam, Muhammad Sohaib; Kaplunovsky, VadimWe investigate phase transitions in holographic models of QCD. In chapter I, we explore the effect of constant external U(1) fields on the physics of chiral symmetry breaking, as realized in the D3/D7 model. We discover that this model exhibits the phenomenon of magnetic catalysis, which is what one would expect from a weakly coupled field theory intuition. In chapter II, we continue exploring the effect of external U(1) fields but now on the backreacted D3/D7 model, where the backreaction is obtained via a smearing procedure. We again find the magnetic catalysis effect, however the results differ from the previous case depending on the backreaction parameters. In chapter III, we investigate lattices of instantons in the D4/D8 model of chiral symmetry breaking. These instanton lattices can change dimensionality, and in particular we investigate the 1D [right arrow] 2D transition as a simpler case of the more complicated 3D [right arrow] 4D transition which is conjectured to be holographically dual to the baryonic to quarkyonic phase transition. Besides this interpretation, one could also view this as a hypothetical condensed matter system. We have a lattice of instantons dominated by two-body forces, whose interactions depend not only on their mutual distance in physical space but also on their relative orientations in the internal isospace. We obtain a rich variety of instanton crystals whose description could serve to be useful beyond holography.Item Traveling waves and impact parameter correlations in QCD beyond the 1D approximation(2011-08) Haley, Matthew Troy; Chiu, Charles; Dicus, Duane; Gonzales, Oscar; Markert, Christina; Sudarshan, E. C. GeorgeThe theory of quantum chromodynamics (QCD) predicts that at high energies, such as those investigated in deep inelastic scattering experiments, hadrons evolve into dense gluonic states described by the BFKL equation, and at very high densities, the more general BK equation. In certain approximations, the BK equation reduces to a well studied reaction-diffusion type nonlinear partial differential equation, the FKPP equation, for which analytical results are known. In this work, we model the BK equation using a classical branching process rooted in the dipole model of QCD evolution. Because the BK equation is inherently two dimensional, our model allows dipole impact parameters to occupy the full transverse space. A one dimensional limit of this model is studied as well. Results are compared with the predictions of the FKPP equation, and correlations between evolution at different impact parameters are presented. The general features of previously studied one dimensional impact parameter models are verified, but the details are refined in what we believe to be a more accurate model.