Polarized Deep Inelastic Scattering Off the "Neutron" From Gauge/String Duality

We investigate deep inelastic scattering off the polarized "neutron" using gauge/string duality. The "neutron" corresponds to a supergravity mode of the neutral dilatino. Through introducing the Pauli interaction term into the action in $\textrm{AdS}_{5}$ space, we calculate the polarized deep inelastic structure functions of the "neutron" in supergravity approximation at large t' Hooft coupling $\lambda$ and finite $x$ with $\lambda^{-1/2}\ll x<1$. In comparison with the charged dilatino "proton," which has been obtained in the previous work by Gao and Xiao, we find the structure functions of the "neutron" are power suppressed at the same order as the ones of the "proton." Especially, we find the Burkhardt-Cottingham-like sum rule, which is satisfied in the work by Gao and Xiao, is broken due to the Pauli interaction term. We also illustrate how such a Pauli interaction term can arise naturally from higher dimensional fermion-graviton coupling through the usual Kaluza-Klein reduction.Comment: 21pages,5figures, published versio

Dilepton distributions at backward rapidities

The dilepton production at backward rapidities in $pAu$ and $pp$ collisions at RHIC and LHC energies is investigated in the dipole approach. The results are shown through the nuclear modification ratio $R_{pA}$ considering transverse momentum and rapidity spectra. The dilepton modification ratio presents interesting behavior at the backward rapidities when compared with the already known forward ones, since it is related with the large $x$ kinematical region that is being probed. The rapidity dependence of the nuclear modification ratio in the dilepton production is strongly dependent on the Bjorken $x$ behavior of the nuclear structure function ratio $R_{F_{2}}=F_{2}^{A}/F_{2}^{p}$. The $R_{pA}$ transverse momentum dependence at backward rapidities is modified due to the large $x$ nuclear effects: at RHIC energies, for instance, the ratio $R_{pA}$ is reduced as $p_T$ increases, presenting an opposite behavior when compared with the forward one. It implies that the dilepton production at backward rapidities should carry information of the nuclear effects at large Bjorken $x$, as well as that it is useful to investigate the $p_T$ dependence of the observables in this kinematical regime.Comment: 15 pages, 6 figures. Version published in the Phys. Rev.

Investigating the high energy QCD approaches for prompt photon production at the LHC

We investigate the rapidity and transverse momentum distributions of the prompt photon production at the CERN LHC energies considering the current perturbative QCD approaches for this scattering process. Namely, we compare the predictions from the usual NLO pQCD calculations to the the color dipole formalism, using distinct dipole cross sections. Special attention is paid to parton saturation models at high energies, which are expected to be important at the forward rapidities in pp collisions at the LHC.Comment: Contribution to the proceedings of the 3rd International Conference on Hard and Electro-Magnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2008), 8-14 June 2008, Illa da Toxa (Galicia-Spain). Talk presented by M.V.T. Machad

γ∗p\gamma^*p cross section from the dipole model in momentum space

We reproduce the DIS measurements of the proton structure function at high energy from the dipole model in momentum space. To model the dipole-proton forward scattering amplitude, we use the knowledge of asymptotic solutions of the Balitsky-Kovchegov equation, describing high-energy QCD in the presence of saturation effects. We compare our results with the previous analysis in coordinate space and discuss possible extensions of our approach.Comment: 9 pages, 3 figure

Dilepton low pTp_T suppression as an evidence of the Color Glass Condensate

The dilepton production is investigated in proton-nucleus collisions in the forward region using the Color Glass Condensate approach. The transverse momentum distribution ($p_T$), more precisely the low $p_T$ region, where the saturation effects are expected to increase, is analyzed. The ratio between proton-nucleus and proton-proton differential cross section for RHIC and LHC energies is evaluated, showing the effects of saturation at small $p_T$, and presenting a Cronin type peak at moderate $p_T$. These features indicate the dilepton as a most suitable probe to study the properties of the saturated regime and the Cronin effect.Comment: 10 pages, 8 figures, replaced with the version to appear in Physical Review

Non-linear QCD dynamics in two-photon interactions at high energies

Perturbative QCD predicts that the growth of the gluon density at high energies should saturate, forming a Color Glass Condensate (CGC), which is described in mean field approximation by the Balitsky-Kovchegov (BK) equation. In this paper we study the $\gamma \gamma$ interactions at high energies and estimate the main observables which will be probed at future linear colliders using the color dipole picture. We discuss in detail the dipole - dipole cross section and propose a new relation between this quantity and the dipole scattering amplitude. The total $\gamma \gamma$, $\gamma^{*} \gamma^{*}$ cross-sections and the real photon structure function $F_2^{\gamma}(x,Q^2)$ are calculated using the recent solution of the BK equation with running coupling constant and the predictions are compared with those obtained using phenomenological models for the dipole-dipole cross section and scattering amplitude. We demonstrate that these models are able to describe the LEP data at high energies, but predict a very different behavior for the observables at higher energies. Therefore we conclude that the study of $\gamma \gamma$ interactions can be useful to constrain the QCD dynamics.Comment: 11 pages, 5 figures. Version to be published in European Physical Journal

Proposição de níveis críticos de nutrientes através da metodologia CND em folhas de pessegueiros.

O estudo objetivou estabelecer os NC e FS de nutrientes em folhas de pessegueiro, através do CND

Non-linear QCD dynamics and exclusive production in epep collisions

The exclusive processes in electron-proton ($ep$) interactions are an important tool to investigate the QCD dynamics at high energies as they are in general driven by the gluon content of proton which is strongly subject to parton saturation effects. In this paper we compute the cross sections for the exclusive vector meson production as well as the deeply virtual Compton scattering (DVCS) relying on the color dipole approach and considering the numerical solution of the Balitsky-Kovchegov equation including running coupling corrections. We show that the small-$x$ evolution given by this evolution equation is able to describe the DESY-HERA data and is relevant for the physics of the exclusive observables in future electron-proton colliders and in photoproduction processes to be measured in coherent interactions at the LHC.Comment: 6 pages, 4 figure