Nonuniversality Aspects of Nonlinear k_\perp-factorization for Hard Dijets

The origin of the breaking of conventional linear k_\perp-factorization for hard processes in a nuclear environment is by now well established. The realization of the nonlinear nuclear k_\perp-factorization which emerges instead was found to change from one jet observable to another. Here we demonstrate how the pattern of nonlinear k_\perp-factorization, and especially the role of diffractive interactions, in the production of dijets off nuclei depends on the color properties of the underlying pQCD subprocess.Comment: 4 pages, 1 eps-fi

The connection between single transverse spin asymmetries and the second moment of g2g_2

We point out that the size of the photon single spin asymmetry in high--energy proton proton collisions with one transversely polarized proton can be related to $d^{(2)}$, the twist three contribution to the second moment of $g_2$. Both quantities should be measured in the near future. The first was analysed by Qiu and Sterman, the second was estimated by Balitsky, Braun, and Kolesnichenko. Both experiments measure effectively the strength of the collective gluon field in the nucleon oriented relative to the nucleon spin. The sum rule results suggest that the single spin asymmetry is rather small for the proton, but could be substantial for the neutron.Comment: 6 pages, UFTP preprint 348/199

On Advanced Mobility Concepts for Intelligent Planetary Surface Exploration

Surface exploration by wheeled rovers on Earth's Moon (the two Lunokhods) and Mars (Nasa's Sojourner and the two MERs) have been followed since many years already very suc-cessfully, specifically concerning operations over long time. However, despite of this success, the explored surface area was very small, having in mind a total driving distance of about 8 km (Spirit) and 21 km (Opportunity) over 6 years of operation. Moreover, ESA will send its ExoMars rover in 2018 to Mars, and NASA its MSL rover probably this year. However, all these rovers are lacking sufficient on-board intelligence in order to overcome longer dis-tances, driving much faster and deciding autonomously on path planning for the best trajec-tory to follow. In order to increase the scientific output of a rover mission it seems very nec-essary to explore much larger surface areas reliably in much less time. This is the main driver for a robotics institute to combine mechatronics functionalities to develop an intelligent mo-bile wheeled rover with four or six wheels, and having specific kinematics and locomotion suspension depending on the operational terrain of the rover to operate. DLR's Robotics and Mechatronics Center has a long tradition in developing advanced components in the field of light-weight motion actuation, intelligent and soft manipulation and skilled hands and tools, perception and cognition, and in increasing the autonomy of any kind of mechatronic systems. The whole design is supported and is based upon detailed modeling, optimization, and simula-tion tasks. We have developed efficient software tools to simulate the rover driveability per-formance on various terrain characteristics such as soft sandy and hard rocky terrains as well as on inclined planes, where wheel and grouser geometry plays a dominant role. Moreover, rover optimization is performed to support the best engineering intuitions, that will optimize structural and geometric parameters, compare various kinematics suspension concepts, and make use of realistic cost functions like mass and consumed energy minimization, static sta-bility, and more. For self-localization and safe navigation through unknown terrain we make use of fast 3D stereo algorithms that were successfully used e.g. in unmanned air vehicle ap-plications and on terrestrial mobile systems. The advanced rover design approach is applica-ble for lunar as well as Martian surface exploration purposes. A first mobility concept ap-proach for a lunar vehicle will be presented

Intrinsic quark transverse momentum in the nucleon from lattice QCD

A better understanding of transverse momentum (k_T-) dependent quark distributions in a hadron is needed to interpret several experimentally observed large angular asymmetries and to clarify the fundamental role of gauge links in non-abelian gauge theories. Based on manifestly non-local gauge invariant quark operators we introduce process-independent k_T-distributions and study their properties in lattice QCD. We find that the longitudinal and transverse momentum dependence approximately factorizes, in contrast to the behavior of generalized parton distributions. The resulting quark k_T-probability densities for the nucleon show characteristic dipole deformations due to correlations between intrinsic k_T and the quark or nucleon spin. Our lattice calculations are based on N_f=2+1 mixed action propagators of the LHP collaboration.Comment: 4 pages, 3 figure

Lattice QCD study of the Boer-Mulders effect in a pion

The three-dimensional momenta of quarks inside a hadron are encoded in transverse momentum-dependent parton distribution functions (TMDs). This work presents an exploratory lattice QCD study of a TMD observable in the pion describing the Boer-Mulders effect, which is related to polarized quark transverse momentum in an unpolarized hadron. Particular emphasis is placed on the behavior as a function of a Collins-Soper evolution parameter quantifying the relative rapidity of the struck quark and the initial hadron, e.g., in a semi-inclusive deep inelastic scattering (SIDIS) process. The lattice calculation, performed at the pion mass m_pi = 518 MeV, utilizes a definition of TMDs via hadronic matrix elements of a quark bilocal operator with a staple-shaped gauge connection; in this context, the evolution parameter is related to the staple direction. By parametrizing the aforementioned matrix elements in terms of invariant amplitudes, the problem can be cast in a Lorentz frame suited for the lattice calculation. In contrast to an earlier nucleon study, due to the lower mass of the pion, the calculated data enable quantitative statements about the physically interesting limit of large relative rapidity. In passing, the similarity between the Boer-Mulders effects extracted in the pion and the nucleon is noted.Comment: 16 pages, 9 figures, 3 table

Meson Supercurrent State in High Density QCD

We study the effect of a non-zero strange quark mass on the color-flavor-locked (CFL) phase of high density quark matter. We have previously shown that for a strange quark mass $m_s\sim m_u^{1/3}\Delta^{2/3}$ the CFL state becomes unstable toward the formation of a neutral kaon condensate. Recently, several authors discovered that for $m_s\sim (2\Delta p_F)^{1/2}$ the CFL state contains gapless fermions, and that the gapless modes lead to an instability in current-current correlation functions. Using an effective theory of the CFL state we demonstrate that this instability is resolved by the formation of an inhomogeneous meson condensate, analogous to Migdal's p-wave pion condensate. This state has a non-zero meson current which is canceled by a backflow of gapless fermions.Comment: 4 pages, one figure, revised version, to appear in PRL (title changed in journal