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

Ein Vater der kognitiven Psychologie: Adriaan Dingeman de Groot (1914–2006)/A father of cognitive psychology: Adriaan Dingeman de Groot (1914-2006)

Adriaan D. de Groot wurde am 26. Oktober 1914 in Santpoort (Holland) geboren. An der Universität Amsterdam studierte er Physik, Mathematik und Psychologie; daneben betrieb er seine große Leidenschaft, das Schachspiel, in dem er es zu Meisterehren brachte. In seiner bahnbrechenden Promotion (De Groot, 1946; engl. “Thought and Choice in Chess”, 1965) vereinte er sein Interesse am Schach und an der Psychologie und präsentierte eine detaillierte Analyse der Denkvorgänge beim Schachspiel, die einen Meilenstein der beginnenden kognitiven Revolution in der Psychologie setzte und schnell zum Klassiker wurde

Sivers and Boer-Mulders observables from lattice QCD

We present a first calculation of transverse momentum dependent nucleon observables in dynamical lattice QCD employing non-local operators with staple-shaped, "process-dependent" Wilson lines. The use of staple-shaped Wilson lines allows us to link lattice simulations to TMD effects determined from experiment, and in particular to access non-universal, naively time-reversal odd TMD observables. We present and discuss results for the generalized Sivers and Boer-Mulders transverse momentum shifts for the SIDIS and DY cases. The effect of staple-shaped Wilson lines on T-even observables is studied for the generalized tensor charge and a generalized transverse shift related to the worm gear function g_1T. We emphasize the dependence of these observables on the staple extent and the Collins-Soper evolution parameter. Our numerical calculations use an n_f = 2+1 mixed action scheme with domain wall valence fermions on an Asqtad sea and pion masses 369 MeV as well as 518 MeV.Comment: 25 pages, 13 figures; version accepted by journal. Contains additional section explaining and summarizing the methodolog