Generalized parton distributions and transversity from full lattice QCD

We present here the latest results from the QCDSF collaboration for moments of generalized parton distributions and transversity in two-flavour QCD, including a preliminary analysis of the pion mass dependence.Comment: Talks presented by Ph.Hagler and J.Zanotti at BARYONS 2004, Paris, Oct. 25-29, 2004, 8 pages, 5 figure

Quark helicity flip generalized parton distributions from two-flavor lattice QCD

We present an initiatory study of quark helicity flip generalized parton distributions (GPDs) in n_f=2 lattice QCD, based on clover-improved Wilson fermions for a large number of coupling constants and pion masses. Quark helicity flip GPDs yield essential information on the transverse spin structure of the nucleon. In this work, we show first results on their lowest moments and dipole masses and study the corresponding chiral and continuum extrapolations.Comment: 15 pages, 6 figure

Generalized parton distributions and structure functions from full lattice QCD

We present here the latest results from the QCDSF collaboration for (moments of) structure functions and generalized form factors in full QCD with Nf=2 O(a)-improved Wilson fermions based on simulations closer to the chiral and continuum limit.Comment: Talks presented by D.Pleiter and J.Zanotti at Lattice2004(weak), Fermilab, June 21-26, 2004, 6 pages, 9 figure

Surface critical exponents at a uniaxial Lifshitz point

Using Monte Carlo techniques, the surface critical behaviour of three-dimensional semi-infinite ANNNI models with different surface orientations with respect to the axis of competing interactions is investigated. Special attention is thereby paid to the surface criticality at the bulk uniaxial Lifshitz point encountered in this model. The presented Monte Carlo results show that the mean-field description of semi-infinite ANNNI models is qualitatively correct. Lifshitz point surface critical exponents at the ordinary transition are found to depend on the surface orientation. At the special transition point, however, no clear dependency of the critical exponents on the surface orientation is revealed. The values of the surface critical exponents presented in this study are the first estimates available beyond mean-field theory.Comment: 10 pages, 7 figures include

Density functional study of the adsorption of K on the Ag(111) surface

Full-potential gradient corrected density functional calculations of the adsorption of potassium on the Ag(111) surface have been performed. The considered structures are Ag(111) (root 3 x root 3) R30degree-K and Ag(111) (2 x 2)-K. For the lower coverage, fcc, hcp and bridge site; and for the higher coverage all considered sites are practically degenerate. Substrate rumpling is most important for the top adsorption site. The bond length is found to be nearly identical for the two coverages, in agreement with recent experiments. Results from Mulliken populations, bond lengths, core level shifts and work functions consistently indicate a small charge transfer from the potassium atom to the substrate, which is slightly larger for the lower coverage.Comment: to appear in Phys Rev

Efimov physics from the functional renormalization group

Few-body physics related to the Efimov effect is discussed using the functional renormalization group method. After a short review of renormalization in its modern formulation we apply this formalism to the description of scattering and bound states in few-body systems of identical bosons and distinguishable fermions with two and three components. The Efimov effect leads to a limit cycle in the renormalization group flow. Recently measured three-body loss rates in an ultracold Fermi gas $^6$Li atoms are explained within this framework. We also discuss briefly the relation to the many-body physics of the BCS-BEC crossover for two-component fermions and the formation of a trion phase for the case of three species.Comment: 28 pages, 13 figures, invited contribution to a special issue of "Few-Body Systems" devoted to Efimov physics, published versio

Increased intensity of treatment and decreased mortality in elderly patients in an intensive care unit over a decade

Objectives: Data collected from two cohorts of patients aged ≥80 yrs and admitted to an intensive care unit in France were compared to determine whether intensive care unit care and survival had evolved from the 1990s to the 2000s.Design: Retrospective cohort study on patient data attained during intensive care unit stays. Setting: 18-bed intensive care unit in an academic medical center. Patients: Two cohorts of patients aged ≥80 yrs, admitted to an intensive care unit at a 10-yr interval. Interventions: None. Measurements and Main Results: The first cohort comprised 348 patients admitted between January 1992 and December 1995, and the second cohort, 373 patients admitted between January 2001 and December 2004. There was no difference in age between the two cohorts, but patients in the second had significantly less history of functional limitation and significantly more acute illness (Simplified Acute Physiology Score II 43 ± 18 vs. 57 ± 25, respectively, p < .0001). Patients in the second cohort had a significantly higher Omega Score, had a higher occurrence of renal replacement therapy, and received vasopressors more frequently than the patients in the first cohort, even when adjusted for age, sex, Knaus classification, Simplified Acute Physiology Score II, and intensive care unit admission cause. Intensive care unit mortality was 65% and 64% for the first and second cohorts, respectively. In multivariate analysis (including age, Knaus classification, Simplified Acute Physiology Score II and first vs. second period) for association with intensive care unit survival, the 2001–2004 period was associated with a near tripling of chances of survival (odds ratio 2.9; 95% confidence interval, 1.92–4.47, p < .0001). Conclusions: The characteristics and intensity of treatment for elderly people admitted to the intensive care unit changed significantly over a decade. The intensity of treatments has increased over time and survival has improved over time as well. A potential link between increased treatment and improved survival in the elderly may be evoked

Second moment of the pion's distribution amplitude

We present preliminary results from the QCDSF/UKQCD collaborations for the second moment of the pion's distribution amplitude with two flavours of dynamical fermions. We use nonperturbatively determined renormalisation coefficients to convert our results to the MSbar scheme at 5 GeV^2. Employing a linear chiral extrapolation from our large pion masses >550 MeV, we find =0.281(28), leading to a value of a_2=0.236(82) for the second Gegenbauer moment.Comment: 6 pages, 5 figures, 1 table. To appear in: Procs. of the Workshop on Light-Cone QCD and Nonperturbative Hadron Physics 2005 (LC 2005), Cairns, Australia, 200

Sum rules and dualities for generalized parton distributions: is there a holographic principle?

To leading order approximation, the physical content of generalized parton distributions (GPDs) that is accessible in deep virtual electroproduction of photons or mesons is contained in their value on the cross-over trajectory. This trajectory separates the t-channel and s-channel dominated GPD regions. The underlying Lorentz covariance implies correspondence between these two regions through their relation to GPDs on the cross-over trajectory. This point of view leads to a family of GPD sum rules which are a quark analogue of finite energy sum rules and it guides us to a new phenomenological GPD concept. As an example, we discuss the constraints from the JLab/Hall A data on the dominant u-quark GPD H. The question arises whether GPDs are governed by some kind of holographic principle.Comment: 45 pages, 4 figures, Sect. 2 reorganized for clarity. Typos in Eq. (20) corrected. 4 new refs. Matches published versio

Generalized Parton Distributions from Hadronic Observables: Non-Zero Skewness

We propose a physically motivated parametrization for the unpolarized generalized parton distributions, H and E, valid at both zero and non-zero values of the skewness variable, \zeta. Our approach follows a previous detailed study of the \zeta=0 case where H and E were determined using constraints from simultaneous fits of the experimental data on both the nucleon elastic form factors and the deep inelastic structure functions in the non singlet sector. Additional constraints at \zeta \neq 0 are provided by lattice calculations of the higher moments of generalized parton distributions. We illustrate a method for extracting generalized parton distributions from lattice moments based on a reconstruction using sets of orthogonal polynomials. The inclusion in our fit of data on Deeply Virtual Compton Scattering is also discussed. Our method provides a step towards a model independent extraction of generalized distributions from the data. It also provides an alternative to double distributions based phenomenological models in that we are able to satisfy the polynomiality condition by construction, using a combination of experimental data and lattice, without resorting to any specific mathematical construct.Comment: 29 pages, 8 figures; added references, changed text in several place