651 research outputs found
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
Exploring quark transverse momentum distributions with lattice QCD
We discuss in detail a method to study transverse momentum dependent parton
distribution functions (TMDs) using lattice QCD. To develop the formalism and
to obtain first numerical results, we directly implement a bi-local quark-quark
operator connected by a straight Wilson line, allowing us to study T-even,
"process-independent" TMDs. Beyond results for x-integrated TMDs and quark
densities, we present a study of correlations in x and transverse momentum. Our
calculations are based on domain wall valence quark propagators by the LHP
collaboration calculated on top of gauge configurations provided by MILC with
2+1 flavors of asqtad-improved staggered sea quarks.Comment: 36 pages, 24 figures; revised version of May 2011, one appendix adde
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
Quark Contributions to Nucleon Momentum and Spin from Domain Wall fermion calculations
We report contributions to the nucleon spin and momentum from light quarks
calculated using dynamical domain wall fermions with pion masses down to 300
MeV and fine lattice spacing a=0.084 fm. Albeit without disconnected diagrams,
we observe that spin and orbital angular momenta of both u and d quarks are
opposite, almost canceling in the case of the d quark, which agrees with
previous calculations using a mixed quark action. We also present the full
momentum dependence of n=2 generalized form factors showing little variation
with the pion mass.Comment: 7 pages, 5 figures, NT-LBNL-11-020, MIT-CTP-4323. Presented at the
29th International Symposium on Lattice Field Theory (Lattice 2011), Squaw
Valley, California, 10-16 Jul 201
Angiotensin II directly regulates intestinal epithelial NHE3 in Caco2BBE cells
<p>Abstract</p> <p>Background</p> <p>Angiotensin II (AII) effects on intestinal Na<sup>+ </sup>transport may be multifactorial. To determine if AII might have a direct effect on intestinal epithelial Na<sup>+ </sup>transport, we investigated its actions on Na<sup>+ </sup>transport in human intestinal epithelial Caco2BBE cells.</p> <p>Results</p> <p>AII increased apical (brush border) sodium-hydrogen exchanger (NHE)-3, but not NHE2, activity within one hour. Similarly, only apical membrane NHE3 abundance increased at 1â2 hours without any change in total NHE3 protein abundance. From 4â48 hours, AII stimulated progressively larger increases in apical NHE3 activity and surface abundance, which was associated with increases in NHE3 protein expression. At 4â24 hours, NHE3 mRNA increases over baseline expression, suggesting increased gene transcription. This was supported by AII induced increases in rat NHE3 gene promoter-reporter activity. AII induction of NHE3 was blocked by the AII type I receptor antagonist losartan. Acute changes in AII-induced increases in NHE3 exocytosis were blocked by a phospholipase C inhibitor, an arachidonic acid cytochrome P450 epoxygenase inhibitor, as well as phosphatidylinositol 3 kinase (PI3K) inhibitors and Akt inhibitor, partially blocked by a metalloproteinase inhibitor and an EGF (epidermal growth factor) receptor kinase inhibitor, but not affected by an inhibitor of MEK-1 (MAPKK-1, mitogen activated protein kinase kinase-1).</p> <p>Conclusion</p> <p>We conclude that angiotensin II has a direct role in regulating intestinal fluid and electrolyte absorption which may contribute to its overall effects in regulation systemic volume and blood pressure. AII activates several key signaling pathways that induce acute and chronic changes in NHE3 membrane trafficking and gene transcription.</p
Transverse momentum distributions inside the nucleon from lattice QCD
We study transverse momentum dependent parton distribution functions (TMDs) with
non-local operators in lattice QCD, using MILC/LHPC lattices. Results obtained with a simplified
operator geometry show visible dipole deformations of spin-dependent quark momentum densities.United States. Dept. of Energy (grant DE-FG02-94ER40818
Transverse momentum dependent quark densities from Lattice QCD
We study transverse momentum dependent parton distribution functions (TMDs) with nonâlocal operators in lattice QCD, using MILCâLHPC lattices. We discuss the basic concepts of the method, including renormalization of the gauge link. Results obtained with a simplified operator geometry show visible dipole deformations of spinâdependent quark momentum densities.United States. Dept. of Energy (grant DEFG02- 94ER40818
Lattice QCD Studies of Transverse Momentum-Dependent Parton Distribution Functions
Transverse momentum-dependent parton distributions (TMDs) relevant for semi-inclusive deep inelastic scattering and the DrellâYan process can be defined in terms of matrix elements of a quark bilocal operator containing a staple-shaped gauge link. Such a definition opens the possibility of evaluating TMDs within lattice QCD. 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. Results for selected TMD observables are presented, including a particular focus on their dependence on a CollinsâSoper-type evolution parameter, which quantifies proximity of the staple-shaped gauge links to the light cone.United States. Dept. of Energy. Office of Nuclear Physics (Grants DE-SC0011090 and DE-AC05-06OR23177
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