4,987 research outputs found
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
One-dimensional classical adjoint SU(2) Coulomb Gas
The equation of state of a one-dimensional classical nonrelativistic Coulomb
gas of particles in the adjoint representation of SU(2) is given. The problem
is solved both with and without sources in the fundamental representation at
either end of the system. The gas exhibits confining properties at low
densities and temperatures and deconfinement in the limit of high densities and
temperatures. However, there is no phase transition to a regime where the
string tension vanishes identically; true deconfinement only happens for
infinite densities and temperatures. In the low density, low temperature limit,
a new type of collective behavior is observed.Comment: 6 pages, 1 postscript figur
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
Nucleon electromagnetic form factors from lattice QCD using a nearly physical pion mass
We present lattice QCD calculations of nucleon electromagnetic form factors
using pion masses = 149, 202, and 254 MeV and an action with
clover-improved Wilson quarks coupled to smeared gauge fields, as used by the
Budapest-Marseille-Wuppertal collaboration. Particular attention is given to
removal of the effects of excited state contamination by calculation at three
source-sink separations and use of the summation and generalized
pencil-of-function methods. The combination of calculation at the nearly
physical mass = 149 MeV in a large spatial volume ( = 4.2)
and removal of excited state effects yields agreement with experiment for the
electric and magnetic form factors and up to = 0.5
GeV.Comment: v2: published version; 30 pages, 25 figures, 6 table
Signals of confinement in Green functions of SU(2) Yang-Mills theory
The vortex picture of confinement is employed to explore the signals of
confinement in Yang-Mills Green functions. By using SU(2) lattice gauge theory,
it has been well established that the removal of the center vortices from the
lattice configurations results in the loss of confinement. The running coupling
constant, the gluon and the ghost form factors are studied in Landau gauge for
both cases, the full and the vortex removed theory. In the latter case, a
strong suppression of the running coupling constant and the gluon form factor
at low momenta is observed. At the same time, the singularity of the ghost form
factor at vanishing momentum disappears. This observation establishes an
intimate correlation between the ghost singularity and confinement. The result
also shows that a removal of the vortices generates a theory for which
Zwanziger's horizon condition for confinement is no longer satisfied.Comment: 4 pages, 4 figure
The function of postconflict interactions: new prospects from the study of a tolerant species of primate
Aggression can generate anxiety, create uncertainty about its aftermath and jeopardise social relationships. Postconflict interactions serve as conflict management strategies to mitigate these consequences. Whereas postconflict interactions are well characterized in many animals, their functions are still insufficiently investigated. Four functional hypotheses have been proposed: stress reduction, relationship repair, self-protection and benign intent. We aimed to test these hypotheses in females of a tolerant macaque species, the crested macaque, Macaca nigra, under natural conditions, for three postconflict interactions: reconciliation, affiliation and aggression with third parties. Our results provide meaningful contrasts compared with findings in other species. We found no evidence that aggression had consequences for individuals' behavioural indicators of anxiety, although it increased the likelihood of secondary aggression with third parties. There was little evidence for the stress reduction hypothesis as the occurrence of any of the three postconflict interactions investigated had little effect on the measured behavioural indicators of anxiety. Conflict and dyad characteristics also had limited influence on anxiety. The relationship repair function was only partly validated: dyads with stronger bonds or that exchanged more support did not reconcile more often, but dyads with attributes related to the symmetry, stability and predictability (i.e. security) within relationships did. Patterns of initiation and directionality of postconflict interactions in this study population suggest that reconciliation may constitute the signalling of appeasement and benign intent. Furthermore, we found that aggression towards third parties may serve as a source of self-protection and reassertion of the females' social status. The distinctive pattern of postconflict management strategies revealed in wild female crested macaques appears to be related to their typically tolerant social style. These results demonstrate the usefulness of concomitantly studying aggression, postconflict interactions and their functions, to understand conflict management strategies comprehensively, while taking into account the level of social tolerance characterizing the studied society
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
Mesonic Spectra of Bosonized QCD_2 Models
We discuss bosonized two-dimensional QCD with massless fermions in the
adjoint and multi-flavor fundamental representations. We evaluate the massive
mesonic spectra of several models by using the light-front quantization and
diagonalizing the mass operator . We recover previous results in
the case of one flavor adjoint fermions and we find the exact massive spectrum
of multi flavor QCD in the limit of large number of flavors.Comment: 17 pages, Late
Topological Susceptibility of Yang-Mills Center Projection Vortices
The topological susceptibility induced by center projection vortices
extracted from SU(2) lattice Yang-Mills configurations via the maximal center
gauge is measured. Two different smoothing procedures, designed to eliminate
spurious ultraviolet fluctuations of these vortices before evaluating the
topological charge, are explored. They result in consistent estimates of the
topological susceptibility carried by the physical thick vortices
characterizing the Yang-Mills vacuum in the vortex picture. This susceptibility
is comparable to the one obtained from the full lattice Yang-Mills
configurations. The topological properties of the SU(2) Yang-Mills vacuum can
thus be accounted for in terms of its vortex content.Comment: 12 revtex pages, 6 ps figures included using eps
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