1,524 research outputs found
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
On the spectrum of QCD(1+1) with large numbers of flavours N_F and colours N_C near N_F/N_C = 0
QCD(1+1) in the limit of a large number of flavours N_F and a large number of
colours N_C is examined in the small N_F/N_C regime. Using perturbation theory
in N_F/N_C, stringent results for the leading behaviour of the spectrum
departing from N_F/N_C = 0 are obtained. These results provide benchmarks in
the light of which previous truncated treatments of QCD(1+1) at large N_F and
N_C are critically reconsidered.Comment: 6 revtex page
Review of the Crown-of-thorns Starfish Research Committee (COTSREC) Program
In December 1988, following criticism in the media of the Great Barrier Reef Marine Park Authority's
handling of the crown-of-thorns starfish (COTS) issue, the then Minister for the Arts, Sport, the
Environment, Tourism and Territories, Senator the Honourable Graham Richardson, requested a
review of the Authority's crown-of-thorns starfish research program and policies. The research
program had been recommended to the Authority by the Crown-of-thorns Starfish Advisory
Committee (COTSAC), a body of experts convened by the Authority in 1984 for this purpose.
Funding of $3 million over four years for the program (1985-86 to 1988-89) was provided by the
Federal Government. The program was reviewed annually by another advisory body established by the
Authority, the Crown-of-thorns Starfish Advisory Review Committee (COTSARC). Zann and Moran
(1988), Moran and Johnson (1990) and Lassig (1991) have summarised the structure and results of
this program
From the Western Alps across Central Europe: Postglacial recolonisation of the tufa stream specialist Rhyacophila pubescens (Insecta, Trichoptera)
Background: Dispersal rates, i.e. the effective number of dispersing individuals per unit time, are the product of dispersal capacity, i.e. a species physiological potential for dispersal, dispersal behaviour, i.e. the decision to leave a habitat patch in favour of another, and connectivity of occupied habitat. Dispersal of species that are highly specialised to a certain habitat is thus strongly limited by habitat availability. Additionally, species inhabiting very stable environments may adopt a sedentary life-style. Both factors should lead to strong genetic differentiation in highly specialised species inhabiting stable environments. These two factors apply to our model species Rhyacophila pubescens a highly specialised freshwater insect that occurs in tufa springs, a very stable habitat. Results: We examined the genetic population structure and phylogeography using range-wide mtCOI sequence and AFLP data from 333 individuals of R. pubescens. We inferred the location of Pleistocene refugia and postglacial colonisation routes of R. pubescens, and examined ongoing local differentiation. Our results indicate intraregional differentiation with a high number of locally endemic haplotypes, that we attributed to habitat specificity and low dispersal rates of R. pubescens. We observed high levels of genetic diversity south of the Alps and genetic impoverishment north of the Alps. Estimates of migrants placed the refugium and the source of the colonisation in the Dauphine Alps (SW Alps). Conclusions: This is the first example of an aquatic insect with a colonisation route along the western margin of the Alps to the Central European highlands. The study also shows that specialisation to a stable environment may have promoted a behavioural shift to decreased dispersal rates, leading to stronger local population differentiation than in less specialised aquatic insects. Alternatively, the occurrence of highly specialised tufa spring habitats may have been more widespread in the past, leading to range regression and fragmentation among present day R. pubescens populations
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 spectrum of multi-flavor QCD_2 and the non-Abelian Schwinger equation
Massless is dominated by classical configurations in the large
limit. We use this observation to study the theory by finding solutions to
equations of motion, which are the non-Abelian generalization of the Schwinger
equation. We find that the spectrum consists of massive mesons with which correspond to Abelian solutions. We generalize previously
discovered non-Abelian solutions and discuss their interpretation. We prove a
no-go theorem ruling out the existence of soliton solutions. Thus the
semi-classical approximation shows no baryons in the case of massless quarks, a
result derived before in the strong-coupling limit only.Comment: 17 pages, Latex. 1 figur
On the Spectrum of QCD(1+1) with SU(N_c) Currents
Extending previous work, we calculate in this note the fermionic spectrum of
two-dimensional QCD (QCD_2) in the formulation with SU(N_c) currents. Together
with the results in the bosonic sector this allows to address the as yet
unresolved task of finding the single-particle states of this theory as a
function of the ratio of the numbers of flavors and colors, \lambda=N_f/N_c,
anew. We construct the Hamiltonian matrix in DLCQ formulation as an algebraic
function of the harmonic resolution K and the continuous parameter \lambda.
Amongst the more surprising findings in the fermionic sector chiefly considered
here is that the fermion momentum is a function of \lambda. This dependence is
necessary in order to reproduce the well-known 't Hooft and large N_f spectra.
Remarkably, those spectra have the same single-particle content as the ones in
the bosonic sectors. The twist here is the dramatically different sizes of the
Fock bases in the two sectors, which makes it possible to interpret in
principle all states of the discrete approach. The hope is that some of this
insight carries over into the continuum. We also present some new findings
concerning the single-particle spectrum of the adjoint theory.Comment: 21 pp., 13 figures, version published in PR
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