32 research outputs found
Model-independent calculation of violation in baryon octet light-cone distribution amplitudes
In this work we present a minimal parametrization of the light-cone
distribution amplitudes of the baryon octet including higher twist
contributions. Simultaneously we obtain the quark mass dependence of the
amplitudes at leading one-loop accuracy by the use of three-flavor baryon
chiral perturbation theory (BChPT), which automatically yields
model-independent results for the leading flavor breaking effects. For
that purpose we have constructed the nonlocal light-cone three-quark operators
in terms of baryon octet and meson fields and have carried out a
next-to-leading order BChPT calculation. We were able to find a minimal set of
distribution amplitudes (DAs) that do not mix under chiral extrapolation
towards the physical point and naturally embed the baryon.
Additionally they are chosen in such a way that all DAs of a certain symmetry
class have a similar quark mass dependence (independent of the twist of the
corresponding amplitude), which allows for a compact presentation. The results
are well-suited for the extrapolation of lattice data and for model building.Comment: We have updated the text to match the version published in JHE
Chiral perturbation theory for generalized parton distributions and baryon distribution amplitudes
In this thesis we apply low-energy effective field theory to the first moments of generalized parton distributions and to baryon distribution amplitudes, which are both highly relevant for the parametrization of the nonperturbative part in hard processes. These quantities yield complementary information on hadron structure, since the former treat hadrons as a whole and, thus, give information about the (angular) momentum carried by an entire parton species on average, while the latter parametrize the momentum distribution within an individual Fock state. By performing one-loop calculations within covariant baryon chiral perturbation theory, we obtain sensible parametrizations of the quark mass dependence that are ideally suited for the subsequent analysis of lattice QCD data
Pion and Kaon Distribution Amplitudes from lattice QCD: towards the continuum limit
We present the current status of a non-perturbative lattice calculation of
the moments of the pion and kaon distribution amplitudes by the RQCD
collaboration. Our investigation is carried out using dynamical,
non-perturbatively O(a)-improved Wilson fermions on the CLS ensembles with 5
different lattice spacings and pion masses down to the physical pion mass. A
combined continuum and chiral extrapolation to the physical point is performed
along two independent quark mass trajectories simultaneously. We employ
momentum smearing in order to decrease the contamination by excited states and
increase statistical precision.Comment: Proceedings of the 36th Annual International Symposium on Lattice
Field Theory - LATTICE201
Light-cone distribution amplitudes of the baryon octet
We present results of the first ab initio lattice QCD calculation of the
normalization constants and first moments of the leading twist distribution
amplitudes of the full baryon octet, corresponding to the small transverse
distance limit of the associated S-wave light-cone wave functions. The P-wave
(higher twist) normalization constants are evaluated as well. The calculation
is done using flavors of dynamical (clover) fermions on lattices of
different volumes and pion masses down to 222 MeV. Significant SU(3) flavor
symmetry violation effects in the shape of the distribution amplitudes are
observed.Comment: Update to the version published in JHE
Light-cone distribution amplitudes of octet baryons from lattice QCD
We present lattice QCD results for the wave function normalization constants
and the first moments of the distribution amplitudes for the lowest-lying
baryon octet. The analysis is based on a large number of ensembles
comprising multiple trajectories in the quark mass plane including physical
pion (and kaon) masses, large volumes, and, most importantly, five different
lattice spacings down to . This allows us to perform a
controlled extrapolation to the continuum and infinite volume limits by a
simultaneous fit to all available data. We demonstrate that the formerly
observed violation of flavor symmetry breaking constraints can, indeed, be
attributed to discretization effects that vanish in the continuum limit
Mellin moments of spin dependent and independent PDFs of the pion and rho meson
We compute the second moments of pion and rho parton distribution functions in lattice QCD with Nf=2+1 flavors of improved Wilson fermions. We determine both singlet and nonsinglet flavor combinations and, for the first time, take disconnected contributions fully into account. In the case of the rho, we also calculate the additional contribution arising from the b1 structure function. The numerical analysis includes 26 ensembles, mainly generated by the CLS effort, with pion masses ranging from 420 down to 214 MeV and with 5 different lattice spacings in the range of 0.1 to 0.05 fm. This enables us to take the continuum limit, as well as to resolve the quark mass dependencies reliably. Additionally we discuss the contaminations of rho correlation functions by two-pion states
An automated optimization pipeline for clinical-grade computer-assisted planning of high tibial osteotomies under consideration of weight-bearing
3D preoperative planning for high tibial osteotomies (HTO) has increasingly replaced 2D planning but is complex, time-consuming and therefore expensive. Several interdependent clinical objectives and constraints have to be considered, which often requires multiple rounds of revisions between surgeons and biomedical engineers. We therefore developed an automated preoperative planning pipeline, which takes imaging data as an input to generate a ready-to-use, patient-specific planning solution. Deep-learning based segmentation and landmark localization was used to enable the fully automated 3D lower limb deformity assessment. A 2D-3D registration algorithm allowed the transformation of the 3D bone models into the weight-bearing state. Finally, an optimization framework was implemented to generate ready-to use preoperative plannings in a fully automated fashion, using a genetic algorithm to solve the multi-objective optimization (MOO) problem based on several clinical requirements and constraints. The entire pipeline was evaluated on a large clinical dataset of 53 patient cases who previously underwent a medial opening-wedge HTO. The pipeline was used to automatically generate preoperative solutions for these patients. Five experts blindly compared the automatically generated solutions to the previously generated manual plannings. The overall mean rating for the algorithm-generated solutions was better than for the manual solutions. In 90% of all comparisons, they were considered to be equally good or better than the manual solution. The combined use of deep learning approaches, registration methods and MOO can reliably produce ready-to-use preoperative solutions that significantly reduce human workload and related health costs
Pion distribution amplitude from Euclidean correlation functions: Exploring universality and higher-twist effects
Building upon our recent study [G. S. Bali et al., Eur. Phys. J. C 78, 217 (2018)], we investigate the feasibility of calculating the pion distribution amplitude from suitably chosen Euclidean correlation functions at large momentum. We demonstrate in this work the advantage of analyzing several correlation functions simultaneously and extracting the pion distribution amplitude from a global fit. This approach also allows us to study higher-twist corrections, which are a major source of systematic error. Our result for the higher-twist parameter delta(pi)(2) is in good agreement with estimates from QCD sum rules. Another novel element is the use of all-to-all propagators, calculated using stochastic estimators, which enables an additional volume average of the correlation functions, thereby reducing statistical errors