15 research outputs found
Interplay of Monopoles and P-Vortices
We show that P-Vortices in the confinement phase of SU(2) lattice gauge
theory form one large percolating (infrared) cluster and a number of small
(ultraviolet) clusters. We discuss the interrelation of clusters of monopoles
in the maximal Abelian projection with clusters of P-vortices. To extract
P-vortices we use both direct and indirect central projections and find
qualitatively similar results.Comment: 3 pages, 4 figures; talk given at Lattice 2003 (Tsukuba, Japan
Self-tuning of the P-vortices
We observe that on the currently available lattices the non-Abelian action
associated with the P-vortices is ultraviolet divergent. On the other hand, the
total area of the vortices scales in physical units. Since both the ultraviolet
and infrared scales are manifested and there is no parameter to tune, the
observed phenomenon can be called self tuning.Comment: Lattice2003(topology
New features of the maximal abelian projection
After fixing the Maximal Abelian gauge in SU(2) lattice gauge theory we
decompose the nonabelian gauge field into the so called monopole field and the
modified nonabelian field with monopoles removed. We then calculate respective
static potentials and find that the potential due to the modified nonabelian
field is nonconfining while, as is well known, the monopole field potential is
linear. Furthermore, we show that the sum of these potentials approximates the
nonabelian static potential with 5% or higher precision at all distances
considered. We conclude that at large distances the monopole field potential
describes the classical energy of the hadronic string while the modified
nonabelian field potential describes the string fluctuations. Similar
decomposition was observed to work for the adjoint static potential. A check
was also made of the center projection in the direct center gauge. Two static
potentials, determined by projected and by modified nonabelian field
without component were calculated. It was found that their sum is a
substantially worse approximation of the SU(2) static potential than that found
in the monopole case. It is further demonstrated that similar decomposition can
be made for the flux tube action/energy density.Comment: 8 pages, to appear in the proceedings of the Workshop on
Computational Hadron Physics, Nicosia, September 200
Nucleon Structure from Lattice QCD Using a Nearly Physical Pion Mass
We report the first Lattice QCD calculation using the almost physical pion
mass mpi=149 MeV that agrees with experiment for four fundamental isovector
observables characterizing the gross structure of the nucleon: the Dirac and
Pauli radii, the magnetic moment, and the quark momentum fraction. The key to
this success is the combination of using a nearly physical pion mass and
excluding the contributions of excited states. An analogous calculation of the
nucleon axial charge governing beta decay has inconsistencies indicating a
source of bias at low pion masses not present for the other observables and
yields a result that disagrees with experiment.Comment: journal version; 15 pages, 6 figure
Fine tuned vortices in lattice SU(2) gluodynamics
We report measurements of the action associated with center vortices in SU(2)
pure lattice gauge theory. In the lattice units the excess of the action on the
plaquettes belonging to the vortex is approximately a constant, independent on
the lattice spacing 'a'. Therefore the action of the center vortex is of order
'A/a^2', where 'A' is its area. Since the area 'A' is known to scale in the
physical units, the measurements imply that the suppression due to the surface
action is balanced, or fine tuned to the entropy factor which is to be an
exponential of 'A/a^2'.Comment: Version accepted for publication in PLB, stylistic change
Hadron Structure on the Lattice
A few chosen nucleon properties are described from a lattice QCD perspective:
the nucleon sigma term and the scalar strangeness in the nucleon; the vector
form factors in the nucleon, including the vector strangeness contribution, as
well as parity breaking effects like the anapole and electric dipole moment;
and finally the axial and tensor charges of the nucleon. The status of the
lattice calculations is presented and their potential impact on phenomenology
is discussed.Comment: 17 pages, 9 figures; proceedings of the Conclusive Symposium of the
Collaborative Research Center 443 "Many-body structure of strongly
interacting systems", Mainz, February 23-25, 201
Form factors in lattice QCD
Lattice simulations of QCD have produced precise estimates for the masses of
the lowest-lying hadrons which show excellent agreement with experiment. By
contrast, lattice results for the vector and axial vector form factors of the
nucleon show significant deviations from their experimental determination. We
present results from our ongoing project to compute a variety of form factors
with control over all systematic uncertainties. In the case of the pion
electromagnetic form factor we employ partially twisted boundary conditions to
extract the pion charge radius directly from the linear slope of the form
factor near vanishing momentum transfer. In the nucleon sector we focus
specifically on the possible contamination from contributions of higher excited
states. We argue that summed correlation functions offer the possibility of
eliminating this source of systematic error. As an illustration of the method
we discuss our results for the axial charge, gA, of the nucleon.Comment: 16 pages, 11 figures, presented at Conclusive Symposium, CRC443,
"Many-body structure of strongly interacting systems", 23-25 Feb 2011, Mainz,
German
The present and future of QCD
This White Paper presents an overview of the current status and future perspective of QCD research, based on the community inputs and scientific conclusions from the 2022 Hot and Cold QCD Town Meeting. We present the progress made in the last decade toward a deep understanding of both the fundamental structure of the sub-atomic matter of nucleon and nucleus in cold QCD, and the hot QCD matter in heavy ion collisions. We identify key questions of QCD research and plausible paths to obtaining answers to those questions in the near future, hence defining priorities of our research over the coming decades
Diquark correlations in hadron physics : origin, impact and evidence
The last decade has seen a marked shift in how the internal structure of hadrons is understood. Modern experimental facilities, new theoretical techniques for the continuum bound-state problem and progress with lattice-regularised QCD have provided strong indications that soft quark+quark (diquark) correlations play a crucial role in hadron physics. For example, theory indicates that the appearance of such correlations is a necessary consequence of dynamical chiral symmetry breaking, viz. a corollary of emergent hadronic mass that is responsible for almost all visible mass in the universe; experiment has uncovered signals for such correlations in the flavour-separation of the proton’s electromagnetic form factors; and phenomenology suggests that diquark correlations might be critical to the formation of exotic tetra- and penta-quark hadrons. A broad spectrum of such information is evaluated herein, with a view to consolidating the facts and therefrom moving toward a coherent, unified picture of hadron structure and the role that diquark correlations might play.peerReviewe
Diquark correlations in hadron physics: Origin, impact and evidence
The last decade has seen a marked shift in how the internal structure of hadrons is understood. Modern experimental facilities, new theoretical techniques for the continuum bound-state problem and progress with lattice-regularised QCD have provided strong indications that soft quark+quark (diquark) correlations play a crucial role in hadron physics. For example, theory indicates that the appearance of such correlations is a necessary consequence of dynamical chiral symmetry breaking, viz. a corollary of emergent hadronic mass that is responsible for almost all visible mass in the universe; experiment has uncovered signals for such correlations in the flavour-separation of the proton's electromagnetic form factors; and phenomenology suggests that diquark correlations might be critical to the formation of exotic tetra- and penta-quark hadrons. A broad spectrum of such information is evaluated herein, with a view to consolidating the facts and there from moving toward a coherent, unified picture of hadron structure and the role that diquark correlations might play. (C) 2020 Published by Elsevier B.V