922,807 research outputs found
Constituent Quarks as Solitons
We exhibit soliton solutions of QCD in two dimensions that have the quantum
numbers of quarks. They exist only for quarks heavier than the dimensional
gauge coupling, and have infinite energy, corresponding to the presence of a
string carrying the non-singlet color flux off to spatial infinity. The quark
solitons also disappear at finite temperature, as the temperature-dependent
effective quark mass is reduced in the approach to the quark/hadron phase
transition.Comment: 14 page
Constituent quarks, chiral symmetry, and chiral point of the constituent quark model
We construct the full axial current of the constituent quarks by a summation
of the infinite number of diagrams describing constituent-quark soft
interactions. By requiring that the conservation of this current is violated
only by terms of order , where is the mass of the lowest
pseudoscalar bound state, we derive important constraints on (i) the
axial coupling of the constituent quark and (ii) the potential
at large distances. We define the chiral point of the constituent quark model
as those values of the parameters, such as the masses of the constituent quarks
and the couplings in the potential, for which vanishes. At
the chiral point the main signatures of the spontaneously broken chiral
symmetry are shown to be present, namely: the axial current of the constituent
quarks is conserved, the leptonic decay constants of the excited pseudoscalar
bound states vanish, and the pion decay constant has a nonzero value.Comment: 10 pages, typo in eq. (46) of the published version is correcte
Immediate Constituent Analysis (IC analysis)
Immediate Constituent Analysis is a structural method for analysing the hierarchical relations among the constituents of complex linguistic constructions, proceeding consecutively from the higher to the next lower level until no further breakdown into smaller units is possible
Constituent Parsing as Sequence Labeling
We introduce a method to reduce constituent parsing to sequence labeling. For
each word w_t, it generates a label that encodes: (1) the number of ancestors
in the tree that the words w_t and w_{t+1} have in common, and (2) the
nonterminal symbol at the lowest common ancestor. We first prove that the
proposed encoding function is injective for any tree without unary branches. In
practice, the approach is made extensible to all constituency trees by
collapsing unary branches. We then use the PTB and CTB treebanks as testbeds
and propose a set of fast baselines. We achieve 90.7% F-score on the PTB test
set, outperforming the Vinyals et al. (2015) sequence-to-sequence parser. In
addition, sacrificing some accuracy, our approach achieves the fastest
constituent parsing speeds reported to date on PTB by a wide margin.Comment: EMNLP 2018 (Long Papers). Revised version with improved results after
fixing evaluation bu
Beyond the Constituent Quark Model
Modern experiment requires a reliable theoretical framework for low energy
QCD. Some of the requirements for constructing a new model of QCD are presented
here. Progress toward these requirements are highlighted.Comment: 10 pages, 5 ps figures, based on a plenary talk at Hadron 2001,
Protvino, Russi
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