15,599 research outputs found
Hadron Physics: The Essence of Matter
Dynamical chiral symmetry breaking (DCSB) is a remarkably effective mass
generating mechanism. It is also, amongst other things, the foundation for a
successful application of chiral effective field theories, the origin of
constituent-quark masses, and intimately connected with confinement in QCD.
Using the Dyson-Schwinger equations (DSEs), we explain the origin and nature of
DCSB, and elucidate some of its consequences, e.g.: a model-independent result
for the pion susceptibility; the generation of a quark anomalous chromomagnetic
moment, which may explain the longstanding puzzle of the a_1-rho mass
splitting; its impact on the behaviour of the electromagnetic pion form factor
-- thereby illustrating how data can be used to chart the momentum-dependence
of the dressed-quark mass function; in the form of the pion and kaon
valence-quark parton distribution functions, and the relation between them; and
aspects of the neutron's electromagnetic form factors, in particular
F_1^u/F_1^d and G_M^n. We argue that in solving QCD, a constructive feedback
between theory and extant and forthcoming experiments will most rapidly enable
constraints to be placed on the infrared behaviour of QCD's \beta-function, the
nonperturbative quantity at the core of hadron physics; and emphasise
throughout the role played by confrontation with data as a means of verifying
our understanding of Nature.Comment: 24 pages, 6 figures, 3 tables. Contribution to the proceedings of the
XII Mexican Workshop on Particles and Fields, based on presentations by
C.D.Roberts at the Workshop (9-14 Nov. 2009, Mazatlan, Mexico) and at the
preceding Mini-School (5-8 Nov. 2009, Culiacan, Mexico)
Empirically Charting Dynamical Chiral Symmetry Breaking
We provide a snapshot of recent progress in hadron physics made using QCD's
Dyson-Schwinger equations, reviewing the generation of a quark anomalous
chromomagnetic moment, which may explain the longstanding puzzle of the
- mass splitting, and the form of the pion and kaon valence-quark
parton distribution functions.Comment: 6 pages, 1 figure, 1 table. Contribution to the proceedings of
"Achievements and New Directions in Subatomic Physics: Workshop in Honour of
Tony Thomas' 60th Birthday," Special Centre for the Subatomic Structure of
Matter, Adelaide, South Australia, February 15 - February 19, 2010
LEXTALE_CH: A quick, character-based proficiency test for Mandarin Chinese
Research in second language acquisition suggests that objective performance-based assessments may provide more reliable and valid measures of second language proficiency than subjective self-ratings. To measure proficiency in English as a second language, a quick, vocabulary-based test called LexTALE (Lexical Test for Advanced Learners of English) was developed and shown to be able to differentiate between various levels of English proficiency. Following in the line of adaptations of this test for other languages, we created a character-based adaptation for Mandarin Chinese: LEXTALE_CH. In this paper, we discuss the development and validation of LEXTALE_CH in detail. In short, LEXTALE_CH can discriminate between high and low levels of Mandarin proficiency and is sensitive to the significant differences in vocabulary size between native speakers and second language learners of Mandarin; further, it takes only a few minutes to administer and is simple to score, making it a practical tool for low-stakes estimation of Mandarin proficiency.http://www.lingref.com/bucld/42/BUCLD42-09.pdfPublished versio
Phase Transition of Finite Size Quark Droplets with Isospin Chemical Potential in the Nanbu--Jona-Lasinio Model
Making use of the NJL model and the multiple reflection expansion
pproximation, we study the phase transition of the finite size droplet with u
and d quarks. We find that the dynamical masses of u, d quarks are different,
and the chiral symmetry can be restored at different critical radii for u, d
quark. It rovides a clue to understand the effective nucleon mass splitting in
nuclear matter. Meanwhile, it shows that the maximal isospin chemical potential
at zero temperature is much smaller than the mass of pion in free space.Comment: 12 pages, 3 figures. To appear in Physical Review
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