134,122 research outputs found
Fitting Precision Electroweak Data with Exotic Heavy Quarks
The 1999 precision electroweak data from LEP and SLC persist in showing some
slight discrepancies from the assumed standard model, mostly regarding and
quarks. We show how their mixing with exotic heavy quarks could result in a
more consistent fit of all the data, including two unconventional
interpretations of the top quark.Comment: 7 pages, no figure, 2 typos corrected, 1 reference update
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
Experimental evaluation of atmospheric effects on radiometric measurements using the EREP of Skylab
There are no author-identified significant results in this report
Experimental evaluation of atmospheric effects on radiometric measurement using the EREP of Skylab
There are no author-identified significant results in this report
Experimental evaluation of atmospheric effects on radiometric measurements using the EREP of Skylab
There are no author-identified significant results in this report
Source Mergers and Bubble Growth During Reionization
The recently introduced models of reionization bubbles based on extended
Press-Schechter theory (Furlanetto, Zaldarriaga & Hernquist 2004) are
generalized to include mergers of ionization sources. Sources with a recent
major merger are taken to have enhanced photon production due to star
formation, and accretion onto a central black hole if a black hole is present.
This produces a scatter in the number of ionized photons corresponding to a
halo of a given mass and a change in photon production over time for any given
halo mass. Photon production histories, bubble distributions, and ionization
histories are computed for several different parameter and recombination
assumptions; the resulting distributions interpolate between previously
calculated limiting cases.Comment: 44 pages, 11 figures, version to appear in MNRAS. Some discussion of
case with WMAP parameters and expanded explanation
- …