6,417 research outputs found
New Relations for Excited Baryons in Large N_c QCD
We show that excited baryons in large N_c QCD form multiplets, within which
masses are first split at O(1/N_c). The dominant couplings of resonances to
various mesons are highly constrained: The N(1535) decays at leading 1/N_c
order exclusively to eta-N rather than pi-N, and vice versa for the N(1650).
This multiplet structure is reproduced by a simple large N_c quark model, well
studied in the literature, that describes resonances as single-quark
excitations.Comment: 4 pages, no figures, ReVTeX 4. Includes new discussion of previous
work on excited baryon tower
An Analysis of Pricing Strategy and Price Dispersion on the Internet
Using prices obtained from shopbots, we test several hypotheses regarding the economics of information and optimal search. We find that price dispersion is positively (negatively) related to product price and the number of sellers in cross-sectional (time series) analysis. Price dispersion increases over time when the sample includes new entrants, but decreases in the absence of entry. Controlling for shipping charges and seller heterogeneity reduces, but does not eliminate, price dispersion. Finally, prices appear to be correlated across products and over time – low price sellers for one product (time period) generally charge low prices for all items (time periods).
Interplay of the Chiral and Large N_c Limits in pi N Scattering
Light-quark hadronic physics admits two useful systematic expansions, the
chiral and 1/N_c expansions. Their respective limits do not commute, making
such cases where both expansions may be considered to be especially
interesting. We first study pi N scattering lengths, showing that (as expected
for such soft-pion quantities) the chiral expansion converges more rapidly than
the 1/N_c expansion, although the latter nevertheless continues to hold. We
also study the Adler-Weisberger and Goldberger-Miyazawa-Oehme sum rules of pi N
scattering, finding that both fail if the large N_c limit is taken prior to the
chiral limit.Comment: 10 pages, ReVTe
SU(3) Clebsch-Gordan Coefficients for Baryon-Meson Coupling at Arbitrary N_c
We present explicit formulae for the SU(3) Clebsch-Gordan coefficients that
are relevant for the couplings of large N_c baryons to mesons. In particular,
we compute the Clebsch-Gordan series for the coupling of the octet (associated
with mesons, and remains the correct representation at large N_c) to the large
N_c analogs of the baryon octet and decuplet representations.Comment: 8 pages, no figures, ReVTe
Pion Photoproduction Amplitude Relations in the 1/N_c Expansion
We derive expressions for pion photoproduction amplitudes in the 1/N_c
expansion of QCD, and obtain linear relations directly from this expansion that
relate electromagnetic multipole amplitudes at all energies. The leading-order
relations in 1/N_c compare favorably with available data, while the
next-to-leading order relations seem to provide only a small improvement.
However, when resonance parameters are compared directly, the agreement at
O(1/N_c) or O(1/N_c^2) is impressive.Comment: 19 pages, ReVTeX, 50 eps files combine into 5 compound figure
Methods and apparatus for determining cardiac output
The present invention provides methods and apparatus for determining a dynamical property of the systemic or pulmonary arterial tree using long time scale information, i.e., information obtained from measurements over time scales greater than a single cardiac cycle. In one aspect, the invention provides a method and apparatus for monitoring cardiac output (CO) from a single blood pressure signal measurement obtained at any site in the systemic or pulmonary arterial tree or from any related measurement including, for example, fingertip photoplethysmography.According to the method the time constant of the arterial tree, defined to be the product of the total peripheral resistance (TPR) and the nearly constant arterial compliance, is determined by analyzing the long time scale variations (greater than a single cardiac cycle) in any of these blood pressure signals. Then, according to Ohm's law, a value proportional to CO may be determined from the ratio of the blood pressure signal to the estimated time constant. The proportional CO values derived from this method may be calibrated to absolute CO, if desired, with a single, absolute measure of CO (e.g., thermodilution). The present invention may be applied to invasive radial arterial blood pressure or pulmonary arterial blood pressure signals which are routinely measured in intensive care units and surgical suites or to noninvasively measured peripheral arterial blood pressure signals or related noninvasively measured signals in order to facilitate the clinical monitoring of CO as well as TPR
- …