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Geoffrey B. West

Publications and source records attributed to Geoffrey B. West.

27 records · Page 2Linked to original sources
arXiv2002

Red herrings and rotten fish

A longstanding problem in biology has been the origin of pervasive quarter-power allometric scaling laws that relate many characteristics of organisms to body mass (M) across the entire spectrum of life from molecules and microbes to ecosystems and mammals. In particular, whole-organism metabolic rate, B=aM^b, where a is a taxon-dependent normalisation constant and b is approximately equal to 3/4 for both animals and plants. Recently Darveau et al. (hereafter referred to as DSAH) proposed a "multiple-causes model" for B as "the sum of multiple contributors to metabolism", B_i, which were assumed to scale as M^(b_i). They obtained for average values of b: 0.78 for the basal rate and 0.86 for the maximally active rate. In this note we show that DSAH contains serious technical, theoretical and conceptual errors, including misrepresentations of published data and of our previous work. We also show that, within experimental error, there is no empirical evidence for an increase in b during aerobic activity as suggested by DSAH. Moreover, since DSAH consider only metabolic rates of mammals and make no attempt to explain why metabolic rates for other taxa and many other attributes in diverse organisms also scale with quarter-powers (including most of their input data), their formulation is hardly the "unifying principle" they claim. These problems were not addressed in commentaries by Weibel and Burness.

physics.bio-ph↗
arXiv1999

Asymptotic Series and Precocious Scaling

Some of the basic concepts regarding asymptotic series are reviewed. A heuristic proof is given that the divergent QCD perturbation series is asymptotic. By treating it as an asymptotic expansion we show that it makes sense to keep only the first few terms. The example of e^+e^- annihilation is considered. It is shown that by keeping only the first few terms one can get within a per cent (or smaller) of the complete sum of the series even at very low momenta where the coupling is large. More generally, this affords an explanation of the phenomena of precocious scaling and why keeping only leading order corrections generally works so well.

hep-ph↗
arXiv1999

A New Approach to y-scaling and the Universal Features of Scaling Functions and Nucleon Momentum Distributions

Some systematic general features of y-scaling structure functions, which are essentially independent of detailed dynamics, are pointed out. Their physical interpretation in terms of general characteristics, such as a mean field description and nucleon-nucleon correlations, is given and their relationship to the momentum distributions illustrated. A new relativistic scaling variable is proposed which incorporates the momentum dependence of the excitation energy of the (A-1) system, with the resulting scaling function being closely related to the longitudinal momemtum distributions and being free from removal-energy scaling violating effects.

nucl-th↗
arXiv1997

Old and New Facets of y-Scaling: the Universal Features of Nuclear Structure Functions and Nucleon Momentum Distributions

Some systematic general features of y-scaling structure functions, which are essentially independent of detailed dynamics, are pointed out. Their physical interpretation in terms of general characteristics, such as a mean field description and nucleon-nucleon correlations, is given and their relationship to the momentum distributions illustrated. A new scaling variable is proposed which allows a direct expression of the scaling function in term of an integral over the momemtum distributions thereby avoiding explicit consideration of binding corrections.

nucl-th↗
arXiv1996

A Proof of Duality in Structure Functions Near x = 1

A proof of Bloom-Gilman duality which relates an integral over the low-mass resonances in deep inelastic structure functions to an integral over the scaling region near x = 1 is given. It is based on general analytic properties of the corresponding virtual Compton amplitude but is insensitive to its asymptotic behaviour.

hep-ph↗
arXiv1996

The Glueball; The Fundamental Particle of Non-Perturbative QCD

Theoretical ideas related to the existence of glueballs in QCD are reviewed. These include non-perturbative phenomena such as confinement, instantons, vacuum condensates and renormalons. We also discuss glueball dominance of the trace of the stress-tensor, the mass content of the nucleon and a theorem on the lightest glueball state.

hep-ph↗
arXiv1996

Theorem on the Lightest Glueball State

This paper is devoted to proving that, in QCD, the lightest glueball state must be the scalar with $J^{PC} = 0^{++}$. The proof relies upon the positivity of the path integral measure in Euclidean space and the fact that interpolating fields for all spins can be bounded by powers of the scalar glueball operator. The problem presented by the presence of vacuum condensates is circumvented by considering the time evolution of the propagators and exploiting the positivity of the Hamiltonian.

hep-ph↗
arXiv1994

Deep Inelastic Electropion Production

This paper is devoted to a study of possible scaling laws, and their logarithmic corrections, occurring in deep inelastic electropion production. Both the exclusive and semi-exclusive processes are considered. Scaling laws, originally motivated from PCAC and current algebra considerations are examined, first in the framework of the parton model and QCD peturbation theory and then from the more formal perspective of the operator product expansion and asymptotic freedom, (as expressed through the renormalization group). We emphasize that these processes allow scaling to be probed for the full amplitude rather than just its absorbtive part (as is the case in the conventional structure functions). Because of this it is not possible to give a formal derivation of scaling for deep inelastic electropion production processes even if one believes that they are unambiguously sensitive to the light cone behavior of the operator product. The origin of this is shown to be related to its behavior near $x\approx 0$. Investigations, both theoretical and experimental, of these processes is therefore strongly encouraged.

hep-ph↗