560 research outputs found
Application of the Worldline Path Integral Method to the Calculation of Inverse Mass Expansions
Higher order coefficients of the inverse mass expansion of one-loop effective
actions are obtained from a one-dimensional path integral representation. For
the case of a massive scalar loop in the background of both a scalar potential
and a (non Abelian) gauge field explicit results to in the proper time
parameter are presented.Comment: 6 pages, LaTeX. Talk given at 5th International Workshop on Software
Engineering and Artificial Intelligence for High Energy and Nuclear Physics
(AIHENP96), Lausanne (Switzerland), 2-6 September 199
Determinant Calculations Using Random Walk Worldline Loops
We use statistical ensembles of worldline loops generated by random walk on
hypercubic lattices to calculate matter determinants in background Yang-Mills
fields.Comment: 3 pages, 3 ps figures, Lattice2002 (algor
Resummed effective action in the world-line formalism
Using the world-line method we resum the scalar one-loop effective action.
This is based on an exact expression for the one-loop action obtained for a
background potential and a Taylor expansion of the potential up to quadratic
order in x-space. We thus reproduce results of Masso and Rota very
economically. An alternative resummation scheme is suggested using ``center of
mass'' based loops which is equivalent under the assumption of vanishing third
and higher derivatives in the Taylor expansion but leads to simplified
expressions. In an appendix some general issues concerning the relation between
world-line integrals with fixed end points versus integrals with fixed center
are clarified. We finally note that this method is also very valuable for gauge
field effective actions where it is based on the Euler--Heisenberg type
resummation.Comment: 15 page
Effective Action in a General Chiral Model: Next to Leading Order Derivative Expansion in the Worldline Method
We present a formalism to determine the imaginary part of a general chiral
model in the derivative expansion. Our formalism is based on the worldline path
integral for the covariant current that can be given in an explicit chiral and
gauge covariant form. The effective action is then obtained by integrating the
covariant current, taking account of the anomaly.Comment: 33 pages, minor changes, published versio
An Improved Heat Kernel Expansion from Worldline Path Integrals
The one--loop effective action for the case of a massive scalar loop in the
background of both a scalar potential and an abelian or non--abelian gauge
field is written in a one--dimensional path integral representation. From this
the inverse mass expansion is obtained by Wick contractions using a suitable
Green function, which allows the computation of higher order coefficients. For
the scalar case, explicit results are presented up to order O(T**8) in the
proper time expansion. The relation to previous work is clarified.Comment: 13 pages, Plain TEX, no figure
Ingestive behaviour and physiology of the medicinal leech
Ingestion lasts 25 min in Hirudo medicinalis and is characterized by pharyngeal peristalsis which fills the crop. This peristalsis has an initial rate of 2.4 Hz which decays smoothly to 1.2 Hz at termination of ingestion. During ingestion, the leech body wall undergoes peristalsis which appears to aid in filling the crop diverticula. Body peristalsis begins at a rate of 10 min^(-1) and decreases linearly to 2 min^(-1) at termination. The body also undergoes dorsoventral flexions when blood flow is occluded. Blood meal size increases slightly with leech size: 8.4 g for 1-g leeches and 9.7 g for 2-g leeches. However, relative meal size decreases markedly with increasing animal size; from 8.15 times body mass for 1-g to 4.80 times for 2-g leeches. When intact leeches were exposed to micromolar concentrations of serotonin, there was an increase in the rate of pharyngeal peristalsis and the size of the blood meals. Leeches excrete the plasma from their ingested blood meals. Excretion is activated during ingestion, which increases feeding efficiency by increasing the proportion of blood cells in the ingestate. Excretion continues for 4–6 days following ingestion, removing all the remaining plasma from the ingestate. Leech ingestion comprises stereotyped muscular movements, secretion of saliva and excretion of plasma. A strikingly similar feeding physiology is seen in the blood-sucking insect Rhodnius, and we suggest that efficient sanguivory may require the convergent evolution of similar ingestive mechanisms
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