384 research outputs found
Worldline Green Functions for Multiloop Diagrams
We propose a multiloop generalization of the Bern-Kosower formalism, based on
Strassler's approach of evaluating worldline path integrals by worldline Green
functions. Those Green functions are explicitly constructed for the basic
two-loop graph, and for a loop with an arbitrary number of propagator
insertions. For scalar and abelian gauge theories, the resulting integral
representations allow to combine whole classes of Feynman diagrams into compact
expressions.Comment: 12 pages, uuencoded compressed ps-file, HD-THEP-94-
Large N limit of orbifold field theories
We consider certain orbifoldization of the field theories that
leads to field theories in 4 dimensions. These theories were
recently analyzed using the string theory perturbation technique. It was found
that in the large limit all correlation functions of the orbifold theories
coincide with those of , modulo the rescaling of the gauge coupling
constant. In this paper we repeat the same analysis using the field theoretical
language.Comment: 12 pages, 3 figures, harvmac. Minor change
Exact Combinatorics of Bern-Kosower-type Amplitudes for Two-Loop Theory
Counting the contribution rate of a world-line formula to Feynman diagrams in
theory, we explain the idea how to determine precise combinatorics of
Bern-Kosower-like amplitudes derived from a bosonic string theory for -point
two-loop Feynman amplitudes. In this connection we also present a method to
derive simple and compact world-line forms for the effective action.Comment: 26 pages, two figures by picte
On the Calculation of Effective Actions by String Methods
Strassler's formulation of the string-derived Bern-Kosower formalism is
reconsidered with particular emphasis on effective actions and form factors.
Two- and three point form factors in the nonabelian effective action are
calculated and compared with those obtained in the heat kernel approach of
Barvinsky, Vilkovisky et al. We discuss the Fock-Schwinger gauge and propose a
manifestly covariant calculational scheme for one-loop effective actions in
gauge theory.Comment: 12 pages, Plain TEX, HD-THEP-93-2
Fixed-term employment, work organization and job satisfaction: Evidence from German individual-level data
The present paper examines the joint effect of fixed-term employment and work organization on job satisfaction using individual-level data from the German Socio-Economic Panel (GSOEP). Specifically, we analyze whether workers who are heterogeneous in terms of the type of working contract (fixed-term vs. permanent) do also differ with regard to job satisfaction, when they perform under comparable work organizational conditions. Such information would be quite valuable for employers, because they can learn about the responsiveness of heterogeneous workers to innovative work organizational practices. For this purpose, we at first estimate a linear fixed effects model, thereby controlling for unobserved time-constant characteristics. In a second step, we account for potential remaining endogeneity by combining the fixed effects approach with a two-stage estimation strategy. Our empirical results show that in terms of job satisfaction fixed-term workers and their permanent counterparts respond differently to a number of organizational practices including task diversity, employee involvement, social relations at work, general working conditions, and career prospects. The results may be used by employers to improve their concept of diversity management and specifically the job design of heterogeneous workers.Fixed-term employment, permanent employment, job satisfaction, work organization, selectivity bias, unobserved heterogeneity
Manifesting enhanced cancellations in supergravity: integrands versus integrals
Examples of "enhanced ultraviolet cancellations" with no known
standard-symmetry explanation have been found in a variety of supergravity
theories. By examining one- and two-loop examples in four- and five-dimensional
half-maximal supergravity, we argue that enhanced cancellations in general
cannot be exhibited prior to integration. In light of this, we explore
reorganizations of integrands into parts that are manifestly finite and parts
that have poor power counting but integrate to zero due to integral identities.
At two loops we find that in the large loop-momentum limit the required
integral identities follow from Lorentz and SL(2) relabeling symmetry. We carry
out a nontrivial check at four loops showing that the identities generated in
this way are a complete set. We propose that at loops the combination of
Lorentz and SL() symmetry is sufficient for displaying enhanced
cancellations when they happen, whenever the theory is known to be ultraviolet
finite up to loops.Comment: 28 pages, 5 figure
World-line approach to the Bern-Kosower formalism in two-loop Yang-Mills theory
Based on the world-line formalism with a sewing method, we derive the
Yang-Mills effective action in a form useful to generate the Bern-Kosower-type
master formulae for gluon scattering amplitudes at the two-loop level. It is
shown that four-gluon ( type sewing) contributions can be encapsulated
in the action with three-gluon ( type) vertices only, the total action
thus becoming a simple expression. We then derive a general formula for a
two-loop Euler-Heisenberg type action in a pseudo-abelian background.
The ghost loop and fermion loop cases are also studied.Comment: 37(+1) pages, details added for section
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