13,788 research outputs found
From euclidean field theory to quantum field theory
In order to construct examples for interacting quantum field theory models,
the methods of euclidean field theory turned out to be powerful tools since
they make use of the techniques of classical statistical mechanics.
Starting from an appropriate set of euclidean n-point functions (Schwinger
distributions), a Wightman theory can be reconstructed by an application of the
famous Osterwalder-Schrader reconstruction theorem. This procedure (Wick
rotation), which relates classical statistical mechanics and quantum field
theory, is, however, somewhat subtle. It relies on the analytic properties of
the euclidean n-point functions.
We shall present here a C*-algebraic version of the Osterwalder-Scharader
reconstruction theorem. We shall see that, via our reconstruction scheme, a
Haag-Kastler net of bounded operators can directly be reconstructed.
Our considerations also include objects, like Wilson loop variables, which
are not point-like localized objects like distributions. This point of view may
also be helpful for constructing gauge theories.Comment: 35 page
A non-chiral extension of the standard model with mirror fermions
The difficulties of defining chiral gauge theories non-perturbatively suggest
a vector-like extension of the standard model with three mirror fermion
families. Some phenomenological implications of such an extension are
discussed.Comment: latex, 6 pages, 1 figure with epsfig. Talk given at the workshop
"Beyond the Standard Model V", Balholm, Norway, May 199
Numerical simulation with light Wilson-quarks
The computational cost of numerical simulations of QCD with light dynamical
Wilson-quarks is estimated by determining the autocorrelation of various
quantities. In test runs the expected qualitative behaviour of the pion mass
and coupling at small quark masses is observed.Comment: 5 pages, 3 figures, to appear in the Proceedings of SEWM, Heidelberg,
200
Modeled nitrogen loading to Narragansett Bay: 1850 to 2015
Nutrient loading to estuaries with heavily populated watersheds can have profound ecological consequences. In evaluating policy options for managing nitrogen (N), it is helpful to understand current and historic spatial loading patterns to the system. We modeled N inputs to Narragansett Bay from 1850 to 2000, using data on population, human waste disposal, livestock, fertilizer, and atmospheric deposition. We found that total N loading to the bay increased 250% from 1850 to 2000, and 80% from 1900 to 2000. Loading to the upper bay increased far more than that to the lower bay, and the most important source shifted from non-point animal waste to human waste concentrated at sewage treatment facilities. We also modeled future N loads in 2015 under four management scenarios. Planned improvements in sewage treatment would reduce N loads 9% below business-as-usual, to the 1990 loading rate. Greater reductions, to circa 1900 rates of loading, may be possible
Validation and refinement of allometric equations for roots of northern hardwoods
The allometric equations developed by Whittaker et al. (1974. Ecol. Monogr. 44: 233â252), at the Hubbard Brook Experimental Forest have been used to estimate biomass and productivity in northern hardwood forest systems for over three decades. Few other species-specific allometric estimates of belowground biomass are available because of the difficulty in collecting the data, and such equations are rarely validated. Using previously unpublished data from Whittakerâs sampling effort, we extended the equations to predict the root crown and lateral root components for the three dominant species of the northern hardwood forest: American beech (Fagus grandifolia Ehrh.), yellow birch (Betula alleghaniensis Britt), and sugar maple (Acer saccharum Marsh.). We also refined the allometric models by eliminating the use of very small trees for which the original data were unreliable. We validated these new models of the relationship of tree diameter to the mass of root crowns and lateral roots using root mass data collected from 12 northern hardwood stands of varying age in central New Hampshire. These models provide accurate estimates of lateral roots (diameter) in northern hardwood stands \u3e20 years old (mean error 24%â32%). For the younger stands that we studied, allometric equations substantially underestimated observed root biomass (mean error \u3e60%), presumably due to remnant mature root systems from harvested trees supporting young root-sprouted trees
Consumption, Wealth and Business Cycles in Germany
This paper studies the long-run relationship between consumption, asset wealth and income in Germany, based on data from 1980 to 2003. While earlier studies â mostly for the Anglo-Saxon economies â have generally documented that departures of these three variables from their common trend signal changes in asset prices, we find that for Germany they predict changes in income. Asset price changes are found to have virtually no effect on consumption â both in the short as well as in the long-run. We offer an explanation of this finding that emphasizes differences between the bank-based German financial system and the rather market-based Anglo-American system: stock ownership by private households is much less widespread in Germany than in the Anglo-Saxon economies and the share of publicly traded equity in household wealth is much smaller in Germany than in the U.S., the UK or Australia.wealth effect on consumption, business cycles, monetary policy transmission, financial systems, asset price predictability, permanent income hypothesis
Ice storm effects on the canopy structure of a northern hardwood forest after 8 years
Ice storms can cause severe damage to forest canopies, resulting in differential mortality among tree species and size classes and leading to long-lasting changes in the vertical structure and composition of the forest. An intense ice storm in 1998 damaged large areas of the northern hardwood forest, including much of the Hubbard Brook Experimental Forest, New Hampshire (USA). Following up on detailed poststorm assessments, we measured changes in the vertical structure of the forest canopy 8 years poststorm. We focused on how the presence of disease-induced advance regeneration of American beech (Fagus grandifolia Ehrh.) has affected canopy structure in the recovering forest. We measured foliage-height profiles using a point-quadrat approach and a pole-mounted leaf area index (LAI) sensor. Although the total LAIs of damaged and undamaged areas were similar, areas damaged in 1998 showed an increased proportion of total leaf area between 6 and 10 m above the ground. The foliage at this height is largely (54%) beech. To the extent that this heavily beech-dominated understory layer suppresses regeneration of other species, these findings suggest that rare disturbances of mature northern hardwood forests affected by beech bark disease will increase the importance of damage-prone and economically marginal beech
Confinement in Three Dimensions and the Electroweak Phase Transition
The infrared behaviour of the standard model at finite temperature is
determined by the confining phase of the SU(2)-Higgs model in three dimensions.
Due to the Landau singularity of the three-dimensional gauge theory the
perturbative treatment of the electroweak phase transition breaks down for
Higgs masses above a critical mass . Based on a renormalization group
improved effective potential we find 70 GeV. The scalar
self-coupling has a Landau-type singularity also in the abelian U(1)-Higgs
model, which leads to a breakdown of perturbation theory in the symmetric
phase.Comment: 9 pages, DESY-94-045, 4 figures can be obtained via e-mail from
[email protected]
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