2,192 research outputs found
Lambda-parameter of lattice QCD with Symanzik improved gluon actions
We compute the ratio Lambda_L/Lambda_MS, where the scale parameter Lambda_L
is associated with a lattice formulation of QCD. We consider a 3-parameter
family of gluon actions, which are most frequently used for O(a) improvement a`
la Symanzik. The gluon action is put togeter with standard discretizations for
fermions (Wilson/clover, overlap), to provide Lambda_L for several possible
combinations of fermion and gluon actions. We employ the background field
technique in order to calculate the 1PI 2-point function of the background
field; this leads to the coupling constant renormalization function, Z_g, at
1-loop level.
Our results are obtained for an extensive range of values for the Symanzik
coefficients.Comment: 11 pages, 3 figures, 3 table
Revolutions in energy input and material cycling in Earth history and human history
Major revolutions in energy capture have occurred in both Earth and human history, with each transition
resulting in higher energy input, altered material cycles and major consequences for the internal organization
of the respective systems. In Earth history, we identify the origin of anoxygenic photosynthesis, the origin of oxygenic
photosynthesis, and land colonization by eukaryotic photosynthesizers as step changes in free energy input
to the biosphere. In human history we focus on the Palaeolithic use of fire, the Neolithic revolution to farming,
and the Industrial revolution as step changes in free energy input to human societies. In each case we try to quantify
the resulting increase in energy input, and discuss the consequences for material cycling and for biological
and social organization. For most of human history, energy use by humans was but a tiny fraction of the overall
energy input to the biosphere, as would be expected for any heterotrophic species. However, the industrial revolution
gave humans the capacity to push energy inputs towards planetary scales and by the end of the 20th century
human energy use had reached a magnitude comparable to the biosphere. By distinguishing world regions and
income brackets we show the unequal distribution in energy and material use among contemporary humans.
Looking ahead, a prospective sustainability revolution will require scaling up new renewable and decarbonized
energy technologies and the development of much more efficient material recycling systems – thus creating a
more autotrophic social metabolism. Such a transition must also anticipate a level of social organization that can
implement the changes in energy input and material cycling without losing the large achievements in standard
of living and individual liberation associated with industrial societies.The initial outline and ideas developed
in this manuscript were first conceived at the inaugural LOOPS
workshop (Chorin, Berlin, 17–18 February 2014). Timothy M.
Lenton was supported by a Royal Society Wolfson Research Merit
Award. We thank Kirsten Thonicke, Carsten Lemmen, Wilfried
Winiwarter, and Marina Fischer-Kowalski for useful comments
Perturbative Renormalization Factors of Bilinear Quark Operators for Improved Gluon and Quark Actions in Lattice QCD
We calculate one-loop renormalization factors of bilinear quark operators for
gluon action including six-link loops and -improved quark action in the
limit of massless quark. We find that finite parts of one-loop coefficients of
renormalization factors diminish monotonically as either of the coefficients
or of the six-link terms are decreased below zero. Detailed
numerical results are given, for general values of the clover coefficient, for
the tree-level improved gluon action in the Symanzik approach and for the choices suggested by Wilson and by Iwasaki and from renormalization-group analyses. Compared with the case of
the standard plaquette gluon action, finite parts of one-loop coefficients are
reduced by 10--20% for the Symanzik action, and approximately by a factor two
for the renormalization-group improved gluon actions.Comment: 19 pages, REVTeX, with 3 epsf figure
The Lattice Parameter in Domain Wall QCD
We evaluate the ratio of the scale parameter in domain wall QCD to
the one in the continuum theory at one loop level incorporating the effect of
massless quarks. We show that the Pauli-Villars regulator is required to
subtract the unphysical massive fermion modes which emerge in the fermion loop
contributions to the gluon self energy. Detailed results are presented as a
function of the domain wall height .Comment: 16 pages, 1 figure as eps-file, some references adde
Episymbiotic microbes as food and defence for marine isopods : unique symbioses in a hostile environment
Author Posting. © Royal Society, 2005. This article is posted here by permission of
Royal Society for personal use, not for redistribution. The definitive version was published
in Proceedings of the Royal Society of London B 272 (2005): 1209-1216, doi:10.1098/rspb.2005.3082.Symbioses profoundly affect the diversity of life, often through novel biochemical services that symbionts provide to their hosts. These biochemical services are typically nutritional enhancements and less commonly defensive, but rarely both simultaneously. On the coral reefs of Papua New Guinea, we discovered unique associations between marine isopod crustaceans (Santia spp.) and episymbiotic microbes. Transmission electron microscopy and pigment analyses show that episymbiont biomass is dominated by large (20–30μm) cyanobacterial cells. The isopods consume these photosymbionts and ‘cultivate’ them by inhabiting exposed sunlit substrates, a behaviour made possible by symbionts' production of a chemical defence that is repulsive to fishes. Molecular phylogenetic analyses demonstrated that the symbiotic microbial communities are diverse and probably dominated in terms of population size by bacteria and small unicellular Synechococcus-type cyanobacteria. Although largely unknown in the oceans, defensive symbioses probably promote marine biodiversity by allowing niche expansions into otherwise hostile environments.This work was supported by an NSF Predoctoral Fellowship
awarded to J.B.W and a grant from the North Carolina
Biotechnology Center to N.L and Richard Manderville
(Wake Forest University)
Correlation functions at small quark masses with overlap fermions
We report on recent work on the determination of low-energy constants
describing Delta{S}=1 weak transitions, in order to investigate the origins of
the Delta{I}=1/2 rule. We focus on numerical techniques designed to enhance the
statistical signal in three-point correlation functions computed with overlap
fermions near the chiral limit.Comment: Talk presented at Lattice2004(weak), Fermilab, 21-26 June 2004, 3
pages, 2 figure
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