Freezing of the QCD coupling constant and solutions of Schwinger-Dyson equations

We compare phenomenological values of the frozen QCD running coupling constant (alpha(s)) with two classes of infrared finite solutions obtained through nonperturbative Schwinger-Dyson equations. We use these same solutions with frozen coupling constants as well as their respective nonperturbative gluon propagators to compute the QCD prediction for the asymptotic pion form factor. Agreement between theory and experiment on alpha(s)(0) and F (pi)(Q(2)) is found only for one of the Schwinger-Dyson equation solutions.

Schwinger-Dyson equations and dynamical gluon mass generation

We obtain a solution for the gluon propagador in Landau gauge within two distinct approximations for the Schwinger-Dyson equations (SIDE). The first, named Mandelstam's approximation, consist in neglecting all contributions that come from fermions and ghosts fields while in the second, the ghosts fields are taken into account leading to a coupled system of integral equations. In both cases we show that a dynamical mass for the gluon propagator can arise as a solution.

Collective Perspective on Advances in Dyson-Schwinger Equation QCD

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

SELF-CONSISTENT SOLUTION OF THE SCHWINGER-DYSON EQUATIONS FOR THE NUCLEON AND MESON PROPAGATORS

The Schwinger-Dyson equations for the nucleon and meson propagators are solved self-consistently in an approximation that goes beyond the Hartree-Fock approximation. The traditional approach consists in solving the nucleon Schwinger-Dyson equation with bare meson propagators and bare meson-nucleon vertices; the corrections to the meson propagators are calculated using the bare nucleon propagator and bare nucleon-meson vertices. It is known that such an approximation scheme produces the appearance of ghost poles in the propagators. In this paper the coupled system of Schwinger-Dyson equations for the nucleon and the meson propagators are solved self-consistently including vertex corrections. The interplay of self-consistency and vertex corrections on the ghosts problem is investigated. It is found that the self-consistency does not affect significantly the spectral properties of the propagators. In particular, it does not affect the appearance of the ghost poles in the propagators.

A dynamical gluon mass solution in a coupled system of the Schwinger-Dyson equations

We study numerically the Schwinger-Dyson equations for the coupled system of gluon and ghost propagators in the Landau gauge and in the case of pure gauge QCD. We show that a dynamical mass for the gluon propagator arises as a solution while the ghost propagator develops an enhanced behavior in the infrared regime of QCD. Simple analytical expressions are proposed for the propagators, and the mass dependency on the ΛQCD scale and its perturbative scaling are studied. We discuss the implications of our results for the infrared behavior of the coupling constant, which, according to fits for the propagators infrared behavior, seems to indicate that α s(q2) → 0 as q2 → 0. © SISSA/ISAS 2004.

Schwinger-dyson equations and dynamical gluon mass generation

We discuss the solutions obtained for the gluon propagador in Landau gauge within two distinct approximations for the Schwinger-Dyson equations (SDE). The first, named Mandelstam's approximation, consist in neglecting all contributions that come from fermions and ghosts fields while in the second, the ghosts fields are taken into account leading to a coupled system of integral equations. In both cases we show that a dynamical mass for the gluon propagator can arise as a solution. © 2005 American Institute of Physics.

Matt Christopher Papers - Accession 1092

The Matt Christopher Papers consist of published manuscripts, published short stories (1943-1994) (drafts, synopses, plot outlines, and magazines, comics, and newspapers with articles and short stories), galleys (1954-1990s), leather bound author’s editions (1954-1991), and publisher’s editions of Matt Christopher’s children’s books (1954-2004). The collection contains many unpublished manuscripts and drafts outside the children’s book field (1954-1997), unpublished poems (1938-1993), unpublished screenplays (1940-1997), and unpublished short stories (1954-1997). Also included are taped (audio and video) interviews of Matt Christopher, as well as, puzzles for children (1988-1992), research materials and notes (1954-1997), sports rule-books (1954-1995), and writing guides (1909-1995), personal (1949-1997) and business correspondence (1952-2002), contract agreements (1952-1993), royalty statements (1954-1999), and biographical information (1917-2004), memorabilia (personalized baseball bat, framed pictures and award certificates, etc.), fan mail (1964-1999) and his personal book collection (1847-1995) (some signed by authors).

Review of Prairie Time: A Blackland Portrait by Matt White

Nowadays, the Blackland Prairies of north Texas are the kind of landscape most people think of as great for subdivisions and strip malls: generally flat, easily bulldozed, and not too far from Dallas-Fort Worth. Prairie Time: A Blackland Portrait traces a similar utilitarian vision of the prairie in 19th-century pioneer descriptions as well: good for plowing, grazing, and-once the buffalo and Native Americans are exterminated-not too far from outposts of commerce. The book serves as an environmental jeremiad for a place too easily seen as useful and thus too often ignored for preservation. Matt White gives readers a context in which to begin to value the Blackland Prairie by combining a heartfelt story with a thorough sense of its ecological wonder, our post-settlement history and its environmental impact on the land, and some remarkable stories of current preservationists working to find and save remnant gems of unplowed prairie.

Ectomycorrhizae of sessile oak (Quercus petraea (Matt.) Liebl.)

Investigations were performed during the years 1999 to 2001 on a limed and unlimed plot within a high-elevated sessile oak forest. The oak forest (with 90 years old European beech at the understorey) was 170 to 197 years old. It is located at forest district Merzalben, location 04/0705, which is situated in the Palatinate Forest in south-west Germany. Liming was performed in December 1988 when 6 tons/ha of powdered Dolomite were brought up by the forestry department. Liming was performed to counteract the effects of soil acidification (pH(H2O) at Horizon A (0-10 cm): 3.9), which is induced by long-term (anthropogenic) acidic cloud cover and precipitation. Potentially toxic Al3+ ions, which become solubilized below pH 5, were suspected to be responsible for forest dieback and sudden death of the mature oaks. The most logical entry point for these toxic ions was suspected to occur in the highly absorptive region of the ectomycorrhizae (fungal covered root tips). However, the diversity and abundance of oak-ectomycorrhizal species and their actual roles in aluminum translocation (or blockage) were unknown. It was hypothesized that the ectomycorrhizae of sessile oaks in a limed forest would exhibit greater seasonal diversity and abundance with less evidence of incorporated aluminum than similar oak ectomycorrhizae from unlimed soils. To test this hypothesis, 12 oaks in the limed plot and 12 in an adjacent unlimed plot were selected. Each spring and fall for 2 years (1999 & 2000), 2 sets of soil cylinders (9.9 cm dia.) were extracted from Horizon A (0-10 cm), Horizon B (30-40 cm) and Horizon C (50-60 cm depth) at a distance of 1 meter from each tree base. Roots were extracted from each probe by gentle sieving and rinsing. Soil samples were retained for pH (H2O, CaCl2, and KCl) and moisture analysis. One set of roots was sorted by size and air-dried for biomass analysis. The finest mycorrhizal roots of this set were used for bound and unbound (cytosolic) mineral [Al, Ca, Mg, K, Na, Mn, S, Zn, Fe, Cd and Pb] analysis (by Landwirtschaftliche Untersuchungs- und Forschungsanstalt Rheinland Palatinate (LUFA)). Within 7 days of collection, the mycorrhizal tips from the second set of probes were excised, sorted, identified (using Agerer’s Color Atlas), counted and weighed. Seasonal diversity and abundance was characterized for 50 of the 93 isolates. The location and relative abundance of Al within the fungal and root cell walls was characterized for 68 species using 0.01% Morin dye and fluorescence microscopy. Morin complexes with Al to produce an intense yellow fluorescence. The 4 most common species (Cenococcum geophilum, Quercirhiza fibulocsytidiata, Lactarius subdulcis, Piceirhiza chordata) were prepared for bound Al, Ca, Fe and K mineral analysis by LUFA. The unlimed and limed plots were then compared. Only 46 of the 93 isolated ectomycorrhizal species had been previously associated with oaks in the literature. Mycorrhizal biomass was most abundant in Horizon A, declining with depth, drought and progressive soil acidification. Mycorrhizae were most diverse (32 species) in the limed plot, but individual species abundance was low (R Selection) in comparison to the unlimed plot, where there were fewer species (24) but each species present was abundant (K Selection). Liming increased diversity and altered dominance hierarchy, seasonal distributions and succession trends of ectomycorrhizae at all depths. Despite an expected reduction in Al content, the limed ectomycorrhizae both qualitatively (fluorescence analysis) and quantitatively (mineral analysis) contained more bound Al, especially so in Horizon A. The Al content qualitatively and quantitatively increased with depth in the unlimed and limed plots. The bound Al content fluctuated between 4000-and 20000 ppm while the unbound component was consistently lower (4 -14 ppm). The relative amount of unbound Al declined upon liming implying less availability for translocation to the crown area of the trees. This correspouds with the findings of good crown appearance and lower tree mortality in the limed zone. Each ectomycorrhizal species was unique in its ability to block, sequester (hold) or translocate Aluminum. In several species, Al uptake varied with changes in moisture, pH, depth and liming. According to the fluorescence study, about 48% of the isolated ectomycorrhizal species blocked and/or sequestered (held) Al in their mantle and/or Hartig net walls, qualitatively lowering bound Al in the adjacent root cell walls. Generally, if Al was more concentrated in the fungal walls, it was less evident in the cortex and xylem and conversely, if Al was low or absent from the fungal walls it was frequently more evident in the cortex and xylem.