Can the sneutrino be the lightest supersymmetric particle ?

Within the framework of the constrained Minimal Supersymmetric extension of the Standard Model we show that recent LEP I limits on the invisible Z width exclude the possibility that the lightest sparticle is the sneutrino

IST Austria Thesis

Hybrid zones represent evolutionary laboratories, where recombination brings together alleles in combinations which have not previously been tested by selection. This provides an excellent opportunity to test the effect of molecular variation on fitness, and how this variation is able to spread through populations in a natural context. The snapdragon Antirrhinum majus is polymorphic in the wild for two loci controlling the distribution of yellow and magenta floral pigments. Where the yellow A. m. striatum and the magenta A. m. pseudomajus meet along a valley in the Spanish Pyrenees they form a stable hybrid zone Alleles at these loci recombine to give striking transgressive variation for flower colour. The sharp transition in phenotype over ~1km implies strong selection maintaining the hybrid zone. An indirect assay of pollinator visitation in the field found that pollinators forage in a positive-frequency dependent manner on Antirrhinum, matching previous data on fruit set. Experimental arrays and paternity analysis of wild-pollinated seeds demonstrated assortative mating for pigmentation alleles, and that pollinator behaviour alone is sufficient to explain this pattern. Selection by pollinators should be sufficiently strong to maintain the hybrid zone, although other mechanisms may be at work. At a broader scale I examined evolutionary transitions between yellow and anthocyanin pigmentation in the tribe Antirrhinae, and found that selection has acted strate that pollinators are a major determinant of reproductive success and mating patterns in wild Antirrhinum

Gaugino Condensation, Moduli Potentials and Supersymmetry Breaking in M-Theory Models

We derive the explicit form, and discuss some properties of the moduli dependent effective potential arising from M-theory compactified on $M_4 \times X\times S^1 / Z_2$, when one of the boundaries supports a strongly interacting gauge sector and induces gaugino condensation. We discuss the relation between the explicit gaugino condensate and effective superpotential formulations and find interesting differences with respect to the situation known from the weakly coupled heterotic string case. The moduli dependence of the effective potential turns out to be more complicated than expected, and perhaps offers new clues to the stabilization problem.Comment: Latex file, 21 pages, various typos corrected, references added. Version to appear in Nuclear Physics

Crank Shaped Notes

Crank Shaped Note

Baryons and Dark Matter from the Late Decay of a Supersymmetric Condensate

The possibility that both the baryon asymmetry and dark matter arise from the late decay of a population of supersymmetric particles is considered. If the decay takes place below the LSP freeze out temperature, a nonthermal distribution of LSPs results. With conserved $R$ parity these relic LSPs contribute to the dark matter density. A net asymmetry can exist in the population of decaying particles if it arises from coherent production along a supersymmetric flat direction. The asymmetry is transferred to baryons if the condensate decays through the lowest order nonrenormalizable operators which couple to $R$ odd combinations of standard model particles. This also ensures at least one LSP per decay. The relic baryon and LSP number densities are then roughly equal. The ratio of baryon to dark matter densities is then naturally \Omegab / \OmegaLSP \sim {\cal O}(\mb / \mLSP). The resulting upper limit on the LSP mass is model dependent but in the range ${\cal O}(30-140)$ GeV. The total relic density is related to the order at which the flat direction which gives rise to the condensate is lifted. The observed density is obtained for a direction which is lifted by a fourth order Planck scale suppressed operator in the superpotential.Comment: 14 pages, phyzz

The Phase Transitions of 4’-n-pentyl-4-cyanobiphenyl + C60 Colloidal Composites

This project experimentally determined how the nematic-isotropic phase transitions of colloidal composites consisting of 5CB and C60 change as C60 mass concentration increases. Using MDSC comparisons of the concentration\u27s reversible and nonreversible heat capacitance signals were analyzed which yielded values for phase transition temperature, enthalpy, and coexistence region of both phases. The analysis showed fluctuating results. Polarized light microscope images showed isolated domains of C60 and 5CB. A mechanically quenched macroscopic model of the composites was constructed and tested. Steric modeling confirmed that the local domains were due to the unique geometries of 5CB and C60 and that steric packing may account for the unexpected thermal results

Correlation by Insoluble Residues in the Austin Chalk of southern Dallas County, Texas

A partial composite section totalling 300 feet was constructed for the Upper Cretaceous Austin Chalk through correlation of overlapping portions of some of the larger incomplete sections. The correlations were effected primarily by insoluble residues in conjunction with thicknesses and weathering profiles. Bar graphs based on insoluble percentages indicate that the formation is composed of the following principal lithologic types: marly limestone, marlstone-limestone, limy marlstone, and marlstone. These are variably distributed vertically and to a lesser degree laterally. The subdivisions of lower chalk, middle marl, and upper chalk are a function of the proportions in which the basic lithologic types are present in these portions of the column. Based on insoluble residue correlations, composite sections of approximately 100 feet each were constructed for the basal lower chalk, the lower chalk-middle marl, and the middle marl-upper chalk contact. The intraformational contacts are both conformable and transitional. The use of insoluble residue determinations to correlate incomplete sections is an effective, but exceedingly time-consuming procedure. Correlations are most readily made with proximate sections 30-40 feet or more, but the number of such sections in any given area is limited. The method is not recommended as a readily applicable technique for construction of a detailed stratigraphic section of the Austin Chalk in Dallas County