Dilaton Stabilization in Brane Gas Cosmology

Brane Gas Cosmology is an M-theory motivated attempt to reconcile aspects of the standard cosmology based on Einstein's theory of general relativity. Dilaton gravity, when incorporating winding p-brane states, has verified the Brandenberger--Vafa mechanism --a string-motivated conjecture which explains why only three of the nine spatial dimensions predicted by string theory grow large. Further investigation of this mechanism has argued for a hierarchy of subspaces, and has shown the internal directions to be stable to initial perturbations. These results, however, are dependent on a rolling dilaton, or varying strength of Newton's gravitational constant. In these proceedings we show that it is not possible to stabilize the dilaton and maintain the stability of the internal directions within the standard Brane Gas Cosmology setup.Comment: 6 pages, no figures. To appear in the Proceedings of MRST 2004, held at Concordia University, Montreal, QC, 12-14 May 200

Non-Isotropic Angular Distribution for Very Short-Time Gamma-Ray Bursts

While most gamma-ray bursts (GRBs) are now believed to be from cosmological distances, the origin of very short-time GRBs is still not known. In the past, we have shown that GRBs with time duration (T90) less than 100 ms may form a separate class of GRBs based on the hardness and time distribution of these events. We have also shown that the ln N ln S distribution is consistent with the expectation of quasi-Euclidean distribution of sources. In this paper, we report the study of the angular location of these GRBs showing a strong deviation from isotropy within the Galactic coordinates of plus 180 degrees < longitude < 90 degrees and -30 degrees < latitude < 30 degrees. We have studied the rest of the GRBs and do not find a similar deviation. This further indicates that the very-short GRBs likely form a separate class of GRBs, most probably from sources of Galactic or near solar origin

Thermochronological evolution of calcite formation at the potential Yucca Mountain repository site, Nevada: Part 2 fluid inclusion analyses and UPb dating

The presence of two-phase fluid inclusions in thin secondary mineral crusts at the potential Yucca Mountain nuclear waste repository has raised questions regarding the origin, timing, and temperature of past fluid flow through the repository horizon. The geologically recent passage of fluids with high temperatures would call into question the suitability of the site for the storage of high level nuclear waste. This study determined the thermal history of fluid flow through the site using fluid inclusion analyses and constrained the timing of thermal fluids by dating silica minerals spatially associated with the fluid inclusions using U-Pb techniques. Results provide a detailed time-temperature history of fluid migration through primary and secondary pore spaces during the past 8 to 9 million years. One hundred and fifty-five samples were collected in the unsaturated zone from the C-shaped Exploratory Studies Facility (ESF), the ECRB cross drift which crosses the potential repository horizon, and exploratory alcoves. Detailed petrographic and paragenetic studies indicated that the oldest secondary minerals consisted of heterogeneously distributed calcite with lesser chalcedony, quartz, opal, and fluorite. The oldest secondary minerals were overgrown by intermediate bladed calcite. The youngest secondary minerals include chemically distinct Mgenriched, growth-zoned sparry calcite (MGSC) and intergrown U-enriched opal. Fluid inclusion petrography indicated that 50 % of the samples (n = 78) contained fluid inclusion assemblages with two-phase fluid inclusions, and that assemblages of liquid-only fluid inclusions represent \u3e 96% of all fluid inclusions within the secondary minerals. Assemblages of two-phase inclusions also contain liquid-only inclusions that did not nucleate a vapor-bubble owing to formation at relatively low temperatures. Virtually all two-phase fluid inclusions occur in paragenetically old calcite; rare two-phase inclusion assemblages were observed in old fluorite (n = 3) and quartz (n = 2). Rare two-phase fluid inclusions were observed in early-intermediate calcite; sparse, irregularly shaped liquid-only inclusions form the only fluid inclusion assemblages observed in late-intermediate minerals and young MGSC. Homogenization temperatures for calcite across the site are generally 45 - 60 °C, but higher temperatures reaching 83 °C were recorded in the north portal and ramp of the ESF and cooler temperatures of ~ 35 - 45 °C were recorded in the intensely fracture zone. Samples from lithophysal cavities in the ESF and ECRB contain multiple populations of two-phase inclusions. Inclusion temperatures are highest in early calcite (\u3e 45 °C) and cooler in paragenetically younger early calcite, indicating cooling with time. The cooler temperatures coincide with temperatures recorded in the intensely fractured zone and indicate that secondary minerals in the intensely fractured zone began to precipitate later than secondary minerals in other locations. Freezing point depressions determined for inclusions range from -0.2 to -1.6 °C indicating trapping of a low salinity fluid. A small number of fluid inclusions in fluorite and quartz were identified and evaluated. Four inclusions in these minerals homogenized at temperatures higher than those recorded for calcite (91 ° - 95 °C) . Two approaches were used to constrain the timing of thermal fluids at Yucca Mountain. First, the age of MGSC was determined, and it provides a minimum age for fluids with elevated temperatures owing to the presence of only liquid-only inclusions in MGSC. Results indicate that MGSC began to precipitate across the site between 2.90 ± 0.06 Ma and about 1.95 ± 0.06 Ma, and MGSC has continued to precipitate to within the last half million years. These ages constrain fluids with elevated temperatures to have accessed the site more than about 2.90 Ma. Second, more precise temporal constraints were determined for samples in which datable opal or chalcedony occur in the intermediate or older parts of the mineral crusts, or are spatially related to 2-phase fluid inclusions. Such ages indicate that two-phase fluid inclusions are older than 5.32 ± 0.02 Ma, and that fluids with elevated temperatures were present at Yucca Mountain before this time. Results from this study are consistent with a model of descending meteoric water that infiltrated the cooling tuff sequence, became heated, and precipitated secondary minerals within the vadose zone. Fluid inclusions indicate that fluids with elevated temperatures were present during the early history of Yucca Mountain. Sparse, liquid-only fluid inclusions in late intermediate to young calcite indicate that secondary minerals were precipitated from low temperature fluids during the past 5 million years. This study demonstrates that the hypothesis of geologically recent upwelling hydrothermal fluids is untenable and should not disqualify Yucca Mountain as a potential nuclear waste storage site

Representations of reductive normal algebraic monoids

The rational representation theory of a reductive normal algebraic monoid (with one-dimensional center) forms a highest weight category, in the sense of Cline, Parshall, and Scott. This is a fundamental fact about the representation theory of reductive normal algebraic monoids. We survey how this result was obtained, and treat some natural examples coming from classical groups.Comment: 10 pages. To appear in a volume of the Fields Communications Series: "Algebraic Monoids, Group Embeddings, and Algebraic Combinatorics," edited by Mahir Can, Zhenheng Li, Benjamin Steinberg, and Qiang Wan

Prediction of Small-Scale Densities Using the Chemical and Optical Spread Functions

Development adjacency effects and optical spread in photographic systems cause difficulties in predicting small-scale densities. These effects can be quantified as spread functions. The optical spread func tion describes the light scatter of the film. The chemical spread func tion describes the lateral diffusion of development- inhibiting and dev elopment-accelerating reaction products. These spread functions can be used along with the sensitometry and covering power relationships of the system to predict small-area densities from the object exposure profile. A study based on C. N. Nelson\u27s work was undertaken to develop a math ematical model that uses the optical and chemical spread functions to predict small-area densities of an image from the original object ex posure profile. This model was developed for a fine-grain aerial dup licating film processed in KODAK D-76 (1:4). It was found that the model predicted the image profile of a log-periodic target to within 0.02 D on the peaks of the bars. However, the model overshot the edges of the bars by about -0.0$ D. This difference, even though significantly greater than the experimental error, does not affect the usefulness of this model to image quality studies

Observational constraints on the nature of very short gamma-ray bursts

We discuss a very peculiar subgroup of gamma-ray bursts among the BATSE sources. These bursts are very short ($T_{90} \le$0.1 s), hard, and came predominantly from a restricted direction of the sky (close to the Galactic anti-center). We analyze their arrival times and possible correlations, as well as the profiles of individual bursts. We find no peculiarities in the arrival times of Very Short Bursts (VSBs) despite their highly non-uniform spatial distribution. There is no dependence in the burst shapes on location. Bursts coming both from the burst-enhancement Galactic Anticenter region and from all other directions show considerable dispersion in their rise and fall times. Significant fraction of VSBs have multiple peaks despite their extremely short duration. Burst time properties are most likely to be consistent with two origin mechanisms: either with binary NS-NS mergers with low total masses passing through a phase of hypermassive neutron star, or with evaporation of the primordial black holes in the scenario of no photosphere formation.Comment: 25 pages, 14 figures; accepted to New Astronom

Leptogenesis with Left-Right domain walls

The presence of domain walls separating regions of unbroken $SU(2)_L$ and $SU(2)_R$ is shown to provide necessary conditions for leptogenesis which converts later to the observed Baryon aymmetry. The strength of lepton number violation is related to the majorana neutrino mass and hence related to current bounds on light neutrino masses. Thus the observed neutrino masses and the Baryon asymmetry can be used to constrain the scale of Left-Right symmetry breaking.Comment: References added, To appear in Praman

Resolution of Nearly Mass Degenerate Higgs Bosons and Production of Black Hole Systems of Known Mass at a Muon Collider

The direct s-channel coupling to Higgs bosons is 40000 times greater for muons than electrons; the coupling goes as mass squared. High precision scanning of the lighter $h^0$ and the higher mass $H^0$ and $A^0$ is thus possible with a muon collider. The $H^0$ and $A^0$ are expected to be nearly mass degenerate and to be CP even and odd, respectively. A muon collider could resolve the mass degeneracy and make CP measurements. The origin of CP violation in the $K^{0}$ and $B^{0}$ meson systems might lie in the the $H^0/A^0$ Higgs bosons. If large extra dimensions exist, black holes with lifetimes of $\sim 10^{-26}$ seconds could be created and observed via Hawking radiation at the LHC. Unlike proton or electron colliders, muon colliders can produce black hole systems of known mass. This opens the possibilities of measuring quantum remnants, gravitons as missing energy, and scanning production turn on. Proton colliders are hampered by parton distributions and CLIC by beamstrahlung. The ILC lacks the energy reach.Comment: Latex, 5 pages, 2 figures, proceedings to the DPF 2004: Annual Meeting of the Division of Particles and Fields of APS, 26 August-31 August 2004, Riverside, CA, US