Dynamical Supersymmetry Breaking and Low Energy Gauge Mediation

Dynamical breaking of supersymmetry was long thought to be an exceptional phenomenon, but recent developments have altered this view. A question of great interest in the current framework is the value of the underlying scale of supersymmetry breaking. The "little hierarchy" problem suggests that supersymmetry should be broken at low energies. Within one class of models, low energy breaking be achieved as a consequence of symmetries, without requiring odd coincidences. The low energy theories are distinguished by the presence or absence of $R$ symmetries; in either case, and especially the latter one often finds modifications of the minimal gauge-mediated spectrum which can further ameliorate problems of fine tuning. Various natural mechanisms exist to solve the $\mu$ problem in this framework.Comment: 20 pages (minor change in referencing

Gauge Mediation with a small mu term and light squarks

We consider a solution to the mu problem in the context of Non-Minimal Gauge Mediation with two Singlets and Low-Scale Messengers. This solution reduces tuning associated with the "Little Hierarchy" problem by permitting a naturally small mu term (100-300 GeV) due to small mixing between the Singlets. The smallness of mu also relies crucially on compressing the Gauge Mediated sparticle spectrum resulting in 330-400 GeV squarks. In addition to a small mu term, the theory achieves a Higgs mass > 114.4 GeV through a large Higgs quartic coupling when tanbeta ~ 1.5. The vacua studied are globally stable with all couplings perturbative to the GUT scale. The amount of tuning required to get the correct Electroweak scale is of order 10%, with a similar residual tuning associated with the region of parameter space where the lightest CP-even Higgs mass is above the LEP bound.Comment: 34 pages, 8 figures. References and minor clarifications added. To appear in PR

Higgs Boson Decays to Neutralinos in Low-Scale Gauge Mediation

We study the decays of a standard model-like MSSM Higgs boson to pairs of neutralinos, each of which subsequently decays promptly to a photon and a gravitino. Such decays can arise in supersymmetric scenarios where supersymmetry breaking is mediated to us by gauge interactions with a relatively light gauge messenger sector (M_{mess} < 100 TeV). This process gives rise to a collider signal consisting of a pair of photons and missing energy. In the present work we investigate the bounds on this scenario within the minimal supersymmetric standard model from existing collider data. We also study the prospects for discovering the Higgs boson through this decay mode with upcoming data from the Tevatron and the LHC.Comment: 18 pages, 5 figures, added references and discussion of neutralino couplings, same as journal versio

Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems

We present results of a reconnaissance for stellar companions to all 131 radial-velocity-detected candidate extrasolar planetary systems known as of July 1, 2005. CPM companions were investigated using the multi-epoch DSS images, and confirmed by matching the trigonometric parallax distances of the primaries to companion distances estimated photometrically. We also attempt to confirm or refute companions listed in the Washington Double Star Catalog, the Catalogs of Nearby Stars, in Hipparcos results, and in Duquennoy & Mayor (1991). Our findings indicate that a lower limit of 30 (23%) of the 131 exoplanet systems have stellar companions. We report new stellar companions to HD 38529 and HD 188015, and a new candidate companion to HD 169830. We confirm many previously reported stellar companions, including six stars in five systems that are recognized for the first time as companions to exoplanet hosts. We have found evidence that 20 entries in the Washington Double Star Catalog are not gravitationally bound companions. At least three, and possibly five, of the exoplanet systems reside in triple star systems. Three exoplanet systems have potentially close-in stellar companions ~ 20 AU away from the primary. Finally, two of the exoplanet systems contain white dwarf companions. This comprehensive assessment of exoplanet systems indicates that solar systems are found in a variety of stellar multiplicity environments - singles, binaries, and triples; and that planets survive the post-main-sequence evolution of companion stars.Comment: 52 pages, 7 figures, Accepted for publication in Ap

Elevated aggrecan mRNA in early murine osteoarthritis

SummaryMale STR/ort mice develop osteoarthritis in the tibial articular cartilage. Low grade histological lesions first appear between 10–20 weeks of age. A previous study showed that the level of aggrecan, the major cartilage proteoglycan, is approximately twofold greater in the tibial cartilage of 16–19-week-old STR/ort mice compared with that in normal cartilage in control CBA mice. In the present investigation aggrecan gene transcription was investigated in 20-week-old STR/ort and CBA tibial cartilage using a quantitative reverse transcription-polymerase chain reaction (RT-PCR). The amount of aggrecan cDNA obtained from the STR/ort medial and lateral plateau was 2.8- and 4.6-fold greater per milligram of wet cartilage than that from the CBA tibial plateau. The difference was not due to differences in cellularity of tibial cartilage in the two strains and indicates that aggrecan gene transcription is elevated in early osteoarthritis

Note and Comment

The Death of Professor Knowlton - The loss to the Law School and to his colleagues of the law faculty in the death of Jerome Cyril Knowlton cannot be expressed. For thirty-one years, the longest period of active service ever given by any man to this Law School, Mr. Knowlton was an effective factor in the development of the institution and in the moulding of the character and the legal ideas and ideals of the thousands of graduates who have passed through the Law School into the service of community and state and country, at the bar, upon the bench, in legislative halls, and indeed in all of the walks of life. Few if any men now living have been known to as many law students as was Mr. Knowlton. And few indeed are they whose influence has been as widely felt, for he made a vivid and lasting impression upon all who came in contact with him

Counter Chemotactic Flow in Quasi-One-Dimensional Path

Quasi-one-dimensional bidirectional particle flow including the effect of chemotaxis is investigated through a modification of the John-Schadschneider-Chowdhury-Nishinari model. Specifically, we permit multiple lanes to be shared by both directionally traveling particles. The relation between particle density and flux is studied for several evaporation rates of pheromone, and the following results are obtained: i) in the low-particle-density range, the flux is enlarged by pheromone if the pheromone evaporation rate is sufficiently low, ii) in the high particle-density range, the flux is largest at a reasonably high evaporation rate and, iii) if the evaporation rate is at the level intermediate between the above two cases, the flux is kept small in the entire range of particle densities. The mechanism of these behaviors is investigated by observing the spatial-temporal evolution of particles and the average cluster size in the system.Comment: 4 pages, 9 figure

An assessment of chemical contaminants in the marine sediments of southwest Puerto Rico

This report summarizes the results of a characterization of chemical contaminants in the sediments in southwest Puerto Rico. The report is part of a project to integrate various analytical specialties to assess linkages between chemical contaminants and the condition of coral reefs. In this phase of the project, over 120 chemical contaminants were analyzed in sediments collected, including a number of organic (e.g., hydrocarbons), inorganic (e.g., metals), and biological (bacterial) compounds/analytes. The report also provides a preliminary analysis of the association between sediment contaminants and coral species richness. Overall, the levels of chemical contaminants in the study area between Guanica Bay and the town of La Parguera were fairly low. At most of the sites sampled, particularly adjacent to the town of La Parguera, concentrations of organic and inorganic contaminants were below the median values from NOAA’s National Status and Trends Program, which monitors the Nation’s coastal and estuarine waters for chemical contaminants. Elevated levels of a number of contaminant classes were seen at the two sites sampled within Guanica Bay. An initial analysis of modeled PAH (hydrocarbon) data and coral species richness (reef building species) indicated a strong negative correlation between the presence of PAHs in the sediments and coral species richness. Additional work is needed to assess possible reasons for this observed pattern. (PDF contains 126 pages)

Physical and biological controls on fine sediment transport and storage in rivers

Excess fine sediment, comprising particles <2 mm in diameter, is a major cause of ecological degradation in rivers. The erosion of fine sediment from terrestrial or aquatic sources, its delivery to the river, and its storage and transport in the fluvial environment are controlled by a complex interplay of physical, biological and anthropogenic factors. Whilst the physical controls exerted on fine sediment dynamics are relatively well-documented, the role of biological processes and their interactions with hydraulic and physico-chemical phenomena has been largely overlooked. The activities of biota, from primary producers to predators, exert strong controls on fine sediment deposition, infiltration and resuspension. For example, extracellular polymeric substances (EPS) associated with biofilms increase deposition and decrease resuspension. In lower energy rivers, aquatic macrophyte growth and senescence are intimately linked to sediment retention and loss, whereas riparian trees are dominant ecosystem engineers in high energy systems. Fish and invertebrates also have profound effects on fine sediment dynamics through activities that drive both particle deposition and erosion depending on species composition and abiotic conditions. The functional traits of species present will determine not only these biotic effects but also the responses of river ecosystems to excess fine sediment. We discuss which traits are involved and put them into context with spatial processes that occur throughout the river network. Whilst strides towards better understanding of the impacts of excess fine sediment have been made, further progress to identify the most effective management approaches is urgently required through close communication between authorities and scientists