Electroweak Symmetry Breaking by Strong Dynamics and the Collider Phenomenology

We discuss the possible signatures in the electroweak symmetry breaking sector by new strong dynamics at future hadron colliders such as the Tevatron upgrade, the LHC and VLHC, and $e^+e^-$ linear colliders. Examples include a heavy Higgs-like scalar resonance, a heavy Technicolor-like vector resonance and pseudo-Goldstone states, non-resonance signatures via enhanced gauge-boson scattering and fermion compositeness.Comment: Summary report of the Strong Electroweak Symmetry Breaking Working Group at 2001 Snowmass Summer Studie

Modeling Mg II h, k and Triplet Lines at Solar Flare Ribbons

Observations from the \textit{Interface Region Imaging Spectrograph} (\textsl{IRIS}) often reveal significantly broadened and non-reversed profiles of the Mg II h, k and triplet lines at flare ribbons. To understand the formation of these optically thick Mg II lines, we perform plane parallel radiative hydrodynamics modeling with the RADYN code, and then recalculate the Mg II line profiles from RADYN atmosphere snapshots using the radiative transfer code RH. We find that the current RH code significantly underestimates the Mg II h \& k Stark widths. By implementing semi-classical perturbation approximation results of quadratic Stark broadening from the STARK-B database in the RH code, the Stark broadenings are found to be one order of magnitude larger than those calculated from the current RH code. However, the improved Stark widths are still too small, and another factor of 30 has to be multiplied to reproduce the significantly broadened lines and adjacent continuum seen in observations. Non-thermal electrons, magnetic fields, three-dimensional effects or electron density effect may account for this factor. Without modifying the RADYN atmosphere, we have also reproduced non-reversed Mg II h \& k profiles, which appear when the electron beam energy flux is decreasing. These profiles are formed at an electron density of $\sim 8\times10^{14}\ \mathrm{cm}^{-3}$ and a temperature of $\sim1.4\times10^4$ K, where the source function slightly deviates from the Planck function. Our investigation also demonstrates that at flare ribbons the triplet lines are formed in the upper chromosphere, close to the formation heights of the h \& k lines

The Stability of Double White Dwarf Binaries Undergoing Direct Impact Accretion

We present numerical simulations of dynamically unstable mass transfer in a double white dwarf binary with initial mass ratio, q = 0.4. The binary components are approximated as polytropes of index n = 3/2 and the initially synchronously rotating, semi-detached equilibrium binary is evolved hydrodynamically with the gravitational potential being computed through the solution of Poisson's equation. Upon initiating deep contact in our baseline simulation, the mass transfer rate grows by more than an order of magnitude over approximately ten orbits, as would be expected for dynamically unstable mass transfer. However, the mass transfer rate then reaches a peak value, the binary expands and the mass transfer event subsides. The binary must therefore have crossed the critical mass ratio for stability against dynamical mass transfer. Despite the initial loss of orbital angular momentum into the spin of the accreting star, we find that the accretor's spin saturates and angular momentum is returned to the orbit more efficiently than has been previously suspected for binaries in the direct impact accretion mode. To explore this surprising result, we directly measure the critical mass ratio for stability by imposing artificial angular momentum loss at various rates to drive the binary to an equilibrium mass transfer rate. For one of these driven evolutions, we attain equilibrium mass transfer and deduce that effectively q_crit has evolved to approximately 2/3. Despite the absence of a fully developed disk, tidal interactions appear effective in returning excess spin angular momentum to the orbit.Comment: 27 pages, 6 figures. Please see http://www.phys.lsu.edu/faculty/tohline/astroph/mftd07/ for animations and full resolution figures. Accepted for publication in the Astrophysical Journa

Comparison of [11C]TZ1964B and [18F]MNI659 for PET imaging brain PDE10A in nonhuman primates

Phosphodiesterase 10A (PDE10A) inhibitors show therapeutic effects for diseases with striatal pathology. PET radiotracers have been developed to quantify in vivo PDE10A levels and target engagement for therapeutic interventions. The aim of this study was to compare two potent and selective PDE10A radiotracers, [(11)C]TZ1964B and [(18)F]MNI659 in the nonhuman primate (NHP) brain. Double scans in the same cynomolgus monkey on the same day were performed after injection of [(11)C]TZ1964B and [(18)F]MNI659. Specific uptake was determined in two ways: nondisplaceable binding potential (BP(ND)) was calculated using cerebellum as the reference region and the PDE‐10A enriched striatum as the target region of interest (ROI); the area under the time–activity curve (AUC) for the striatum to cerebellum ratio was also calculated. High‐performance liquid chromatography (HPLC) analysis of solvent‐extracted NHP plasma identified the percentage of intact tracer versus radiolabeled metabolites samples post injection of each radiotracer. Both radiotracers showed high specific accumulation in NHP striatum. [(11)C]TZ1964B has higher striatal retention and lower specific striatal uptake than [(18)F]MNI659. The BP(ND) estimates of [(11)C]TZ1964B were 3.72 by Logan Reference model (LoganREF) and 4.39 by simplified reference tissue model (SRTM); the BP(ND) estimates for [(18)F]MNI659 were 5.08 (LoganREF) and 5.33 (SRTM). AUC ratios were 5.87 for [(11)C]TZ1964B and 7.60 for [(18)F]MNI659. Based on BP(ND) values in NHP striatum, coefficients of variation were ~10% for [(11)C]TZ1964B and ~30% for [(18)F]MNI659. Moreover, the metabolism study showed the percentage of parent compounds were ~70% for [(11)C]TZ1964B and ~50% for [(18)F]MNI659 60 min post injection. These data indicate that either [(11)C]TZ1964B or [(18)F]MNI659 could serve as suitable PDE10A PET radiotracers with distinguishing features for particular clinical application