Complex Scalar Singlet Dark Matter: Vacuum Stability and Phenomenology

We analyze one-loop vacuum stability, perturbativity, and phenomenological constraints on a complex singlet extension of the Standard Model (SM) scalar sector containing a scalar dark matter candidate. We study vacuum stability considerations using a gauge-invariant approach and compare with the conventional gauge-dependent procedure. We show that, if new physics exists at the TeV scale, the vacuum stability analysis and experimental constraints from the dark matter sector, electroweak precision data, and LEP allow both a Higgs-like scalar in the mass range allowed by the latest results from CMS and ATLAS and a lighter singlet-like scalar with weak couplings to SM particles. If instead no new physics appears until higher energy scales, there may be significant tension between the vacuum stability analysis and phenomenological constraints (in particular electroweak precision data) to the extent that the complex singlet extension with light Higgs and singlet masses would be ruled out. We comment on the possible implications of a scalar with ~125 GeV mass and future ATLAS invisible decay searches.Comment: 24 pages, 12 figures; v2 - fixed minor typos, added reference, changed layou

Civic Associations That Work: The Contributions of Leadership to Organizational Effectiveness

Why are some civic associations more effective at advancing their public agendas, engaging members, and developing leaders? We introduce a multi-dimensional framework for analyzing the comparative effectiveness of member-based civic associations in terms of public influence, member engagement, and leader development. Theoretical expectations in organization studies, sociology, political science, and industrial relations hold that organizations benefiting from either a favorable environment or abundant resources will be most effective. Using systematic data on the Sierra Clubs 400 local organizations, we assess these factors alongside an alternative approach focusing on the role of leaders, how they work together, and the activities they carry out to build capacity and conduct programs. While we find modest support for the importance of an organizations available resources and external environment, we find strong evidence for each of our three outcomes supporting our claim that effectiveness in civic associations depends to a large degree on internal organizational practices.This publication is Hauser Center Working Paper No. 36. The Hauser Center Working Paper Series was launched during the summer of 2000. The Series enables the Hauser Center to share with a broad audience important works-in-progress written by Hauser Center scholars and researchers

Constraining the top-quark mass within the global MSHT PDF fit

We examine the ability of experimental measurements of top-quark pair production to constrain both the top-quark mass and the strong coupling within the global MSHT parton distribution function (PDF) fit. Specifically, we consider ATLAS and CMS measurements of differential distributions taken at a centre-of-mass energy of 8 TeV, as well as $t\bar{t}$ total cross section data taken at a variety of experiments, and compare to theoretical predictions including next-to-next-to-leading order corrections. We find that supplementing the global fit with this additional information results in relatively strong constraints on the top-quark mass, and is also able to bound the strong coupling in a limited fashion. Our final result is $m_t=173.0\pm0.6~\mathrm{GeV}$ and is compatible with the world average pole mass extracted from cross section measurements of $172.5\pm0.7~\mathrm{GeV}$ by the Particle Data Group. We also study the effect of different top-quark masses on the gluon parton distribution function, finding changes at high $x$ which nonetheless lie within the large PDF uncertainties in this region.Comment: 35 pages, 13 figures, 3 table

Vibration Modeling of Bladed Disks Subject to Geometric Mistuning and Design Changes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76928/1/AIAA-2004-1686-437.pd