Massive, Topologically Massive, Models

In three dimensions, there are two distinct mass-generating mechanisms for gauge fields: adding the usual Proca/Pauli-Fierz, or the more esoteric Chern-Simons (CS), terms. Here we analyze the three-term models where both types are present, and their various limits. Surprisingly, in the tensor case, these seemingly innocuous systems are physically unacceptable. If the sign of the Einstein term is ``wrong'' as is in fact required in the CS case, then the excitation masses are always complex; with the usual sign, there is a (known) region of the two mass parameters where reality is restored, but instead we show that a ghost problem arises, while, for the ``pure mass'' two-term system without an Einstein action, complex masses are unavoidable. This contrasts with the smooth behavior of the corresponding vector models. Separately, we show that the ``partial masslessness'' exhibited by (plain) massive spin-2 models in de Sitter backgrounds is formally shared by the three-term system: it also enjoys a reduced local gauge invariance when this mass parameter is tuned to the cosmological constant.Comment: 7 pages, typos corrected, reference adde

On a Three-Dimensional Gravity Model with Higher Derivatives

The purpose of this work is to present a model for 3D massive gravity with topological and higher-derivative terms. Causality and unitarity are discussed at tree-level. Power-counting renormalizability is also contemplated.Comment: 9 pages, Latex, no figures; to be published in Gen. Rel. Gra

Environmental Correlates of Physical Activity Among African-American Adults

The purpose of this cross-sectional study was to identify perceived environmental correlates of meeting physical activity guidelines among African-American adults living in Southern Nevada. Trained interviewers phoned potential participants who lived in the 12 zip codes of Clark County, Nevada with the highest proportions of African-American residents. Respondents (n=237) answered 52 health-related and demographic questions. Slightly less than 50% of participants met physical activity guidelines. A factor analysis procedure produced two environmental variables, neighborhood safety and environmental supports for physical activity. Age, gender and educational attainment (p\u3c.05) predicted the meeting of those guidelines (R2=.214), while neighborhood support for physical activity, neighborhood safety, and BMI failed to do so. This finding suggests that environmental factors are not strong predictors of physical activity among African- American adults, although environmental supports for physical activity approached significance. Future studies should consider assessing additional aspects of the built environment as an influence on physical activity