Tests of chameleon gravity

Theories of modified gravity, where light scalars with non-trivial self-interactions and non-minimal couplings to matter—chameleon and symmetron theories—dynamically suppress deviations from general relativity in the solar system. On other scales, the environmental nature of the screening means that such scalars may be relevant. The highly-nonlinear nature of screening mechanisms means that they evade classical fifth-force searches, and there has been an intense effort towards designing new and novel tests to probe them, both in the laboratory and using astrophysical objects, and by reinterpreting existing datasets. The results of these searches are often presented using different parametrizations, which can make it difficult to compare constraints coming from different probes. The purpose of this review is to summarize the present state-of-the-art searches for screened scalars coupled to matter, and to translate the current bounds into a single parametrization to survey the state of the models. Presently, commonly studied chameleon models are well-constrained but less commonly studied models have large regions of parameter space that are still viable. Symmetron models are constrained well by astrophysical and laboratory tests, but there is a desert separating the two scales where the model is unconstrained. The coupling of chameleons to photons is tightly constrained but the symmetron coupling has yet to be explored. We also summarize the current bounds on f(R) models that exhibit the chameleon mechanism (Hu and Sawicki models). The simplest of these are well constrained by astrophysical probes, but there are currently few reported bounds for theories with higher powers of R. The review ends by discussing the future prospects for constraining screened modified gravity models further using upcoming and planned experiments

Ecological Observations on Pteridophyta in the Kangra Himalaya

Volume: 44Start Page: 49End Page: 6

Christella dentata

Pteridophyte

Aspects of the phytogeography of African Pteridophyta

A diversity of distribution patterns exhibited by African pteridophytes on intercontinental and continental scales are presented. Occasional random dispersal among the Pteridophyta over long distances is accepted. The ecological importance of the gametophyte phase is inferred. Future progress in the elucidation of African fern phytogeography will require a broader alpha-taxonomic pan-African base and the plotting of many more distribution maps

A checklist of the Pteridophytes of the ‘Flora of Southern Africa’ region

The 250 species, both indigenous and naturalized, in th e 75 genera of southern African Pteridophytes are listed with their subspecies and varieties (263 tax a in all ) . Coded distribution ranges are given for each taxon

MELIANTHACEAE

TWO NEW COMBINATIONS IN MELIANTHU