The best of the rest from the physics arXiv this week:
The Dark Side of Gravity: Modified Theories of Gravity
Approaches to Single Photon Detection
Failure of Antibiotic Treatment in Microbial Populations
Transfer of an Optical Frequency Over an Urban Fiber Link
Random Matrix Theory and the Evolution of Business Cycle Synchronisation 1886-2006
Alternative theories of gravity aren’t quite different from the existing ones, they just introducing calibration members (mostly the stress energy tensor/vector field) into existing field equations.
The basic idea is, the curvature of space corresponds the energy density, which is the source of additional gravitational field in additional global metric (Yilmaz, Heim). Another approach is the modification of MOND theory, which is based on omni-directional expansion of universe (TeVeS of Bekenstein).
The Universe expansion can be considered as a primary source of gravity, as follows from dual role of gravity and universe expansion in quantum mechanics and geometrodynamics. Briefly speaking, the gravity prohibits the expansion of quantum wave of free particle, while the expansion of Universe prohibits the collapse of geons – it means, the gravity field is the dual to Universe expansion, the speed of which is proportional to local vacuum energy density.