MOND and its bimetric formulation
  I first give a succinct account of the MOND paradigm--emphasizing the
centrality of scale invariance in the nonrelativistic, deep-MOND limit--and
describing rudiments of its phenomenology. I then present my credo, and some
generalities, concerning existing MOND theories. Then I concentrate on one
relativistic formulation of MOND in the form of a bimetric theory (BIMOND). I
describe its various limits: the weak field, with application to gravitational
waves, the nonrelativistic limit, and their further deep-MOND (low
acceleration) limits, which are scale invariant. Other aspects of BIMOND that
have been explored are aspects of cosmology, matter fluctuations in cosmology,
and matter-twin-matter interactions. BIMOND remains largely unexplored, despite
its promise in several regards: It tends to GR for a0 goes to 0 (a0 is the MOND
constant); it has a simple nonrelativistic limit; it describes gravitational
lensing correctly; and, it has a generic appearance of a cosmological-constant
term that is of order a0^2/c^4, as observed.
