The Science Case for STEP
Abstract
: STEP will advance experimental limits on violations of Einstein's equivalence principle (EP) from their present sensitivity of 3 parts in 1013 to 1 part in 1018 through multiple comparison of the motions of four pairs of test masses of different compositions in an earthorbiting drag-free satellite. Dimensional arguments suggest that violations, if they exist, should be found in this range, and they are also predicted by many of the leading attempts at unified theories of fundamental interactions (e.g. string theory), as well as cosmological theories involving dynamical dark energy. Discovery of a violation would constitute the discovery of a new force of nature and provide us with a critical signpost toward unification. A null result would be just as profound, because it would close off any possibility of a natural-strength coupling between standard-model fields and the new light degrees of freedom that nearly all such theories generically predict (e.g., dilatons, moduli, quintessence). STEP should thus be seen as the intermediate-scale component of an integrated strategy for fundamental physics experiments that already includes particle acclerators (at the smallest scales) and supernova probes (at the largest). The former may find indirect evidence for new fields via their missing-energy signatures, and the latter may produce direct evidence through changes in cosmological equation of state - but only a gravitational experiment like STEP can go further and reveal how or whether such a field couples to the rest of the standard model. It is at once complementary to the other two kinds of tests, and a uniquely powerful probe of fundamental physics in its own right.
- Publication:
-
37th COSPAR Scientific Assembly
- Pub Date:
- 2008
- Bibcode:
- 2008cosp...37.2314O