# The Science Case for STEP - General Relativity and Quantum Cosmology

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Abstract: STEP the Satellite Test of the Equivalence Principle will advanceexperimental limits on violations of Einstein-s equivalence principle EP fromtheir present sensitivity of 2 parts in 10^13 to 1 part in 10^18 throughmultiple comparison of the motions of four pairs of test masses of differentcompositions in an earth-orbiting drag-free satellite. Dimensional argumentssuggest that violations, if they exist, should be found in this range, and theyare also suggested by leading attempts at unified theories of fundamentalinteractions e.g. string theory and cosmological theories involving dynamicaldark energy. Discovery of a violation would constitute the discovery of a newforce of nature and provide a critical signpost toward unification. A nullresult would be just as profound, because it would close off any possibility ofa natural-strength coupling between standard-model fields and the new lightdegrees of freedom that such theories generically predict e.g., dilatons,moduli, quintessence. STEP should thus be seen as the intermediate-scalecomponent of an integrated strategy for fundamental physics experiments thatalready includes particle accelerators at the smallest scales and supernovaprobes at the largest. The former may find indirect evidence for new fieldsvia their missing-energy signatures, and the latter may produce direct evidencethrough changes in cosmological equation of state-but only a gravitationalexperiment like STEP can go further and reveal how or whether such a fieldcouples to the rest of the standard model. It is at once complementary to theother two kinds of tests, and a uniquely powerful probe of fundamental physicsin its own right.

Author: ** James Overduin, Francis Everitt, John Mester, Paul Worden**

Source: https://arxiv.org/