  We try to address quantitatively the question whether a new mass is needed to
fit current supernovae data. For this purpose, we consider an infra-red
modification of gravity that does not contain any new mass scale but systematic
subleading corrections proportional to the curvature. The modifications are of
the same type as the one recently derived by enforcing the "Ultra Strong
Equivalence Principle" (USEP) upon a Friedmann-Lemaitre-Robertson-Walker
universe in the presence of a scalar field. The distance between two comoving
observers is altered by these corrections and the observations at high redshift
affected at any time during the cosmic evolution. While the specific values of
the parameters predicted by USEP are ruled out, there are regions of parameter
space that fit SnIa data very well. This allows an interesting possibility to
explain the apparent cosmic acceleration today without introducing either a
dark energy component or a new mass scale.

Cosmology and Nongalactic Astrophysics;General Relativity and Quantum Cosmology;High Energy Physics - Phenomenology;High Energy Physics - Theory