Determine the origin and gravity-test implications of dynamical dark-energy degeneracy

Determine whether the degeneracy among dynamical dark-energy models arises from a fundamental geometric information limit in low-redshift distance measurements rather than from limited statistical precision, and quantify its implications for systematic biases in extragalactic gravity tests.

Background

The paper discusses the longstanding difficulty of distinguishing dynamical dark-energy models because different equation-of-state parameterizations can produce nearly identical distance–redshift relations over the redshift range probed by low-redshift geometric observations. The authors note that this degeneracy is commonly attributed to insufficient statistical precision, with the expectation that more precise data could resolve it.

The unresolved issue is whether the degeneracy instead reflects an intrinsic geometric information limit of low-redshift distance measurements. Establishing its origin is important because the answer determines whether improved statistical precision alone can distinguish dark-energy models and whether dark-energy assumptions can induce systematic biases in strong-lensing tests of gravity, particularly constraints on the post-Newtonian parameter.