The quantum field theoretic prediction for the vacuum energy density leads to a value for the effective cosmological constant that is incorrect by between 60 to 120 orders of magnitude. In a paper, George Ellis et al. (2010) review an old proposal of replacing Einstein's Field Equations by their trace-free part (the Trace-Free Einstein Equations), together with an independent assumption of energy--momentum conservation by matter fields. While this does not solve the fundamental issue of why the cosmological constant has the value that is observed cosmologically, it is indeed a viable theory that resolves the problem of the discrepancy between the vacuum energy density and the observed value of the cosmological constant. Therefore they confirm that no problems arise in such a scheme: hence, the Trace-Free Einstein Equations are indeed viable for cosmological and astrophysical applications.
So what do you think? Can the Trace-Free Einstein Equations be a Viable Alternative to General Relativity? Your comments are welcome