Assessing observational constraints on dark energy

          @misc{ pirsa_PIRSA:24070095,
            doi = {10.48660/24070095},
            url = {https://pirsa.org/24070095},
            author = {Shlivko, David},
            keywords = {},
            language = {en},
            title = {Assessing observational constraints on dark energy},
            publisher = {Perimeter Institute},
            year = {2024},
            month = {jul},
            note = {PIRSA:24070095 see, \url{https://pirsa.org}}
          }
          

Abstract

Observational constraints on time-varying dark energy are commonly presented in terms of the two CPL parameters $w_0$ and $w_a$. Recent observations favor a sector of this parameter space in which $w_0 > -1$ and $w_0 + w_a < -1$, suggesting that the equation of state underwent a transition from violating the null energy condition (NEC) at early times to obeying it at late times. In this talk, I will demonstrate that this initial impression is misleading, by showing that simple quintessence models satisfying the NEC at all times predict an observational preference for the same sector. The upshot is that the CPL parameterization is simultaneously useful for detecting deviations from cosmological-constant dynamics ($w = -1$) but unreliable for predicting the true behavior of $w(z)$.