High Energy Theory Seminar: Jim Cline

Title: Quintessential dark energy crossing the phantom divide

Abstract: The Dark Energy Spectrometer Instrument second data release has strengthened indications of evolving dark energy, including the violation of the null energy condition ρ > −p. DESIy finds that the dark energy equation of state evolved from w < −1 to w > −1,known as crossing the phantom divide. I will discuss challenges to constructing theoretical models realizing this scenario, focusing on “ghost condensation,” in which higher-derivative terms in the action play an essential role. We find that the simplest such theory can provide a good fit to the w(z) evolution that best fits the DESI + CMB + Union3 data sets. Theories of dark matter interacting with dark energy also provide an attractive explanation.