The Cosmological Constant Problem (and its sequester)

          @misc{ pirsa_PIRSA:15040109,
            doi = {10.48660/15040109},
            url = {https://pirsa.org/15040109},
            author = {Padilla, Antonio},
            keywords = {Cosmology},
            language = {en},
            title = {The Cosmological Constant Problem (and its sequester)},
            publisher = {Perimeter Institute},
            year = {2015},
            month = {apr},
            note = {PIRSA:15040109 see, \url{https://pirsa.org}}
          }
          

Abstract

I will review the notorious cosmological constant problem, sometimes described as the worst fine tuning problem in Physics. I will explain the true nature of the problem, which is one of radiative instability against any change in the effective description. I will recall Weinberg’s venerable no-go theorem that prohibits certain attempts to “solve” this problem before going on to explain a new mechanism that circumvents Weinberg. This is the vacuum energy sequester, a global modification of GR that results in the cancellation of large vacuum energy contributions from a protected matter sector (taken to include the Standard Model) at each and every order in the perturbative loop expansion. Cosmological consequences are a Universe which has finite space-time volume, will ultimately crunch, and for which dark energy can only be a transient. Furthermore, using a linear scalar potential within the sequestering set-up, I will show that dark energy today can be intimately related to the trigger that brings about cosmological collapse in the not too distant future, at the same time providing a possible solution to the “Why Now?” problem.