Dark energy in the swampland
Abstract
In this article, we study the implications of string swampland criteria for dark energy in view of ongoing and future cosmological observations. If string theory should be the ultimate quantum gravity theory, there is evidence that exact de Sitter solutions with a positive cosmological constant cannot describe the fate of the latetime universe. Even though cosmological models with dark energy given by a scalar field π evolving in time are not in direct tension with string theory, they have to satisfy the swampland criteria ∆ π <d ̃O (1 ) and V^{'}/V >c ̃O (1 ), where V is the scalar field potential. In view of the restrictive implications that the swampland criteria have on dark energy, we investigate the accuracy needed for future observations to tightly constrain standard darkenergy models. We find that current 3 σ constraints with c ≲1.35 are still well in agreement with the string swampland criteria. However, stage4 surveys such as Euclid, LSST, and DESI, tightly constraining the equation of state w (z ), will start putting surviving quintessence models into tensions with the string swampland criteria by demanding c <0.4 . We further investigate whether any idealized futuristic survey will ever be able to give a decisive answer to the question whether the cosmological constant would be preferred over a timeevolving darkenergy model within the swampland criteria. Hypothetical surveys with a reduction in the uncertainties by a factor of ̃20 compared to Euclid would be necessary to reveal strong tension between quintessence models obeying the string swampland criteria and observations by pushing the allowed values down to c <0.1 . In view of such perspectives, there will be fundamental observational limitations with future surveys.
 Publication:

Physical Review D
 Pub Date:
 December 2018
 DOI:
 10.1103/PhysRevD.98.123502
 arXiv:
 arXiv:1808.02877
 Bibcode:
 2018PhRvD..98l3502H
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 5 pages, 3 figures, version 2: small changes and references added