Abstract
The string theory swampland proposes that there is no UV-completion for an effective field theory with an exact (metastable) de Sitter vacua, thereby ruling out standard ΛCDM cosmology if the conjecture is taken seriously. The swampland criteria have also been shown to be in sharp tension with quintessence models under current and forthcoming observational bounds. As a logical next step, we introduce higher derivative self-interactions in the low-energy effective Lagrangian and show that one can satisfy observational constraints as well as the swampland criteria for some specific models. In particular, the cubic Galileon term, in the presence of an exponential potential, is examined to demonstrate that parts of the Horndeski parameter space survives the swampland and leads to viable cosmological histories.
Highlights
The string theory swampland proposes that there is no UV-completion for an effective field theory with an exact de Sitter vacua, thereby ruling out standard ΛCDM cosmology if the conjecture is taken seriously
The dS constraint clearly rules out standard ΛCDM cosmology, our simplest proposal for late-time acceleration, due to the unavailability of any local dS extrema in the effective potential
It has been proposed that the current era of accelerated expansion be explained by models of quintessence, i.e. by assuming a scalar field beyond the Standard Model. (In a similar manner, the same swampland conjectures have put appreciable pressure on the simplest models of vanilla single-field inflation — an era of accelerated expansion in the early-universe — thereby necessitating the introduction of more complicated models, e.g. [5,6,7,8,9, 16, 17, 25, 26, 29].) On the bright side, such quintessence models can be embedded in string theory through slowly rolling moduli fields, thereafter suitably imposing the swampland conjectures on them
Summary
The late-time acceleration of the universe shall be explained through the dynamics of an effective scalar field — the Galileon π. Note that our primary aim is to show how the swampland conjectures can be satisfied when including non-canonical higher-derivative terms in the action, going beyond quintessence models. As it is, quantum corrections can lead to the appearance of higher derivative terms when the non-renormalizable theorem is violated [76], when the Galileon symmetry is not weakly-broken. Generalizations of the cubic Galileon models have been shown to be compatible with the ISW data [84] Keeping these in mind, we shall only consider the cubic Galileon term, (∇π) π, in our action.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
