Well-tempered teleparallel Horndeski cosmology: a teleparallel variation to the cosmological constant problem

Well-tempering is a promising classical method of dynamically screening an arbitrarily large vacuum energy and generating a late-time, low energy de Sitter vacuum state. In this paper, we study for the first time self-tuning in teleparallel gravity and obtain well-tempered cosmological models in the teleparallel gravity analogue of Horndeski theory. This broadens the scope of well-tempered cosmology and teases the potentially far richer cosmological dynamics that could be anchored on teleperallel gravity. We expand the well-tempered recipe to its most general form so far and use it to search for the first well-tempered cosmologies in teleparallel gravity. We also study the cosmological dynamics in a well-tempered model and demonstrate the dynamical stability of the vacuum, the compatibility with a matter era, and the stability of the vacuum through a phase transition.