Tadpole Cosmology: Self Tuning Without Degeneracy

Abstract

Degeneracy is a method to accommodate exact, low energy vacuum states in scalar-tensor gravitational models despite the presence of an arbitrarily large vacuum energy. However, this approach requires very particular combinations of scalar field and metric couplings in the Lagrangian. In this work we study departures from the restrictive degeneracy condition -- starting from a fiducial model containing an exact Minkowski space solution, we break the degeneracy condition in numerous simple ways to test if the resulting models maintain certain key features -- specifically the dynamical cancellation of a large vacuum energy by the scalar field and the existence of a low energy vacuum state. We highlight the role the tadpole plays in eliminating the fixed points of the dynamical system, generically rendering both the scalar field and metric time dependent. Our results indicate that when violating the degeneracy condition but preserving shift symmetry, the metric maintains an asymptotic Minkowski state, irrespective of the presence of the cosmological constant. In contrast, when shift symmetry is also broken the asymptotic behaviour can radically alter. Regardless, the non-degenerate models in this work share an attractive quality; harboring low energy, late-time asymptotic states that are independent of the vacuum energy. The tadpole allows for a broader class of non-degenerate, self-tuning models than was previously realized.

arXiv comment19 pages, 4 figures, 1 table, v2: to appear in JCAP

References in corpus (25)

• Modified Gravity and Cosmology
• Modified Gravity Theories on a Nutshell: Inflation, Bounce and Late-time Evolution
• Beyond the Cosmological Standard Model
• The Effective Field Theory of Dark Energy
• General second order scalar-tensor theory, self tuning, and the Fab Four
• Maximal freedom at minimum cost: linear large-scale structure in general modifications of gravity
• Essential Building Blocks of Dark Energy
• Dark Energy or Modified Gravity? An Effective Field Theory Approach
• The Effective Theory of Quintessence: the w<-1 Side Unveiled
• Self-tuning and the derivation of the Fab Four
• The cosmology of the Fab-Four
• Fab 5: Noncanonical Kinetic Gravity, Self Tuning, and Cosmic Acceleration
• The Well-Tempered Cosmological Constant
• Well-tempered teleparallel Horndeski cosmology: a teleparallel variation to the cosmological constant problem
• Self Tuning Scalar Fields in Spherically Symmetric Spacetimes
• Well-Tempered Minkowski Solutions in Teleparallel Horndeski Theory
• Beyond Fab Four
• Well-Tempered Cosmology
• Spherical Cows in the Sky with Fab Four
• A minimal self tuning model to solve the cosmological constant problem
• The Well-Tempered Cosmological Constant: The Horndeski Variations
• The Well-Tempered Cosmological Constant: Fugue in B${}^{♭}$
• Self-tuning kinetic gravity braiding: Cosmological dynamics, shift symmetry, and the tadpole
• Generalised scalar-tensor theories and self-tuning
• An Expansion of Well Tempered Gravity