Abstract
We argue that dark energy with multiple fields is theoretically well-motivated and predicts distinct observational signatures, in particular when cosmic acceleration takes place along a trajectory that is highly non-geodesic in field space. Such models provide novel physics compared to ΛCDM and quintessence by allowing cosmic acceleration on steep potentials. From the theoretical point of view, these theories can easily satisfy the conjectured swampland constraints and may in certain cases be technically natural, potential problems which are endemic to standard single-field dark energy. Observationally, we argue that while such multi-field models are likely to be largely indistinguishable from the concordance cosmology at the background level, dark energy perturbations can cluster, leading to an enhanced growth of large-scale structure that may be testable as early as the next generation of cosmological surveys.
Highlights
Introduction. — Dark energy beyond the cosmological standard model is usually studied in the context of theories with a single scalar field, such as quintessence [1] or scalar-tensor gravity [2]
We argue that dark energy with multiple fields is theoretically well-motivated and predicts distinct observational signatures, in particular when cosmic acceleration takes place along a trajectory that is highly non-geodesic in field space
Further theoretical motivation for considering dark energy with multiple fields comes from the recently-proposed swampland conjectures [5–8], parameter constraints which, it is claimed,1 must be satisfied by any low-energy model which possesses a UV completion in string theory
Summary
Introduction. — Dark energy beyond the cosmological standard model is usually studied in the context of theories with a single scalar field, such as quintessence [1] or scalar-tensor gravity [2]. Multi-field dark energy: cosmic acceleration on a steep potential
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