Abstract
Quintessential inflation provides a unified description of inflation and dark energy in terms of a single scalar degree of freedom, the cosmon. We present here a comprehensive overview of this appealing paradigm, highlighting its key ingredients and keeping a reasonable and homogeneous level of details. After summarizing the cosmological evolution in a simple canonical case, we discuss how quintessential inflation can be embedded in a more general scalar-tensor formulation and its relation to variable gravity scenarios. Particular emphasis is placed on the role played by symmetries. In particular, we discuss the evolution of the cosmon field in terms of ultraviolet and infrared fixed points potentially appearing in quantum gravity formulations and leading to the emergence of scale invariance in the early and late Universe. The second part of the review is devoted to the exploration of the phenomenological consequences of the paradigm. First, we discuss how direct couplings of the cosmon field to matter may affect neutrinos masses and primordial structure formation. Second, we describe how Ricci-mediated couplings to spectator fields can trigger the spontaneous symmetry breaking of internal symmetries such as, but not limited to, global U(1) or Z2 symmetries, and affect a large variety of physical processes in the early Universe.
Highlights
Academic Editors: Konstantinos “Once upon a time the Universe sped up, out of emptiness
The embedding of quintessential inflation in a more general variable gravity framework is presented in Section 3, where we summarize the alternative representations and equivalence classes in the literature
Inflation and dark energy are usually understood as two independent epochs in the expansion history of the Universe
Summary
Academic Editors: Konstantinos “Once upon a time the Universe sped up, out of emptiness. The lack of satisfactory answers to these questions has motivated a plethora of alternative explanations to the present accelerated expansion of the Universe, usually coined under the generic name of dark energy models Many of these proposals involve a time-dependent (non-homogeneous) scalar field with an evolving equation of state different from that of baryons, neutrinos, dark matter, or radiation. This fifth or quintessential entity is generically designed to mimic, with sufficient accuracy, a de Sitter-like behaviour at the present cosmological epoch, in full analogy with the inflationary stage but at an energy scale many orders of magnitude lower.
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