Open Questions in Dark Energy and Cosmological Constant

Dear Colleagues,

The two main “standard models” that describe particle physics and cosmology appear to be in tension due to several aspects. Among all, the cosmological constant problem appears particularly hard to fix: quantum field theory predicts vacuum energy, whose (constant) value disagrees with cosmological observations. However, the universe sped up can be simply explained through either the six-parameter minimal ΛCDM model (that adopts some sort of “bare cosmological constant”, which is compatible with observations) or dark energy scenarios (spanning from barotropic fluids to alternatives to Einstein’s theory of gravity). In all these cases, strong discrepancies between quantum expectations and cosmic observations have been severely found, leading to a huge challenge: if the ΛCDM model is not the final paradigm, which extensions or modifications are expected to better reproduce cosmic data and, at the same time, to remove the “weight” of a vacuum, namely, the cosmological constant?

Quite surprisingly, recent Planck observations confirm the ΛCDM scenario with suitable accuracy, although the presence of cosmological tensions (e.g., on H₀ and s₀) and evidence in favor of the Starobinsky inflationary potential, may suggest that more complicated paradigms can be invoked. What is currently more accepted is that a self-consistent final paradigm that describes the universe and includes the standard model of particle physics has not been developed yet, leaving late-time acceleration, inflation, reheating, baryogenesis, etc., which are all different and very distinct phases, that are, therefore, not unified under a single Lagrangian description.

The main purpose of this Special Issue is to expand on the idea of “dark cosmology”, inviting efforts that try to unify those scenarios to solve the cosmological constant problem and reconcile early with late times. Thus, we embrace a wide number of proposals based on phenomenological dark energy constructions, modified and extended gravity theories, effective field theory approaches, and so on. In this respect, we strongly encourage both theoretical and observational works and we welcome manuscripts based on the interplay between theory and experiments in subjects such as field theories, dark energy, dark matter, early time cosmology, late time cosmology, quantum cosmology, quantum aspects of gravity, extended and modified theories of gravity, etc.

You may choose our Joint Special Issue in Universe.

Dr. Orlando Luongo
Guest Editor

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• dark energy
• dark matter
• inflation
• cosmological constant
• baryogenesis
• leptogenesis
• nucleosynthesis
• Big Bang