Beyond the Standard Cosmological Model in the Multi-messenger Era

Dear Colleagues,

The most accredited paradigm which traces out the universe expansion history is the standard ΛCDM model. The model has captured renewed attention, since, from a genuine observational point of view, it well adapts to cosmic data. Further, the model makes use of the fewest number of assumptions possible, because it employs a cosmological constant Λ which drives the current acceleration. Even though appealing and straightforward, the discrepancies between quantum field predictions and cosmic observations, as well as the unexpected coincidence problem between the matter and Λ densities today, are dramatic. In these respects, the ΛCDM model seems to be incomplete, albeit its simplicity turns out to be the startling suit to admit its validity. Therefore, if on the one hand the cosmic acceleration is a well-consolidated fact, on the other hand it is not so clear whether the ΛCDM model is effectively the final paradigm of the whole dynamics.

In the recent years, alternative scenarios, such as dark energy models, extended theories of gravity, non-homogeneous scenarios, back-reaction, etc., have been widely explored to ascertain if the ΛCDM model is the correct paradigm. However, all these attempts have been so far unsuccessful to portray large-scale dynamics. More likely, the final paradigm to describe the universe dynamics would be the one unifying the late-time acceleration with other cosmic phases, among which the Big Bang, the Inflation, the reheating, and so forth.

The main purpose of this Special Issue is to sketch alternative treatments to the ΛCDM model, dusting off Λ as interchangeable with other possibilities. To this end, the guidelines to follow are wide, spanning from phenomenological dark energy reconstructions, passing through barotropic fluids as alternative frameworks, to higher-dimensional theories of gravity. We thus embrace scenarios involving different epochs of universe’s evolution: at early times, concerning the effects of quantum cosmology and quantum field theories, in intermediate epochs, dealing with galaxy formation and dark matter models, up to the late-time era, in which dark energy is the most prominent ingredient within the cosmic puzzle. Therefore, manuscripts based on a vast number of topics, such as dark energy, dark matter, small perturbations, early time cosmology, quantum gravity, extended theories of gravity, etc., are warmly welcome.

Prof. Orlando Luongo
Guest Editor

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