Dark energy: a quantum fossil from the inflationary universe?

Abstract

The discovery of dark energy (DE) as the physical cause for the accelerated expansion of the Universe is the most remarkable experimental finding of modern cosmology. However, it leads to insurmountable theoretical difficulties from the point of view of fundamental physics. Inflation, on the other hand, constitutes another crucial ingredient, which seems necessary to solve other cosmological conundrums and provides the primeval quantum seeds for structure formation. One may wonder if there is any deep relationship between these two paradigms. In this work, we suggest that the existence of the DE in the present Universe could be linked to the quantum field theoretical mechanism that may have triggered primordial inflation in the early Universe. This mechanism, based on quantum conformal symmetry, induces a logarithmic, asymptotically-free, running of the gravitational coupling. If this evolution persists in the present Universe, and if matter is conserved, the general covariance of Einstein's equations demands the existence of dynamical DE in the form of a running cosmological term, Λ, whose variation follows a power law of the redshift.

Starobinsky-Like Inflation and Running Vacuum in the Context of Supergravity

“…It is important to notice at this point that in the original Starobinsky model [5], the R 2 terms crucial for inflation arise from the conformal anomaly in the path integral of massless (conformal) matter in a de Sitter background, and thus, their coefficient is arbitrary and can only be fixed phenomenologically. A similar, although not identical, situation occurs in the context of anomaly-induced inflation [11][12][13], where the term R 2 is absent at the classical level, but is generated from the conformal anomaly. In this case, however, the coefficient of R (entering the β-functions and controlling the stability of inflation) presents also some arbitrariness, which can only be fixed by a special re-normalization condition.…”

“…Also very important for our considerations is the framework of the running vacuum model (RVM) [13][14][15][16][17][18][19]; see [20][21][22] and the references therein for a recent detailed exposition. The implications of these dynamical vacuum models have recently been analysed both for the early Universe [22][23][24][25][26][27][28], as well as for the phenomenology of the current Universe [29][30][31]; see also [32][33][34][35][36][37][38][39][40] for previous analyses.…”

Why is the running vacuum energy more benign than the holographic Ricci dark energy?

“…In addition, the constant 1 C 0 is given by [11,14] 5) and 0 Ã ¼ Ã ðH 0 Þ is the energy density defined at the present time t 0 or equivalently at the current Hubble rate H 0 ¼ Hðt 0 Þ. In addition, M i is the masses of particles contributing in the loops [12]. The dimensionless parameter provides the main coefficient of the function for the running of the vacuum energy, and B i are coefficients computed from the quantum loop contributions of fields with masses M i [12].…”

“…In addition, M i is the masses of particles contributing in the loops [12]. The dimensionless parameter provides the main coefficient of the function for the running of the vacuum energy, and B i are coefficients computed from the quantum loop contributions of fields with masses M i [12]. Meanwhile, C H and C _ H are dimensionless coefficients that can be fitted to the observations.…”

“…Another very interesting approach to explain the latetime speedup of the Universe is to invoke an evolving vacuum energy which was named the running vacuum energy [11][12][13]. This approach is related to the cosmological constant à (problem), where à would be no longer constant along the expansion of the Universe but changing as predicted from the renormalization group equation for the vacuum energy [11].…”