On the possible running of the cosmological “constant”

Abstract

Despite the many outstanding cosmological observations leading to a strong evidence for a nonvanishing cosmological constant (CC) term Λ in the gravitational field equations, the theoretical status of this quantity seems to be lagging well behind the observational successes. It thus seems timely to revisit some fundamental aspects of the CC term in Quantum Field Theory (QFT). We emphasize that, in curved space-time, nothing a priori prevents this term from potentially having a mild running behavior associated to quantum effects. Remarkably, this could be the very origin of the dynamical nature of the Dark Energy, in contrast to many other popular options considered in the literature. In discussing this possibility, we also address some recent criticisms concerning the possibility of such running. Our conclusion is that, while there is no comprehensive proof of the CC running, there is no proof of the non-running either. The problem can be solved only through a deeper understanding of the vacuum contributions of massive quantum fields on a curved spacetime background. We suggest that such investigations are at the heart of one of the most important endeavors of fundamental theoretical cosmology in the years to come.

Phenomenological Fluids from Interacting Tachyonic Scalar Fields

“…Alternative models of dark energy suggest a dynamical form of dark energy, which at least in an effective level, can originate from a variable cosmological constant [24,25], or from various fields, such as a canonical scalar field [26][27][28][29][30] (quintessence), a phantom field [31][32][33][34][35][36][37][38] or the quintom [39][40][41][42][43][44][45][46][47][48][49][50][51]. By using some basic of quantum gravitational principles, we can formulate several other models for dark energy and in literature they are known as holographic dark energy paradigm [52][53][54][55][56][57][58][59][60][61][62][63] and agegraphic dark energy models [64][65][66].…”

Solar System constraints on renormalization group extended general relativity: The PPN and Laplace-Runge-Lenz analyses with the external potential effect

“…Among the possible extensions of GR that have consequences at astrophysical or cosmological scales, we consider here extensions that are based on the Renormalization Group (RG) framework applied to gravity [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In this context, either from Quantum Field Theory (QFT) in curved spacetime [7,22], or in certain quantum-gravity theories, like the asymptotic safety program [17,23,24], the GR constants G and Λ necessarily run in the ultraviolet limit.…”

Braneworld gravity within non-conservative gravitational theory

“…(12) that this model of gravity provides a braneworld scenario with a running effective cosmological "constant". As such this novel aspect is promising for cosmology as it can make feasible the emerging of interactions between dark energy and dark matter [17][18][19][20][21][22][23][24][25][26].…”

“…This equation carries an effective cosmological constant which now becomes a function of the coordinates due to the terms inherited from the modified gravity. This feature is attractive from the cosmological point of view, as a time-dependent cosmological "constant" makes possible a construction of a model of universe where the components of the dark sector are able to interact each other, exchanging energy and momentum [17][18][19][20][21][22][23][24][25][26]. This class of cosmologies usually comes into play as an attempt of addressing the socalled "coincidence problem" [27].…”