Running vacuum models propose dynamical vacuum energy unifying inflation and dark energy

Towards a unified quantum field theory of dark energy and inflation: unstable de Sitter vacuum and running vacuum

arXiv:2601.05218v3 Announce Type: replace-cross Abstract: Inflation is a necessary cosmic mechanism to cure basic inconsistencies of the standard model of cosmology. These problems are usually `fixed' by postulating the existence of a scalar field (called the ``inflaton''). However, other less ad hoc options are possible. In the running vacuum model (RVM) framework, the vacuum energy density (VED) $\rho_{\rm vac}$ is a function of the Hubble rate $H$ and its time derivatives. In this context, the VED is dynamical (there is no rigid cosmological constant $\Lambda$). In the FLRW epoch, $\rho_{\rm vac}$ evolves very slowly with expansion. In contrast, in the very early universe the vacuum fluctuations induce higher powers $H^N$ capable of unleashing fast inflation in a short period in which $H\simeq$ const. We call this mechanism `RVM-inflation'. It does not require an inflaton field since inflation is brought about by pure quantum field theory (QFT) effects on the dynamical background. It is different from Starobinsky's inflation, in which $H$ is never constant. In this work, we study a closely related scenario: the decay of the exact de Sitter vacuum into FLRW spacetime in its radiation epoch and the subsequent impact on the current universe, and compare with the RVM. We find that in both cases inflation is driven by $H^4$ powers together with subleading contributions of order $H^2$ that ease a graceful-exit transition into the radiation-dominated epoch, where the FLRW regime starts and ultimately develops a mildly evolving VED in the late universe: $\delta\rho_{\rm vac}\sim {\cal O}(m_{\rm Pl} ^2 H^2)$. The proposal presented here aims at a unified QFT approach to inflation and dark energy (conceived as dynamical vacuum energy) with potentially measurable phenomenological consequences in the present universe, and constitutes a first step toward establishing its full theoretical and phenomenological consistency.

2 hours ago

Running Vacuum in the expanding Universe: a unified QFT paradigm for Inflation and Dark Energy

arXiv:2606.05352v2 Announce Type: replace-cross Abstract: The concordance $\Lambda$CDM model, based on a rigid $\Lambda$-term for the entire cosmic history, has been in crisis for a long time. In our expanding Universe, an evolving $\Lambda$ with the expansion is intuitively much more reasonable. In the running vacuum model (RVM) framework, based on quantum field theory (QFT) in curved spacetime, quantum effects induce a vacuum energy density (VED) $\rho_{\rm vac}=\Lambda/(8\pi G)$ which is a function of the Hubble rate $H$ and its time derivatives, $\rho_{\rm vac}=\rho_{\rm vac}(H, \dot{H},\ddot{H},\dots)$. Currently, $\rho_{\rm vac}$ evolves very slowly with the expansion, $\delta\rho_{\rm vac}\sim {\cal O}(m_{Pl} ^2 H^2)$, and this fact provides a possible fundamental origin of dark energy (DE), conceived as dynamical vacuum energy. In the RVM, Newton's $G$ is also evolving, but much more slowly (logarithmically with $H$): $G=G(\ln H)$. In the very early universe, the vacuum fluctuations induce higher (even) powers, e.g. $\sim H^4$, capable of triggering fast inflation in a very short period, in which $H$ is very large and approximately constant. This is the mechanism of `RVM-inflation'. It does not require an `inflaton' field since inflation is brought about by pure QFT effects on the dynamical background. It differs from Starobinsky's inflation, where $H$ is never constant. Furthermore, the dynamics of $\rho_{\rm vac}(H)$ and $G(H)$ can also have implications on the frequently discussed possibility that the fundamental `constants' of Nature can be mildly evolving with the cosmic expansion. Putting things together, a unified QFT framework of dark energy and inflation ensues as a realistic theory for the description of the universe as a whole on fundamental grounds. In it, dynamical VED is predicted and is much welcomed, since it fits in with current DESI measurements, preferring dynamical DE over a rigid $\Lambda$ term.

2 hours ago