Safe Quantum Gravity Research Articles

Ghost wavefunction renormalization in asymptotically safe quantum gravity

Motivated by Weinberg's asymptotic safety scenario, we investigate the gravitational renormalization group flow in the Einstein–Hilbert truncation supplemented by the wavefunction renormalization of the ghost fields. The latter induces non-trivial corrections to the β-functions for Newton's constant and the cosmological constant. The resulting ghost-improved phase diagram is investigated in detail. In particular, we find a non-trivial ultraviolet fixed point, in agreement with the asymptotic safety conjecture which also survives in the presence of extra dimensions. In four dimensions the ghost anomalous dimension at the fixed point is η*c = −1.8, supporting spacetime being effectively two dimensional at short distances.

Running gauge coupling in asymptotically safe quantum gravity

We investigate the non-perturbative renormalization group behavior of the gauge coupling constant using a truncated form of the functional flow equation for the effective average action of the Yang-Mills-gravity system. We find a non-zero quantum gravity correction to the standard Yang-Mills beta function which has the same sign as the gauge boson contribution. Our results fit into the picture according to which Quantum Einstein Gravity (QEG) is asymptotically safe, with a vanishing gauge coupling constant at the non-trivial fixed point.

Bare action and regularized functional integral of asymptotically safe quantum gravity

Investigations of quantum Einstein gravity (QEG) based upon the effective average action employ a flow equation which does not contain any ultraviolet (UV) regulator. Its renormalization group trajectories emanating from a non-Gaussian fixed point define asymptotically safe quantum field theories. A priori these theories are, somewhat unusually, given in terms of their effective rather than bare action. In this paper we construct a functional integral representation of these theories. We fix a regularized measure and show that every trajectory of effective average actions, depending on an IR cutoff only, induces an associated trajectory of bare actions which depend on a UV cutoff. Together with the regularized measure these bare actions give rise to a functional integral which reproduces the prescribed effective action when the UV cutoff is removed. In this way we are able to reconstruct the underlying microscopic (classical) system and identify its fundamental degrees of freedom and interactions. The bare action of the Einstein-Hilbert truncation is computed and its flow is analyzed as an example. Various conceptual issues related to the completion of the asymptotic safety program are discussed.

A minimal length from the cutoff modes in asymptotically safe quantum gravity

Within asymptotically safe Quantum Einstein Gravity (QEG), the quantum 4-sphere is discussed as a specific example of a fractal spacetime manifold. The relation between the infrared cutoff built into the effective average action and the corresponding coarse graining scale is investigated. Analyzing the properties of the pertinent cutoff modes, the possibility that QEG generates a minimal length scale dynamically is explored. While there exists no minimal proper length, the QEG sphere appears to be "fuzzy" in the sense that there is a minimal angular separation below which two points cannot be resolved by the cutoff modes.

From big bang to asymptotic de Sitter: complete cosmologies in a quantum gravityframework

Using the Einstein–Hilbert approximation of asymptotically safe quantum gravity wepresent a consistent renormalization group based framework for the inclusion of quantumgravitational effects into the cosmological field equations. Relating the renormalizationgroup scale to cosmological time via a dynamical cutoff identification this frameworkapplies to all stages of the cosmological evolution. The very early universe is found tocontain a period of ‘oscillatory inflation’ with an infinite sequence of time intervals duringwhich the expansion alternates between acceleration and deceleration. For asymptoticallylate times we identify a mechanism which prevents the universe from leaving the domain ofvalidity of the Einstein–Hilbert approximation and obtain a classical de Sitter era.