Alfio Bonanno, Friederike Ihssen, Jan M. Pawlowski
SciPost Phys. Core 9, 005 (2026) ·
published 2 February 2026
|
· pdf
We solve the anharmonic oscillator using physics-informed renormalisation group (PIRG) flows, focusing on the weak coupling regime dominated by instanton-induced tunnelling processes. We demonstrate that the instanton physics underlying the exponential suppression of the energy gap is already captured at the first order of the derivative expansion within the PIRG framework. The key advances of this work are the implementation of a ground-state expansion in the PIRG flow and the adoption of high-precision Galerkin-based numerics. Our determination of the decay constant, $ a_{\mathrm{inst}} = 1.910(2) $, agrees quantitatively with the analytic value $ a_{\mathrm{inst}} = 1.886 $, differing by only $1\%$. While the present formulation relies on a heuristic mapping that will be systematically refined in future extensions of the PIRG approach, these results already highlight the remarkable ability of the method to capture non-perturbative quantum phenomena within relatively simple truncations.
Alfio Bonanno, Tobias Denz, Jan M. Pawlowski, Manuel Reichert
SciPost Phys. 12, 001 (2022) ·
published 4 January 2022
|
· pdf
We reconstruct the Lorentzian graviton propagator in asymptotically safe quantum gravity from Euclidean data. The reconstruction is applied to both the dynamical fluctuation graviton and the background graviton propagator. We prove that the spectral function of the latter necessarily has negative parts similar to, and for the same reasons, as the gluon spectral function. In turn, the spectral function of the dynamical graviton is positive. We argue that the latter enters cross sections and other observables in asymptotically safe quantum gravity. Hence, its positivity may hint at the unitarity of asymptotically safe quantum gravity.
