arXiv subjects

Riccardo Gandolfo

Publications and source records attributed to Riccardo Gandolfo.

5 recordsLinked to original sources

arXiv2026

Infrared Screening of the Cosmological Constant

The observed cosmological constant is set by the deepest infrared scale of the present universe rather than by the microscopic scales that contribute to the vacuum energy. We show that this emerges as the quantum fluctuations of the gravitational field are progressively taken into account. Considering the Einstein-Hilbert+$R^2$ truncation of gravity, we find that in a wide region of the parameter space the theory develops instabilities that give rise to large amplitude quantum fluctuations which govern the renormalization group flow. Once the flow enters this region, it remains there all the way towards the infrared and progressively loses memory of its boundary conditions. The running cosmological constant $Λ_k$ ($k$ is the running scale) is driven towards the universal infrared scaling $Λ_k\sim λ_{_{\rm IR}}\,k^2$, with $λ_{_{\rm IR}}= \frac{1}{2(π-2)}$. At the deepest infrared scale $k\sim H_0$ (the current Hubble scale), the cosmological constant is then screened to its observed value $Λ_{_{\rm IR}}\sim H_0^2$.

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arXiv2026

Quantum gravity and spectral running cutoff

We have recently shown that a natural way to implement the Wilsonian paradigm in gauge theories is through the introduction of a ``spectral cutoff", a cut on the eigenvalues of the covariant Laplacian, pointing out that this provides the route toward the renormalization group (RG) construction. Here we apply this idea to quantum gravity, resorting to two realizations of the spectral running cutoff: ``hard" and ``smooth". We derive the RG equations for the Newton and cosmological constant and find the RG pattern of the asymptotic safety scenario, with a non-Gaussian UV-attractive fixed point.

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arXiv2025

Gravity and the Higgs boson mass

According to usual calculations in quantum field theory, both in flat and curved spacetime, the mass $m^2$ of a scalar particle is quadratically sensitive to the ultimate scale of the theory, the UV physical cutoff $Λ$. In the present work, paying attention to the path integral measure and to the way $Λ$ is introduced, we calculate the one-loop effective action $Γ^{1l}$ for a scalar field on a non-trivial gravitational background. We find that $m^2$ presents only a (mild) logarithmic sensitivity to $Λ$. This is obtained without resorting to a supersymmetric embedding of the theory, nor to regularization schemes (as dimensional or zeta-function regularization) where power-like divergences are absent by construction. In view of the results of the present work, we finally speculate on the way the Minkowski limit should be approached.

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arXiv2025

Diffeomorphism invariance of the effective gravitational action

We investigate on the diffeomorphism invariance of the effective gravitational action, focusing in particular on the path integral measure. In the literature, two different measures are mainly considered, the Fradkin-Vilkovisky and the Fujikawa one. With the help of detailed calculations, we show that, despite claims to the contrary, the Fradkin-Vilkovisky measure is diffeomorphism invariant, while the Fujikawa measure is not. In particular, we see that, contrary to naive expectations, the presence of $g^{00}$ factors in the Fradkin-Vilkovisky measure is necessary to ensure the invariance of the effective gravitational action. We also comment on results recently appeared in the literature, and show that formal calculations can easily miss delicate points.

hep-th↗

arXiv2025

On the RG flow of the Newton and cosmological constant

In this note we comment on the RG flow of the Newton and cosmological constants, also in view of some recent claims [1] that would rise some doubts on the validity of our recent work [2,3]. Here we show that the arguments and claims of [1] are seriously flawed and cannot be trusted.

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