arXiv subjects

Lorenzo Orlando

Publications and source records attributed to Lorenzo Orlando.

3 recordsLinked to original sources

arXiv2026

Microscopic entropy of de Sitter spacetime and entropic solution to the old cosmological constant problem

We study the role of Weyl symmetry breaking in conformal gravity and the residual scale symmetry of Einstein gravity. The corresponding action is characterized by a dimensionless coupling $α$, determined by the ratio between the de Sitter and Planck scales. We show that this quantity admits a natural interpretation as the Bekenstein-Hawking entropy of de Sitter spacetime. Combining ideas from the functional renormalization group, holography, and emergent gravity, we propose a microscopic interpretation of $α$ as a measure of the degrees of freedom associated with the de Sitter horizon. In this framework, the renormalization group flow of $α(k)$ encodes the scale dependence of these microscopic degrees of freedom. Requiring this flow to be monotonically increasing toward the infrared leads to a cosmological constant of the same order as the observed one, suggesting an entropic solution to the old cosmological constant problem. This remarkably small value can therefore be understood as a direct consequence of the extraordinarily large number of degrees of freedom in our de Sitter universe.

hep-th↗

arXiv2026

Ultraviolet completion of the inflationary paradigm

After an exhaustive introduction highlighting the strengths and weaknesses of the non-local models proposed so far as ultraviolet completions of the Starobinsky theory, we propose a new nonlocal completion of a general $f(R)$ theory (in the Einstein's frame) suitable for driving inflation in the early universe consistently with observations. The nonlocal theory shares with $f(R)$ the same background solutions and the same equations of motion for perturbations at linear and nonlinear level. Therefore, the classical cosmological observables are not affected by the nonlocal operators needed for the quantum completion. Our construction applies to any local action written in the Einstein's frame, but we will provide the details only for two explicit examples: the Starobinsky model and a general $f(R)$ theory. The new model overcomes the incompatibility of renormalizability and stability present in the previous proposals. Since the nonlocal theory is at least super-renormalizable, but can also be finite depending on the details of the model, this work shows the consistency of the inflationary paradigm with a well-defined quantum theory of gravity at high energy. We could rephrase the latter statement saying that the success of the $f(R)$ theories in cosmology can be traced back to the existence of an ultraviolet completion that preserves all the classical features. The inflationary paradigm survives, or it is actually insensitive to quantum gravity, because it is an exact solution of quantum gravity, up to perturbative corrections.

gr-qc↗

arXiv2026

Eikonal, nonlocality and regular black holes

We investigate the leading gravitational eikonal in nonlocal $D$ dimensional theories of gravity. We analyze the simplest cases of $2\rightarrow2$ massless and massive scalar scattering at tree level, studying the effects of nonlocal form factors in the gravitational sector. We give an interpretation of our results in terms of geodesic motion in effective generalized Aichelburg-Sexl geometries for the massless case, and in smeared linearized Schwarzschild metrics for the massive case in the probe limit. Combining our results for the geometries at linearized level with general requirements about the behaviour of the solutions in the core, we propose a nonlinear completion of the geometries. The resulting spacetimes describe singularity-free, asymptotically flat deformations of the Schwarzschild solution with a de Sitter core. We also analyze the main geometric and thermodynamic features of these solutions.

hep-th↗