arXiv subjects

Alfio M. Bonanno

Publications and source records attributed to Alfio M. Bonanno.

7 recordsLinked to original sources

arXiv2026

Gravitationally Induced UV Completion of an $O(N)$ Scalar Theory

We investigate the ultraviolet completion of an $O(N)$ scalar field theory non-minimally coupled to gravity using the Wilsonian functional renormalization group in the proper-time formulation. Focusing on the spontaneously broken phase, we study the RG flow of the scalar potential and the non-minimal curvature coupling expanded around a running minimum. We identify two distinct classes of fixed-point solutions, one of which is ultraviolet attractive and characterized by a vanishing quartic coupling together with finite, interacting gravitational couplings. For a finite region of infrared initial conditions, the RG trajectories remain regular at all scales and approach this fixed point. This mechanism renders the theory asymptotically safe and leads to a flat scalar potential in the ultraviolet. We show that this mechanism is robust under changes of cutoff scheme and truncation, allowing the ultraviolet completion requirement to constrain the infrared values of the scalar couplings and the mass scale in the broken phase.

hep-th↗

arXiv2026

Fifth-Force Constraints from UV-Complete Scalar-Tensor Gravity

We study an $O(N)$ scalar multiplet nonminimally coupled to gravity and follow its renormalization-group (RG) flow in the vicinity of an interacting, nonperturbatively UV-complete scaling regime of scalar-tensor theory. In the broken phase, the radial mode mediates a universal Yukawa correction to Newtonian gravity, parametrized by a strength $α$ and range $λ$. Imposing UV completeness -- regular RG trajectories that reach the UV scaling regime -- restricts the infrared data to a finite wedge, which maps to a narrow region in the $(α,λ)$ plane. Its complement is, therefore, ruled out by UV completeness alone. Remarkably, part of this theory-excluded domain lies below current experimental exclusion envelopes, so improved fifth-force searches can directly test and potentially falsify this class of UV-complete scalar-tensor models.

gr-qc↗

arXiv2026

Coarse graining from within: Wilson-Fisher universality on $S^3$

Wilsonian renormalization is usually formulated in momentum space, but on curved backgrounds momentum shells have no invariant meaning. We replace them by an intrinsic spectral cutoff, ordering modes by the covariant Laplacian and setting the cutoff resolution by the system size in renormalization group (RG) units. For a scalar field on $S^3$, this yields a covariant, momentum-free RG flow whose trace is an exact sum over spherical harmonics. The standard flat-space flow is recovered when the sphere is large compared with the coarse-graining scale. As a nontrivial test, the compact spectral flow realizes Wilson-Fisher universality without momentum shells: the interacting fixed point survives at finite resolution, has one relevant direction, and approaches its flat-space counterpart smoothly, with critical exponents only weakly affected by the compact spectrum.

hep-th↗

arXiv2026

Scaling Solutions of Matter Form Factors in Asymptotically Safe Quantum Gravity

We investigate the renormalization group flow of a gravity--matter system in which a scalar field is minimally coupled to Einstein gravity and its kinetic term is given by a scale-dependent form factor $f_Λ(-\Box)$. Employing the Wilsonian proper-time flow equation, we derive a closed integro-differential equation that encodes the dependence of the form factor on the UV cutoff $Λ$. We solve the resulting fixed-point problem with a pseudospectral discretization and find a non-trivial fixed point for which $f_\ast(-\Box)$ departs from the canonical $-\Box$ behavior. Linearizing the flow about this solution yields a discrete spectrum of perturbations and a corresponding set of critical exponents, indicating a non-trivial scaling structure in this non-local sector compatible with asymptotic safety. We also observe that the form factor becomes local once the UV cutoff is removed, suggesting that the bare action associated with this fixed point is local in the scalar two-point sector.

hep-th↗

arXiv2026

Proper-time functional renormalization in $O(N)$ scalar models coupled to gravity

We focus on the use of the functional Wilsonian renormalization group framework characterized by a proper time regulator and test its use in the search of the scaling solutions and the critical properties of an O(N)-invariant scalar field multiplet coupled to gravity in d=4 and d=3 dimensions. We employ the same background-fluctuation splitting and gauge fixing procedure, already adopted in a previous study based, instead, on the effective average action framework and a similar truncation of the effective action. Our main goal is to compare the results for the scaling solutions and some of the associated critical exponents. In this analysis, performed in a different framework, most of the picture previously uncovered is confirmed both at qualitative and quantitative level. There are, neverthelss, few differences both at finite N and in its large value limit, depending also on the schemes which in both frameworks are called 'improved'

hep-th↗

arXiv2025

RG studies of scalar-field models of long-range interactions

In this work we studies the long-range interactions in non-gravitational field theories and their behaviour in the deep infrared. To model such effects, we consider a nonlocal scalar theory obtained by adding a $ϕ\Box^{-1}ϕ$ term to the local action. Using the functional renormalisation group, we analyse its infrared fixed-point structure. Within the LPA, we show that nonlocality modifies phase-transition patterns and can induce symmetry breaking. Extending the LPA beyond polynomial truncations, we examine the convexity property of the effective potential as $k\rightarrow 0$ and find that the flow becomes singular for $λ^{2}>0$ before reaching the deep infrared. In the LPA$'$ framework, we find that the infrared-stable fixed point is the nonlocal Gaussian fixed point. We then generalise the model to $ϕ\Box^{σ/2}ϕ$ and analyse how the infrared properties depend on $σ$. With appropriate scaling choices, we show that the infrared behaviour remains unchanged up to $σ=d/2$ and follows Sak's prediction up to $σ=2$. Finally, we study higher-derivative cases within the LPA, focusing on $σ=4$, which corresponds to isotropic Lifshitz criticality, and obtain results consistent with earlier work.

hep-th↗

arXiv2025

Veiled Singularities in Einstein-Weyl Gravity: Stability and Physical Interpretation of Horizonless Solutions

We investigate a class of horizonless solutions in Einstein-Weyl gravity, corresponding to the so-called attractive naked singularities of the (-2,2) type. In contrast to General Relativity, where naked singularities are generically unstable and excluded by the cosmic censorship conjecture, we show that these configurations are linearly stable under tensor perturbations. By numerically evolving the perturbation equations in the time domain, we find that all modes decay with characteristic oscillatory tails, a behavior consistent with the dynamics of massive field perturbations in quadratic gravity. This establishes that attractive naked singularities in Einstein-Weyl gravity are dynamically stable and can persist as stationary configurations. We argue that these horizonless configurations are observationally concealed, and therefore we refer to them as veiled singularities. Their stability and phenomenological similarity to black holes suggest that they may represent viable horizonless alternatives in higher-derivative theories of gravity, offering a novel perspective on the interplay between singularity resolution, stability, and effective field dynamics beyond Einstein's theory.

gr-qc↗