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Giuseppe Fabiano

Publications and source records attributed to Giuseppe Fabiano.

16 recordsLinked to original sources
arXiv2026

Indefinite probabilities in quantum spacetime: A deepening of unpredictability

Non-commutative spacetime and quantum groups have been argued to capture non-classical features of spacetime and its symmetries in quantum gravity. In this letter, we show that employing the $SU_q(2)$ quantum group to describe rotational symmetry for spin-$\frac{1}{2}$ systems and Stern-Gerlach apparatuses leads to the description of probabilities of outcomes of spin measurements in terms of non-commuting operators. As a result, we obtain an uncertainty principle between different probability operators, realising a notion of indefinite probabilities. This is then reflected in the non-commutativity of the entries of the rotation matrix relating the reference frames of two observers, hence fundamentally preventing them from sharply measuring their relative orientation.

quant-ph↗
arXiv2026

Minimal noise in non-quantized gravity

An elementary prediction of the quantization of the gravitational field is that the Newtonian interaction can entangle pairs of massive objects. Conversely, in models of gravity in which the field is not quantized, the gravitational interaction necessarily comes with some level of noise, i.e., non-reversibility. Here, we give a systematic classification of all possible such models consistent with the basic requirements that the non-relativistic limit is Galilean invariant and reproduces the Newtonian interaction on average. We demonstrate that for any such model to be non-entangling, a quantifiable, minimal amount of noise must be injected into any experimental system. Thus, measuring gravitating systems at noise levels below this threshold would be equivalent to demonstrating that Newtonian gravity is entangling. As concrete examples, we analyze our general predictions in a number of experimental setups, and test it on the classical-quantum gravity models of Oppenheim et al., as well as on a recent model of Newtonian gravity as an entropic force.

quant-ph↗
arXiv2025

Universality of free fall in Planck-scale deformed Newtonian gravity

The universality of free fall is one of the most cherished principles in classical gravity. Its fate in the quantum world is one of the key questions in fundamental physics. We investigate the universality of free fall in the context of Planck scale modifications of Newtonian gravity. Starting from a doubly-special-relativity setting we take the Newtonian limit to obtain deformed Galilean relativity. We study the interaction between two test particles, subject to deformed Galilean relativity, and a classical, undeformed gravitational source, the Earth. Such an interaction is investigated here for the first time. Considering the two test particles falling freely in the source's gravitational field, we examine whether the universality of free fall is affected by deformed relativistic symmetries. We show that, in general, the universality of free fall is violated. Remarkably, we find that there exist distinguished models for which the universality of free fall is realized and which predict a specific modification of the Newtonian potential.

gr-qc↗
arXiv2025

Planckian bound on IR/UV mixing from cold-atom interferometry

IR/UV mixing (a mechanism causing ultraviolet quantum-gravity effects to manifest themselves also in a far-infrared regime) is a rare case of feature found in several approaches to the quantum-gravity problem. We here derive the implications for "soft" IR/UV mixing (corrections to the dispersion relation that are linear in momentum) of some recent cold-atom-interferometry measurements. For both signs of the IR/UV-mixing correction term we establish bounds on the characteristic length scale which reach the Planck-length milestone. Intriguingly, for values of the characteristic scale of about half the Planck length we find that IR/UV mixing provides a solution for a puzzling discrepancy between Cesium-based and Rubidium-based atom-interferometric measurements of the fine structure constant.

gr-qc↗
arXiv2025

Covariant quantization of field theories on T-Minkowski noncommutative spacetimes

We develop a quantization scheme for the quantum theory of a real scalar field on a class of non-commutative spacetime models collectively known as T-Minkowski. Requiring the theory to be covariant under T-Poincaré transformations, we find that for a subclass of models the Wightmann functions are equal to their commutative counterparts, and we are able to prove a Wick theorem for Wightmann functions that is structurally equivalent to the one encountered in commutative QFT. For some of these models we further extend the result to Green functions and to N-point functions of interacting QFT, which we also find to be commutative, leaving no space for IR/UV mixing effects advocated in other approaches to noncommutative QFT.

hep-th↗
arXiv2025

On testing in-vacuo dispersion with the most energetic neutrinos: KM3-230213A case study

The phenomenology of in-vacuo dispersion, an effect such that quantum properties of spacetime slow down particles proportionally to their energies, has been a very active research area since the advent of the Fermi telescope. One of the assumptions made in this 15-year effort is that the phenomenology of in-vacuo dispersion has a particle-energy sweet spot: the energy of the particle should be large enough to render the analysis immune to source-intrinsic confounding effects but still small enough to facilitate the identification of the source of the particle. We use the gigantic energy of KM3-230213A as an opportunity to challenge this expectation. For a neutrino of a few hundred PeVs a transient source could have been observed at lower energies several years earlier, even assuming the characteristic scale of in-vacuo dispersion to be close to the Planck scale. We report that GRB090401B is in excellent directional agreement with KM3-230213A, and we discuss a strategy of in-vacuo-dispersion analysis suitable for estimating the significance of KM3-230213A as a GRB090401B-neutrino candidate. The $p$-value resulting from our analysis (0.015) is not small enough to warrant any excitement, but small enough to establish the point that a handful of such coincidences would be sufficient to meaningfully test in-vacuo dispersion.

astro-ph.HE↗
arXiv2025

Transverse relative locality effects in de Sitter spacetime

Doubly Special Relativity (DSR) models are characterized by the deformation of relativistic symmetries at the Planck scale and constitute one of the cornerstones for quantum gravity phenomenology research, due to the possibility of testing them with cosmological messengers. Some of their predictions manifest themselves as relative locality effects, implying that events local to an observer might not appear to be so for a distant one. In this work we focus on transverse relative locality models, where the delocalization occurs along the direction perpendicular to the one connecting two distant observers. We present the first generalization of these models in curved spacetime, constructing a transverse deformation of the de Sitter algebra in 2 + 1 D and investigating its phenomenological implications on particle propagation.

gr-qc↗
arXiv2025

Redshift leverage for the search of GRB neutrinos affected by quantum properties of spacetime

Some previous studies based on IceCube neutrinos had found intriguing preliminary evidence that some of them might be GRB neutrinos with travel times affected by quantum properties of spacetime delaying them proportionally to their energy, an effect often labeled as "quantum-spacetime-induced in-vacuo dispersion". Those previous studies looked for candidate GRB neutrinos in a fixed (neutrino-energy-independent) time window after the GRB onset and relied rather crucially on crude estimates of the redshift of GRBs whose redshift has not been measured. We here introduce a complementary approach to the search of quantum-spacetime-affected GRB neutrinos which restricts the analysis to GRBs of sharply known redshift, and, in a way that we argue is synergistic with having sharp information on redshift, adopts a neutrino-energy-dependent time window. We find that knowing the redshift of the GRBs strengthens the analysis enough to compensate for the fact that of course the restriction to GRBs of known redshift reduces the number of candidate GRB neutrinos. And rather remarkably our estimate of the magnitude of the in-vacuo-dispersion effects is fully consistent with what had been found using the previous approach. Our findings are still inconclusive, since their significance is quantified by a $p$-value of little less than $0.01$, but provide motivation for monitoring the accrual of neutrino observations by IceCube and KM3NeT as well as for further refinements of the strategy of analysis here proposed.

gr-qc↗
arXiv2025

Doubly Quantum Mechanics

Motivated by the expectation that relativistic symmetries might acquire quantum features in Quantum Gravity, we take the first steps towards a theory of ''Doubly'' Quantum Mechanics, a modification of Quantum Mechanics in which the geometrical configurations of physical systems, measurement apparata, and reference frame transformations are themselves quantized and described by ''geometry'' states in a Hilbert space. We develop the formalism for spin-$\frac{1}{2}$ measurements by promoting the group of spatial rotations $SU(2)$ to the quantum group $SU_q(2)$ and generalizing the axioms of Quantum Theory in a covariant way. As a consequence of our axioms, the notion of probability becomes a self-adjoint operator acting on the Hilbert space of geometry states, hence acquiring novel non-classical features. After introducing a suitable class of semi-classical geometry states, which describe near-to-classical geometrical configurations of physical systems, we find that probability measurements are affected, in these configurations, by intrinsic uncertainties stemming from the quantum properties of $SU_q(2)$. This feature translates into an unavoidable fuzziness for observers attempting to align their reference frames by exchanging qubits, even when the number of exchanged qubits approaches infinity, contrary to the standard $SU(2)$ case.

quant-ph↗
arXiv2024

Quantum Euler angles and agency-dependent spacetime

Quantum gravity is expected to introduce quantum aspects into the description of reference frames. Here we set the stage for exploring how quantum gravity induced deformations of classical symmetries could modify the transformation laws among reference frames in an effective regime. We invoke the quantum group $SU_q(2)$ as a description of deformed spatial rotations and interpret states of a representation of its algebra as describing the relative orientation between two reference frames. This leads to a quantization of one of the Euler angles and to the new paradigm of agency-dependence: space is reconstructed as a collection of fuzzy points, exclusive to each agent, which depends on their choice of reference frame. Each agent can choose only one direction in which points can be sharp, while points in all other directions become fuzzy in a way that depends on this choice. Two agents making different choices will thus observe the same points with different degrees of fuzziness.

gr-qc↗
arXiv2024

New Physics Pathways from B Processes

We re-consider recent measures of $R_{K}$ and $R_{K^*}$, now compatible with the Standard Model expectations, as well as the results for the process $\text{BR}(B_s \rightarrow μ^+ μ^-)$ alongside earlier determinations of $R_{D^{(\ast)}}$ and $\text{BR}(B_c \rightarrow τν)$. We provide analytic constraints on the associated Wilson coefficients in both the $b \to s$ and the $b \to c$ sectors. These allow us to estimate the scale of potential New Physics for generic extensions of the Standard Model. We then use the results to constrain the leptoquark landscape.

hep-ph↗
arXiv2023

Multiparticle states in braided lightlike $κ$-Minkowski noncommutative QFT

In this study, we construct a 1+1-dimensional, relativistic, free, complex scalar Quantum Field Theory on the noncommutative spacetime known as lightlike $κ$-Minkowski. The associated $κ$-Poincaré quantum group of isometries is triangular, and its quantum R matrix enables the definition of a braided algebra of N points that retains $κ$-Poincaré invariance. Leveraging our recent findings, we can now represent the generators of the deformed oscillator algebra as nonlinear redefinitions of undeformed oscillators, which are nonlocal in momentum space. The deformations manifest at the multiparticle level, as the one-particle states are identical to the undeformed ones. We successfully introduce a covariant and involutive deformed flip operator using the R matrix. The corresponding deformed (anti-)symmetrization operators are covariant and idempotent, allowing for a well-posed definition of multiparticle states, a result long sought in Quantum Field Theory on $κ$-Minkowski. We find that P and T are not symmetries of the theory, although PT (and hence CPT) is. We conclude by noticing that identical particles appear distinguishable in the new theory, and discuss the fate of the Pauli exclusion principle in this setting.

hep-th↗
arXiv2023

The fate of Galilean relativity in minimal-length theories

A number of arguments at the interplay of general relativity and quantum theory suggest an operational limit to spatial resolution, conventionally modelled as a generalized uncertainty principle (GUP). Recently, it has been demonstrated that the dynamics postulated as a part of these models are only loosely related to the existence of the minimal-length scale. In this paper, we intend to make a more informed choice on the Hamiltonian by demanding, among other properties, that the model be invariant under (possibly) deformed Galilean transformations in one dimension. In this vein, we study a two-particle system with general interaction potential under the condition that the composition as well as the action of Galilean boosts on wave numbers be deformed so as to comply with the cut-off. We find that the customary GUP-Hamiltonian does not allow for invariance under (any kind of) generalised Galilean transformations. Those Hamiltonians which allow for a deformed relativity principle have to be related to the ordinary Galilean ones by virtue of a momentum-space diffeomorphism, i.e. a canonical transformation. Far from being trivial, the resulting dynamics is deformed, as we show at the example of the harmonic interaction.

gr-qc↗
arXiv2023

Total momentum and other Noether charges for particles interacting in a quantum spacetime

There has been strong interest in the fate of relativistic symmetries in some quantum spacetimes, also because of its possible relevance for high-precision experimental tests of relativistic properties. However, the main technical results obtained so far concern the description of suitably deformed relativistic-symmetry transformation rules, whereas the properties of the associated Noether charges, which are crucial for the phenomenology, are still poorly understood. We here tackle this problem focusing on first-quantized particles described within a Hamiltonian framework and using as toy model the so-called ``spatial kappa-Minkowski noncommutative spacetime'', where all the relevant conceptual challenges are present but, as here shown, in technically manageable fashion. We derive the Noether charges, including the much-debated total-momentum charges, and we expose a strong link between the properties of these Noether charges and the structure of the laws of interaction among particles.

hep-th↗
arXiv2022

Standard model anomalies: Lepton flavour non-universality, g-2 and W-mass

We critically analyze the body of results that hints to the existence of New Physics from possible violations of lepton universality observed by the LHCb experiment in the $μ/e$ ratios $R_{K}$ and $R_{K^*}$ to the $g-2$ lepton anomalies. The analysis begins with a theoretical, in depth, study of the $μ/e$ ratios $R_{K}$ and $R_{K^*}$ as well as the process $B_s \rightarrow μ^+ μ^-$. Here we consider the impact of complex Wilson coefficients and derive constraints on their imaginary and real parts. We then move to a comprehensive comparison with experimental results. We show that, by fitting a single Wilson coefficient, the deviations from the Standard Model are at the $4.7σ$ level when including only the hadronic insensitive observables while it increases to $6.1σ$ when including also the hadronic sensitive ones. When switching on all relevant Wilson coefficients and combining both hadronic sensitive and insensitive data into the fit, the deviation from the Standard Model peaks at $7.2σ$ and decreases at the $4.9σ$ level if we assume that the central values of $R_K$ and $R_{K^{\ast}}$ are taken to be unity. We further estimate other unaccounted for SM contributions and show that their inclusion still requires New Physics to fit the data. We then introduce the $g-2$ lepton anomalies as well as the most recent $W$-mass results. Different theoretical models are considered that can explain the discrepancies from the Standard Model. In the final part of our work we estimate the impact of the forthcoming data from LHCb (coming from LHC Run3) and Belle II, when it will have accumulated about $5~ab^{-1}$.

hep-ph↗