We will give a brief overview of current approaches to quantum gravity and its phenomenology, with an emphasis on some of the core topics of the working group WG1 “High Energy Quantum Gravity”.
In this talk, we will review key experiments testing quantum gravity–related effects, outline current experimental results, and explore future prospects in the field. Most notably, we will highlight key peculiarities in our observations and analyses that influence results and may not be immediately apparent to those outside the field.
Our goal is to offer deeper insight into this area of...
This talk introduces the research foundations of WG3, which focuses on the theoretical development of gravitational interactions in quantum systems within the low-energy regime. We explore foundational questions about the nature of gravity and the role of observers, with an emphasis on identifying experimentally testable phenomena. Topics include quantum clocks, quantum reference frames,...
I offer a perspective on some research directions relevant for the COST Action, including IR/UV mixing, quantum-gravity-induced decoherence, spacetime fuzziness, quantum reference frames and the laws of particle propagation in a quantum spacetime. I also highlight two opportunities for phenomenology: the mystery concerning the origin of the KM3-230213A neutrino and the Caesium-Rubidium...
Status report of WG6 "Dissemination and Diversity" activities and future prospects.
Working Group 4 (WG4) of the BridgeQG COST Action is dedicated to exploring how low-energy, high-precision experiments can offer unique insights into the relation between quantum physics and gravity. While high-energy approaches seek to probe gravity at the Planck scale, WG4 focuses on tabletop experiments to test predictions from quantum mechanics and General Relativity, including theories...
To develop observational tests of quantum gravity, we require lever arms that translate Planck-scale predictions into predictions at observationally accessible scales. In my talk, I will use asymptotically safe quantum gravity as a case study. I will show, how the interplay of quantum gravity with matter (both visible and "dark") shapes the properties of matter fields in and beyond the...
A renowned tool for relating theories at different scales is the famous Renormalization Group (RG). The RG flow enables the connection of theories at varying coarse-grained scales, ultimately aiming to bridge observations on cosmological scales with predictions from quantum theories of general relativity. In this talk, we adapt the RG framework to the Hamiltonian level, a key requirement for...
The transparency of the universe to high-energy gamma rays is governed by interactions with low-energy photons from the Cosmic Microwave Background (CMB) and Extragalactic Background Light (EBL) via Breit-Wheeler pair production. New physics models that suppress this process predict increased transparency, offering a testable scenario. This talk explores how such suppression arises within...
In this talk, the role of gravitationally induced decoherence in open quantum systems is explored in the context of neutrinos. A microscopic quantum mechanical model introduced by Blencowe and Xu is applied to neutrino oscillations, motivated by the coupling between neutrinos and the gravitational wave environment suggested by linearised gravity. The analysis demonstrates that, for neutrino...
One of the main challenges in theoretical physics is the unification of general relativity and quantum field theory, leading to the development of a consistent theory of quantum gravity. In this talk, we explore how the deformation of special relativistic kinematics can provide a framework to describe residual effects of quantum gravity at low energies. We analyze how introducing a curved...
Black holes provide a setting to test assumptions about the interplay of quantum theory and gravity. These tests have led to several puzzles, such as the xeroxing or firewall paradox. A common feature of these puzzles is that they combine the perspectives of an infalling observer and an exterior observer, who, for fundamental reasons, have access to different systems. In quantum foundations,...
This talk presents recent developments on a non-perturbative quantisation of gravitational subsystems on a light cone. Starting from the covariant phase space for the γ-Palatini--Holst action, we identify an auxiliary conformal field theory (CFT), which carries a representation of the constraint algebra of general relativity on a null surface. In the model, the radiative data, which is encoded...
Lorentz invariance can be tested by making use of ultra-high energy cosmic rays (UHECRs), namely the highest energy particles in the Universe. Their interactions in the extragalactic space can be altered if some level of Lorentz invariance violation (LIV) is present, which may lead to detectable fingerprints in the expected fluxes.
The scenario is actually more complicated than expected, due...
Lorentz invariance is a cornerstone of modern physics. However, certain quantum gravity models suggest potential violations of Lorentz symmetry (LIV) at high energy scales. Blazars, such as PKS 2155-304, are powerful, variable sources of very high-energy gamma rays and provide an ideal setting for testing such phenomena. We analyze the temporal and spectral properties of the July 29, 2006 PKS...
This work presents a sensitivity study exploring the capability of the planned Southern Wide-Field Gamma-Ray Observatory (SWGO)—a future water Cherenkov detector array to be built in Chile and designed to probe gamma rays up to the PeV scale—enabling studies such as the search for potential signatures of Lorentz Invariance Violation (LIV). Focusing on transparency studies, we simulate the...
Decoherence plays a key role in neutrino oscillations by describing how environmental interactions—such as with matter or gravity—can alter flavor oscillation patterns and reveal aspects of neutrino quantum behavior. Typically, studies of neutrino oscillations encode decoherence by making a phenomenological ansatz for the dissipator. Such decoherence effects can also be systematically derived...
The recent detection of a neutrino event with an energy of approximately 100 PeV by KM3NeT has opened the window of ultra-high-energy (UHE) neutrino astronomy. This newly accessible regime offers an unprecedented opportunity to explore new physics. In particular, a population of UHE neutrinos has implications for scenarios of Lorentz Invariance Violation (LIV), where neutrinos with a modified...
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".
We introduce a novel approach to the search of quantum-spacetime-affected GRB...
The Einstein Equivalence Principle (EEP) underlies general relativity, asserting, from operational viewpoint, that a freely falling laboratory can locally eliminate gravitational effects. But does EEP still hold when the lab is a quantum system—delocalized, entangled, or in a nonclassical spacetime? In such cases, no single classical coordinate choice may exist to render spacetime Minkowskian....
The emergence of quantum mechanics and general relativity has transformed our understanding of the natural world significantly. However, integrating these two theories presents immense challenges, and their interplay remains untested. Recent theoretical studies suggest that single-photon interference over large spatial separations offers a promising approach to probing the interface between...
Is gravity fundamentally quantum, like the other three fundamental interactions, or is it classical? Could gravity play a fundamental role in wave function collapse, as suggested by models such as the Diósi–Penrose (DP) model? These questions remain open.
Many proposed experiments aimed at addressing these questions rely on creating spatial superpositions of large masses. For instance,...
The quest to determine whether gravity is quantum has challenged physicists since the mid-20th century, due to the impracticability of accessing the Planck scale, where potential quantum gravity effects are expected to become relevant. While recent entanglement-based tests have provided a more promising theoretical path forward, the difficulty of preparing and controlling large mass quantum...
Understanding physical phenomena at the intersection of quantum mechanics and general relativity remains one of the major challenges in modern physics. Among various approaches, experimental tests have been proposed to investigate the dynamics of quantum systems in curved spacetime and to examine the quantum nature of gravity in the low-energy regime. However, most previous studies have...
La relativité générale et la mécanique quantique sont deux théories fondamentales de la physique : la relativité générale décrit la gravité et la structure à grande échelle de l’Univers, tandis que la mécanique quantique décrit le comportement de la matière et de l’énergie aux niveaux atomique et subatomique. Elles sont incompatibles lorsqu’elles sont appliquées à l’Univers primitif ou aux...
It is possible to couple quantum and classical variables consistently (i.e. without paradoxes like faster than light signalling) provided one accepts a certain amount of stochasticity. This is useful, for example, if one wants to entertain the possibility that spacetime is fundamentally classical. These hybrid dynamics are not trivial (like meanfield) but they are nothing fancy either, and one...
An ordinary change between two classical reference frames (RF) A, B can be seen as a point $g$ in a Lie group manifold $G$; $g$ sharply specifies the orientation and motion (of the origin) of B relative to A, while the group product encodes the composition of two changes into a third one. So far, physical theories are characterized by their covariance under a suitable $G$. If A, B are...
Currently envisaged tests for probing the quantum nature of the gravitational interaction in the low-energy regime typically focus either on the quantized center-of-mass degrees of freedom of two spherically-symmetric test masses or on the rotational degrees of freedom of non-symmetric masses under a gravitational interaction in the Newtonian limit. In this talk, I am going to present a novel...
Starting from operationally motivated principles, we derive a relational theory of observables in Minkowski spacetime from which the notion of scalar quantum fields naturally emerges. We expand on quantum reference frames in spacetime and demonstrate that most properties of quantum fields arise as direct consequences of constraints on quantum reference frames -- that is, quantum fields should...
Lorentz Invariance Violation (LIV) is a feature of several quantum gravity models in which Lorentz symmetry is broken at high energies, leading to potential changes in particle behavior and interactions. In this study, we present simulations (and the corresponding methods) of the propagation of astrophysical electromagnetic cascades with LIV, which in particular results in new types of...
Spacetime singularities are often regarded as evidence of the fundamental incompleteness of General Relativity (GR). It is generally expected that a quantum theory of gravity will prevent their formation. In this talk, I will explore various proposed 'regular' geometrical structures that could effectively replace classical singularities as the end states of gravitational collapse. I will...
Relativistic deformed kinematics leads to a loss of the absolute locality of interactions. In previous studies, some models of noncommutative spacetimes in a two-particle system that implements locality were considered. In this talk, we present a characterization of the Poisson-Lie algebras formed by the noncommutative space-time coordinates of a multi-particle system and Lorentz generators as...
The Hubble tension poses serious questions not only to cosmology, but also to fundamental physics. In this talk, we will summarize our results so far as to how combining Lorentz Invariance Violation (LIV) time-delay measurements from gamma-ray bursts (GRBs) with standard cosmological datasets (BAO, SN) reveal interdependence between quantum gravity phenomena and cosmological models, how the...
I will show how to derive finite boost transformations within the theory of Deformed Special Relativity based on the bicrossproduct-basis κ-Poincarè Hopf algebra.
This enables to establish key properties of the theory, such as worldline covariance and the spacetime metric.
These results allow the derivation of a Planck-scale-modified time dilation factor, which may be relevant for quantum...
Instead of quantizing a classical phase space, the program of quantum mereology takes abstract Hamiltonian operators defined in some Hilbert space as its starting point, and investigates under which conditions such a setting induces semi-classical dynamics. We advance this program by studying the emergence of entire sets of degrees-of-freedom from random Hamiltonians. We show that these...
The status of three optomechanical experiments is presented. The first one sets upper bounds on possible deformations of the standard commutator between position and momentum. The second one aims to detect the gravitational force between two silicon micro-oscillators in a high-purity state. The third one explores the motion of levitated nanospheres in the quantum regime.
We are experimentally investigating possible departures from the standard quantum mechanics’ predictions at the Gran Sasso underground laboratory in Italy.
In particular, with radiation detectors we are searching for signals predicted by the collapse models (spontaneous emission of radiation) which were proposed to solve the “measurement problem” in quantum physics and signals coming from a...
The combination of time dilation in general relativity with the possibility in quantum mechanics for masses to exist in a quantum superposition of being in two places at the same time leads to a prediction of quantum uncertainty in the definition of local time, something incompatible with our understanding of quantum mechanics. With no theoretical solution to the fundamental conflict,...
In this talk I will review recent progress in our understanding of large-distance features of gravity in (3+1)-dimensional asymptotically flat spacetimes. I will explain how one can extract from the asymptotic expansions of Einstein’s equations a tower of charges whose conservation governs the low-energy (or soft) expansion of a graviton to all orders. The first in this tower are...
We investigate the emergence of quantum coherence and quantum correlations in a two-particle system with deformed symmetries arising from the quantum nature of spacetime. We demonstrate that the deformation of energy-momentum composition induces a momentum-dependent interaction that counteracts the decoherence effects described by the Lindblad equation in quantum spacetime. This interplay...
The interplay between quantum mechanics and general relativity is one of the most profound open problems in fundamental physics. After decades of purely theoretical investigations, recent experimental advances turned the prospect of a phenomenological approach into a realistic possibility. On the one hand, searches for quantum gravity effects in astrophysical signals constitute nowadays an...
Far from the quantum regime, quantum gravity effects may be imminent in the form of modifications of the dynamics of classical systems. Such effects can be modeled by effective theories. One common approach of this type is to describe the influence of quantum gravity effects on the motion of massive or massless test particles by modified dispersion relations. Applying these relations to a...
I will briefly examine the connection between modified theories of gravity and models based on the Generalized Uncertainty Principle (GUP). This relationship provides a framework for testing gravity proposals using tabletop experiments. Using the Landau model of liquid helium as a representative example, we will analyze the underlying details. Similarly, GUP models can be reformulated in terms...
The effective models of quantum gravity are expected to make phenomenological predictions of the fundamental theories. The issue of general covariance in effective models of quantum gravity will be addressed in this talk, which arises when canonical quantum gravity leads to a semiclassical model described by an effective Hamiltonian constraint. In the context of spherically symmetric models,...
Working within the relational framework of group field theories and specifically its application to cosmology, we derive the explicit solution to the GFT condensate effective dynamics including the treatment of scalar perturbations. This first step allowed us to investigate further the matter content and formulate its dynamics in the form of QFT on a curved background. This, in turn, produced...
Quantum gravity and quantum information both call for a generalization of reference frame transformations. In quantum gravity, quantum groups naturally implement such generalization in some noncommutative spacetimes. In quantum mechanics, the concept of quantum reference frame emerged when linking reference frames to quantum systems. The connection between quantum groups and quantum reference...
I will discuss the theory behind some of the black holes in both loop quantum gravity and generalized uncertainty approaches, and present a number of phenomenological signatures they exhibit.
I will present recent advances in the theory of free scalar and fermionic fields defined on κ-Minkowski noncommutative spacetime, emphasizing how the choice of Lagrangian (which becomes trivial in the commutative limit) affects the canonical conserved charges associated with κ-Poincaré symmetries and their algebra. These results will be analyzed through the lens of discrete symmetries – C, P,...
In the quest of finding a quantum description of the early universe, we consider a quantised flat FLRW background together with quantum perturbations. We compute quantum trajectories for a universe that can be in a superposition of semiclassical background (and perturbation) states and investigate how the evolution of cosmological perturbations is influenced by the quantum nature of the...
We explore the modifications to fundamental geometric variables of Loop Gravity induced by the presence of fermions, and examine the resulting gravitational dynamics. This analysis is then extended to incorporate Quantum Electrodynamics (QED). Finally, we discuss potential approaches for quantizing the system, outlining possible directions for future research.
