Quantum Universe 2025

Gravity is derived from an action given by the geometrical quantum relative entropy coupling matter fields with geometry. The fundamental idea is to relate the metric of Lorentzian spacetime to a quantum operator, playing the role of an renormalizable effective density matrix and to describe the matter fields topologically, according to a Dirac-Kähler formalism, as the direct sum of a 0-form, a 1-form and a 2-form. While the geometry of spacetime is defined by its metric, the matter fields can be used to define an alternative metric, the metric induced by the matter fields, which geometrically describes the interplay between spacetime and matter. The proposed entropic action is the geometric quantum relative entropy between the metric of spacetime and the metric induced by the matter fields. The modified Einstein equations obtained from this action reduce to the Einstein equations with zero cosmological constant in the regime of low coupling. By introducing the G-field, which acts as a set of Lagrangian multipliers, the proposed entropic action reduces to a dressed Einstein-Hilbert action with an emergent small and positive cosmological constant only dependent on the G-field. The obtained equations of modified gravity remain second order in the metric and in the G-field. A canonical quantization of this field theory could bring new insights into quantum gravity while further research might clarify the role that the G-field could have for dark matter. We furthermore show that the geometrical quantum relative entropy associated to the Schwarzschild metric, which provides an approximate solution of the modified gravity equations, follows the area law for large Schwarzschild radius.

Neutron scattering, a complementary technique to light scattering, is well-established for investigating the static and dynamic properties of materials. Furthermore, neutrons have also proven extremely useful in fundamental and particle physics. For example, neutrons provide i) important information about the weak and strong interactions relevant to nuclear structure, and ii) they are very useful for investigating the symmetries underlying the Standard Model. Precision measurements of the electric dipole moment and neutron lifetime provide fundamental information on the consistency of the Standard Model. Recently, efforts have focused on searching for neutron-antineutron oscillations and the appearance of mirror neutrons, which could play a central role in the search for dark matter. However, since the brilliance of existing neutron sources is limited for technical reasons, sophisticated optics are required to improve the sensitivity of the experiments. For example, elliptical focusing mirrors have been proposed for neutron-antineutron experiments to reduce beam losses, while appropriately designed polarization and reflection mirror systems form the basic building blocks of the interferometer for measuring the interference properties of neutrons and/or neutron-mirror-neutrons. In my talk, I will give a brief overview of important particle physics experiments in which neutrons play a key role. I will then present technical concepts for optimizing reflective mirror optics based on supermirror technology which are suitable for their use for neutron interferometric studies.

Brief review of the universe history from modified gravity is considered. Special attention is paid to F(R) gravity and Einstein-Gauss-Bonnet gravity. It is shown that such theories may describe the  unified universe evolution from the early-time inflation till late-time acceleration. Few realistic models of such theories which give excellent confrontation with LCDM observational data including latest DESI data are briefly described. The realistic inflation scenario consistent with Planck data is also briefly presented. Extra constraint to Einstein-Gauss-Bonnet gravity making gravitational waves speed consistent with speed of light is used in the study of inflation. Some remarks on black holes and neutron stars in modified gravity are also made.

I will discuss how the first images of the supermassive black holes M87* and Sgr A* were obtained by the EHT collaboration. In particular, I will describe the theoretical aspects that have allowed us to model the dynamics of the plasma accreting onto the black hole and how the comparison between the theoretical images and the observations on a broad range of frequencies has allowed us to deduce the presence of supermassive black holes and to extract information about the accretion process. In addition, I will describe the lessons we have learned from these imaging process about strong-field gravity and alternatives to black holes.

According to usual calculations in quantum field theory, both in flat and curved spacetime, the mass of a scalar particle is quadratically sensitive to the ultimate scale of the theory, the UV physical cutoff. Elaborating on previous work in quantum gravity, I will show that (when due  attention is paid to the path integral measure and to the way the physical cutoff is introduced) the mass of the scalar particle presents only a (mild) logarithmic sensitivity to the cutoff. This result is obtained without resorting to any supersymmetric embedding of the theory. Moreover, no regularization scheme (as dimensional regularization), where power-like divergences are absent by construction, is used. I will finally present some speculations (inspired by these results) on the way the Minkowski limit should be taken.

An important theoretical achievement of the last century was the realization that strict renormalizability can be a powerful criterion to select Lagrangians in the framework of perturbative quantum field theory. The Standard Model Lagrangian (without gravity) is strictly renormalizable from a perturbative point of view. On the other hand, the inclusion of gravity seems not to respect this criterion, since general relativity is perturbatively non-renormalizable. The aim of this talk is to provide concrete evidence that strict renormalizability is still a valid criterion even when applied to gravity. First, we show that adding quadratic curvature terms to the Einstein-Hilbert action gives rise to a strictly renormalizable theory known as quadratic gravity. Second, we argue that this unique theory represents the most conservative approach to quantum gravity and, at the same time, is highly predictive, as it can explain new physics beyond general relativity already in the sub-Planckian regime. In particular, it provides one of the best fits to the CMB anisotropies via Starobinsky inflation and makes sharp cosmological predictions that can be tested in the near future. Finally, we comment on open questions and conclude with a historical note.

We reformulate spinor theory in a specific form, called ‘polar form,’ which relies solely on real variables, is independent of the particular representation of gamma matrices, and is manifestly covariant. In this form, the spinor field can be associated with a (fluid) continuum, and the corresponding Dirac theory can be reinterpreted as a type of hydrodynamics. We found that this effective spinor fluid exhibits, among other features, anisotropic pressures that have recently been measured inside the proton. We then apply the Ehlers-Ellis-Clarkson approach to relativistic hydrodynamics, known as the 1+1+2 covariant approach, to analyze the gravitation of spinor fields in hydrodynamic form. This method allows us to gain insights into the geometry of the gravitational fields produced by spinors, and to develop the essential systems of equations needed to explore a wide range of physical phenomena, from singularity theorems to Oppenheimer-Snyder gravitational collapse, to isotropic and anisotropic cosmologies.

The Galactic Centre of the Milky Way can serve as a test bed to investigate physical phenomena at the intersection of astrophysics and fundamental physics. As such, it offers a unique laboratory to probe General Relativity, modified theories of gravity, different paradigms of dark matter, and black hole mimickers. I will provide a general overview of the results achieved in recent years, emphasising their importance in opening a new avenue to improve our understanding of the underlying theory of gravity in the surroundings of a supermassive compact object.

We consider the effects of combining periodic boundary conditions inducing geometrical frustration with quantum interaction, a setting called “topological frustration” (TF). In this way, the ground state of a system host one (or more) topological, fractionalized, delocalized excitations, giving it unique properties. Already in 1D spin chains we observe the emergence of phenomenologies precursor of systems with massive amount of frustration, rendering it an ideal platform for bottom-up studies that clarifies the effect of frustration. In this seminar I will introduce these concepts and focus on the augmented quantum complexity of these systems, which have allowed us to construct a high performance quantum battery and the experimental preparation of a W-state.

Assuming that the degrees of freedom of a black hole are more fundamental than those we have access to at out energies and that they include those relative to spacetime itself, we naturally obtain, within a second-quantized toy model of the evaporation, that the Bekenstein bound is a consequence of the Pauli exclusion principle for these fundamental degrees of freedom. We assume that they are finite in number and of fermionic nature. We then show that the three involved entropies of the black hole, entanglement, Bekenstein, and thermodynamic entropies, all stem from the same approach, based on the entropy operator whose structure is the one typical of Takahashi and Umezawa’s thermofield dynamics. Furthermore, we evaluate the von Neumann black hole-environment entropy and noticeably obtain a Page-like evolution. We finally show that this is a consequence of a duality between our model and a quantum dissipative like fermionic system.

It is discussed the fractal structure of the vacuum in quantum field theory associated to the cosmic microwave background radiation and to the cosmic neutrino background.

We present quantum cosmological models within the framework of modified gravity theories. By employing the ADM formalism, we derive the wave function of the Universe and recover classical trajectories in the semi-classical limit. In this context, it is shown that symmetries play a fundamental role in simplifying the dynamics and enabling the construction of exact cosmological solutions to the Wheeler–DeWitt equation. In all examined cases, the Hartle criterion is recovered.

The Maldacena-Shenker-Stanford (MSS) conjecture establishes the existence of an upper bound to the Lyapunov exponent of a thermal quantum system with a large number of degrees of freedom. Holographic calculations of out-of-time order correlation functions (OTOCs), which are conveniently employed as indicators of the magnitude of quantum chaos, motivate such a statement, leading to the identification of black holes as the fastest scramblers in nature. This talk aims to give an insight into the universality of the MSS conjecture. We claim that it can be violated in various metric $f(R)$ gravity models as a consequence of the propagation of metric instabilities in a degenerate Schwarzschild-de Sitter background. Then, following a detailed investigation of the Extended Geometric Trinity of Gravity, a set of three dynamically equivalent theories arising from an ad-hoc extension of the corresponding constituting theories of the Trinity of Gravity (namely General Relativity, the Teleparallel Equivalent to General Relativity, and the Symmetric Teleparallel Equivalent to General Relativity), we conclude that the violation occurs independently of the conferred representation of gravity in such a framework.

The stability analysis of the electroweak vacuum plays a crucial role in constraining Standard Model and beyond the Standard Model physics. For a long time, the analysis was performed under the assumption that, if the Standard Model were valid all the way up to  the Planck scale, new physics at this scale should have no impact on the stability condition.  On the contrary, it has been shown that the electroweak vacuum lifetime $\tau$ is extremely  sensitive to Planck scale new physics, and that the latter might lower $\tau$ below the age of the Universe. In this talk, I will mainly focus on the role played by gravity on the vacuum stability condition. In particular, I will consider the case of the Higgs field  minimally coupled to gravity and show that the effect of new physics is still dominant (although gravity shows the tendency to push towards stabilization). This poses a serious problem for the stability of our Universe, and demands a physical mechanism thatprotects it from a disastrous decay. I will show that there exists a stabilizing mechanism that originates from the non-minimal coupling between gravity and the Higgs boson. As this  direct Higgs-gravity interaction necessarily arises from the quantum dynamics of the Higgs field in a gravitational background, such a mechanism seems to be natural and universal, and it is not related to any specific model.

I will discuss recent progress in string cosmology. Including all-order α′ corrections leads to a richer and consistent picture of the pre-Big Bang universe. In this framework, the early universe can evolve smoothly through a non-singular bounce, connecting two dual phases without encountering a singularity. When a suitable potential is added for the dilaton, this setup can also stabilize the string coupling and lead to realistic late-time cosmologies, such as matter-dominated or inflationary expansion. These theoretical improvements open up new phenomenological possibilities. During the high-curvature string phase, small changes in the sound speed of perturbations can greatly enhance the production of primordial black holes. Similarly, recent observations from NANOGrav hint at a gravitational wave background that could be naturally explained by non-minimal versions of the pre-Big Bang scenario. These results suggest non-perturbative string correction, could leave observable imprints in today’s universe.

In this talk, I will present a detailed analysis of gravitational-wave propagation in bimetric gravity in a late-time de Sitter epoch. In this regime, the dynamical equations for the massless and massive graviton modes can be decoupled and solved exactly. The system admits different dynamical regimes, depending on the propagation properties of the massive graviton, and whether the massless and massive components of the signal can be temporally resolved or not. The gravitational-wave luminosity distance is computed analytically in each regime as a function of redshift. Further, the massless and massive components of the signal are shown to retain their coherence also in the regime where they can be temporally resolved, even when couplings to incoherent matter degrees of freedom are included.

Generalised theories of electromagnetism as a framework offer new insight on what is perceived as the best understood model in physics. While successful, Maxwell’s theory remains fundamentally linear and rely on the sole free massless particle in the Standard-Model (SM), the photon. Previous work within extended theories of electromagnetism shows that they all exhibit non-conservations of the energy-momentum tensor when photons interact with an electromagnetic background, when the latter is non-constant. For (effective) mass theories as the de Broglie-Proca and the SM Extention based on Lorentz symmetry violation, non-conservative terms appear also when the background is constant. This behaviour hints towards violations of the translational symmetry, and to a larger extent Poincaré symmetry. The objective of this work is to show that within a generic generalised non-linear model it is possible to alter the action in a way to have a quadric term in potentials before considering the mechanical reduction of the model to ensure the positivity of the mass. We then study the constraint algebra of the model and show that we shift from a model with two first class to two second class constraints, which implies the propagation of an additional degree of freedom. We also show that the Hamiltonian is bound from below and as thus does not suffer from Ostrogradski type instabilities. We conclude by deriving the propagator for the model, and discussing a potential link between this additional polarisation and an effective mass in this family of models.

We investigate the impact of a non-minimal Yukawa-like coupling between curvature and the inflaton field within the spontaneous baryogenesis background. Accordingly, we demonstrate that this coupling may lead to significant enhancement in particle production, even ensuring small coupling constant. To explore this, we assume a perfectly homogeneous and isotropic universe during the reheating stage, guaranteeing the inflaton to decay into fermion-antifermion pairs. We report the simplest approach in which the inflaton is minimally coupled to baryons, and non-minimally with gravity. We perturbatively solve the equations of motion for the inflaton and then compute the difference in the number densities of baryons and antibaryons produced through the inflaton decay into fermion-antifermion pairs. We show that the non-minimal coupling term de facto increases inflaton mass, letting fermion-antifermion decays be more probable, and thus enhancing the overall baryogenesis process. As a further outcome, we find that the non-minimal Yukawa coupling also leads to a renormalization of the inflaton mass. Finally, since the fermionic fields appear not to be mass eigenstates, we specialize the mass-mixing between them only. To this end, we thus include the effects of mass-mixing and cosmic expansion into our calculations. Physical consequences of baryon production are therefore explored. Then, still in the context of spontaneous baryogenesis, we study how the presence of a scalar spectator field affects the baryon asymmetry production. In so doing, we move in the same scenario as before. However, in place of the non minimal coupling term, we introduce in the background model a scalar spectator field weakly coupled to the inflaton and see how the equations of motion of the latter change. Consequently, we study the modifications in the produced baryon asymmetry, including at the end the effects of mass-mixing and of the expansion of the universe.

Spin-squeezed states are a prototypical example of metrologically useful quantum states where structured entanglement allows for enhanced sensing with respect to the one possible using classically correlated particles. Relevant aspects are both the efficient preparation of spin-squeezed states and the scalability of estimation precision with the number N of probes. Recently, in the context of the generation of spin-squeezed states via coupling of three-level atoms to an optical cavity, it was shown that increasing the atom-cavity coupling can be detrimental to spin-squeezing generation, an effect that is not appreciated in the standard second-order cavity removal approximation. We describe adiabatic elimination techniques to derive an effective Lindblad master equation up to third order for the atomic degrees of freedom. We then show through numerical simulations that the spin-squeezing scalability loss is correctly reproduced by the reduced open system dynamics, pinpointing the relevant role of higher order

Considering the Einstein-Hilbert truncation for the (euclidean) quantum gravity action, I will mainly focus on the derivation of the Wisonian renormalization group (RG) equations for the Newton and cosmological constant, $G$ and $\Lambda$ respectively. I will show that particular attention has to be paid to the path integral measure and to a proper  introduction of the physical running scale. It will turn out that, differently from other implementations in previous literature, the RG flow of the effective action is not driven by the fourth power of the running scale. This gives rise to a significantly different RG flow. In particular, I will show that there is no sign of the non-trivial UV-attractive fixed point of the so called asymptotic safety scenario. I will also discuss more general aspects related to its RG structure, with particular reference to its effective (or fully fledged) field theory nature.

The Bianchi IX model, whose primordial phase is also called Mixmaster model, has been widely studied for its chaotic properties near the initial singularity. Here, we face the question about the fate of chaos when quantum gravity effects come into play. In particular, we construct a framework in which the Misner anisotropic variables obey Deformed Commutation Relations inspired by different Quantum Gravity theories. We consider three different deformations, two of which have been able to remove the initial singularity similarly to Loop Quantum Cosmology when implemented to the single volume variable. Here, the two-dimensional Algebras naturally implement a form of Non-Commutativity between the space variables that affects the dynamics of the anisotropies. In particular, we implement the modifications in their classical limit, where the Deformed Commutators become Deformed Poisson Brackets. We derive the modified Belinskii-Khalatnikov-Lifshitz map in all the three cases, and we study the fate of the chaotic behavior that the model classically presents. Depending on the sign of the deformation, the dynamics will either settle into oscillations between two almost-constant angles, or stop reflecting after a finite number of iterations and reach the singularity as one last simple Kasner solution. In either case, chaos is removed.

I will show how the Belinfante-Rosenfeld improvement terms, that render the energy-momentum tensor symmetric, emerge by coupling the matter to the affine-connection. In this sense the improvement terms correspond to the hypermomentum of matter. I will show how this is realized in two standard examples, the Maxwell field and the Dirac field. I will also show how the connection-matter couplings can also result in a traceless energy tensor when the theory is invariant under frame rescalings, by revisiting the known example of a conformally invariant scalar field. Generalizations to higher derivative theories will also be discussed.

The concept of the Quantum Ratio is born from the efforts to find a simple but universally valid criterion to tell whether the center of mass (CM) of an isolated, microscopic or macroscopic body behaves quantum mechanically or classically. It is defined in terms of the ratio between the space extension of the CM wave function and the body’s size, the support of the internal, bound-state wave function describing the body. Though simple, the implication of such a criterion turn out to be surprisingly far-reaching and profound. A particularly important consequence of the quantum ratio is the fact that the environment-induced decoherence does not imply that the degrees of freedom involved become classical. Indeed, even if the CM of a mesoscopic or macroscopic body behaves classically, the internal, microscopic degrees of freedom (the electrons, protons and photons) remains quantum mechanical. This fact is of fundamental relevance in the emergent science of Quantum Biology.

I present the a study on the production of magnetic fields in the primordial universe coupling the inflaton field with the electromagnetic sector by means of an interacting term in the Lagrangian in the form of f^2(ϕ)F^{μν} F_{μν} . The study will be carried out in the framework of the non minimal coupling between inflaton and geometry, which is represented in the action by a term in the form of Rϕ^2.  After a brief introduction on the history of the model, I will introduce the equations of motion of the system and I will explain two important effects that influence the dynamics: the Schwinger effect and backreaction.  I will show how the models can be verified with observations at the present day and I will conclude the presentation with a brief insight on the numerical solutions for some inflation potentials.

Josephson Traveling Wave Parametric Amplifiers (JTWPAs) represent key technology for broadband, quantum-limited amplification, specific for the readout of superconducting qubits and quantum microwave sensors. We report on the design, fabrication, and modeling of JTWPAs optimized for operation in the C- and X-bands, based on a Nb/AlOx/Nb trilayer process. The devices consist of nonlinear transmission lines implemented as periodic arrays of Josephson junctions. This amplifier architecture, supporting efficient three-and four-wave mixing over multi-GHz bandwidths, is specifically developed for compatibility with niobium trilayer fabrication, offering enhanced junction uniformity, providing higher critical magnetic fields and reduced quasiparticle generation compared to aluminum-based alternatives. These properties are critical for achieving reliable performance in cryogenic environments and enable greater scalability for applications involving multi-qubit systems and large sensor arrays. Key aspects of the Nb-JTWPA design, including constraints imposed by fabrication and lithographic resolution, are presented as well as results from numerical simulations that predict the amplifiers gain and bandwidth characteristics.

The gravitational interaction, in the form of the Einstein—Cartan theory, can emerge from a pre-geometric gauge theory via a mechanism of spontaneous symmetry breaking. In this context, pre-geometry refers to the lack of a metric structure for spacetime, which can be recovered only in the spontaneously broken phase, below a critical energy near the Planck scale. The fundamental field of this formulation à la Yang—Mills is the gauge potential of the (anti-)de Sitter group, which yields both the tetrads and the spin connection of the Lorentz group after the spontaneous symmetry breaking. The Higgs-like field that allows such dynamics is a supermassive boson with implications for Cosmology. In the ultra-high-energy limit of the unbroken phase where the gauge symmetry is restored, the metric theory of gravity is then superseded by the pre-geometric one and all notions of spacetime singularity cease to be meaningful. At a cosmological level, a pre-geometric de Sitter universe is an exact and regular solution of the theory, and can represent the pre-geometric state of the early Universe from which the inflationary epoch emerges. This framework can thus provide a simple resolution for the problem of the Big Bang singularity.

Gravitational waves (GW), whose existence was predicted by Einstein in 1916, were only directly detected almost a hundred years later, in 2015, opening a new window on the Universe, inaugurating the era of GW astronomy. Among the multitude of possible sources of gravitational waves, those of primordial origin stand out. Produced in the early stages of the Universe’s evolution, they carry valuable information about the details of the inflationary period and the transition to the epoch of radiation dominance. Considerable effort has been devoted to the creation of the next generation of ground- and space-based gravitational wave detectors, which, operating over a wide range of frequencies with enhanced sensitivity, could reveal this information, shedding light on the physics of the early Universe. Specifically, we mainly focus on a two-scalar field model unifying the Dark Sector with inflation into a single theoretical framework, discussing its features and how it enhances primordial GW generation. To calculate this GW spectrum within the two-scalar-field cosmological model, we employ the formalism of continuous Bogoliubov coefficients. According to it, the changes in the graviton (gravitational waves) creation and annihilation operators as the Universe evolves can be found by using Bogoliubov coefficients, defined as continuous functions of time. Within this framework, we calculate the full energy spectrum of the GW generated within the two-scalar-field cosmological model, whose angular frequency takes values ranging from about $10^{-17}$ rad/s to about $10^9$ rad/s. These frequencies correspond to wavelengths equal to the Hubble distance today and at the end of the inflationary period, respectively.

We discuss the cosmological solutions of the extended geometric trinity of gravity, in the classical and quantum cosmology framework. Using the Noether symmetry method to select viable theories, we examine the minisuperspace dynamics of extended metric-affine gravity formulations. We then show that, at the level of solutions, the equivalence among the different formulations can be restored by including the divergence terms that relate their respective geometric invariants to the Ricci scalar.

Usual calculations of the (Euclidean) effective action in quantum gravity, performed within the heat-kernel formalism, give rise to quartic and quadratic UV-sensitive contributions (Planck scale) to the vacuum energy. The comparison of this result to the observed value of the vacuum energy unveils a severe naturalness problem, the strongest facet of the long-standing “cosmological constant problem”. In this talk, I will show that the appearance of these UV-sensitive terms in usual calculations is due to an improper treatment of the path integral measure and of the UV physical cutoff of the theory. When the diffeomorphism invariant measure proposed by Fradkin and Vilkovisky is used, and the UV physical cutoff properly introduced, the radiative correction to the vacuum energy turns out to be only logarithmically sensitive to the UV scale. In this respect, the Fradkin-Vilkovisky measure is sometimes claimed not to be diffeomorphism invariant due to the presence in it of non-covariant $g^{00}$ factors of the time-time component of the inverse metric. I will show that such a claim is incorrect, and that, on the contrary, these $g^{00}$ factors turn out to be crucial to ensure the diffeomorphism invariance of the path integral measure.

We show that global properties of an unknown quantum network, such as the average degree, hub density, and the number of closed paths of fixed length, can be inferred from strictly local quantum measurements. In particular, we demonstrate that a malicious agent with access to only a small subset of nodes can initialize quantum states locally and, through repeated short-time measurements, extract sensitive structural information about the entire network. The intrusion strategy is inspired by extreme learning and quantum reservoir computing and combines short-time quantum evolution with a non-iterative linear readout with trainable weights. These results suggest new strategies for intrusion detection and structural diagnostics in future quantum Internet infrastructures.

There are still many unanswered questions from General Relativity, such as black holes singularity and dark energy: these puzzles have led to the development of extended theories of gravity. One approach to modifying General Relativity consists of adding new degrees of freedom, such vector fields, resulting in the so-called Generalized Proca theories. In order to determine whether these theories are consistent and can provide predictions, this work investigates the possibility of an “asymptotically safe” ultraviolet completion, which would make them free from unphysical ultraviolet divergences. This involves analyzing their beta functions and establishing whether there exist fixed points acting as partial ultraviolet attractors.

Only lepton states with definite chirality participate in charged-current weak interactions. However, chirality is not conserved for massive particles. As a result, a massive leptonproduced with a definite chirality can undergo chiral oscillations over time. In this work, we present a finite-time quantum field theory approach that allows for a consistent description of this phenomenon [1], following the methodology already developed for flavor oscillations [2] and particle decay [3]. In particular, we show that a perturbative treatment of the mass term as an interaction reproduces the well-known formula for chiral oscillations. Furthermore, we demonstrate thatthe pion decay rate can also be consistently reinterpreted in terms of chiral oscillations.

Photons remain by large the main carriers of information, but read with the XIX Maxwellian theory. Conversely, we assess whether ETEM induce a reinterpretation of physics and cosmology. The SM Extension dresses the photon with an effective mass [1,2], the only free massless particle remained in the SM. Such a mass is compatible with the upper limits by Fast Radio Bursts [3-5] and solar wind [6,7], recognised by the Particle Data Group. Birefringence, group velocity dispersion, second-order QED are tested or searched ETEM effects in experiments, e.g., BMV Toulouse, ATLAS CERN, DeLLlight Paris. Other phenomenology can be addressed too. Indeed, all photons either massive – ab initio as in the de Broglie-Proca theory or with an effective mass from the SME or from the Born-Infeld, Heisenberg-Euler non-linear type of theories – undergo a frequency shift in presence of an electromagnetic and/or a LSV background [8,9]. This shift, even when small, added to the expansion redshift, determines new cosmological scenarios, e.g., without accelerated expansion [10-12] and dark matter. We are now turning to study the self-force [13-15] on a photon, for which the frequency shift would occur due to the interaction of the photon energy with the curvature produced by an electromagnetic field. Testing this shift through interferometry is of pivotal importance [16,17]. The upper limit lies at 3 x 10-18 in Df/f for an optical length equal to the Earth-Moon distance. Expansion is not falsifiable at laboratory scale since it occurs only at large scale. Thereby a frequency shift would imply a small- scale expansion or an ETEM effect. Finally, we implement the Heisenberg principle at cosmological distances. The minimal mass is drawn from the energy-time relation and the Hubble tension [18] would be a quantum measurement interpreted as intrinsic limit of the observations [19,20].

Throughout the years, various theoretical and experimental findings have challenged the validity of General Relativity at both ultraviolet and infrared scales. In an effort to address some of these shortcomings, extendend gravity models considering modifications of the gravitational action have been proposed. One possible extension involves including the so-called Gauss-Bonnet term in the Lagragian. In doing so, additional geometric contributions can effectively play the role of a cosmological constant, without the need to invoke dark energy models. Among the different possible formulations, the starting action can be selected using the Noether symmetry approach, a physically motivated criterion based on Noether’s theorem, aimed at identifying viable models that exhibit symmetries. We demonstrate that applying this approach to a scalar-tensor Gauss Bonnet model allows for a reduction of the dynamical system and the associated minisuperspace, thus enabling the derivation of exact solutions to the equations of motion. In particular, we consider a cosmological context, where the method proves useful in addressing both the early- and late-time accelerated phases of the Universe.

We study the conditions for finding an island in an anisotropic universe – Bianchi Type-I filled with radiation. We find that islands may form at certain times, near the turnaround point – where the universe turns from contraction to expansion in one of the directions. This is in line with previous analyses regarding cosmological space-times where islands form if one has two energy scales in the problem, such as the typical temperature of the universe and, on top of that, cosmological constant, curvature, anisotropy, or some mass scale.