Publications SISSA
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PubblicazioneCharacterizing the roles of transitory obscured phases and inner torus in shaping the fractions of obscured Active Galactic Nuclei at cosmic noon( 2026)The origin of obscuration in active galactic nuclei (AGN) is still a matter of contention. It is unclear whether obscured AGN are primarily due to line-of-sight effects (Orientation model), a transitory, dust-enshrouded phase in galaxy evolution (Evolution models), or a combination of both. The role of an inner torus around the central supermassive black hole also remains unclear in pure Evolution models. We use cosmological semi-analytic models and semi-empirical prescriptions to explore obscuration effects in AGN at cosmic noon, in the range (Formula presented). We consider a realistic object-by-object modelling of AGN evolution including different AGN light curves (LCs) composed of phases of varying levels of obscuration, usually (but not uniquely) with a larger degree of obscuration before the peak of AGN activity, mimicking the possible clearing effects of strong AGN feedback. Evolution models characterized by AGN LCs with relatively short pre-peak obscured phases followed by more extended optical/ultraviolet (UV) visible post-peak phases, struggle to reproduce the high fraction of obscured AGN at (Formula presented) 2–3 inferred from X-ray surveys. Evolution models characterized by AGN LCs with sharp post-peak declines or persistent or multiple obscuration phases are more successful, although they still face challenges in reproducing the steady drop in the fractions of obscured AGN with increasing luminosity measured by some groups. Invoking a fine-tuning in the input LCs, with more luminous AGN defined by longer optical/UV visible windows, can improve the match to the decreasing fractions of obscured AGN with luminosity. Alternatively, a long-lived central torus-like component, with thickness decreasing with increasing AGN power, naturally boosts the luminosity-dependent fractions of obscured AGN, suggesting that small-scale orientation effects may still represent a key component even in Evolution models. We also find that in our models major mergers and starbursts, when considered in isolation, fall short in accounting for the large fractions of highly obscured faint AGN detected at cosmic noon.
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PubblicazioneUltrahigh-redshift or closer-by, dust-obscured galaxies?( 2026)Context. The James Webb Space Telescope (JWST) is revolutionizing our understanding of the Universe by unveiling faint, near-infrared dropouts previously beyond our reach, ranging from exceptionally dusty sources to galaxies up to redshift z ∼ 14. Aims. In this paper, we identify F200W-dropout objects in the Cosmic Evolution Early Release Science (CEERS) survey that are absent from existing catalogs. Our selection method can effectively identify obscured low-mass (logM*/M⊙ ≤ 9) objects at z ≤ 6, massive dust-rich sources up to z ∼ 12, and ultrahigh-redshift (z > 15) candidates. Our goal is to uncover promising targets for further studies using deep mid-infrared imaging and/or spectroscopic follow-ups. Methods. We utilize two photometric catalogs optimized for detecting faint, red objects. Primarily relying on NIRCam photometry from the latest CEERS data release and supplementing with mid-infrared/(sub)millimeter data when available, our analysis pipeline combines multiple SED-fitting codes, star formation histories, and the novel CosMix tool for astronomical stacking to maximize available photometric information. Results. Our work highlights three 2 < z < 3 dusty dwarf galaxies that have higher masses compared to the typical dusty dwarfs previously identified in CEERS. Additionally, we reveal five faint sources with a significant probability of lying above z > 15, with best-fit masses compatible with Λ cold dark matter and a standard baryon-to-star conversion efficiency. We exploit these candidates to compute the z ∼ 17 UV luminosity function, finding estimates in good agreement with other similar studies. Their bimodal redshift probability distributions suggest they could also be z < 1.5 dwarf galaxies with extreme dust extinction. We also identify a strong line emitter galaxy at z ∼ 5 mimicking the near-infrared emission of a z ∼ 13 galaxy. Conclusions. Our sample holds promising candidates for future follow-ups. Confirming ultrahigh-redshift galaxies or lower-redshift dusty dwarfs will offer valuable insights into early galaxy formation, evolution with their central black holes and the nature of dark matter, and/or cosmic dust production mechanisms in low-mass galaxies, and will help us to understand degeneracies and contamination in high-redshift object searches.
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PubblicazioneError convergence of quantum linear system solvers( 2026)The Harrow-Hassidim-Lloyd (HHL) algorithm remains a paradigmatic quantum routine for solving linear systems and a widely used benchmark in theoretical and experimental studies. Several circuit-level variants have been proposed to simplify its implementation, including constructions in which the clock register is factorized via Hadamard gates to reduce circuit depth and entanglement. In this work, we show that this commonly deployed modification can fundamentally alter the asymptotic behavior of the algorithm and may fail to converge in the limit of large clock size due to persistent phase interference effects. This phenomenon is not a finite-size artifact and compromises the correctness guarantees of the factorized-clock implementation. We provide an analytic characterization of the underlying mechanism and demonstrate that a minimal and experimentally feasible modification suffices to restore convergence while preserving the practical advantages of the simplified circuit. Our results clarify an overlooked correctness issue in a widely used HHL implementation pattern and delineate the conditions under which simplified realizations faithfully reproduce the intended algorithmic behavior.
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PubblicazioneUnveiling the Interaction between Dark Matter and Gravity: from Galaxy Kinematics to Cosmology(SISSA, 2026-09-22)The Cold Dark Matter paradigm emerged as the prevailing solution to the cosmic missing mass conundrum. While highly successful on cosmological scales, this model is partially inconsistent with galaxy-scale observations. This thesis addresses such a challenge by pursuing a dual approach. The first part presents a model featuring a non-local interaction between cold dark matter and gravity. The model, referred to as fractional gravity, in its Newtonian setting is based on a modified Poisson equation featuring the fractional Laplacian and two new parameters: the fractional index s and length scale l. To begin with, I will provide the solution to this equation for the gravitational potential generated by a Navarro-Frenk-White distribution of cold dark matter. Remarkably, the result can be interpreted in terms of an almost cored effective density distribution, similar in shape to a cored isothermal sphere, thus solving the cusp-core problem of cold dark matter. Moreover, the predicted profiles are consistent with the core-surface density relation observed for dwarf galaxies. A Bayesian analysis will then test fractional gravity against stacked rotation curves of a broad sample of spiral galaxies. In terms of reduced chi-squared and BIC, the fits yielded by this model are always superior to the standard, cold dark matter Navarro–Frenk–White profile. On the other hand, I will show how this model can explain the observed interplay between dark matter and baryons in late-type galaxies, embodied by tight dynamical scaling relations such as the Radial Acceleration Relation. The analysis predicts a scaling between the parameters s and l and the virial mass of dark matter haloes, with non-local effects being stronger in smaller systems. After using the fractional gravity model to fit galaxy clusters’ pressure profiles from the X-COP collaboration, I will show that such scaling holds consistently from the dwarf-galaxy regime up to galaxy clusters’ virial masses. Overall, fractional gravity shows a rich phenomenology in a comprehensive set of scales capable of addressing long-standing issues of the cold dark matter paradigm. To go beyond the Newtonian setting, I will extend fractional gravity to a relativistic framework, deriving it from a suitable action. I will show that the resulting field equations can be interpreted as Einstein equations sourced by an effective stress-energy tensor for the dark matter component, with pressure, heat vectors, and anisotropic stresses emerging dynamically from the coupling with gravity. I will then study propagating degrees of freedom in this model, from scalar fields to gravitational waves, showing that non-locality introduces memory effects which extend the propagation inside the past light-cone. The second part of this thesis is devoted to study a relativistic model, named non-minimally coupled dark matter. Although models of this kind had been already studied in other contexts [1, 2, 3, 4], in the present case this provides a localization of fractional gravity. The greater simplicity of this model enables to do explicit calculations in the strong gravity regime, giving a taste of the corresponding solutions in the non-local theory. I will solve the equations of non-minimally coupled dark matter in three relevant scenarios. First, I will show how the dynamically generated pressure is able to balance gravity by supporting spherically-symmetric, static equilibrium configurations of dark matter. The resulting objects are regular and horizonless, but ultra-compact, so that, if formed in the early universe, could have provided the seeds for supermassive black holes observed at high redshifts by the JWST collaboration. Next, I will turn the attention to cosmology, computing the evolution of the universe in the non-minimally coupled dark matter framework. Remarkably, at early times a phase of accelerated expansion driven by the non-minimal coupling emerges, so that inflation is a natural prediction of the model. At even earlier times the fate of the universe depends on the spatial curvature, with the remarkable possibility of avoiding the initial singularity in favour of a bouncing universe in the case of negative curvature. Since no inflationary model can call itself complete without discussing the formation and growth of linear perturbations, in the final chapter I will provide a complete analysis. In particular I will compute the linear power spectrum of scalar, vector, and tensor perturbations, and show that in the case of a bouncing cosmology one obtains near scale-invariant power spectra, in agreement with observations of the Cosmic Microwave Background. All in all, the non-minimally coupled dark matter model presents a rich and interesting phenomenology, providing seeds for supermassive black holes, naturally predicting inflation, and generating a power spectrum of perturbations compatible with observations.
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PubblicazioneA bootstrap study of confinement in AdS( 2026)Yang-Mills theory in AdS4 with Dirichlet boundary conditions is expected to undergo a transition as the AdS radius varies, since the boundary data is incompatible with confinement in flat space. Various mechanisms have been proposed for the disappearance of the Dirichlet boundary condition. From the boundary viewpoint, the associated 3d CFT is a deformation of a generalised free theory of non-Abelian conserved currents, with the deformation governed by the bulk gauge coupling. We test these scenarios by deriving non-perturbative constraints from the numerical conformal bootstrap of the four-point function of non-Abelian conserved currents. We rule out the scenario in which the boundary current decouples. Bounds on the lightest scalar operators disfavour a bulk Higgs mechanism and instead point to a transition driven by a scalar singlet becoming marginal. We also obtain bounds on other scalar operators and on the current central charge, and we refine character-based techniques incorporating parity and charge-conjugation symmetry to determine the operator spectrum of the 3d Generalised Free Vector theory. These results may be of independent interest beyond Yang-Mills theory in AdS.