Marco Chianese

We refine the constraints on the lifetime of decaying super-heavy dark matter particles (SHDM), with masses ranging from 10 ⁷ to 10 ¹⁵ GeV, by analyzing ultra-high-energy (UHE) gamma-ray data. Our approach involves an accurate comparison of the primary gamma-ray emissions resulting from prompt SHDM decays in the galactic halo with the most recent upper limits on isotropic UHE gamma-ray fluxes provided by various extensive air shower experiments. We demonstrate that a precise consideration of the field of view and the geometric acceptance of different UHE gamma-ray observatories has significant implications for the inferred limits of dark matter lifetime. In addition, we examine the influence of uncertainties linked to the current models of the galactic dark matter distribution, employing diverse halo density profiles while varying both their radial extent and the local dark matter density. Our findings indicate that the newly established UHE gamma-ray constraints are marginally less stringent than earlier evaluations, thereby revisiting the SHDM parameter space and allowing for observable neutrino fluxes.

Quantum backreaction effects may quench Hawking evaporation through a “memory burden,” allowing primordial black holes (PBHs) with formation masses well below 10 15 g to survive to the present and contribute to the dark matter. We show that ultrahigh-energy cosmic rays (UHECRs) provide a powerful and previously unexplored probe of this scenario. We compute the proton and neutron emission from memory-burdened PBHs, including the Galactic-halo contribution and the extragalactic proton component, and confront it with the Pierre Auger Observatory proton spectrum and its EeV neutron limits from the Galactic plane. This yields new constraints on the PBH dark-matter fraction as a function of the PBH formation mass and the evaporation-suppression parameter k . For k ≳ 3 the nonobservation of ultrahigh-energy protons leads to bounds competitive with those from UHE gamma rays, while neutron limits remain comparable to high-energy neutrino constraints. Our results highlights the key role of multimessenger astronomy in constraining beyond-the-standard-model scenarios.

We study the formation of asteroid-mass primordial black holes (PBHs) as a dark matter candidate in supersymmetric extensions of the Standard Model. We show that the presence of heavy particles predicted in the minimal supersymmetric Standard Model (MSSM) can lead to a transient softening of the equation of state of the Universe during their nonrelativistic transition, enhancing PBH formation. We compute the effective equation of state for different realizations of the MSSM mass spectrum, parametrized by three characteristic mass scales. Assuming a broad and approximately scale-invariant primordial curvature power spectrum, we evaluate the resulting PBH mass functions and compare them with current observational constraints. We find that, for supersymmetric masses above ∼ 10 5 GeV , the PBH mass function is significantly enhanced in the asteroid-mass window, allowing PBHs to account for the total dark matter abundance without violating existing bounds. In contrast, within the Standard Model the same configurations lead to PBH mass functions that are observationally excluded. For lighter supersymmetric mass spectra, PBH production is shifted toward masses above ∼ 10 22 g , which are strongly constrained by microlensing searches, thereby reducing their allowed contribution to the dark matter density.

We demonstrate that induced gravitational waves (IGWs) can naturally emerge within well-motivated realizations of thermal leptogenesis, thereby providing a possible observational handle on this framework at remarkably high energy scales. To illustrate this principle, we put forth a simple leptogenesis model in which an early matter-dominated phase, connected to the leptogenesis scale, enhances the generation of gravitational waves induced by early structure formation. Leveraging recent N-body and lattice simulation results for IGW computations in the non-linear regime, we show that, within the assumptions of the model, the frequency and amplitude of these IGWs can be correlated with the thermal leptogenesis scale.

Astrophysical jets from powerful active galactic nuclei (AGN) have recently been proposed as promising probes of dark matter (DM) in the sub-GeV mass range. AGN launch relativistic jets that accelerate cosmic rays (CRs) to very high energies, which can then interact with their surroundings and produce multiwavelength (MW) emission spanning from radio frequencies to TeV γ rays. If DM consists of light particles, their interactions with CRs could lead to an additional cooling mechanism that modifies the expected MW emission. In this work, we analyze the MW spectrum of Markarian 421, a well-studied AGN, using a multizone leptonic jet model that includes the interactions between CR electrons and DM particles. For the first time, we account for the uncertainties in the astrophysical jet dynamics, which have been previously neglected when constraining the CR-DM interactions. By fitting simultaneously jet parameters and DM-electrons interactions, we use the MW data from Markarian 421 to set constraints on the DM-induced CR cooling. We obtain 5 σ upper limit σ DM − e ≲ 1 × 10 − 34 cm 2 for a DM mass of 1 MeV. We demonstrate that this is about a factor of 2–10 stronger than traditional approaches depending on DM mass. This improvement originates from having indeed considered the full multiwavelength emission from the source, instead if a simplified approach. Properly accounting for degeneracies between jet dynamics and DM interactions is also key to deriving robust constraints on DM interactions.

Blue-tilted Gravitational Waves (BGWs) have been proposed as a potential candidate for the cosmic gravitational waves detected by Pulsar Timing Arrays (PTA). In the standard cosmological framework, BGWs are constrained in their frequency range by the Big Bang Nucleosynthesis (BBN) limit on GW amplitude, which precludes their detection at interferometer scales. However, introducing a phase of early matter domination dilutes BGWs at higher frequencies, ensuring compatibility with both the BBN and LIGO constraints on stochastic GWs. This mechanism allows BGWs to align with PTA data while producing a distinct and testable GW signal across a broad frequency spectrum. Ultralight Primordial Black Holes (PBHs) could provide the required early matter-dominated phase to support this process. Interpreted through the lens of BGWs, the PTA results offer a way to constrain the parameter space of a new scenario involving modified Hawking radiation, known as the “memory burden” effect, associated with ultralight PBHs. This interpretation can be further probed by high-frequency GW detectors. Specifically, we demonstrate that PBHs as light as 10^2-3 g can leave detectable imprints on BGWs at higher frequencies while remaining consistent with PTA observations.

We explore the impact of the backreaction of evaporation on the quantum state of primordial black holes (PBHs), known as “memory burden,” on the baryon asymmetry production in the Universe through high-scale leptogenesis. Focusing on PBH masses ranging from 1 to 1000 g, we investigate the interplay between the nonthermal production of heavy sterile neutrinos and the entropy injection within this nonstandard cosmological framework. By assuming appropriate values for the memory-burden parameters, q = 1 / 2 and k = 1 , we derive mutual exclusion limits between PBHs and thermal leptogenesis in the mixed parameter space. Our analysis reveals that the primary contribution of PBHs to baryon asymmetry stems from entropy injection. Indeed, we find that, different from earlier studies based on the semiclassical Hawking evaporation, the memory-burden effect suppresses the nonthermal source term in the PBH mass range explored. This has significant implications for understanding baryogenesis in such alternative cosmological scenarios.

Cosmic strings radiate detectable gravitational waves in models featuring high-scale symmetry breaking, e.g., high-scale leptogenesis. In this Letter, for the first time, we show that different flavored regimes of high-scale leptogenesis can be tested with the spectral features in cosmic string-radiated gravitational waves. This is possible if the scalar field that makes right-handed neutrinos massive is feebly coupled to the Standard Model Higgs. Each flavored regime, sensitive to low-energy neutrino experiments, leaves a marked imprint on the gravitational waves spectrum. A three-flavor and a two-flavor regime could be probed by a characteristic fall-off of the gravitational wave spectrum at the LISA-DECIGO-ET frequency bands with preceding scale-invariant amplitudes bounded from above and below. We present gravitational waves windows for flavored regimes of leptogenesis testable in the upcoming experiments. We also provide the first construction of a leptogenesis framework where a testable distinction of flavor regimes is possible without constraining the flavor structure of the theory.

We explore a scenario where an early epoch of matter domination is driven by the mass scale M_N of the right-handed neutrinos, which also characterizes the different flavour regimes of leptogenesis. Such a matter-domination epoch gives rise to peculiar spectral imprints on primordial Gravitational Waves (GWs) produced during inflation. We point out that the characteristic spectral features are detectable in multiple frequency bands with current and future GW experiments in case of Blue GWs (BGWs) described by a power-law with a positive spectral index (n_T > 0) and an amplitude compatible with Cosmic Microwave Background (CMB) measurements at the CMB scale. We find that the three-flavour leptogenesis regime with M_N ≲ 10⁹ GeV imprints BGWs more prominently than the two-flavour and one-flavour regimes characterized by a higher right-handed neutrino mass. In particular, a two-flavour (three-flavour) leptogenesis regime is expected to leave distinct imprints in the mHz–Hz (μHz–mHz) band. Moreover, we translate the current Big Bang Nucleosynthesis (BBN) and LIGO limits on the GW energy density into constraints on the flavour leptogenesis parameter space for different GW spectral indices n_T . We provide a rigorous statistical analysis of how the future GW detectors would be conjointly able to distinguish the flavour regimes. Interestingly, the scenario also offers unique GW signals testable in the next LIGO run with a correlated signature in the PTA frequency band with an amplitude comparable to the one expected from supermassive black holes.