arXiv subjects

Ninetta Saviano

Publications and source records attributed to Ninetta Saviano.

At least 19 recordsLinked to original sources

arXiv2026

Probing super-heavy dark matter with ultra-high-energy gamma rays

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.

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arXiv2025

Induced Gravitational Waves as Cosmic Tracers of Leptogenesis

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.

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arXiv2025

Neutrino Theory in the Precision Era

This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers unique opportunities to address some of the most fundamental questions in physics. This motivates a vigorous experimental programme which the theory community fully supports. \textbf{A strong effort in theoretical neutrino physics is paramount to optimally take advantage of upcoming neutrino experiments and to explore the synergies with other areas of particle, astroparticle, and nuclear physics, as well as cosmology.} Progress on the theory side has the potential to significantly boost the physics reach of experiments, as well as go well beyond their original scope. Strong collaboration between theory and experiment is essential in the precision era. To foster such collaboration, \textbf{we propose to establish a CERN Neutrino Physics Centre.} Taking inspiration from the highly successful LHC Physics Center at Fermilab, the CERN Neutrino Physics Centre would be the European hub of the neutrino community, covering experimental and theoretical activities.

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arXiv2025

Probing flavored regimes of leptogenesis with gravitational waves from cosmic strings

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 (GWFRL) 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.

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arXiv2025

Impact of memory-burdened primordial black holes on high-scale leptogenesis

We explore the impact of the back-reaction 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 grams, we investigate the interplay between the non-thermal production of heavy sterile neutrinos and the entropy injection within this non-standard 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, differently from earlier studies based on the semi-classical Hawking evaporation, the memory-burden effect suppresses the non-thermal source term in the PBH mass range explored. This has significant implications for understanding baryogenesis in such alternative cosmological scenarios.

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arXiv2024

Tomography of flavoured leptogenesis with primordial blue gravitational waves

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 $M_N \lesssim 10^9~{\rm GeV}$ imprints BGWs more prominently than the two-flavour and one-flavour regimes characterized by a higher right-handed neutrino mass scale. In particular, a two-flavour (three-flavour) leptogenesis regime is expected to leave distinct imprints in the mHz-Hz ($μ$Hz-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.

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arXiv2024

Impact of memory-burdened black holes on primordial gravitational waves in light of Pulsar Timing Array

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 $10^{2-3}~{\rm g}$ can leave detectable imprints on BGWs at higher frequencies while remaining consistent with PTA observations.

astro-ph.CO↗

arXiv2024

Light burden of memory: Constraining primordial black holes with high-energy neutrinos

Recent studies point out that quantum effects, referred to as "memory burden", may slow down the evaporation of black holes. As a result, a population of light primordial black holes could potentially survive to the present day, thus contributing to the energy density of dark matter. In this work, we focus on light primordial black holes with masses $M_{\rm PBH} \lesssim 10^{9}~{\rm g}$ that, due to the memory burden effect, are currently evaporating, emitting high-energy particles, among which neutrinos, in the local Universe. Analyzing the latest IceCube data, we place novel constraints on the combined parameter space of primordial black holes and the memory burden effect. We also study the projected reach of future neutrino telescopes such as IceCube-Gen2 and GRAND. We find that the neutrino observations are crucial to probe scenarios with highly-suppressed evaporation and light masses for primordial black holes.

astro-ph.HE↗

arXiv2024

Impact of primordial black holes on heavy neutral leptons searches in the framework of resonant leptogenesis

We investigate the effects on sub-TeV resonant leptogenesis of Primordial Black Holes with masses from $10^6$ to $\sim 10^9$ g. The latter might dominate the energy content of the Universe altering its evolution and, eventually, diluting the final baryon asymmetry. We find that, depending on the mass and abundance of Primordial Black Holes, the parameter space of sub-TeV resonant leptogenesis shrinks towards higher Right-Handed Neutrino masses and smaller active-sterile mixing. Remarkably, this translates into important implications for the experimental searches of heavy neutral leptons. Conversely, we demonstrate that a possible future detection of sub-TeV heavy neutral leptons would disfavour regions of the parameter space of Primordial Black Holes currently allowed.

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arXiv2023

Synergy between cosmological and laboratory searches in neutrino physics

The intersection of the cosmic and neutrino frontiers is a rich field where much discovery space still remains. Neutrinos play a pivotal role in the hot big bang cosmology, influencing the dynamics of the universe over numerous decades in cosmological history. Recent studies have made tremendous progress in understanding some properties of cosmological neutrinos, primarily their energy density. Upcoming cosmological probes will measure the energy density of relativistic particles with higher precision, but could also start probing other properties of the neutrino spectra. When convolved with results from terrestrial experiments, cosmology can become even more acute at probing new physics related to neutrinos or even Beyond the Standard Model (BSM). Any discordance between laboratory and cosmological data sets may reveal new BSM physics and/or suggest alternative models of cosmology. We give examples of the intersection between terrestrial and cosmological probes in the neutrino sector, and briefly discuss the possibilities of what different laboratory experiments may see in conjunction with cosmological observatories.

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arXiv2023

Limits on light primordial black holes from high-scale leptogenesis

We investigate the role that the evaporation of light primordial black holes may have played in the production of the baryon asymmetry of the Universe through the high-scale leptogenesis. In particular, for mass of primordial black hole in the range [$10^6$-$10^9$] g, we find a dilution of thermally generated lepton asymmetry via entropy injection in the primordial plasma after the sphaleron freeze-out. As a consequence, we can put strong constraints on the primordial black hole parameters, showing the mutual exclusion limits between primordial black holes and high-scale leptogenesis. Remarkably, we point out an interplay between the upper bound on the initial abundance of primordial black holes and the active neutrino mass scale.

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arXiv2023

Heavy decaying dark matter at future neutrino radio telescopes

In the next decades, ultra-high-energy neutrinos in the EeV energy range will be potentially detected by next-generation neutrino telescopes. Although their primary goals are to observe cosmogenic neutrinos and to gain insight into extreme astrophysical environments, they can also indirectly probe the nature of dark matter. In this paper, we study the projected sensitivity of up-coming neutrino radio telescopes, such as RNO-G, GRAND and IceCube-gen2 radio array, to decaying dark matter scenarios. We investigate different dark matter decaying channels and masses, from $10^7$ to $10^{15}$ GeV. By assuming the observation of cosmogenic or newborn pulsar neutrinos, we forecast conservative constraints on the lifetime of heavy dark matter particles. We find that these limits are competitive with and highly complementary to previous multi-messenger analyses.

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arXiv2022

Electron scattering of light new particles from evaporating primordial black holes

Primordial black holes are a possible component of dark matter, and a most promising way of investigating them is through the product of their Hawking evaporation. As a result of this process, any species lighter than the Hawking temperature is emitted, including possible new particles beyond the Standard Model. These can then be detected in lab-based experiments via their interaction with the Standard Model particles. In a previous work, we have first proposed and studied this scenario in the presence of an interaction between the light new species and nucleons. Here we extend this discussion to include the case of interaction with electrons. We show that the simultaneous presence of primordial black holes and species lighter than about $100$ MeV can be constrained by the measurements of direct detection experiments, such as XENON1T, and water Cherenkov neutrino detectors, such as Super-Kamiokande. Our results provide a complementary and alternative way of investigation with respect to cosmological and collider searches.

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arXiv2022

Neutrino Self-Interactions: A White Paper

Neutrinos are the Standard Model (SM) particles which we understand the least, often due to how weakly they interact with the other SM particles. Beyond this, very little is known about interactions among the neutrinos, i.e., their self-interactions. The SM predicts neutrino self-interactions at a level beyond any current experimental capabilities, leaving open the possibility for beyond-the-SM interactions across many energy scales. In this white paper, we review the current knowledge of neutrino self-interactions from a vast array of probes, from cosmology, to astrophysics, to the laboratory. We also discuss theoretical motivations for such self-interactions, including neutrino masses and possible connections to dark matter. Looking forward, we discuss the capabilities of searches in the next generation and beyond, highlighting the possibility of future discovery of this beyond-the-SM physics.

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arXiv2022

Neutrino Flavor Conversions in High-Density Astrophysical and Cosmological Environments

Despite being a well understood phenomenon in the context of current terrestrial experiments, neutrino flavor conversions in dense astrophysical environments probably represent one of the most challenging open problems in neutrino physics. Apart from being theoretically interesting, such a problem has several phenomenological implications in cosmology and in astrophysics, including the primordial nucleosynthesis of light elements abundance and other cosmological observables, nucleosynthesis of heavy nuclei and the explosion of massive stars. In this review, we briefly summarize the state of the art on this topic, focusing on three environments: early universe, core-collapse supernovae and compact binary mergers.

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arXiv2022

Direct Detection of Light Dark Matter from Evaporating Primordial Black Holes

The direct detection of sub-GeV dark matter interacting with nucleons is hampered by the low recoil energies induced by scatterings in the detectors. This experimental difficulty is avoided in the scenario of boosted dark matter where a component of dark matter particles is endowed with large kinetic energies. In this Letter, we point out that the current evaporation of primordial black holes with masses from $10^{14}$ to $10^{16}$ g is a source of boosted light dark matter with energies of tens to hundreds of MeV. Focusing on the XENON1T experiment, we show that these relativistic dark matter particles could give rise to a signal orders of magnitude larger than the present upper bounds. Therefore, we are able to significantly constrain the combined parameter space of primordial black holes and sub-GeV dark matter. In the presence of primordial black holes with a mass of $10^{15}~\mathrm{g}$ and an abundance compatible with present bounds, the limits on DM-nucleon cross-section are improved by four orders of magnitude.

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arXiv2021

Constraints on heavy decaying dark matter with current gamma-ray measurements

Among the several strategies for indirect searches of dark matter, one very promising one is to look for the gamma-rays from decaying dark matter. Here we use the most up-to-date upper bounds on the gamma-ray flux from $10^5$ to $10^{11}$ GeV, obtained from CASA-MIA, KASCADE, KASCADE-Grande, Pierre Auger Observatory, and Telescope Array. We obtain global limits on dark matter lifetime in the range of masses $m_\mathrm{DM}=[10^7-10^{15}]~\mathrm{GeV}$. We provide the bounds for a set of decay channels chosen as representatives. The constraints derived here are new and cover a region of the parameter space not yet explored. We compare our results with the projected constraints from future neutrino telescopes, in order to quantify the improvement that will be obtained by the complementary high-energy neutrino searches.

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arXiv2021

Massive sterile neutrinos in the early universe: From thermal decoupling to cosmological constraints

We consider relatively heavy neutrinos $ν_H$, mostly contributing to a sterile state $ν_s$, with mass in the range 10 MeV $\lesssim m_s \lesssim m_π \sim 135$ MeV, which are thermally produced in the early universe in collisional processes involving active neutrinos, and freezing out after the QCD phase transition. If these neutrinos decay after the active neutrino decoupling, they generate extra neutrino radiation, but also contribute to entropy production. Thus, they alter the value of the effective number of neutrino species $N_{\rm eff}$ as for instance measured by the cosmic microwave background (CMB), as well as affect primordial nucleosynthesis (BBN), notably ${}^4$He production. We provide a detailed account of the solution of the relevant Boltzmann equations. We also identify the parameter space allowed by current Planck satellite data and forecast the parameter space probed by future Stage-4 ground-based CMB observations, expected to match or surpass BBN sensitivity.

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