arXiv subjects

Nicolao Fornengo

Publications and source records attributed to Nicolao Fornengo.

At least 19 recordsLinked to original sources

arXiv2026

On the Clustering Bias of Unresolved Gamma-Ray Sources

The Unresolved $γ$-Ray Background (UGRB) encodes the collective emission of source populations that are too faint to be detected individually, and its cross-correlation with tracers of the large-scale structure has emerged as a powerful tool to characterize those populations. In this work, we analyze the weak-lensing--UGRB cross-correlation using a reference blazar model. By modeling the relation between blazar $γ$-ray luminosity and host-halo mass, we infer the average linear bias $\langle b(z) \rangle$ and host-halo mass $\langle M(z) \rangle$ of the unresolved blazar population. We find that the signal is dominated by moderately biased sources, with $\langle b \rangle \gtrsim 2$ at $z\simeq 1$, hosted by halos with $\langle M \rangle \sim \mathcal{O}(10^{13}\,M_\odot)$. Repeating the analysis with a misaligned-AGN model yields consistent bias values, indicating that the result is determined by the clustering properties of the UGRB rather than by the details of the $γ$-ray source model.

astro-ph.CO↗

arXiv2026

Toward universal coalescence models for antideuteron production

Cosmic-ray (CR) antinuclei, especially antideuteron $\overline{\rm D}$ and antihelium-3 nuclei ${}^3\overline{\rm He}$, are among the most promising messengers for indirect dark matter (DM) searches. This is because secondary production in CR interactions with the interstellar medium is strongly suppressed at kinetic energies $K\simeq (0.1 - 1)$ GeV/$n$, typically one to two orders of magnitude below fluxes expected in standard DM scenarios. From the theoretical side, the formation of $\overline{\rm D}$ and ${}^3\overline{\rm He}$ is governed by coalescence, whose dynamics cannot yet be reliably derived from first principles. Phenomenological approaches therefore introduce effective coalescence parameters, possibly dependent on collision energy and production environment (hadronic versus electroweak). In this work we show that a common set of physically motivated coalescence models can simultaneously reproduce collider data in two qualitatively different regimes: ALICE measurements of (anti)deuteron production in $pp$ collisions at $\sqrt{s}=(0.9 - 13)$ TeV and the ALEPH $\overline{\rm D}$ multiplicity in hadronic $Z$ decays at $\sqrt{s}=m_Z$. We test both simple event-by-event prescriptions based on a relative-momentum cutoff, finding a preferred coalescence scale $p_{\rm coal}\simeq 0.2$ GeV, and quantum-mechanical models in the Wigner formalism. In the latter, a Gaussian bound-state wavefunction gives a best-fit momentum width, corresponding to $δ\simeq 1.7$ fm, while a parameter-free implementation using the Argonne $v_{18}$ wavefunction (constrained by proton-neutron scattering data) agrees with ALICE spectra at the $\sim 25\%$ level. Overall, our results support an approximately universal coalescence description across energies and production environments, strengthening the theoretical basis for interpreting upcoming CR antinuclei searches.

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arXiv2026

Early-universe constraints on the electron mass

We investigate the impact of a nonstandard electron mass $m_e$ on early-Universe thermal history, focusing on neutrino decoupling and Big Bang Nucleosynthesis (BBN). In the standard cosmology, neutrino--electron interactions keep neutrinos in thermal contact with the electromagnetic plasma until shortly before $e^\pm$ annihilation. Varying $m_e$ shifts the decoupling epoch and the entropy transfer from $e^\pm$ annihilation, thereby modifying the neutrino energy density and the inferred effective number of relativistic species, $N_{\mathrm{eff}}$. Independently, during BBN the rates of charged-current weak processes, and hence the neutron-to-proton ratio, depend on $m_e$. By confronting BBN predictions for the primordial light-element abundances with observations and imposing cosmological constraints on $N_{\mathrm{eff}}$, we obtain the following $1σ$ bounds on $m_e$ in the early Universe: $m_e = 0.505^{+0.006}_{-0.007}$ MeV (for the NACRE II nuclear reaction network) or $m_e=0.509^{+0.005}_{-0.004}$ MeV (for the PRIMAT nuclear reaction network). These bounds have been derived by adopting the recent determination of the primordial Helium-4 abundance by the Large Binocular Telescope observations of 54 metal-poor H\,\textsc{ii} regions. If instead we adopt the Particle Data Book Helium-4 abundance, the bounds are: $m_e = 0.503^{+0.011}_{-0.015}$ MeV (NACRE II) or $m_e=0.521^{+0.009}_{-0.007}$ MeV (PRIMAT) The obtained allowed ranges are close to the present laboratory value at the level of $\sim 0.4\%-2\%$, depending on the dataset and nuclear network, thus supporting the constancy of the electron mass over cosmological timescales.

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arXiv2026

Revisiting predictions for cosmic-ray antinucleon fluxes from Galactic Dark Matter

The data on cosmic antiprotons have reached an outstanding precision on energies spanning from GeV to hundreds of TeV, thanks to the space-based AMS-02 experiment. The balloon-borne GAPS experiment, which just completed its first Antarctic flight, will address antiproton and antideuteron fluxes well below GeV energies. Antinuclei in cosmic rays, as well as being produced by spallation reactions between cosmic-ray nuclei and the atoms of the interstellar medium, may hide contributions from exotic sources, such as particle dark matter annihilation in the Galaxy. In this paper, we present predictions for cosmic antiproton, antideuteron and antihelium fluxes both from secondary and dark matter origin. We use state-of-the-art production spectra, nuclear coalescence for antinuclei, and Galactic propagation models to derive upper limits on the dark matter annihilation cross-section from AMS-02 antiproton data in different propagation scenarios (BIG and QUAINT). We quantify the impact of future GAPS data, showing that its sensitivity to sub-GV antiprotons could improve the $\langleσv\rangle$ constraints by up to an order of magnitude for light DM ($m_χ \lesssim 50$ GeV). For heavier antinuclei, the detection perspective with existing and upcoming experiments are derived for those scenarios consistent with AMS-02 antiproton flux. The detectability of such signals strongly depends on the experiment, the propagation model, and the hadronization tuning. Our analysis underscores the complementarity of antinuclei channels for indirect DM searches and the critical role of low-energy windows in constraining light DM candidates.

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arXiv2026

Dark Matter and Galaxy Cross-Correlations with the Cherenkov Telescope Array Observatory

The Cherenkov Telescope Array Observatory (CTAO) will be a ground-based Cherenkov telescope performing wide-sky surveys, ideal for anisotropy studies such as cross-correlations with tracers of the cosmic large-scale structure. Cross-correlations can shed light on high-energy $γ$-ray sources and potentially reveal exotic signals from particle dark matter. In this work, we investigate CTAO sensitivity to cross-correlation signals between $γ$-ray emission and galaxy distributions. We find that by using dense, low-redshift catalogs like 2MASS, and for integration times around 50 hours, this technique achieves sensitivities to both annihilating and decaying dark matter signals that are competitive with those from dwarf galaxy and cluster analyses.

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arXiv2026

Enhanced Cosmic-Ray Antinuclei Fluxes with Dark Matter Annihilation into SUEPs

Standard-Model (SM) hadronic parton showers initiated by secondary cosmic-ray production or dark matter (DM) annihilations robustly predict very low antinuclei yields and a strong additional suppression for heavier antinuclei. We show that an important exception can arise if DM annihilates into a confining dark sector that produces Soft Unclustered Energy Patterns (SUEPs). The hallmark of SUEPs is the emission of very large multiplicities of soft dark mesons ($π_D$), which can overcome the usual phase-space suppression of antinuclei formation in parton showers, provided that the dark mesons decay promptly into SM quarks, i.e. within a SM hadronization length. We study several benchmark realizations and find that for DM masses $m_{\rm DM}\sim\mathcal{O}(10~\mathrm{TeV})$, dark meson masses $m_{π_D} \sim 400~\mathrm{GeV}$, $π_D$ dominantly decaying to $t\bar t$, and a SUEP temperature $T_{\rm SUEP}\simeq 0.1\,m_{πD}$, DM annihilation into SUEPs can yield tens of antideuterons and a few antihelium--3 events at AMS-02 at kinetic energies of $\mathcal{O}(\mathrm{GeV}$/n) and a few antideuterons and antihelium-3 events in GAPS at energies below 0.5 GeV/n. A future confirmation of an antinuclei signal by the AMS-02 or GAPS experiments could provide hints for hidden confining dynamics and would significantly constrain the relevant SUEP parameters.

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arXiv2025

Wiener filtering and multi-tracer techniques for dark matter cross-correlations between gamma-ray emission and galaxy catalogs

Cross-correlations between a gravitational tracer of dark matter and the contribution to the unresolved gamma-ray background (UGRB) from the radiation produced by the annihilation of the particles responsible for the dark matter, have been established as a powerful tool to investigate the particle physics nature of dark matter. Cross-correlations of the UGRB with galaxy catalogs, cluster catalogs and weak lensing have indeed been measured. In this paper we study statistical techniques that could improve the sensitivity of the cross-correlation techniques on the bounds that can be set to the particle dark matter physical properties. The two methods that we investigate are the application of a Wiener filter and the exploitation of the full multi-tracer information. After identifying the optimal strategies, we show that the adoption of a Wiener filter in the cross-correlation analysis can improve the sensitivity to the dark matter annihilation rate by a factor of 2/2.5 as compared to the standard analysis where no filter is applied. The inclusion of the full multi-tracer information can improve the sensitivity up to a factor of 5 for dark matter masses below about 50 GeV, the Wiener filter remaining the best option for heavier dark matter.

astro-ph.CO↗

arXiv2025

Putting all the X in one basket: Updated X-ray constraints on sub-GeV Dark Matter

Sub-GeV dark matter particles can annihilate or decay producing e^\pm pairs which upscatter the low-energy photon fields in the Galaxy and generate an X-ray emission (via the Inverse Compton effect). Using X-ray data from XMM-Newton, INTEGRAL, NuSTAR and Suzaku, we derive new constraints on this class of dark matter (DM). For annihilating DM, they are significant for m_DM > 100 MeV, and dominant if DM is p-wave annihilating. For decaying DM, they are the most stringent to date in the range m_DM ~400 MeV - 3 GeV$.

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arXiv2025

CosmiXs: Improved spectra for dark matter indirect detection

The spectra of stable particles produced from dark matter (DM) are one of the most important ingredients to calculate the fluxes for DM indirect detection experiments. At energies above a few GeV, most of the particles are produced following a complex sequence of phenomena including resonance decays, QED and QCD final-state radiation, radiation of weak gauge bosons, hadronization and hadron decays. In this contribution, we discuss improvements on the calculation of the energy spectra at the source using state-of-the-art tools that include effects that were not taken previously into account. We include helicity information of the particles produced in the annihilation channels, which leads to proper inclusion of electroweak radiation during the entire showering history. These effects are taken into account using the Vincia, which is based on the helicity-dependent antenna shower formalism. Off-shell contributions are also taken into account for annihilation channels into $WW$ and $ZZ$ through the four-body processes into fermions and for DM masses below the gauge boson mass. We also revisit the tune of the Lund fragmentation function parameters in Pythia using LEP data at the $Z$-boson pole. The spectra of cosmic messengers are provided for DM masses between 5 GeV and 100 GeV and are publicly distributed in this \href{https://github.com/ajueid/CosmiXs.git}{GitHub repository}.

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arXiv2024

Nailing down the theoretical uncertainties of $\overline{\rm D}$ spectrum produced from dark matter

The detection of cosmic antideuterons ($\overline{\rm D}$) at kinetic energies below a few GeV/n could provide a smoking gun signature for dark matter (DM). However, the theoretical uncertainties of coalescence models have represented so far one of the main limiting factors for precise predictions of the $\overline{\rm D}$ flux. In this Letter we present a novel calculation of the $\overline{\rm D}$ source spectra, based on the Wigner formalism, for which we implement the Argonne $v_{18}$ antideuteron wavefunction that does not have any free parameters related to the coalescence process. We show that the Argonne Wigner model excellently reproduces the $\overline{\rm D}$ multiplicity measured by ALEPH at the $Z$-boson pole, which is usually adopted to tune the coalescence models based on different approaches. Our analysis is based on Pythia~8 Monte Carlo event generator and the state-of-the-art Vincia shower algorithm. We succeed, with our model, to reduce the current theoretical uncertainty on the prediction of the $\overline{\rm D}$ source spectra to a few percent, for $\overline{\rm D}$ kinetic energies relevant to DM searches with GAPS and AMS, and for DM masses above a few tens of GeV. This result implies that the theoretical uncertainties due to the coalescence process are no longer the main limiting factor in the predictions. We provide the tabulated source spectra for all the relevant DM annihilation/decay channels and DM masses between 5 GeV and 100 TeV, on the CosmiXs github repository (https://github.com/ajueid/CosmiXs.git).

astro-ph.HE↗

arXiv2024

Extracting the gamma-ray source-count distribution below the Fermi-LAT detection limit with deep learning

We reconstruct the extra-galactic gamma-ray source-count distribution, or $dN/dS$, of resolved and unresolved sources by adopting machine learning techniques. Specifically, we train a convolutional neural network on synthetic 2-dimensional sky-maps, which are built by varying parameters of underlying source-counts models and incorporate the Fermi-LAT instrumental response functions. The trained neural network is then applied to the Fermi-LAT data, from which we estimate the source count distribution down to flux levels a factor of 50 below the Fermi-LAT threshold. We perform our analysis using 14 years of data collected in the $(1,10)$ GeV energy range. The results we obtain show a source count distribution which, in the resolved regime, is in excellent agreement with the one derived from catalogued sources, and then extends as $dN/dS \sim S^{-2}$ in the unresolved regime, down to fluxes of $5 \cdot 10^{-12}$ cm$^{-2}$ s$^{-1}$. The neural network architecture and the devised methodology have the flexibility to enable future analyses to study the energy dependence of the source-count distribution.

astro-ph.CO↗

arXiv2023

CosmiXs: Cosmic messenger spectra for indirect dark matter searches

The energy spectra of particles produced from dark matter (DM) annihilation or decay are one of the fundamental ingredients to calculate the predicted fluxes of cosmic rays and radiation searched for in indirect DM detection. We revisit the calculation of the source spectra for annihilating and decaying DM using the Vincia shower algorithm in Pythia to include QED and QCD final state radiation and diagrams for the Electroweak (EW) corrections with massive bosons, not present in the default Pythia shower model. We take into account the spin information of the particles during the entire EW shower and the off-shell contributions from massive gauge bosons. Furthermore, we perform a dedicated tuning of the Vincia and Pythia parameters to LEP data on the production of pions, photons, and hyperons at the $Z$ resonance and discuss the underlying uncertainties. To enable the use of our results in DM studies, we provide the tabulated source spectra for the most relevant cosmic messenger particles, namely antiprotons, positrons, $γ$ rays and the three neutrino flavors, for all the fermionic and bosonic channels and DM masses between 5 GeV and 100 TeV, on https://github.com/ajueid/CosmiXs.git.

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arXiv2023

Dark matter in the Higgs resonance region

The singlet scalar Higgs portal model provides one of the simplest explanations of dark matter in our Universe. Its Higgs resonant region, $m_\text{DM}\approx m_h/2$, has gained particular attention, being able to reconcile the tension between the relic density measurement and direct detection constraints. Interestingly, this region is also preferred as an explanation of the Fermi-LAT $γ$-ray Galactic center excess. We perform a detailed study of this model using $γ$-ray data from the Galactic center and from dwarf spheroidal galaxies and combine them with cosmic-ray antiproton data from the AMS-02 experiment that shows a compatible excess. In the calculation of the relic density, we take into account effects of early kinetic decoupling relevant for resonant annihilation. The model provides excellent fits to the astrophysical data either in the case the dark matter candidate constitutes all or a subdominant fraction of the observed relic density. We show projections for future direct detection and collider experiments to probe these scenarios.

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arXiv2023

Constraining the dark matter contribution of $γ$ rays in Cluster of galaxies using Fermi-LAT data

Clusters of galaxies are the largest gravitationally-bound systems in the Universe. Their dynamics are dominated by dark matter (DM), which makes them among the best targets for indirect DM searches. We analyze 12 years of data collected by the Fermi Large Area Telescope (Fermi-LAT) in the direction of 49 clusters of galaxies selected for their proximity to the Earth and their high X-ray flux, which makes them the most promising targets. We first create physically motivated models for the DM density around each cluster considering different assumptions for the substructure distribution. Then we perform a combined search for a $γ$-ray signal in the {\it Fermi}-LAT data between 500 MeV and 1 TeV. We find a signal of $γ$ rays potentially associated with DM that is at a statistical significance of $2.5σ-3.0σ$ when considering a slope for the subhalo mass distribution $α=1.9$ and minimum mass of $M_{\rm{min}}=10^{-6}$ $M_{\odot}$. The best-fit DM mass and annihilation cross-sections for a $b\bar{b}$ annihilation channel are $m_χ=40-60$ GeV and $\langle σv \rangle = (2-4) \times 10^{-25}$ cm$^3$/s. When we consider $α=2.0$ and $M_{\rm{min}}=10^{-9}$ $M_{\odot}$, the best-fit of the cross section reduces to $\langle σv \rangle = (4-10) \times 10^{-26}$ cm$^3$/s. For both DM substructure models there is a tension between the values of $\langle σv \rangle$ that we find and the upper limits obtained with the non-detection of a $γ$-ray flux from Milky Way dwarf spheroidal galaxies. This signal is thus more likely associated with $γ$ rays produced in the intracluster region by cosmic rays colliding with gas and photon fields.

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arXiv2022

MeV Dark Matter with MeV Dark Photons in Abelian Kinetic Mixing Theories

We consider the cosmology and phenomenology of a dark photon portal to a simple dark sector consisting of a single, light, fermionic dark matter particle species with mass in the MeV range. We entertain three possible kinetic mixing structures of a new Abelian gauge group U(1)$_{\text{dark}}$ with the visible sector through U(1)$_{\text{e.m.}}$, U(1)$_{\text{Y}}$ and T[SU(2)$_{\text{L}}$]. We assume the dark photon to be massive and around the MeV scale, thus close to the mass scale of the dark matter candidate. We compute the dark matter relic density via freeze-out and freeze-in, entertaining the additional possibilities of (i) a late inflationary period that could dilute the dark matter yield of heavy candidates, and (ii) additional production modes, for models with under-abundant thermal production. We explore the parameter space compatible with a variety of experimental and astrophysical bounds, and discuss prospects for discovery with new CMB probes and MeV gamma-ray telescopes.

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arXiv2022

Integral X-ray constraints on sub-GeV Dark Matter

Light Dark Matter (DM), defined here as having a mass between 1 MeV and about 1 GeV, is an interesting possibility both theoretically and phenomenologically, at one of the frontiers of current progress in the field of DM searches. Its indirect detection via gamma-rays is challenged by the scarcity of experiments in the MeV-GeV region. We look therefore at lower-energy X-ray data from the Integral telescope, and compare them with the predicted DM flux. We derive bounds which are competitive with existing ones from other techniques. Crucially, we include the contribution from inverse Compton scattering on galactic radiation fields and the CMB, which leads to much stronger constraints than in previous studies for DM masses above 20 MeV.

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arXiv2022

Flat spectrum radio quasars and BL Lacs dominate the anisotropy of the unresolved gamma-ray background

We analyze the angular power spectrum (APS) of the unresolved gamma-ray background (UGRB) emission and combine it with the measured properties of the resolved gamma-ray sources of the Fermi-LAT 4FGL catalog. Our goals are to dissect the composition of the gamma-ray sky and to establish the relevance of different classes of source populations of active galactic nuclei in determining the observed size of the UGRB anisotropy, especially at low energies. We find that, under physical assumptions for the spectral energy dispersion, i.e. by using the 4FGL catalog data as a prior, two populations are required to fit APS data, namely flat spectrum radio quasars (FSRQs) at low energies and BL Lacs (BLLs) at higher energies. The inferred luminosity functions agree well with the extrapolation of the FSRQ and BLL ones obtained from the 4FLG catalog. We use these luminosity functions to calculate the UGRB intensity from blazars, finding a contribution of 20% at 1GeV and 30% above 10 GeV. Finally, bounds on an additional gamma-ray emission due to annihilating dark matter are derived.

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arXiv2022

The Large High Altitude Air Shower Observatory (LHAASO) Science Book (2021 Edition)

Since the science white paper of the Large High Altitude Air Shower Observatory (LHAASO) published on arXiv in 2019 [e-Print: 1905.02773 (astro-ph.HE)], LHAASO has completed the transition from a project to an operational gamma-ray astronomical observatory LHAASO is a new generation multi-component facility located in Daocheng, Sichuan province of China, at an altitude of 4410 meters. It aims at measuring with unprecedented sensitivity the spectrum, composition, and anisotropy of cosmic rays in the energy range between 10$^{12}$ and 10$^{18}$~eV, and acting simultaneously as a wide aperture (one stereoradiant) continuously operating gamma-ray telescope in the energy range between 10$^{11}$ and $10^{15}$~eV with the designed sensitivity of 1.3\% of the Crab Unit (CU) above 100 TeV. LHAASO's capability of measuring simultaneously different shower components (electrons, muons, and Cherenkov/fluorescence light), will allow it to investigate the origin, acceleration, and propagation of CR through measurement of the energy spectrum, elemental composition, and anisotropy with unprecedented resolution. The remarkable sensitivity of LHAASO will play a key role in CR physics and gamma-ray astronomy for a general and comprehensive exploration of the high energy universe and will allow important studies of fundamental physics (such as indirect dark matter search, Lorentz invariance violation, quantum gravity) and solar and heliospheric physics. The LHAASO Collaboration organized an editorial working group and finished all editorial work of this science book, to summarize the instrumental features and outline the prospects of scientific researches with the LHAASO experiment.

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