arXiv subjects

Elena Pinetti

Publications and source records attributed to Elena Pinetti.

At least 19 recordsLinked to original sources

arXiv2026

Tomography of the gamma-ray sky from cross-correlation with DESI DR2 and unWISE galaxies

We study the origin of extragalactic gamma-ray emission observed by Fermi-LAT, using the cross-correlation of the gamma-ray sky with maps of large-scale structure provided by the DESI and unWISE surveys. Tomographic cross-correlation reveals the bias-weighted redshift distributions of gamma-ray sources. We first illustrate this method by cross-correlating detected gamma-ray point sources with large-scale structure. We find a significant cross-correlation and infer a point source redshift distribution broadly consistent with the distribution of identified optical counterparts previously reported in the literature, as well as a similar linear bias ($b \approx 2$) to massive galaxies that host bright active galactic nuclei. We then study the clustering of the Fermi unresolved gamma-ray background (UGRB), both in auto-correlation and in cross-correlation with large-scale structure. We detect the cross-correlation of the UGRB and LSS at $\sim 10\sigma$ in total, with highly significant detections from both DESI and unWISE. Our measurements suggest that the redshift distribution of the UGRB is broadly consistent with the redshift distribution of detected point sources. Additionally, we find a relatively weak amplitude for the cross-correlation with large-scale structure at z < 2, suggesting a significant fraction of the UGRB does not come from z < 2 large-scale structure. A natural candidate is contamination of from residual Galactic emission, and our best estimate of the contamination level derived from the UGRB auto-spectrum suggests that the mean bias of UGRB sources is indeed quite similar to the bias of detected Fermi point sources. However, we cannot exclude additional emission from gamma-ray sources at high redshift, z > 2, and we suggest that cross-correlation with tracers at z > 2, including CMB lensing, would be the ideal way to determine the fraction of z > 2 emission.

astro-ph.CO↗

arXiv2025

The Tianlai-WIYN North Celestial Cap Redshift Survey

We present the results of a small, low redshift spectroscopic survey of galaxies within 3 degrees of the North Celestial Pole (NCP) selected using V-band photometry obtained from the North Celestial Cap Survey (NCCS) (Gorbikov & Brosch 2014). The purpose of the current survey is to create a redshift space template for 21 cm emission from neutral hydrogen with which to correlate radio line intensity observations by the Tianlai dish and cylinder interferometers. A total of 898 redshifts were obtained from the 2102 extended objects in the NCCS with m_V < 19 in the survey area. After accounting for extinction, the survey geometry and selection effects, the number density and clustering pattern of galaxies in the redshift catalog are consistent with other low redshift surveys. We were also able to identify 11 galaxy cluster candidates from this redshift catalog.

astro-ph.CO↗

arXiv2025

The Impact of Muon and Pion Cooling on the Neutrino Spectrum of NGC 1068

The IceCube Neutrino Observatory has detected a flux of $\sim 1-10 \, {\rm TeV}$ neutrinos from the active galaxy, NGC 1068. The soft spectral index of these neutrinos has previously been interpreted as an indication that this source accelerates protons only up to energies of several hundred TeV. Here, we propose that this source might instead accelerate protons to significantly higher energies, but that the charged pions and muons produced in their interactions undergo significant synchrotron energy losses before they can decay, leading to a cutoff in the neutrino spectrum at TeV-scale energies. This scenario would require very strong magnetic fields to be present in the acceleration region of NGC 1068, on the order of $B \sim 10^7 \, {\rm G}$. We point out that this synchrotron cooling would impact the flavor ratios of the neutrinos from this source, providing a means to test this scenario with future very-large volume neutrino telescopes.

astro-ph.HE↗

arXiv2025

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 $\gamma$-ray sources and potentially reveal exotic signals from particle dark matter. In this work, we investigate CTAO sensitivity to cross-correlation signals between $\gamma$-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.

astro-ph.HE↗

arXiv2025

Dark matter decay signals in cosmic filaments

Cosmic filaments form the backbone of the cosmic web, yet their properties and evolution remain uncertain. Using the EAGLE hydrodynamical simulations, we investigate the dark matter density profiles in filaments and their implications for dark matter decay signals. We show that GeV-scale dark matter particles decaying into electron-positron pairs can produce detectable radio synchrotron emission. By leveraging stacked filament radio data, we place stringent constraints on the dark matter decay lifetime, improving existing limits by up to two orders of magnitude for strong filamentary magnetic fields.

astro-ph.CO↗

arXiv2025

Observing Dark Matter Decays to Gravitons via Graviton-Photon Conversion

Since dark matter is only known to have gravitational interactions, it may plausibly decay to gravitons on cosmological timescales. Although such a scenario can be easily realized, there are currently no known limits on this possibility based on indirect detection searches. We find that the gravitons produced in dark matter decays can convert to photons in large-scale magnetic fields along the line of sight to an observer. These conversions primarily occur within cosmological filaments which occupy a large (order unity) volume fraction and contain $\sim 10-100$ nG fields with $\sim$ Mpc coherence lengths. Thus, dark matter decays to gravitons predict an irreducible population of extragalactic $\textit{photons}$, which we constrain using the extragalactic gamma-ray background measured by the $\textit{Fermi}$-LAT telescope. Using this conservative method, we place the first limits on the dark matter lifetime in the $0.1 {\rm GeV} - 10^8$ GeV mass range, assuming only decays to gravitons. We also make projections for the Advanced Particle-astrophysics Telescope, which can improve sensitivity to this DM decay channel by an order of magnitude beyond those we set using $\textit{Fermi}$-LAT data.

hep-ph↗

arXiv2025

First constraints on QCD axion dark matter using James Webb Space Telescope observations

I present the first constraints on QCD axion dark matter using measurements from the James Webb Space Telescope. By utilizing publicly available MIRI and NIRSpec blank-sky observations, originally collected for sky subtraction purposes, I derive strong limits on the axion-photon coupling constant $g_{a \gamma \gamma}$ in the mass range 0.1-4 eV. These constraints improve upon previous studies by more than two orders of magnitude for a range of masses. This analysis underscores the potential of blank-sky observations as a powerful tool for constraining dark matter models and demonstrates how astrophysical missions can be repurposed for particle physics research.

hep-ph↗

arXiv2024

Cross Correlating the Unresolved Gamma-Ray Background with Cosmic Large-Scale Structure from DESI: Implications for Astrophysics and Dark Matter

The unresolved gamma-ray background (UGRB) is a diffuse gamma-ray emission arising from numerous extragalactic sources below the detection threshold and is an important component of the gamma-ray sky. Studying the UGRB is crucial for understanding high-energy astrophysical processes in the universe and for probing fundamental physics, such as the nature of dark matter. In this work, we forecast the cross-correlation between the UGRB and galaxy catalogs from the Dark Energy Spectroscopic Instrument (DESI) survey. First, we study the expected astrophysical contributions to the UGRB and their cross-correlation with DESI spectroscopic galaxies. Our calculations show that the cross-correlation signal-to-noise ratio is expected to be significant, with the highest value predicted to be 20.6 for DESI luminous red galaxies due to a higher predicted overlap in the redshift distribution with the UGRB. We consider two science cases that the UGRB-spectroscopic galaxies cross-correlation can be applied to: 1) measuring the UGRB flux as a function of redshift, achieving a precision of 10\% in some redshift bins, and 2) searching for annihilating dark matter potentially up to a mass of about 300~GeV, three times higher than the currently strongest constraints. This work underscores the importance of cross correlating the UGRB with cosmic large-scale structure tracers and highlights the multiwavelength approaches to advancing our understanding of high-energy astrophysical phenomena and fundamental physics.

astro-ph.HE↗

arXiv2024

Searching for Synchrotron Emission from the Geminga TeV Halo using the Planck Satellite

Pulsars convert a significant fraction of their total spin-down power into very high-energy electrons, leading to the formation of TeV halos. It is not yet known, however, whether these sources also efficiently accelerate electrons at lower energies and, if so, how those particles propagate through the surrounding environment. If pulsars produce $\sim 50-300 \, {\rm GeV}$ electrons, these particles would produce a spatially extended halo of synchrotron emission in the frequency range measured by Planck. Such emission could be used to constrain the low-energy diffusion coefficient in the regions surrounding these pulsars, as well as the spectrum and intensity of the electrons that are accelerated in this energy range. In this study, we attempt to use Planck data to constrain the nature of the Geminga pulsar's TeV halo. We find no conclusive evidence of this emission in Planck's frequency range, however, and calculate that the synchrotron flux from Geminga should be well below the total flux measured by Planck, even for models with favorable diffusion parameters or soft injection spectra. At this time, these measurements are not capable of significantly constraining the values of these parameters.

astro-ph.HE↗

arXiv2023

Unraveling TeV Halos with the Cherenkov Telescope Array

Pulsars are observed to emit bright and spatially extended emission at multi-TeV energies. Although such "TeV halos" appear to be an approximately universal feature of middle-aged pulsars, there remains much to be understood about these systems. In this paper, we project the ability of the Cherenkov Telescope Array (CTA) to measure the properties of TeV halos, focusing on the case of the nearby Geminga pulsar. We conclude that CTA will be able to provide important information about this source, allowing us to discriminate between a range of different models that are currently consistent with all existing data. In particular, such observations will help us to measure the normalization, energy dependence, and spatial dependence of the diffusion coefficient in the region that surrounds Geminga, as well as the spectrum of the electrons that are injected from this source.

astro-ph.HE↗

arXiv2023

Reviving MeV-GeV Indirect Detection with Inelastic Dark Matter

Thermal relic dark matter below $\sim 10 \ \text{GeV}$ is excluded by cosmic microwave background data if its annihilation to visible particles is unsuppressed near the epoch of recombination. Usual model-building measures to avoid this bound involve kinematically suppressing the annihilation rate in the low-velocity limit, thereby yielding dim prospects for indirect detection signatures at late times. In this work, we investigate a class of cosmologically-viable sub-GeV thermal relics with late-time annihilation rates that are detectable with existing and proposed telescopes across a wide range of parameter space. We study a representative model of inelastic dark matter featuring a stable state $\chi_1$ and a slightly heavier excited state $\chi_2$ whose abundance is thermally depleted before recombination. Since the kinetic energy of dark matter in the Milky Way is much larger than it is during recombination, $\chi_1 \chi_1 \to \chi_2 \chi_2$ upscattering can efficiently regenerate a cosmologically long-lived Galactic population of $\chi_2$, whose subsequent coannihilations with $\chi_1$ give rise to observable gamma-rays in the $\sim 1 \ \text{MeV} - 100 \ \text{MeV}$ energy range. We find that proposed MeV gamma-ray telescopes, such as e-ASTROGAM, AMEGO, and MAST, would be sensitive to much of the thermal relic parameter space in this class of models and thereby enable both discovery and model discrimination in the event of a signal at accelerator or direct detection experiments.

hep-ph↗

arXiv2023

Hunting Dark Matter Lines in the Infrared Background with the James Webb Space Telescope

Dark matter particles with a mass around 1 eV can decay into near-infrared photons. Utilising available public blank sky observations from the NIRSpec IFU on the James Webb Space Telescope (JWST), we search for a narrow emission line due to decaying dark matter and derive leading constraints in the mass range 0.8-3 eV on the decay rate to photons, and more specifically, on the axion-photon coupling for the case of axion-like particles. We exclude $\tau < 6.7\cdot 10^{26}$ s at $m_{\rm DM} \simeq 0.9$ eV and, in the case of axions, $g_{a \gamma \gamma} > 9.4 \cdot 10^{-12}$ GeV$^{-1}$ for $m_a = 2.15$ eV. Our results do not rely on dedicated observations, rather we use blank sky observations intended for sky subtraction, and thus our reach may be automatically strengthened as JWST continues to observe.

hep-ph↗

arXiv2023

On the Neutrino and Gamma-Ray Emission from NGC 1068

IceCube has recently reported the detection of $\sim 1-10 \,{\rm TeV}$ neutrinos from the nearby active galaxy, NGC 1068. The lack of TeV-scale emission from this source suggests that these neutrinos are generated in the dense corona that surrounds NGC 1068's supermassive black hole. In this paper, we present a physical model for this source, including the processes of pair production, pion production, synchrotron, and inverse Compton scattering. We have also performed a new analysis of Fermi-LAT data from the direction of NGC 1068, finding that the gamma-ray emission from this source is very soft but bright at energies below $\sim 1 \, {\rm GeV}$. Our model can predict a gamma-ray spectrum that is consistent with Fermi-LAT observations, but only if the magnetic field within the corona of this active galactic nucleus (AGN) is quite high, namely $B\gtrsim 6 \, {\rm kG}$. To explain the observed neutrino emission, this source must accelerate protons with a total power that is comparable to its intrinsic X-ray luminosity. In this context, we consider two additional nearby active galaxies, NGC 4151 and NGC 3079, which have been identified as promising targets for IceCube.

astro-ph.HE↗

arXiv2023

Probing The Longest Dark Matter Lifetimes with the Line Emission Mapper

In the next decade, the proposed Line Emission Mapper (LEM) telescope concept is poised to revolutionize Galactic and extragalactic X-ray sensitivity. The instruments aboard LEM feature unprecedented eV scale energy resolution and an effective area of 1600 cm$^2$ at 0.5 keV. Such features are ideally suited to explore decaying dark matter candidates that predict X-ray signals, including axion-like particles and sterile neutrinos. We present the first forecast of LEM sensitivity to dark matter decays and find sensitivity to lifetimes beyond $\sim 10^{32}$ s in the keV range, surpassing current limits by several orders of magnitude. Notably, our results show that LEM will be the first ever instrument to probe such long dark matter lifetimes in any mass range for any decay channel.

astro-ph.CO↗

arXiv2023

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$.

hep-ph↗

arXiv2022

From gamma rays to radio waves: Dark Matter searches across the spectrum

In this thesis, we examined the possibilities offered by multi-messenger astronomy in the context of indirect dark matter detection. We have applied a multi-wavelength strategy by studying different signals across the electromagnetic spectrum (gamma-rays, X-rays, radio waves) produced at different scales of the Universe (galactic, extragalactic, cosmic web filaments). In Part I, we obtained the first-ever prediction of the cross-correlation signal between the extragalactic gamma-ray flux and the 21cm line emitted by hydrogen atoms in dark matter halos. We showed that the neutral hydrogen distribution is a highly competitive probe for dark matter searches, especially in view of the next-generation radio telescope Square Kilometre Array. In Part II, we obtained the limits on the annihilation cross-section of dark matter particles by comparing the X-ray flux measured by INTEGRAL with the theoretical signal expected in the case of particles with a mass between 1 MeV and 5 GeV. We derived the most stringent constraints in the literature on such particles with a mass between 150 MeV and 1.5 GeV. The originality of this work resides in including the contribution from the scattering between the low-energy photons in the Milky Way with the electrons and positrons, produced by dark matter particles. In Part III, we focused on an exotic radio signal, emerging from the GLEAM survey, which seems compatible with a filament of the cosmic web and provides direct evidence for one of the pillars of our understanding of structure formation in the Universe. This radio emission can be explained by dark matter candidates with a mass in the range of 5-10 GeV, decaying into pairs of electrons and positrons. This thesis contributes to a broad spectrum of research for particle dark matter on different levels, since we considered different types of signals, multiple targets and different mass scales.

astro-ph.HE↗

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.

astro-ph.HE↗

arXiv2021

The cosmic coincidences of primordial-black-hole dark matter

If primordial black holes (PBHs) contribute more than 10 percent of the dark matter (DM) density, their energy density today is of the same order as that of the baryons. Such a cosmic coincidence might hint at a mutual origin for the formation scenario of PBHs and the baryon asymmetry of the Universe. Baryogenesis can be triggered by a sharp transition of the rolling rate of inflaton from slow-roll to (nearly) ultraslow-roll phases that produces large curvature perturbations for PBH formation in single-field inflationary models. We show that the baryogenesis requirement drives the PBH contribution to DM, along with the inferred PBH mass range, the resulting stochastic gravitational wave background frequency window, and the associated cosmic microwave background tensor-to-scalar ratio amplitude, into potentially observable regimes.

astro-ph.CO↗