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Daniele Montanino

Publications and source records attributed to Daniele Montanino.

12 recordsLinked to original sources
arXiv2026

Investigating Optical Coupling Material Candidates in NaI(Tl) Detectors for the SABRE-North Dark Matter Experiment

Direct dark matter detection with NaI(Tl) scintillators requires ultra-low-background materials. Silicone optical pads can couple NaI(Tl) crystals to photomultiplier tubes (PMTs) if they provide adequate optical transmission and radiopurity. We characterize four candidate materials for the SABRE-North experiment: commercial EJ-560, used as a reference, and three materials produced at the University of Salento (SYLGARD 184, EGel 3002 A/B, and a hybrid formulation) using different catalyst ratios and curing conditions, yielding ten samples in total. Optical transmittance was measured from 310 to 850 nm by UV/Vis/NIR spectrophotometry. Radiopurity was assessed at the STELLA facility at LNGS using high-purity germanium (HPGe) $γ$-ray spectrometry and, for EJ-560, high-resolution ICP-MS. At the 410 nm NaI(Tl) emission peak, EJ-560 shows an absorbance coefficient of $0.064\pm0.017$ mm$^{-1}$. The best locally produced samples reach $0.097\pm0.015$ and $0.093\pm0.014$ mm$^{-1}$ for SYLGARD 184 with a 10:2 base-to-catalyst ratio cured at room temperature and at $40^\circ$C, respectively, $0.125\pm0.015$ mm$^{-1}$ for EGel 3002 with a 2B:A ratio cured at $40^\circ$C, and $0.106\pm0.014$ mm$^{-1}$ for the hybrid 10:1 EGel A:CataSYL formulation cured at room temperature. EJ-560 exhibits detectable $^{232}$Th-chain activity at about 1.8 mBq/kg and the highest $^{40}$K activity, $(120\pm20)$ mBq/kg. The locally produced materials show no detectable Th-chain contamination but exhibit $^{226}$Ra activities of about 2.3 mBq/kg and lower $^{40}$K levels. No single material is optimal across all criteria. Additional ICP-MS screening, HPGe measurements of cured pads, and direct NaI(Tl)-PMT light-yield tests are required for a conclusive SABRE-North material selection.

physics.ins-det↗
arXiv2025

ALP production from light primordial black holes: The role of superradiance

Light primordial black holes (LPBHs) with masses in the range $10$~g~$\leq M_{\rm BH} \leq 10^9$~g, although they evaporate before Big Bang Nucleosynthesis, can play a significant role in the production of both dark matter and dark radiation. In particular, LPBHs can evaporate into light axions or axion-like particles (ALPs) with masses $m_a \lesssim$~MeV, contributing to the effective number of neutrino species, $ΔN_{\rm eff}$. Additionally, heavy scalar particles known as {\em moduli}, predicted by string theory, can be produced both via Hawking evaporation and through amplification by a mechanism called {\em superradiant instability} in the case of spinning primordial black holes (PBHs). These moduli can subsequently decay into ALPs, further amplifying their abundance. In this work, we calculate the number density of ALPs in the presence of moduli enhanced by superradiance for Kerr PBHs. Using current limits on $ΔN_{\rm eff}$ from Planck satellite observations, we derive updated constraints on this scenario.

astro-ph.CO↗
arXiv2022

Constraining axion-like particles with the diffuse gamma-ray flux measured by the Large High Altitude Air Shower Observatory

The detection of very high-energy neutrinos by IceCube experiment supports the existence of a comparable gamma-ray counterpart from the same cosmic accelerators. Under the likely assumption that the sources of these particles are of extragalactic origin, the emitted photon flux would be significantly absorbed during its propagation over cosmic distances. However, in the presence of photon mixing with ultra-light axion-like-particles (ALPs), this expectation would be strongly modified. Notably, photon-ALP conversions in the host galaxy would produce an ALP flux which propagates unimpeded in the extragalactic space. Then, the back-conversion of ALPs in the Galactic magnetic field leads to a diffuse high-energy photon flux. In this context, the recent detection of the diffuse high-energy photon flux by the Large High Altitude Air Shower Observatory (LHAASO) allows us to exclude at the $95\%$ CL an ALP-photon coupling $g_{aγ}\gtrsim 3.9-7.8 \times 10^{-11}~\mathrm{GeV^{-1}}$ for $m_{a}\lesssim 4\times10^{-7}~\mathrm{eV}$, depending on the assumptions on the magnetic fields and on the original gamma-ray spectrum. This new bound is complementary with other ALP constraints from very-high-energy gamma-ray experiments and sensitivities of future experiments.

hep-ph↗
arXiv2021

Axion-like particles from primordial black holes shining through the Universe

We consider a cosmological scenario in which the very early Universe experienced a transient epoch of matter domination due to the formation of a large population of primordial black holes (PBHs) with masses $M \lesssim 10^{9}\,\textrm{g}$, that evaporate before Big Bang nucleosynthesis. In this context, Hawking radiation would be a non-thermal mechanism to produce a cosmic background of axion-like particles (ALPs). We assume the minimal scenario in which these ALPs couple only with photons. In the case of ultralight ALPs ($m_a \lesssim 10^{-9}\,\textrm{eV}$) the cosmic magnetic fields might trigger ALP-photon conversions, while for masses $m_a \gtrsim 10\,\textrm{eV}$ spontaneous ALP decay in photon pairs would be effective. We investigate the impact of these mechanisms on the cosmic X-ray background, on the excess in X-ray luminosity in Galaxy Clusters, and on the process of cosmic reionization.

hep-ph↗
arXiv2021

Turbulent axion-photon conversions in the Milky-Way

The Milky-Way magnetic field can trigger conversions between photons and axion-like particles (ALPs), leading to peculiar features on the observable photon spectra. Previous studies considered only the regular component of the magnetic field. However, observations consistently show the existence of an additional turbulent component, with a similar strength and correlated on a scale of a few 10$\,$pc. We investigate the impact of the turbulent magnetic field on the ALP-photon conversions, characterizing the effects numerically and analytically. We show that the turbulent magnetic field can change the conversion probability by up to a factor of two and may lead to observable irregularities in the observable photon spectra from different astrophysical sources.

hep-ph↗
arXiv2017

Enhancing the Spectral Hardening of Cosmic TeV Photons by Mixing with Axionlike Particles in the Magnetized Cosmic Web

Large-scale extragalactic magnetic fields may induce conversions between very-high-energy photons and axionlike particles (ALPs), thereby shielding the photons from absorption on the extragalactic background light. However, in simplified "cell" models, used so far to represent extragalactic magnetic fields, this mechanism would be strongly suppressed by current astrophysical bounds. Here we consider a recent model of extragalactic magnetic fields obtained from large-scale cosmological simulations. Such simulated magnetic fields would have large enhancement in the filaments of matter. As a result, photon-ALP conversions would produce a significant spectral hardening for cosmic TeV photons. This effect would be probed with the upcoming Cherenkov Telescope Array detector. This possible detection would give a unique chance to perform a tomography of the magnetized cosmic web with ALPs.

astro-ph.HE↗
arXiv2016

Reionization during the dark ages from a cosmic axion background

Recently it has been pointed out that a cosmic background of relativistic axion-like particles (ALPs) would be produced by the primordial decays of heavy fields in the post-inflation epoch, contributing to the extra-radiation content in the Universe today. Primordial magnetic fields would trigger conversions of these ALPs into sub-MeV photons during the dark ages. This photon flux would produce an early reionization of the Universe, leaving a significant imprint on the total optical depth to recombination $τ$. Using the current measurement of $τ$ and the limit on the extra-radiation content $ΔN_{\rm eff} $ by the Planck experiment we put a strong bound on the ALP-photon conversions. Namely we obtain upper limits on the product of the photon-ALP coupling constant $g_{aγ}$ times the magnetic field strength $B$ down to $g_{aγ} B \gtrsim 6 \times 10^{-18} \textrm{GeV}^{-1} \textrm{nG} $ for ultralight ALPs.

astro-ph.CO↗
arXiv2014

On detecting oscillations of gamma rays into axion-like particles in turbulent and coherent magnetic fields

Background radiation fields pervade the Universe, and above a certain energy any $γ$-ray flux emitted by an extragalactic source should be attenuated due to $e^+e^-$ pair production. The opacity could be alleviated if photons oscillated into hypothetical axion-like particles (ALPs) in ambient magnetic fields, leading to a $γ$-ray excess especially at high optical depths that could be detected with imaging air Cherenkov telescopes (IACTs). Here, we introduce a method to search for such a signal in $γ$-ray data and to estimate sensitivities for future observations. Different magnetic fields close to the $γ$-ray source are taken into account in which photons can convert into ALPs that then propagate unimpeded over cosmological distances until they re-convert in the magnetic field of the Milky Way. Specifically, we consider the coherent field at parsec scales in a blazar jet as well as the turbulent field inside a galaxy cluster. For the latter, we explicitly derive the transversal components of a magnetic field with gaussian turbulence which are responsible for the photon-ALP mixing. To illustrate the method, we apply it to a mock IACT array with characteristics similar to the Cherenkov Telescope Array and investigate the dependence of the sensitivity to detect a $γ$-ray excess on the magnetic-field parameters.

astro-ph.HE↗
arXiv2012

The effect of photon-axion-like particle conversions in galaxy clusters on very high energy γ-ray spectra

Very high energy (VHE, energy >~ 100 GeV) γ-rays originating from extragalactic sources interact with low energy photons of background radiation fields and produce electron-positron pairs. Alternatively, in the presence of ambient magnetic fields, they can convert into hypothetical axion-like particles (ALPs), pseudo-scalar spin-0 bosons, predicted by extensions of the standard model. These particles propagate unimpeded over cosmological distances. Here, the effect of photon-ALP oscillations in magnetic fields of galaxy clusters and the Milky Way on VHE γ-ray spectra is studied. It is shown that this mechanism can lead to a substantial enhancement of the VHE flux and a spectral hardening, thus effectively reducing the opacity of the Universe to VHE γ-rays.

astro-ph.HE↗
arXiv2012

Hardening of TeV gamma spectrum of AGNs in galaxy clusters by conversions of photons into axion-like particles

A fraction of AGN producing VHE gamma-rays are located in galaxy clusters. The magnetic field present in the intra-cluster medium would lead to conversions of VHE photons into axion-like particles (ALPs), which are a generic prediction of several extensions of the Standard Model. ALPs produced in this way would traverse cosmological distances unaffected by the extragalactic background light at variance with VHE photons which undergo a substantial absorption. Eventually, a nontrivial fraction of ALPs would re-convert into VHE photons in the magnetic field of the Milky Way. This mechanism produces a significant hardening of the VHE spectrum of AGN in galaxy clusters. As a specific example we consider the energy spectra of two observed VHE gamma-ray sources located in galaxy clusters, namely 1ES 0414+009 at redshift z=0.287 and Mkn 501 at z=0.034. We find that the hardening in the observed spectra becomes relevant at E > 1 TeV. The detection of this signature would allow to indirectly probe the existence of ultra-light ALPs with mass m_a < 10^{-8} eV and photon-ALP coupling g_{a gamma} < 10^{-10} GeV^{-1} with the presently operating Imaging Atmospheric Cherenkov Telescopes like H.E.S.S., MAGIC, VERITAS and CANGAROO-III and even more likely with the planned detectors like CTA, HAWC and HiSCORE. An independent laboratory check of ultra-light ALPs invoked in this mechanism can be performed with the planned upgrade of the photon regeneration experiment ALPS at DESY and with the next generation solar axion detector IAXO.

astro-ph.HE↗
arXiv2009

Stochastic conversions of TeV photons into axion-like particles in extragalactic magnetic fields

Very-high energy photons emitted by distant cosmic sources are absorbed on the extragalactic background light (EBL) during their propagation. This effect can be characterized in terms of a photon transfer function at Earth. The presence of extragalactic magnetic fields could also induce conversions between very high-energy photons and hypothetical axion-like particles (ALPs). The turbulent structure of the extragalactic magnetic fields would produce a stochastic behaviour in these conversions, leading to a statistical distribution of the photon transfer functions for the different realizations of the random magnetic fields. To characterize this effect, we derive new equations to calculate the mean and the variance of this distribution. We find that, in presence of ALP conversions, the photon transfer functions on different lines of sight could have relevant deviations with respect to the mean value, producing both an enhancement or a suppression in the observable photon flux with respect to the expectations with only absorption. As a consequence, the most striking signature of the mixing with ALPs would be a reconstructed EBL density from TeV photon observations which appears to vary over different directions of the sky: consistent with standard expectations in some regions, but inconsistent in others.

astro-ph.HE↗