arXiv subjects

Marco Manno

Publications and source records attributed to Marco Manno.

5 recordsLinked to original sources

arXiv2026

Primordial Black Hole Assisted Dirac Leptogenesis

Dirac leptogenesis offers a qualitatively different route to the baryon asymmetry: total lepton number is conserved, but equal and opposite asymmetries are stored in the Standard Model and right handed neutrino sectors, with only the visible component processed by electroweak sphalerons. We present the first dedicated study of how evaporating primordial black holes (PBHs) modify this mechanism. In a minimal charged-scalar mediator setup, we solve the coupled Boltzmann system including thermal production, Hawking emission of the mediator $X$ and of right handed neutrinos, the PBH contribution to the expansion rate, and entropy injection. We find that Hawking emission can populate $X$ in regions where thermal production is inefficient, allowing its subsequent CP-violating decays to enhance the baryon asymmetry. For representative benchmarks, PBHs extend the successful region from mediator masses around $10^9\,{\rm GeV}$ down to about $10^6\,{\rm GeV}$ and can compensate for smaller effective CP asymmetries. This effect is not universal: where thermal Dirac leptogenesis is already efficient, PBHs can instead reduce the final asymmetry. Their evaporation also deposits energy in the right handed neutrino sector and contributes to $\Delta N_{\rm eff}$. In the PBH parameter scan, part of the region that reproduces the observed baryon asymmetry lies below the Planck reference level $\Delta N_{\rm eff}=0.284$ and above the projected CMB-S4 sensitivity $\Delta N_{\rm eff}=0.06$.

hep-ph↗

arXiv2026

Unveiling Neutrino Nature with the Diffuse Supernova Background

The true nature of neutrinos--whether Dirac or Majorana--is a foundational, unresolved question. We demonstrate that the diffuse supernova neutrino background (DSNB) offers an untapped avenue to resolve this issue, provided neutrino magnetic moments are $\gtrsim 10^{-14}\mu_B$. The intense magnetic fields characteristic of a subset of collapsing massive stars can trigger resonant chirality flips. This flavor conversion physics alters DSNB fluxes in measurable ways that depend on the neutrino nature. A $20$~yr combined exposure at Hyper-Kamiokande loaded with gadolinium and JUNO can unravel this signature at $90\%$ ($99\%$) confidence if the fraction of magnetorotational events exceeds $12\%$ ($20\%$) of cosmic core collapses. This result holds independent of the mass ordering and establishes the DSNB as a critical gateway to unveiling the true identity of the neutrino.

astro-ph.HE↗

arXiv2026

Matter- and magnetically-driven flavor conversion of neutrinos in magnetorotational collapses

The magnetorotational collapse of massive stars copiously emits neutrinos of all flavors, with a prominent hierarchy between the non-electron and electron flavor average energies. Relying on a three-dimensional neutrino-magnetohydrodynamic simulation of a $13 M_\odot$ progenitor, we investigate flavor conversion in matter. We find that, in addition to resonant flavor conversion of neutrinos and antineutrinos in matter, (anti)neutrinos experience chirality-flipping interactions due to their non-zero magnetic moment ($\mu \lesssim 10^{-12} \mu_B$) and large magnetic field in the source ($B \simeq 10^{15}$ G). For Majorana neutrinos, this leads to resonant flavor-changing neutrino-antineutrino mixing. The event rate expected from a Galactic collapse at current and next-generation neutrino telescopes, such as IceCube and Hyper-Kamiokande, strongly depends on the orientation of the magnetorotational collapse with respect to the observer direction and flavor conversion scenario. The event rate is expected to be larger for an observer facing head on the jet launched during the stellar collapse and peaks around $400$-$600$ ms after bounce. Our work highlights that understanding the rich phenomenology of flavor conversion in magnetorotational collapses is essential to take full advantage of the joint detection of neutrinos and gravitational waves from these sources.

astro-ph.HE↗

arXiv2025

Multimessenger Constraints on Supermassive Dark Stars and Their Black Hole Remnants

Dark matter (DM) annihilation can power the first generation of stars as long lived dark stars (DSs) that grow to supermassive scales $M_{\rm DS}\gtrsim 10^{5} M_{\odot}$ and eventually collapse into heavy black holes that could seed the supermassive black holes observed at high redshifts. We compute the diffuse electromagnetic emission from a cosmological population of such supermassive DSs and their black hole remnants, tracking the entire DS history and including thermal surface radiation, DM annihilation in adiabatically contracted halos as well as late-time emission from DM overdensity spikes around the resulting black holes. After accounting for photon attenuation, we find that DS related contributions can exceed the Fermi-LAT extragalactic $\gamma$-ray background for thermal relic annihilation cross-sections and DM masses below $\sim 1$ TeV. Our results constitute the first population integrated diffuse multimessenger constraints on supermassive DSs as progenitors of early black holes and demonstrate that diffuse photon and neutrino backgrounds offer a powerful and complementary avenue for probing the role of DM in the formation of the earliest massive structures.

astro-ph.CO↗

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, $\Delta N_{\rm eff}$. 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 $\Delta N_{\rm eff}$ from Planck satellite observations, we derive updated constraints on this scenario.

astro-ph.CO↗