Cosmic infrared background excess from axion-like particles and implications for multi-messenger observations of blazars

The first measurement of the diffuse background spectrum at 0.8-1.7 $\mu \rm{m}$ from the CIBER experiment has revealed a significant excess of the cosmic infrared background (CIB) radiation compared to the theoretically expected spectrum. We revisit the hypothesis that decays of axionlike particle (ALP) can explain this excess, extending previous analyses to the case of a warm relic population. We show that such a scenario is not excluded by anisotropy measurements nor by stellar cooling arguments. Moreover, we find that the increased extragalactic background light (EBL) does not contradict observations of blazar spectra. Furthermore, the increased EBL attenuates the diffuse TeV gamma-ray flux and alleviates the tension between the detected neutrino and gamma ray fluxes.Comment: 11 pages, 5 figures. Several changes to match published versio

Domain wall interpretation of the PTA signal confronting black hole overproduction

Recently, Pulsar Timing Array (PTA) collaborations have detected a stochastic gravitational wave background (SGWB) at nano-Hz frequencies, with Domain Wall networks (DWs) proposed as potential sources. To be cosmologically viable, they must annihilate before dominating the universe energy budget, thus generating a SGWB. While sub-horizon DWs shrink and decay rapidly, causality requires DWs with super-horizon size to continue growing until they reach the Hubble horizon. Those entering the latest can be heavier than a Hubble patch and collapse into Primordial Black Holes (PBHs). By applying percolation theory, we pioneer an estimation of the PBH abundance originating from DW networks. We conduct a Bayesian analysis of the PTA signal, interpreting it as an outcome of SGWB from DW networks, accounting for PBH overproduction as a prior. We included contributions from supermassive black hole binaries along with their astrophysical priors. Our findings indicate that DWs, as the proposed source of the PTA signal, result in the production of PBHs about ten times heavier than the sun. The binary mergers occurring within these PBHs generate a second SGWB in the kilo-Hz domain which could be observable in on-going or planned Earth-based interferometers if the correlation length of the DW network is greater than approximately 60$\%$ than the cosmic horizon, $L \gtrsim 0.6 t$.Comment: Major improvements of the PBH formation modeling, of the depth of the Bayesian analysis and of the SMBH binary prior (5 pages, 4 figures + appendix, 21 pages in total

Primordial Black Holes and Wormholes from Domain Wall Networks

Domain walls (DWs) are topological defects originating from phase transitions in the early universe. In the presence of an energy imbalance between distinct vacua, enclosed DW cavities shrink until the entire network disappears. By studying the dynamics of thin-shell bubbles in General Relativity, we demonstrate that closed DWs with sizes exceeding the cosmic horizon tend to annihilate later than the average. This delayed annihilation allows for the formation of large overdensities, which, upon entering the Hubble horizon, eventually collapse to form Primordial Black Holes (PBHs). We rely on 3D percolation theory to calculate the number density of these late-annihilating DWs, enabling us to infer the abundance of PBHs. A key insight from our study is that DW networks with the potential to emit observable Gravitational Waves are also likely to yield detectable PBHs. Additionally, we study the production of wormholes connected to baby-universes and conclude on the possibility to generate a multiverse.Comment: 11 pages, 7 figures, and appendi

Astrophysical neutrinos

As the experimental boundaries of the energy and intensity frontiers are pushed forwards, astroparticle physics increasingly becomes a key tool to understand the microscopic and macroscopic mechanisms governing our universe. In this thesis particle physics beyond the Standard Model is explored, especially dark matter and neutrino properties, through the use of astrophysical neutrinos and other messengers. The combined use of neutrinos and photons, as well as cosmic rays and gravitational waves, is at the core of multi-messenger astronomy, a young and rapidly developing field which promises to reshape our understanding of the universe at hugely different energy scales. Neutrinos are of particular interest as they play the double role of possible signal and background. In the first part of the thesis, I present a new analysis of what we will call the “grand unified neutrino spectrum” (GUNS) at Earth, the flux of neutrinos coming from many different sources, both at low and high energies. After a short review of the contributions to the grand unified neutrino spectrum, we will turn to a previously overlooked flux, the low-energy component of neutrinos produced in the Sun by thermal processes, which fills the gap between the cosmic neutrino background and the solar neutrino flux from nuclear reactions. The second part of the thesis is dedicated to the search for physics beyond the Standard Model. First, I will show how solar neutrino observations can be used to constrain neutrino decay to light pseudoscalars, particularly taking advantage of antineutrino searches from the Sun tackled by KamLAND, SNO and Borexino. Finally, I will scrutinize hints for a dark matter signal in the context of multi-messenger, multi-wavelength astronomy, as the decay of axionlike particles with eV mass enhances the infrared cosmic background radiation (as detected by the sounding rocket CIBER), explaining at the same time an existing tension between the observations of Fermi and IceCube, namely that we observe less gamma rays than expected from the measured high-energy neutrino flux.Waehrend die experimentellen Grenzen von Energie und Intensitaet stetig hinausgeschoben werden, entwickelt sich die Astroteilchenphysik immer staerker als Schluessel zum Verstaendnis der mikroskopischen und makroskopischen Mechanismen, die unser Universum bestimmen. In dieser Dissertation wird die Teilchenphysik jenseits des Standardmodells untersucht, insbesondere dunkle Materie und Neutrinoeigenschaften, durch die Benuetzung astrophysikalischer Neutrinos und anderer Botenteilchen. Die gleichzeitige Betrachtung von Neutrinos und Photonen, zusammen mit kosmischer Strahlung und Gravitationswellen, bildet den Kern der Multi-Messenger Astronomie, einem jungen und sich rasch entwickelnden Gebiet, das verspricht, unser Verstaendnis des Universums auf voellig verschiedenen Energieskalen neu zu formen. Gerade Neutrinos sind besonders interessant, da sie sowohl Hintergrund als auch Signal sein koennen. In dem ersten Teil der Arbeit praesentiere ich eine neue Analyse des “grossen vereinheitlichten Neutrinospektrums” (Grand Unified Neutrino Spectrum), womit der irdische Neutrinofluss gemeint ist, der aus unterschiedlichen Quellen ein breites Energiespektrum umfasst. Nach einer kurzen Uebersicht ueber die Beitraege zu diesem vereinheitlichten Neutrinospektrum wenden wir uns einem zuvor nicht beachteten Fluss zu, den niederenergetischen Neutrinos aus thermischen Prozessen in der Sonne. Dieser Fluss schliesst die Luecke zwischen dem kosmischen Neutrinohintergrund und dem solaren Neutrinofluss aus Kernfusionen. Der zweite Teil widmet sich der Suche nach Physik jenseits des Standardmodells. Zunaechst zeigen wir, wie sich aus Sonnenneutrino-Messungen eine obere Schranke an den Neutrinozerfall in leichte Pseudoskalare herleiten laesst, wobei die Suche nach solaren Antineutrinos durch KamLAND, SNO und Borexino besonders nuetzlich ist. Schliesslich untersuche ich Andeutungen eines Signals der dunklen Materie im Kontext der Multi-Messenger Astronomie bei unterschiedlichen Wellenlaengen. Diese Anzeichen stammen von einer erhoehten kosmischen Hintergrundstrahlung im Infrarotspektrum (gemessen von der Sonde CIBER), die mittels des Zerfalls axionartiger Teilchen mit einer eV-Masse erklaert werden kann. Gleichzeitig wuerde damit eine Diskrepanz zwischen Fermi und IceCube Messungen erklaert, naemlich dass weniger Gammastrahlung beobachtet wird, als man aus dem gemessenen Neutrinofluss erwarten wuerde