Why neutrino astronomy ?
Most of our current knowledge of the Universe comes from the observation of photons. Photons have many advantages as cosmic information carriers: they are copiously produced, they are stable and electrically neutral, they are easy to detect over a wide energy range, and their spectrum brings detailed information about the chemical and physical properties of the source.
Their disadvantage is that the hot, dense regions which form the central engines of stars, active galactic nuclei and other astrophysical energy sources are completely opaque to photons, and therefore we cannot investigate the properties of these regions by direct observation, but only by indirect inference. For example, the photons we observe from the Sun come from its photosphere, far from the hydrogen-fusing core. Moreover, high energy photons interact with photons of the infrared radiation background and with the cosmic microwave background to create electron-positron pairs; this is the Greisen-Zatsepin-Kuz’min effect (GZK). This effect suppresses any possibility of surveying the sky over distances greater than 100Mpc with high energy (>10 TeV) gamma rays.
In order to observe the inner workings of the astrophysical objects and to obtain a description of the Universe over a larger range of energies, we need a probe which is electrically neutral, so that its trajectory will not be affected by magnetic fields, stable so that it will reach us from distant sources, and weakly interacting so that it will penetrate regions which are opaque to photons. The only candidate currently known to exist is the neutrino.
Some astrophysical sources are known to emit neutrinos: hydrogen fusion produces electron neutrinos as by-products, and solar neutrino astronomy has a 50 years long history; the conversion of iron nuclei to neutrons when a neutron star is formed in the heart of a supernova produces a burst of neutrinos (augmented by the thermal production of neutrino-antineutrino pairs), and one such burst was observed by Kamiokande and IMB for Supernova 1987A; cosmology predicts a low-energy relic neutrino background similar to the low-energy relic photons of the Cosmic Microwave Background, but these would have an effective temperature of around 1.9 K and are very difficult to observe. Astrophysical sources of high-energy neutrinos have not been observed directly, but their existence can be inferred from the properties of cosmic rays. The only source of high energy neutrinos for which we have observational hints (from IceCube) is the blazar TXS 0506+056.
Primary cosmic rays are mainly protons, with some admixture of heavier nuclei; the energy spectrum is a power law which extends to extremely high energies, values exceeding 1020 eV having been observed in recent years. Protons themselves have limited use as astrophysical information carriers because they are charged, and therefore subject to deflection by cosmic magnetic fields: only the highest-energy cosmic rays are expected to retain any memory of the source direction. The exact source of the high-energy cosmic rays is thus unknown, although supernova remnants and active galactic nuclei have been proposed as candidates. Whatever the source, it is clear that accelerating protons to such high energies is likely to generate a large associated flux of photo-produced pions, which decay to yield gamma rays and neutrinos. These will remember the source direction, and so the existence of a general flux of very high energy cosmic-ray protons implies the existence of sources of high-energy neutrinos.
Neutrino astronomy thus offers the possibility of observing sources which correspond to the central engines of the most energetic astrophysical phenomena. It can also provide long baselines for neutrino oscillation studies, and allow for indirect dark matter searches. The drawback, of course, is that the weak interactions of neutrinos imply that a very massive detector with extremely good background rejection is required to observe a measurable flux.
The ANTARES scientific program can be divided into three broad subject areas:
- Astronomy and Astrophysics
- Dark Matter and particle physics
Astronomy and Astrophysics
The principal mechanism for generating high-energy neutrinos is through decay cascades induced by high-energy protons. Interactions of protons with matter or radiation produce mesons, essentially pions and kaons, whose leptonic decay modes will yield neutrinos.
The first detection of an excess of high-energy neutrinos of astrophysical origin was achieved in 2013 by the IceCube collaboration. This flux is, in the 100 TeV–PeV range, at the level of 10-8 GeV cm−2 s−1 sr-1. However the origin of these neutrinos is still unknown. A list of possible high-energy astrophysical neutrino sources, which involves astrophysical sites for proton acceleration, is shown below.
Search for neutrinos from the tidal disruption events AT2019dsg and AT2019fdr with the ANTARES telescope ApJ 920 (2021) 50
ANTARES search for point sources of neutrinos with 11 years of data: a likelihood stacking analysis ApJ 911 (2021) 48
ANTARES upper limits on the multi-TeV neutrino emission from the GRBs detected by IACTs JCAP 03 (2021) 092
Constraining the contribution of Gamma-Ray Bursts to the high-energy neutrino flux with ten years of ANTARES MNRAS, Volume 500, Issue 4, 2021 (5614-5628)
Search for neutrino counterparts of catalogued gravitational-wave events detected by Advanced-LIGO and Virgo during run O2 with ANTARES Eur. Phys. J. C 80, 487
All-flavor Search for a Diffuse Flux of Cosmic Neutrinos with Nine Years of ANTARES Data ApJL 853, L7 (2018)
The Search for Neutrinos from TXS 0506+056 with the ANTARES Telescope ApJL 863, L30 (2018)
Dark matter & Particle physics
Dark matter searches
A common assumption in the particle physics community is that dark matter is made of Weakly Interacting Massive Particles (WIMPs) that form a halo in which the visible baryonic part of galaxies is embedded. There are a variety of candidates for WIMPs, among which those provided by theories based on supersymmetry (SUSY) attract a great deal of interest. In some classes of minimal supersymmetric and universal extra-dimensional extensions of the Standard Model (MSSM and mUED), the lightest particle is stable. Consequently, these particles can only annihilate in pairs, making them a possible WIMP candidate for dark matter.
In these models, secondary high-energy neutrinos are produced from the self-annihilation products, or decays of them. The search for WIMPs can be performed either directly by recording the recoil energy of nuclei when WIMPs scatter on them in suitable detectors, or indirectly.
Search for Secluded Dark Matter towards the Galactic Center with the ANTARES neutrino telescope
JCAP06 (2022) 028
Search for dark matter towards the Galactic Centre with 11 years of ANTARES data
Phys. Lett. B 805 135439 (2020)
Limits on Dark Matter Annihilation in the Sun using the ANTARES Neutrino Telescope
Physics Letters B, Volume 759 (2016)
Particles from Beyond Standard Model Theories
ANTARES detector is a good tool for the detection and test of particles predicted in Beyond Standard Model theories, magnetic monopoles and nucleates.
Search for Magnetic Monopoles with ten years of the ANTARES neutrino telescope data JHEAp 34 (2022)
Neutrino oscillations & interactions
The observation of atmospheric neutrinos with a neutrino telescope provides a means to study neutrino oscillations with a base-line length up to the order of the diameter of the Earth. The focus of investigation is the muon neutrino, but there is also a very interesting possible signature for extremely high energy (>100 TeV) tau neutrinos.
Measurement of the atmospheric nu_e and nu_mu energy spectra with the ANTARES neutrino telescope Phys. Lett. B 816 (2021) 136228
Measuring the Atmospheric Neutrino oscillation parameters and constraining the 3+1 neutrino model with ten years of ANTARES data J. High Energ. Phys. (2019) 2019:113