Gamma-ray cosmology and fundamental physics with blazars

par Jonathan Biteau (Santa Cruz Institute for Particle Physics, University of California)

lundi 23 mars 2015, 14:00 → 15:00 Europe/Paris

Amphithéâtre (CPPM)

Gamma-ray cosmology aims to constrain the propagation of gamma rays on cosmological distances [1,2]. TeV gamma rays from extragalactic sources, such as blazars, induce the creation of electron-positron pairs when they interact with the eV photon field that populates the voids of the universe, called the extragalactic background light (EBL). The EBL, second most intense cosmological background after the CMB, carries the integral history of star and galaxy emission from infrared to UV wavelengths and is particularly difficult to measure with direct observations. After having detected for the first time the EBL imprint in the spectra of TeV blazars with H.E.S.S. [3], I have collected the most extensive set of archival TeV data to date to reconstruct a detailed spectrum of the EBL, to study the expansion rate of the universe, and to constrain anomalies expected from new physics [4]. I will discuss the insights gained on diffuse eV components, the possible sources of reionization, and the Hubble constant. I will also shed light on the claim of detection of a "pair-production anomaly" [5], which could arise from the mixing of gamma rays with axion-like particles. I will finally discuss the impact on gamma-ray absorption of UV corrections to Lorentz symmetry [6] and show that the probe of the Planck energy scale is within the reach of observations. Current-generation experiments, such as VERITAS, MAGIC, and H.E.S.S. II, are collecting tremendous statistics from blazars and improve at a tremendous pace our knowledge of the astrophysics at play in the sources, as well as of the content and properties of the universe. The next-generation observatory, CTA [7], will be the ultimate tool of gamma-ray cosmology and will revolutionize the field during the next decade. Bibliography: [1] J. Biteau, "Probing the extragalactic background light with H.E.S.S.", Rencontres de Blois 2013, Blois, France (2013). [2] J. Biteau, "Constraining gamma-ray propagation on cosmic distances", SF2A 2013, Montpellier, France (2013). [3] H.E.S.S. collaboration (corresp. author: J. Biteau), "Measurement of the extragalactic background light imprint on the spectra of the brightest blazars observed with H.E.S.S.", A&A 550, 4 (2013). [4] J. Biteau & D. A. Williams, "The extragalactic background light, the Hubble constant, and axion-like particles : conclusions from 20 years of TeV gamma-ray observations". Submitted to ApJ (Jan. 2015). [5] D. Horns & M. Meyer, "Indications for a pair-production anomaly from the propagation of VHE gamma-rays", J. Cosmology Astropart. Phys., 2, 33 (2012). [6] G. Amelino-Camelia, "Quantum-Spacetime Phenomenology", Living Reviews in Relativity, 16, 5 (2013). [7] M. Actis et al, "Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy", Exp. Astronomy, 32, 193 (2011).

Transparents Seminar_Biteau_GammaRayCosmoFundaPhysics.pdf