Testing effects of Lorentz invariance violation in the propagation of astroparticles with the Pierre Auger Observatory

Abstract

Lorentz invariance violation (LIV) is often described by dispersion relations of the form E i 2 = m i 2+p i 2+δi,n E 2+n with delta different based on particle type i, with energy E, momentum p and rest mass m. Kinematics and energy thresholds of interactions are modified once the LIV terms become comparable to the squared masses of the particles involved. Thus, the strongest constraints on the LIV coefficients δi,n tend to come from the highest energies. At sufficiently high energies, photons produced by cosmic ray interactions as they propagate through the Universe could be subluminal and unattenuated over cosmological distances. Cosmic ray interactions can also be modified and lead to detectable fingerprints in the energy spectrum and mass composition observed on Earth. The data collected at the Pierre Auger Observatory are therefore possibly sensitive to both the electromagnetic and hadronic sectors of LIV. In this article, we explore these two sectors by comparing the energy spectrum and the composition of cosmic rays and the upper limits on the photon flux from the Pierre Auger Observatory with simulations including LIV. Constraints on LIV parameters depend strongly on the mass composition of cosmic rays at the highest energies. For the electromagnetic sector, while no constraints can be obtained in the absence of protons beyond 1019 eV, we obtain δγ,0 > -10-21, δγ,1 > -10-40 eV-1 and δγ,2 > -10-58 eV-2 in the case of a subdominant proton component up to 1020 eV. For the hadronic sector, we study the best description of the data as a function of LIV coefficients and we derive constraints in the hadronic sector such as δhad,0 < 10-19, δhad,1 < 10-38 eV-1 and δhad,2 < 10-57 eV-2 at 5σ CL.

Constraints on the proton fraction of cosmic rays at the highest energies and the consequences for cosmogenic neutrinos and photons

“…Our results for this scenario can look similar to what is expected from propagation models involving Lorentz invariance violation (LIV) (compare with [53][54][55], for example), which can suppress the photopion interaction at high energies and strengthen the flux recovery. If a recovery is observed, it is therefore prudent to investigate whether this is due to LIV or a 2SC-dip/recovery scenario.…”

Theoretical and experimental challenges in quantum gravity phenomenology

“…On the other hand, the study of the end of the spectrum of UHECR by the Pierre Auger Observatory in Argentina, the largest cosmic ray observatory in the world, completed in 2008 (but collecting data since 2004), has revealed a number of complexities. While a suppression of the spectrum at high energies is confirmed, its interpretation as a signature of the GZK cutoff is not so immediate; many unknowns about the distribution of astrophysical sources and about the energy spectrum and mass composition of cosmic rays influence the tests of violations of Lorentz invariance [23,24].…”

Low Energy Antimatter Physics

“…These keV antiprotons could then be cooled by various techniques (such as sympathetic cooling) by the experiments located at the AD. Typically, this can lead to the obtainment of ~10 4 confined antiprotons in traps at equivalent temperatures ranging from 10 to 1000 K. At the same time, a plasma of ~10 7 positrons can be made available by positron accumulators powered by Na-22 sources. Subsequently, antiprotons and positrons are mixed, which resulted in a few hundreds of anti-Hydrogen atoms produced, at best, for a very short time (less than 1 s).…”

“…Experimentally, investigations about Lorentz and CPT violation are often conducted in very different energy regimes: while Lorentz invariance is mostly studied in very high energy phenomena (e.g., in Cosmic Rays at the 10 19 eV scale [7]), the study of CPT violation takes its preferred stage at low energies, in the form of measurements of rest masses and in the study of bound systems such as anti-Hydrogen.…”