Searching for New Physics with Ultrahigh Energy Cosmic Rays

📝 Abstract

Ultrahigh energy cosmic rays that produce giant extensive showers of charged particles and photons when they interact in the Earth’s atmosphere provide a unique tool to search for new physics. Of particular interest is the possibility of detecting a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of $\sim 10^{-35} $m. We discuss here the possible signature of Lorentz invariance violation on the spectrum of ultrahigh energy cosmic rays as compared with present observations of giant air showers. We also discuss the possibilities of using more sensitive detection techniques to improve searches for Lorentz invariance violation in the future. Using the latest data from the Pierre Auger Observatory, we derive a best fit to the LIV parameter of $3.0^{+1.5}_{-3.0} \times 10^{-23} $, corresponding to an upper limit of $4.5 \times 10^{-23}$ at a proton Lorentz factor of $\sim 2 \times 10^{11} $. This result has fundamental implications for quantum gravity models.

💡 Analysis

Ultrahigh energy cosmic rays that produce giant extensive showers of charged particles and photons when they interact in the Earth’s atmosphere provide a unique tool to search for new physics. Of particular interest is the possibility of detecting a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of $\sim 10^{-35} $m. We discuss here the possible signature of Lorentz invariance violation on the spectrum of ultrahigh energy cosmic rays as compared with present observations of giant air showers. We also discuss the possibilities of using more sensitive detection techniques to improve searches for Lorentz invariance violation in the future. Using the latest data from the Pierre Auger Observatory, we derive a best fit to the LIV parameter of $3.0^{+1.5}_{-3.0} \times 10^{-23} $, corresponding to an upper limit of $4.5 \times 10^{-23}$ at a proton Lorentz factor of $\sim 2 \times 10^{11} $. This result has fundamental implications for quantum gravity models.

📄 Content

arXiv:0906.1735v2 [astro-ph.HE] 12 Aug 2009 Searching for New Physics with Ultrahigh Energy Cosmic Rays Floyd W Stecker‡ Astrophysics Science Division NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Sean T Scully Dept. of Physics and Astronomy James Madison University, Harrisonburg, VA 22807, USA Abstract. Ultrahigh energy cosmic rays that produce giant extensive showers of charged particles and photons when they interact in the Earth’s atmosphere provide a unique tool to search for new physics. Of particular interest is the possibility of detecting a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of ∼10−35m. We discuss here the possible signature of Lorentz invariance violation on the spectrum of ultrahigh energy cosmic rays as compared with present observations of giant air showers. We also discuss the possibilities of using more sensitive detection techniques to improve searches for Lorentz invariance violation in the future. Using the latest data from the Pierre Auger Observatory, we derive a best fit to the LIV parameter of 3.0+1.5 −3.0 × 10−23, corresponding to an upper limit of 4.5 × 10−23 at a proton Lorentz factor of ∼2 × 1011. This result has fundamental implications for quantum gravity models.

1. Introduction 1.1. Why Test Fundamental Physics at Ultrahigh Energies? Owing to the uncertainty principle, it has long been realized that the higher the particle energy attained, the smaller the scale of physics that can be probed. Thus, optical, UV and X-ray observations led to the understanding of the structure of the atom, γ-ray observations led to an understanding of the structure of the atomic nucleus, and deep inelastic scattering experiments with high energy electrons led to an understanding of the structure of the proton. Accelerator experiments have led to an understanding of quantum chromodynamics and it is hoped that the Large Hadron Collider [1] will eventually reveal new physics at the TeV scale. This could lead to the discovery of the predicted Higgs boson and supersymmetric particles. To go much beyond this scale of fundamental physics, to search for clues to a ‡ Corresponding author: Floyd.W.Stecker@nasa.gov Searching for New Physics with Ultrahigh Energy Cosmic Rays 2 grand unification theory, and even Planck scale physics, one must turn to the extreme high energies provided by the cosmic generators with which Nature has provided us. In this focus paper, we will concentrate on searching for conjectured ultrahigh energy modifications of special relativity. This search will be based on obtaining data on the spectrum of cosmic rays at the highest energies observed and even beyond, using present and future detection techniques. 1.2. Theoretical Motivation for High Energy Violation of Lorentz Invariance The theory of relativity is, of course, one of the fundamental pillars of modern physics. However, because of the problems associated with merging relativity with quantum theory, it has long been felt that relativity will have to be modified in some way in order to construct a quantum theory of gravitation. The group of Lorentz transformations delineated by special relativity can be described as a high energy modification of the unbounded group of Galilean transformations. Since the Lorentz group is also unbounded at the high boost (or high energy) end, in principle it may also be subject to modifications in the high boost limit. There is also a fundamental relationship between the Lorentz transformation group and the assumption that space- time is scale-free, since there is no fundamental length scale associated with the Lorentz group. However, as noted by Planck [2], there is a potentially fundamental scale associated with gravity, viz., the Planck scale. Thus, there has been a particular interest in the possibility that a breakdown of Lorentz invariance (LI) may be associated with the Planck scale, λP l = q G¯h/c3 ∼10−35 m, owing to various speculations regarding quantum gravity scenarios. This scale corresponds to an energy (mass) scale of MP l = ¯hc/λP l ∼1019 GeV. It is at the Planck scale where quantum effects are expected to play a key role in determining the effective nature of space-time that emerges in the classical continuum limit. The idea that LI may indeed be only approximate has been explored within the context of a wide variety of suggested new Planck-scale physics scenarios. These include the concepts of deformed relativity, loop quantum gravity, non-commutative geometry, spin foam models, and some string theory models. Such theoretical explorations and their possible consequences, such as observable modifications in the energy-momentum dispersion relations for free particles and photons, have been discussed under the general heading of “Planck scale phenomenology”. There is an extensive literature on this subject. (See [3] for a review; some recent references are Refs. [4] – [6].) 1.3. Testing Special

This content is AI-processed based on ArXiv data.