Testing fundamental principles with high-energy cosmic rays (I)

In a contribution to the European High-Energy Physics HEP 2011 conference (Grenoble, last July), Luis Gonzalez-Mestres suggests a new explanation of the observed composition of the ultra-high energy cosmic ray (UHECR) spectrum where heavier nuclei seem to dominate at higher energies. He writes : "Present data [1] show a fall of the UHECR spectrum compatible with the GZK cutoff, but the effect can also be explained by other mechanisms. A LSV pattern of the type (1.1) inhibiting the GZK cutoff but allowing for spontaneous emission of gamma rays or e+ e− pairs by hadrons and nuclei can potentially account for the observed composition at the highest energies, where heavier nuclei appear to dominate. If the deformation of the photon or electron energy is to be compared with the mass term of the emitting proton or nucleus, the observed mass composition of the UHE Auger spectrum can naturally emerge, as heavier nuclei will start decaying at higher energies". LSV stands for Lorentz symmetry violation, and the pattern considered incorporates a privileged local reference frame (the vacuum rest frame, VRF).

Formula (1.1) is :

E

p c + m² c³ (2 p)⁻¹ − p c α (p c E_a⁻¹ )²/2

where E is the energy, p the momentum, c the speed of light, m the mass, α a constant standing for the deformation strength and E_a the fundamental energy scale at which the deformation is generated. Then, the (negative) deformation term Δ E

− p c α (p c E_a⁻¹ )²/2 becomes larger than the (positive) mass term m² c³ (2 p)⁻¹ above a transition energy E_trans

α^−1/4 (E_a m)^1/2 c .

Reference [1] is D. Veberic for the Pierre Auger Collaboration, The end of the cosmic ray spectrum, LC10 Workshop Frascati 2010, arXiv:1110.0615.

The Proceedings of the XXIst International Europhysics Conference on High Energy Physics (Grenoble, France, July 2011) have became available at the address :
http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=134

and the reference to the article by Luis Gonzalez-Mestres is :

Testing fundamental principles with high-energy cosmic rays,  PoS(EPS-HEP2011)390
http://pos.sissa.it/archive/conferences/134/390/EPS-HEP2011_390.pdf

(Note about Proceedings of Science where this paper has already been made available : All contributions are published in PoS under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. Every author submitting his/her contribution to PoS retains the copyright, and upon submission (s)he applies this license to his/her work.)

The abstract of the article is :

Testing fundamental principles with high-energy cosmic rays

It is not yet clear [1] whether the observed flux suppression for ultra-high energy cosmic rays (UHECR) at energies above

4.10¹⁹ eV is a signature of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or corresponds, for instance, to the maximum energies available at the relevant sources. Both phenomena can be sensitive to violations of standard special relativity modifying cosmic-ray propagation or acceleration at very high energy [2, 3], and would in principle allow to set bounds on Lorentz symmetry violation (LSV) parameters in models incorporating a privileged local reference frame (the "vacuum rest frame", VRF [4, 5]). But the precise phenomenological analysis of the experimental data is far from trivial, and other effects can be present. The effective parameters can be directly linked to Planck-scale physics, or even to physics beyond Planck scale, as well as to the dynamics and effective symmetries relating LSV mechanisms for nucleons, quarks, leptons and the photon [6, 7]. If a VRF exists, LSV can modify the internal structure of particles at very high energy [7, 8]. Conventional symmetries may also cease to be valid at energies close to the Planck scale. Other possible violations of fundamental principles and conventional basic hypotheses (quantum mechanics, quark confinement, energy and momentum conservation, vacuum homogeneity and "static" properties, effective space dimensions...) can also be considered [8, 9] and possibly tested in high-energy cosmic-ray experiments. Even below UHE (ultra-high energy), exotic signatures cannot be excluded [10, 11]. We present an updated discussion of the theoretical and phenomenological situation, including prospects for earth-based and space experiments and a simple potential interpretation of the observed UHECR composition in terms of LSV where the GZK cutoff would be replaced by spontaneous emission of photons or e⁺ e⁻ pairs. As the OPERA result [12] on a possible superluminal propagation of the muon neutrino was announced after the conference, we briefly comment on the consistency problems [13, 14] that a

2.5 x 10⁻⁵ critical speed anomaly for the muon neutrino can raise taking into account well-established experimental evidence and astrophysical observations.

(end of the abstract)

The full text of the article is included here as an attached file :

http://www.mediapart.fr/files/UHECRter_0.pdf