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Pierre Auger Collaboration(Abreu, P. et al), & Pastor, S. (2013). Constraints on the origin of cosmic rays above 10^18 eV from large-scale anisotropy searches in data of the Pierre Auger Observatory. Astrophys. J. Lett., 762(1), L13–8pp.
Abstract: A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above 10(18) eV at the Pierre Auger Observatory is reported. For the first time, these large-scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above 10(18) eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.
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Botella-Soler, V., Oteo, J. A., Ros, J., & Glendinning, P. (2013). Lyapunov exponent and topological entropy plateaus in piecewise linear maps. J. Phys. A, 46(12), 125101–26pp.
Abstract: We consider a two-parameter family of piecewise linear maps in which the moduli of the two slopes take different values. We provide numerical evidence of the existence of some parameter regions in which the Lyapunov exponent and the topological entropy remain constant. Analytical proof of this phenomenon is also given for certain cases. Surprisingly however, the systems with that property are not conjugate as we prove by using kneading theory.
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Pierre Auger Collaboration(Abreu, P. et al), & Pastor, S. (2013). Interpretation of the depths of maximum of extensive air showers measured by the Pierre Auger Observatory. J. Cosmol. Astropart. Phys., 02(2), 026–20pp.
Abstract: To interpret the mean depth of cosmic ray air shower maximum and its dispersion, we parametrize those two observables as functions of the first two moments of the ln A distribution. We examine the goodness of this simple method through simulations of test mass distributions. The application of the parameterization to Pierre Auger Observatory data allows one to study the energy dependence of the mean ln A and of its variance under the assumption of selected hadronic interaction models. We discuss possible implications of these dependences in term of interaction models and astrophysical cosmic ray sources.
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Cline, J. M., & Vincent, A. C. (2013). Cosmological origin of anomalous radio background. J. Cosmol. Astropart. Phys., 02(2), 011–23pp.
Abstract: The ARCADE 2 collaboration has reported a significant excess in the isotropic radio background, whose homogeneity cannot be reconciled with clustered sources. This suggests a cosmological origin prior to structure formation. We investigate several potential mechanisms and show that injection of relativistic electrons through late decays of a metastable particle can give rise to the observed excess radio spectrum through synchrotron emission. However, constraints from the cosmic microwave background (CMB) anisotropy, on injection of charged particles and on the primordial magnetic field, present a challenge. The simplest scenario is with a greater than or similar to 9 GeV particle decaying into e(+)e(-) at a redshift of z similar to 5, in a magnetic field of similar to 5 μG, which exceeds the CMB B-field constraints, unless the field was generated after decoupling. Decays into exotic millicharged particles can alleviate this tension, if they emit synchroton radiation in conjunction with a sufficiently large background magnetic field of a dark U(1)' gauge field.
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de Putter, R., Verde, L., & Jimenez, R. (2013). Testing LTB void models without the cosmic microwave background or large scale structure: new constraints from galaxy ages. J. Cosmol. Astropart. Phys., 02(2), 047–22pp.
Abstract: We present new observational constraints on inhomogenous models based on observables independent of the CMB and large-scale structure. Using Bayesian evidence we find very strong evidence for homogeneous LCDM model, thus disfavouring inhomogeneous models. Our new constraints are based on quantities independent of the growth of perturbations and rely on cosmic clocks based on atomic physics and on the local density of matter.
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