Anisotropy in the cosmic radiation at TeV energy

TL;DR

This paper reviews recent experimental findings of anisotropy in TeV cosmic ray arrival directions and discusses theoretical efforts to explain these unexpected structures within the current cosmic-ray paradigm.

Contribution

It provides a comprehensive overview of recent experimental results on cosmic ray anisotropy at TeV energies and evaluates current theoretical models addressing these phenomena.

Findings

Detection of unexpected large-scale anisotropy structures at ~10 TeV

Observation of small-scale anisotropies inconsistent with standard models

Summary of theoretical approaches to interpret anisotropy data

Abstract

In recent years very important results were obtained from cosmic ray experiments about the arrival direction distribution of primaries in the TeV energy range. As most of these particles are charged nuclei, they are deflected by the magnetic field they pass through before reaching the Earth surface, the effect of the Lorentz force being inversely proportional to the particle energy. As far as the local interstellar medium is known, the gyroradius of a 10 TeV proton is expected to be only 100 a.u., small enough to make the arrival direction distribution isotropic. Since 1930s a "large scale" (90{\deg}-120{\deg}) anisotropy is known to exist, generally interpreted as the combined effect of sources far away and magnetic fields nearby. Nonetheless, in the last decade experiments like Tibet-ASg, Milagro, ARGO-YBJ and IceCube discovered structures as wide as 10{\deg}-30{\deg} all over the sky at ~ 10 TeV energy, what is unexplainable within the standard model of cosmic rays. In this paper a review of the most recent experimental results about cosmic ray anisotropy is given, together with the status of the art of theoretical efforts aimed at interpreting them within the current cosmic-ray paradigma.