Energy spectrum of cosmic rays is known to extend over 10^20eV. To understand their origin(s) and energetic phenomena in the astrophysical objects is main target of the cosmic-ray physics. Because of the low number flux, high-energy cosmic rays over 10^15eV are measured through atmospheric air showers. To interpret the observed information at the ground level to the information of primary particles, we must rely on the Monte Carlo simulation of air shower development. In the simulation, uncertainty of the hadronic interaction at such high energy is the major source of the uncertainty in the interpretation.
Difficulty in modeling hadronic interaction is because soft interaction is essential in the air shower development that can not be described by perturbative QCD. Many phenomenological models are proposed and they are intensively tested by using the data from LHC.
In this seminar, I will introduce recent problem in the cosmic-ray physics caused by the uncertainty of modeling and efforts to improve them by using the LHC data.