Nonlinear Physics of Epidemics: Part A

AbstractThis chapter is the first of three chapters that present the nonlinear physics of epidemics and pandemics that can be described in terms of deterministic dynamical systems. The chapter focuses on the SIR model and SIR-type models. The amplitude space description is worked out in detail and the SI order parameter is determined. It is demonstrated that within the SIR modeling framework, the SI order parameter determines the initial stage of epidemics. An application to the COVID-19 outbreak in Italy during the year 2020 is also presented.