I am a retired teacher in physics and applied mathematics. During my formation (up to my master`s degree and all the course of my Ph.D.), I never had a course in General Relativity, in Particle Physics, Astrophysics and Cosmology. So, when I retired, I decided to take some online courses (MOOC) in those subjects. They were only introduction courses. For particle physics, I am working with the book of Griffiths; Introduction to Elementary Particles. So give me a chance when I asked questions. Thank you in advance for your comprehension! ©