books.google.com - This is a systematic presentation of Quantum Field Theory from first principles, emphasizing both theoretical concepts and experimental applications. Starting from introductory quantum and classical mechanics, this book develops the quantum field theories that make up the "Standard Model" of elementary...http://books.google.com/books/about/An_Introduction_to_Quantum_Field_Theory.html?id=rB_wdTnfTmoC&q=variables&utm_source=gb-gplus-shareAn Introduction to Quantum Field Theory