Das Ashok Das 
Field Theory: A Path Integral Approach [PDF ebook] 

New Edition: Field Theory (3rd Edition)Traditionally, field theory is taught through canonical quantization with a heavy emphasis on high energy physics. However, the techniques of field theory are applicable as well and are extensively used in various other areas of physics such as condensed matter, nuclear physics and statistical mechanics. The path integral approach brings out this feature most clearly. In this book, the path integral approach is developed in detail completely within the context of quantum mechanics. Subsequently, it is applied to various areas of physics.