Diversification and Firm performance

find at least 20-30 quality journals, articles, thesis ranked by ABS or similar standard and put on the table uploaded ( provide reference and quote in Harvard style). After that, please summarise what is the gap of diversification and firm performance and what can be improve in order to build up a new hypothesis to enhance the relationship between diversification and firm performance ( note: the first example in the table is just a random example to show how to do the research )