For equities:
https://www.sec.gov/marketstructure/research/hft_lit_review_march_2014.pdf
For FX
http://www.bis.org/publ/mktc05.pdf
And then there is
https://www.sec.gov/marketstructure/research/hft_lit_review_march_2014.pdf
For FX
http://www.bis.org/publ/mktc05.pdf
And then there is