  In this paper, we study various new Hawkes processes. Specifically, we
construct general compound Hawkes processes and investigate their properties in
limit order books. With regards to these general compound Hawkes processes, we
prove a Law of Large Numbers (LLN) and a Functional Central Limit Theorems
(FCLT) for several specific variations. We apply several of these FCLTs to
limit order books to study the link between price volatility and order flow,
where the volatility in mid-price changes is expressed in terms of parameters
describing the arrival rates and mid-price process.
