4.0.4.RC1??? That is not even a final version, why are you not running 4.0.4.GA?
If the JBoss AS is beiung shutdown (as you say) then there will be no java process.
Based on what you have provided, there are two possibilities. First, you are running out of heap and the JVM is shutting down. The other possibility is that the JVM is crashing.
1) Is JBoss AS running as a service?
2) What OS is it running on?
3) If it is being run as a service, is stdout/stderr being redirected to a file? If so, you you attach the last 500 or so lines of that file. If not, attache the last 500 lines of the server.log file.
I really recommend that the best way to debug this problem is to run JBoss AS on your local machine and deploy your application there. And run it from the command line, not as a service. Then use JMeter (or something like it) to apply a load. They you can do all the debugging locally and wont need to bother IT.