Hello,
I am facing this problem too (that is, if it is one). What I have found is that it is some sort of a security feature implemented by Microsoft in Windows 8, that monitors how metro apps use personal information and their related permissions. (Source- http://www.groovypost.com/howto/runtimebroker-exe-process-windows-8-running/)
I would like some help as well as it does take up a lot of memory though I haven't yet seen much changes in performance.