Perhaps you should try some spelling variations:
"state vectors" » "state vector", "state detectors"
"state actor" » "state action", "state vector", "state sector"
"state actors" » "state actions", "state vectors", "state sectors", "state factors"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("state actor") OR ((("state actors") OR ("state vectors")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"state actor\") or (((\"state actors\") OR (\"state vectors\"))))".
• Removing quotes may allow a broader search: (( state actor ) or ((( state actors ) OR ( state vectors )))).
• Adding a wildcard symbol may retrieve word variants: (("state actor") or ((("state actors") OR ("state vectors"))))*.