I am actually trying to run my application in 4.3 simulator from xCode 4.6. I copy the sdk for simulator 4.3 at the path, it builds successfully but cant run the application
If you are using Mac OS 10.7.x and have upgraded to Xcode 4.6, then you could have or download simulator 4.3 version. But, if you are using Mac OS 10.8.x, then you can not have simulator 4.3 version. The reason is 4.3 simulator on Mac OS 10.8.x crashed a lot, so Apple has removed that.
Check this link:-
http://iphonedevsdk.com/forum/iphone-sdk-development/111568-what-happened-to-the-ios-4-3-simulator-in-xcode-4-6.html