Would powerful mouthwashes like listerine kill root canal infection ?

No: Listerine can kill bacteria on the surfaces it touches. A dental root is a very deep thing. The listerine may help prevent cavities but it will not get into the tissues at high enoooughlevels to treat root canal infection. You will need to have a dentist take care of this issue, .

Not even close: If your hypothesis was correct, wouldn't dentists have been put out of business years ago? If you have a root canal infection you need root canal treatment if you want to save the tooth and prevent the infection from spreading. Please call your dentist.