The elaboration likelihood model positing central and peripheral routes to persuasion is a well-established concept in psychology, requiring no citation.
The claim states a definitional core of Petty and Cacioppo's Elaboration Likelihood Model (ELM), which universally posits central and peripheral routes to persuasion in communication and social psychology textbooks. As a foundational, definitional fact about a major psychological model, it constitutes common knowledge within the field.