1. Nagin, D. S. (2013). Deterrence in the Twenty-First Century. Crime and Justice, 42(1), 199–263. In the abstract and introduction (pp. 199-201), the paper defines deterrence theory as being "predicated on the idea that if the state punishes offenders, potential offenders will be deterred from committing crimes for fear of punishment." This directly links the fear (perception) of sanctions to the modification of behavior. https://doi.org/10.1086/670398
2. Paternoster, R. (2010). How Much Do We Really Know About Criminal Deterrence?. The Journal of Criminal Law and Criminology, 100(3), 765–824. The article's introduction (p. 766) states, "The simple idea behind deterrence is that the perceived certainty, severity, and celerity of punishment are inversely related to the decision to commit crime." This emphasizes the role of perception of negative sanctions in modifying behavior.
3. Pratt, T. C., Cullen, F. T., Blevins, K. R., Daigle, L. E., & Madensen, T. D. (2006). The Empirical Status of Deterrence Theory: A Meta-Analysis. In F. T. Cullen, J. P. Wright, & K. R. Blevins (Eds.), Taking Stock: The Status of Criminological Theory (pp. 367–395). Transaction Publishers. The chapter (p. 367) defines deterrence as the "omission of a criminal act... because of the fear of sanctions."