There are hundreds of psychological theories, see the Dictionary of Psychological Theories for more details.
Theories listed as subjects in PsycInfo.
Examples of Articles
Article about a theory:
Mulvey, K. L., Gönültaş, S., Herry, E., & Strelan, P. (2021). The role of theory of mind, group membership, and apology in intergroup forgiveness among children and adolescents. Journal of Experimental Psychology: General. https://doi.org/10.1037/xge0001094
1. Example Search statement keyword: "theory of mind"
The quotes find the exact phrase with the of.
2. Example Search statement subject heading:
Article about a theory and a topic:
Cuadrado, D., Salgado, J. F., & Moscoso, S. (2020). Individual differences and counterproductive academic behaviors in high school. PLoS ONE, 15(9). https://doi.org/10.1371/journal.pone.0238892
Subjects: Academic Achievement; Five Factor Personality Model
3. Example Search statement keyword: academic achievement and five factor personality model
The and joins the terms in any order. You could also use quotes around "five factor personality model."
4. Example Search statement subject heading: