I am looking for some words for "cartel" in economics. I did a search and found a good word is "corporate consolidation" from this newspaper. I am wondering if there is any other formal word that can be used in research studies?
I don't think an exact synonym exists. There are words that describe a type of cartel.
You could use syndicate in case of illicit cartels.
When writing a technical paper, it is not bad form to repeat the same technical word over and over again, it avoids confusion.
When looking at synonyms of a word, frequently there are some nuanced differences between them. As a non-native speaker of English it can be years before I learn of the nuances. To be fair, the same is true for words that I rarely hear/use in my native tongue.
Some sources, eg here, regard "price ring" as synonymous with cartel. On the other hand, eg here, a price ring has also been regarded as one kind of cartel that focuses directly on price coordination, as opposed to one which focuses on coordinated output restrictions or other measures as less direct means to increase prices and profits.