I am writing a paper and want to use a word which has the opposite meaning of "aforementioned", i.e. something will be mentioned in following parts.
What is the reason?
Are you trying to introduce the reader to an argument or trying to hold the reader's interest?
Academic papers often need to let the reader know what is going to be said. Otherwise the reader will likely stop reading since the paper will seem irrelevant to them. Sentences that list some topics then end with a "... will be discussed." are fairly common.
Possibly you trying to introduce an argument into the paper. In this case it would be more natural to simply state what you want, without any details about how more will be discussed. The reader will expect justification in the following paragraphs.
These words can be used as part of an opposite meaning: below; ensuing, following, subsequent, succeeding
"The presidential agenda will be discussed below"
"The following evidence will convince the jury beyond a reasonable doubt that my defendant is innocent of all charges."
"The proposed hypothesis will be substantiated by the subsequent details."
"Despite the compelling nature of this argument, the succeeding details provide an alternative explanation."