Galarza was cited for making contact "with the eye or eye area" of New Zealand forward Brodie Retallick during last Sunday's Pool C game between the countries at Wembley.
In a statement, Rugby World Cup Limited said: "G alarza denied the act of foul play.
"Having conducted a detailed review of all the available evidence, including all camera angles and additional evidence, including from Retallick, the player and submissions from his representatives, the judicial officer Christopher Quinlan QC upheld the citing on the basis that the player had committed the act of foul play.
"With respect to the sanction, the judicial officer deemed the act of foul play merited a low-end entry point of 12 weeks.
"Due to the need to deter such acts of foul play, he added an additional period of one week.
"However, taking into account mitigating factors including his excellent disciplinary record, the judicial officer reduced the suspension to a period of nine weeks."
Galarza's ban takes effect immediately, and he cannot play again until November 26.
That means the Gloucester forward will miss part of his club's campaign as his suspension does not expire until more than three weeks after the World Cup final.
.Galarza has 48 hours in which to appeal once he has received the written decision.