[fiprofessor]

No, because the future cash flow per share is not reflected in the current market cap.

Perhaps you are thinking of share price instead: there it is true that dividends reduce share price, while buybacks are share-price neutral at least theoretically, though it is commonly believed by many people that they do affect price.

(Hence, under that same theoretical model, market cap must decrease if share price remains the same because market cap is total number of outstanding shares * share price. So if the former decreases while the latter stays the same, market cap must have decreased.)

[gizmondo]

You're right, I need a coffee.