Your current investment portfolio is the value-weighted US market portfolio (meaning if a stocks market capitalization is 2% of the value of the US market, that stock makes up 2% of your portfolio). If you figure out that a certain stock has a positive expected alpha, you should:

a) Increase your portfolio weight in the stock until doing so no longer increases your portfolio Sharpe ratio.

b) Decrease your portfolio weight in the stock until doing so no longer increases your portfolio Sharpe ratio.

c) Gather as much money as you can to buy the stock, until you have corrected the mispricing.

d) Dont adjust weights at all to keep your portfolio maximally diversified.