A thin, rigid rod of length \(L\) lies along the positive \(x\)-axis with one end fixed at the origin \(O\). A distributed force acts along the rod such that the force acting on an infinitesimal segment \(dx\) located at position \(x\) is given by \(d\vec{F} = (\beta x \hat{j} + \gamma x^2 \hat{k})\,dx\), where \(\beta\) and \(\gamma\) are positive constants. Which of the following expressions represents the net torque vector \(\vec{\tau}\) exerted on the rod about the origin \(O\)?