As you seem to know, the force applied will result in a torque (R cross F). Are you using <*> to represent a vector cross-product? If not, that's incorrect. It is not a multiplication. In any case, it appears you're representing the object as a simple pendulum. I.e., T = mr2 * alpha, where alpha is the angular acceleration. Your equation then would be angular_velocity = dt * (torque)/(mr2). Your "alpha" is, then, not the angle.
Using <x> to represent a cross-product: Torque (R x F) is to angular acceleration as force is to linear acceleration. Torque is a vector whose direction is the axis of rotation, and whose length is the magnitude of the angular acceleration. N.B., although force is applied to the mass of the object, torque is applied to the moment-of-inertia of the object, and that moment-of-inertia is specific with respect to the rotation axis though evaluation of the inertial tensor for the object. You can google for "inertial tensor" or "moment of inertia" to determine how the moment of inertia is specified for a particular distribution of mass.
I.e.,
force = mass * linear_acceleration;
torque = moment-of-inertia * angular_acceleration; // N.B., moment-of-inertia (MOI), not mass.
So, for discrete dt's:
// linear parameters
linear_acceleration = force / mass;
linear_velocity += linear_acceleration * dt;
change_in_linear_position = linear_velocity * dt;
// rotational parameters
angular_acceleration = torque / MOI;
angular_velocity += angular_acceleration * dt; // I think this is the equivalent of your "alpha" equation.
change_in_current_angle = angular_velocity * dt; // is this what you want to approximate?
EDIT - Note: if your looking for the absolute angle, and not the change in the angle, you have to accumulate the changes in angle, as, over time, the angular velocity caused by the torque will continue to change the angle. I.e., you apply a torque for dt, and the object will "spin," not just change angle and stop rotating.