float mouseDX = Mouse.getDX() * 0.005f;
float mouseDY = Mouse.getDY() * 0.005f;

Quat4f differenceX = new Quat4f();
differenceX.set(new AxisAngle4f(new Vector3f(0, 1, 0), -mouseDX));
const_rotation.mul(differenceX);

Quat4f differenceY = new Quat4f();
differenceY.set(new AxisAngle4f(new Vector3f(1, 0, 0), mouseDY));
const_rotation.mul(differenceY);