A thin, nonconducting ring of radius \(R\) lies in the \(yz\)-plane centered at the origin and carries a total positive charge \(+Q\) distributed uniformly along its circumference. A small electric dipole with fixed dipole moment of magnitude \(p\) is located on the \(x\)-axis at position \(x > 0\), oriented with its dipole moment vector \(\vec{p}\) pointing in the \(+x\)-direction away from the ring. Assuming the electric potential energy \(U\) is defined to be zero at infinity, which of the following expressions correctly gives \(U(x)\) as a function of position \(x\)?