In particle physics, NMSSM is an acronym for Next-to-Minimal Supersymmetric Standard Model. It is a supersymmetric extension to the Standard Model that adds an additional singlet chiral superfield to the MSSM and can be used to dynamically generate the term, solving the -problem. Articles about the NMSSM are available for review. The Minimal Supersymmetric Standard Model does not explain why the parameter in the superpotential term is at the electroweak scale. The idea behind the Next-to-Minimal Supersymmetric Standard Model is to promote the term to a gauge singlet, chiral superfield . Note that the scalar superpartner of the singlino is denoted by and the spin-1/2 singlino superpartner by in the following. The superpotential for the NMSSM is given by where gives the Yukawa couplings for the Standard Model fermions. Since the superpotential has a mass dimension of 3, the couplings and are dimensionless; hence the -problem of the MSSM is solved in the NMSSM, the superpotential of the NMSSM being scale-invariant. The role of the term is to generate an effective term. This is done with the scalar component of the singlet getting a vacuum-expectation value of ; that is, we have Without the term the superpotential would have a U(1)' symmetry, so-called Peccei–Quinn symmetry; see Peccei–Quinn theory. This additional symmetry would alter the phenomenology completely. The role of the term is to break this U(1)' symmetry. The term is introduced trilinearly such that is dimensionless. However, there remains a discrete symmetry, which is moreover broken spontaneously. In principle this leads to the domain wall problem. Introducing additional but suppressed terms, the symmetry can be broken without changing phenomenology at the electroweak scale. It is assumed that the domain wall problem is circumvented in this way without any modifications except far beyond the electroweak scale. Other models have been proposed which solve the -problem of the MSSM. One idea is to keep the term in the superpotential and take the U(1)' symmetry into account. Assuming this symmetry to be local, an additional, gauge boson is predicted in this model, called the UMSSM. Phenomenology Due to the additional singlet , the NMSSM alters in general the phenomenology of both the Higgs sector and the neutralino sector compared with the MSSM. Higgs phenomenology In the Standard Model we have one physical Higgs boson. In the MSSM we encounter five physical Higgs bosons. Due to the additional singlet in the NMSSM we have