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NMSSM+

It is well known that the scale invariant NMSSM has lower fine-tuning than the MSSM, but suffers from the domain wall problem. We propose a new improved scale invariant version of the NMSSM, called the NMSSM+, which introduces extra matter in order to reduce even more the fine-tuning of the NMSSM. The NMSSM+ also provides a resolution of the domain wall problem of the NMSSM due to a discrete R-symmetry, which also stabilises the proton. The extra matter descends from an E6 gauge group and fills out three complete 27-dimensional representations at the TeV scale, as in the E6SSM. However the U(1)_N gauge group of the E6SSM is broken at a high energy scale leading to reduced fine-tuning. The extra matter of the NMSSM+ includes charge 1/3 colour triplet D-fermions which may be naturally heavier than the weak scale because they receive their mass from singlet field vacuum expectation values other than the one responsible for the weak scale effective μ parameter.