NMSSM

From Wikipedia, the free encyclopedia

In particle physics, NMSSM 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 mu term, solving the mu problem.

The Minimal Supersymmetric Model does not explain why mu parameter in the superpotential $μ H u H d$ is at the weak scale. The idea behind the Next to Minimal Supersymmetric Model is to promote the $m u$ term to a gauge singlet, chiral superfield. The superpotential for the NMSSM is given by

$W_{NMSSM}=W_{Yuk}+\lambda N H_u H_d + \frac{\kappa}{3} N^3$

where $W Y u k$ are Yukawa couplings for the Standard Model fermions. With these couplings, the NMSSM preserves R-Parity, however, if an $N H u L$ coupling was allowed, it would violate R-parity. This coupling is constrained to be less than $10 - 7$ for neutrinos to be adequately light.

The NMSSM is not the most general Lagrangian that could be written with an additional singlet and the MSSM fields. For instance, a source term and mass term for $N$ is omitted. With the superpotential above, there are only trilinear superpotential couplings and therefore a $\mathbb{Z}_3$ discrete symmetry.

In addition to the superpotential there are also soft susy breaking terms that are added

$L_{soft} = a_\lambda \lambda n h_u h_d + a_\kappa \kappa n^3 + m_n^2 |n|^2$

In order for the $μ$ -term to be generated, the scalar $n$ needs to have a negative mass squared. Typical supersymmetry breaking scenarios, such as gauge mediated supersymmetry breaking or anomaly mediated supersymmetry breaking do not generate a large enough negative mass for $n$ . Additional vector-like matter is introduced in order to generate electroweak-symmetry breaking.

[edit] Phenomenology

The NMSSM alters the phenomenology of both the Higgs sector and the Higgsino-Gaugino sector.

[edit] Higgs Phenomenology

The Higgs sector in the MSSM has the Standard Model-like Higgs $h 0$ , the heavier, neutral CP-even Higgs $H 0$ , the neutral CP-odd Higgs $A 0$ , and the charged Higgs $H^\pm$ . To these states the NMSSM adds an additional neutral CP-even Higgs $s 0$ and a CP-odd Higgs $a 0$ . In the MSSM, the lightest Higgs is always Standard Model-like, and and therefore its production and decays are roughly known. In the NMSSM, the lightest Higgs can in fact be singlet-like (either the $s 0$ or $a 0$ ) meaning that the Higgs can decay dominantly into these states, drastically alterning Higgs phenomenology.