# LOG#064. SM(VI): total lagrangian.

**Posted:**2012/12/14

**Filed under:**Physmatics, Relativity, The Standard Model: Basics Leave a comment

The total SM lagrangian can be written now, with some subtle notational changes, from the previous posts. It is really a monster “thing”:

From what you have learned in previous log-entries, can you identify the meaning of every lagrangian piece there? If you do that, you really understand the SM building. However, such a monster as lagrangian leaves many questions answered, but it does answer many others! And, depending on your mood (bad or good), the SM has passed every test in the last 50 years. Our most complete understanding of matter and energy lies in its structure. I am not going to explain SUSY in this post series, but the parameter space of the smallest supersymmetric theory, called the Minimal Supersymmetric Standard Model (MSSM) has even a more monstruous lagrangian (and at least 105 free parameters! Wow! That is pretty much and even bigger than the “relatively simple” SM lagrangian above…). Believe me, to split into pieces the MSSM is a complete nightmare.

Anyway, the above SM has some interesting sectors, as we have learned: the fermion sector, the gauge sector, the QCD and the EW sectors, and the Higgs sector. These 5 main paices can be read off from the total lagrangian (be aware of my notational changes):

Despite the fact it can be a monster, it can be written in compact ways. For instance:

The particle content and the energy or the different SM fundamental particles are given by:

**Remark:** the complete neutrino spectrum and its structure is unknow. In the previous picture we have supposed that the neutrino spectrum is hierarchical and normal, but that is currently unknown.

The next blog posts in this long series are going the explain some simple aspects of the SM phenomenology.

Stay tuned!