====== Seesaw Models ======

<tabbox Intuitive> 

<note tip>
Explanations in this section should contain no formulas, but instead colloquial things like you would hear them during a coffee break or at a cocktail party.
</note>
  
<tabbox Concrete> 

Seesaw scenarios can be understood systematically by looking at the Weinberg operator. The Weinberg operator $\frac{1}{\Lambda} LL \phi \phi$ is a (non-renormalizable) dimension-5 operator that yields nonzero masses for the neutrinos. Since it is an dimension-5 operator, it is suppressed by some large mass scale $\Lambda$. The origin of the Weinberg operator can be understood in terms of concrete seesaw scenarios (UV-completions).

There are three seesaw scenarios that yield the Weinberg operator in the low-energy limit when we integrate out all heavy fields and thus use an [[advanced_tools:effective_field_theory|effective field theory]] approach. In particular, we can distinguish different scenarios depending on how we understand the contractions of our $SU(2)_L$ multiplets:

{{ :models:speculative_models:weinberg1.png?nolink |}}

{{ :models:speculative_models:weinberg2.png?nolink |}}

In terms of Feynman diagrams, the three scenarios can be understood as follows:

{{ :models:speculative_models:weinberg3.png?nolink |}}

Here, $N_R$ denotes a heavy right-handed ($SU(2)_L$ singlet) neutrino, $\Delta^0$ the neutral component of an 
$SU(2)_L$ scalar triplet and $\Sigma_R^0$, the neutral component of a fermionic $SU(2)_L$ triplet.

A slightly different way of understanding the seesaw scenarios in terms of Feynman diagrams is ([[https://arxiv.org/pdf/0707.4058.pdf|source]]):

{{ :models:speculative_models:weinber4.png?nolink |}}

----

Great reviews are:
  * [[https://arxiv.org/abs/0707.4058|Low energy effects of neutrino masses]] by A. Abada, C.Biggio, F. Bonnet, M.B. Gavela, T. Hambye
  * [[https://arxiv.org/abs/hep-ph/0210271|The Effective Lagrangian for the Seesaw Model of Neutrino Mass and Leptogenesis]] by A. Broncano, M.B. Gavela, E. Jenkins



<tabbox Abstract> 

<note tip>
The motto in this section is: //the higher the level of abstraction, the better//.
</note>

<tabbox Why is it interesting?>   

Seesaw models are extensions of the Standard Model of particle physics that aim to explain why neutrino masses are so tiny.

/*<tabbox FAQ>*/ 

/*<tabbox History>*/ 

</tabbox>