Higgs Standard Model Parity In the Standard Model, the Higgs boson is expected to have spin 0 and even parity. I know how to get the spin-0 approach, but how do I argue for the even parity? Could you give a simple and a more detailed explanation for this even parity expectation?
 A: It is not an assumption; both $0^+$ and $0^-$ were considered as possible Higgs states. The angular distribution of decay products (like in $h\to ZZ$, $h\to WW$, $h\to f\bar{f}$, $h\to \gamma\gamma$ or in Higgstrahlung) is dependent on the parity of the Higgs particle. Alternatively, you can measure the helicities of the outgoing photons (in the $h\to\gamma\gamma$ case); the observed distribution is consistent with an even parity Higgs.
This workshop has a good overview.
A: One argument could be the Yukawa coupling, which is responsible for the coupling to the fermions. 
In the Yukawa coupling term in the Lagrangian, $\mathcal{L}_{\text{Yukawa}}$ , there are no terms that contain a $\gamma^5$ matrix, defined as $$\gamma^5 := i\gamma^0 \gamma^1 \gamma^2 \gamma^3$$ 
This publication states how terms in the Lagrangian transform under parity operation, namely (giving only the relevant information here)
$$ \Psi \bar \Psi \;\;\; \scriptsize transforms\, as \normalsize \;\;\;\text{scalar (parity = +1)}$$ $$ \Psi \gamma^5 \bar \Psi \;\;\; \scriptsize transforms\, as \normalsize \;\;\;\text{pseudoscalar (parity = -1)}$$
and therefore the Yukawa coupling term gives direct hint to the expectation $\text{P}(\text{Higgs})=+1$. However, as the Yukawa coupling theory could be the wrong model, experiments are supposed to check for the parity sign, too.
Thanks go to my university professor for pointing that out in his script.
