Higgs Standard Model Parity - Physics Stack Exchange most recent 30 from physics.stackexchange.com 2019-09-16T06:15:39Z https://physics.stackexchange.com/feeds/question/122383 https://creativecommons.org/licenses/by-sa/4.0/rdf https://physics.stackexchange.com/q/122383 4 Higgs Standard Model Parity mad https://physics.stackexchange.com/users/958 2014-06-29T19:41:19Z 2014-07-25T10:08:13Z <p>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?</p> https://physics.stackexchange.com/questions/122383/-/122387#122387 1 Answer by ArbiterKC for Higgs Standard Model Parity ArbiterKC https://physics.stackexchange.com/users/51870 2014-06-29T20:01:58Z 2014-07-25T10:08:13Z <p>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.</p> <p><a href="http://indico.lal.in2p3.fr/getFile.py/access?contribId=51&amp;sessionId=6&amp;resId=0&amp;materialId=slides&amp;confId=1109" rel="nofollow">This workshop</a> has a good overview.</p> https://physics.stackexchange.com/questions/122383/-/123078#123078 1 Answer by mad for Higgs Standard Model Parity mad https://physics.stackexchange.com/users/958 2014-07-04T10:01:14Z 2014-07-04T10:01:14Z <p>One argument could be the Yukawa coupling, which is responsible for the coupling to the fermions. </p> <p>In the Yukawa coupling term in the Lagrangian, $\mathcal{L}_{\text{Yukawa}}$ , there are no terms that contain a <a href="http://en.wikipedia.org/wiki/Gamma_matrices" rel="nofollow" title="Gamma Matrices">$\gamma^5$ matrix</a>, defined as $$\gamma^5 := i\gamma^0 \gamma^1 \gamma^2 \gamma^3$$ <a href="https://alpha.physics.uoi.gr/foudas_public/APP/Lecture7-Dirac-Covariance-Parity.pdf" rel="nofollow">This publication</a> states how terms in the Lagrangian transform under parity operation, namely (giving only the relevant information here) $$\Psi \bar \Psi \;\;\; \scriptsize transforms\, as \normalsize \;\;\;\text{scalar (parity = +1)}$$ $$\Psi \gamma^5 \bar \Psi \;\;\; \scriptsize transforms\, as \normalsize \;\;\;\text{pseudoscalar (parity = -1)}$$</p> <p>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.</p> <p>Thanks go to my university professor for pointing that out in his script.</p>