How do neutralino interactions differ in amplitude analysis between SM and SUSY?

[ChrisVer]

Do you have any source where I can check for the neutralino (higgsino or chargino/bino -like) interaction processes?
In general I'm trying to find the amplitudes in the Appendix A of:
http://journals.aps.org/prd/abstract/10.1103/PhysRevD.47.376
But without seeing a Lagrangian, I can't understand the possible contributing channels I think...

 

[Greg Bernhardt]

I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?

 

[ChrisVer]

Yes I am able to clear a lot of difficulties I've been having with it. But it's still a little bit complicated.
For example one can have the figures I attached for χχ \rightarrow ZZ... which are 6 in number (n=1,2,3,4 for the neutralinos), and H,h are the two neutral scalar higgs bosons.
So in general I can write the amplitude for each one, right?
However I am not sure how is this kind of amplitudes written... Could someone check if the formula I'm using is correct for the small higgs?

M= [ \bar{u}_{χ} \gamma^{\mu} u_{χ}] \frac{1}{k^{2} -m_{h}^{2} +i m_{h} \Gamma_{h}} j_{\mu}^{ZZ}

where u's are the spinors for the χ neutralinos... k is the momentum of the scalar higgs, m_{h} its mass, \Gamma_{h} its width and j_{\mu}^{ZZ} the current of ZZ bosons (I don't know its form- any help?).
Thanks

 

[ofirg]

I think that the \gamma^{\mu} in the \bar{u}_{\chi}\gamma^{\mu}{u}_{\chi} should be removed since the neutralinos couple to a scalar, not a vector. For the coupling of the higgs to the Z see feynman rules references, peskin for example. I think it it something like \frac{m_{Z}^{2}}{v} .

 

[ChrisVer]

I think in general the M is the coupling of the one current with the other through the propagator.
M= j_{1}^{\mu} [prop]_{\mu \nu} j_{2}^{\nu}
No?
A current then is supposed to have an index.

 

[ChrisVer]

Well I tried to think of someway to do it, can someone check the amplitude please?
it's for: χχ \rightarrow h \rightarrow W^{+} W^{-}
Can someone help me with how I can use the Feynman rules I've found?
For the coupling of χχh I have:
-ig_{2} (c_{L} P_{L} + c_{R} P_{R} )
So for this it's better to work with the left and right neutralinos separately and then add the amplitudes (M= M(χ_{L}χ_{L} \rightarrow W^{+}W^{-}) +M(χ_{R}χ_{R} \rightarrow W^{+}W^{-}) )

For the h W^{\pm} vertex I found:
ig_{2} m_{W} n^{\mu \nu} \cos(\beta-\alpha)

And the propagator is as given:
\frac{i}{k^{2}-m_{h}^{2} + i m_{h} \Gamma_{h}}

What am I missing to get the M is how to represent the outgoing particles...
is it fine to write for the fermionic neutralinos the \bar{u}_{χ} \gamma^{\mu} u_{χ'} ?
I am not sure...
in any case it's like:

i M(χ_{j}χ_{j} \rightarrow W^{+}W^{-})= (-ig_{2} c_{j}) \frac{i }{k^{2}-m_{h}^{2} + i m_{h} \Gamma_{h}} ( ig_{2} m_{W} \cos(\beta-\alpha)) n^{\mu \nu} \epsilon_{\mu} \epsilon^{*}_{\nu}

is that right?

 

[Orodruin]

The vertex for the $\chi\chi h$ interaction is what should be within the fermion bilinear. Basically you should have (given your Feynman rules)
$$
-ig_{2} \bar u_\chi (c_L P_L + c_R P_R) u_{\chi'} \frac{i }{k^{2}-m_{h}^{2} + i m_{h} \Gamma_{h}} ( ig_{2} m_{W} \cos(\beta-\alpha)) n^{\mu \nu} \epsilon_{\mu} \epsilon^{*}_{\nu}.
$$
Since the higgs is a scalar, it cannot interact with the vector current of the form $\bar u \gamma^\mu u$. There is simply no way to contract the free Lorentz index.

 

[ChrisVer]

Aha... so it's more like I'm having a RL and LR helicities.

 

[ChrisVer]

do the self couplings between gauge bosons change from SM to SUSY?
eg the coupling of Z^0 _{\lambda} (q), W^+_{\mu}(k_+), W^-_{\nu}(k_-) is it still
i g \cos(\theta_{w}) [g^{\mu \nu} (k_{-}-k_{+})^{\lambda}+ g^{\nu \lambda} (-q-k_-)^{\mu} + g^{\mu \lambda} (q+k_+)^{\nu}]
as given in Peskin Fig 21.9, or is it changed?