Can SPheno generate spectrum files for models without fermions?

[kdolev]

Hi,

I'm trying to test vevacious on the 2HDM without any fermions. I can get SARAH to make a model file, but SPheno always crashes. Does SPheno require the SM fermions in the model?

[FStaub]

Hi,

yes, SPheno assumes at several places that SM fermions are present. Thus, out of the box, a toy-model without out them will hardly work with SPheno. Do you need vacuum stability at tree or one-loop? If you are happy with tree-level, the fermions should play any role and you could give a spectrum file to Vevacious where they are included. Vevacious will ignore all entries of the file which it doesn't know.

Cheers,
Florian

[kdolev]

Hi,

Ideally I would look to test the 1-loop stability with only scalars, then with only scalars and gauge bosons, then with all three. Do I need to write the spectrum file by hand?

[benoleary]

Hello kdolev,

I would say that the easiest thing to do is to produce the full (scalars, fermions, and vectors) .vin file, then make some copies and by hand delete the bits which you do not want. It should be easy enough, though a bit tedious.

These elements should be left in, as they are necessary and also deal only with scalars:
<input_vevs>
<polynomial_part>
<tadpoles>

You can delete various <mass-squared_matrix> XML elements. You will have to look at their attributes to be able to tell if they are for scalars, fermions, or vectors. If the "factor" attribute is negative, then the <mass-squared_matrix> is for a set of fermions. If there is an attribute spin="vector", then the <mass-squared_matrix> is for a set of vectors.

Deleting <mass-squared_matrix> XML elements should not cause any problems with the actual running of Vevacious. The model files where the vector and/or fermion <mass-squared_matrix> XML elements have been deleted should correspond exactly to what the model files for model which never had those vectors and/or fermions in the first place should have been.

Of course, you may run into technical issues because less particle content may lead to unbounded from below directions. I removed just vectors from the SARAH-SPhenoMSSM_RealHiggsAndStauVevs.vin model file, which then failed to produce a result for a particular test MSSM parameter point, because CosmoTransitions could not cope with the very large separation in field space between the DSB minimum and the place where MINUIT stopped. Removing fermions as well removed the unbounded-from-below directions again (this is typical, I believe).

(All this would change if Vevacious could do 2-loop corrections or higher, as then the full particle content couples to the scalar sector, in general.)

Regards,
Ben

[FStaub]

Hi both,

actually, I think there shouldn't be any problem with the Vevacious model file generated for the THDM without fermions. So, I'm not sure if one has to do changes there by hand. The only potential problem I see comes from the spectrum file: when giving the spc including fermions and one-loop corrections turned on, the fermions show up in the tadpole corrections to some paramerers (like the Higgs mass terms) and therefore, it would be inconsistent to use the numerical values obtained in that way together with Vevacious. The easiest way to circumvent that problem is to set in SPheno.m of the actual model the flag:

Code: Select all

FlagLoopContributions = True;  

If you then re-generate the SPheno code, you can turn off the loop contributions of specific particles to tadpoles, masses and flavour observables via flags in the Les Houches input file. SARAH will write a template for that. For instance, in the THDM-II it will look like

Code: Select all

Block SPhenoInput   # SPheno specific input 
...
1101 1             # Include Fv in 1.loop corrections 
1102 1             # Include Fd in 1.loop corrections 
1103 1             # Include Fu in 1.loop corrections 
1104 1             # Include Fe in 1.loop corrections 
1201 1             # Include hh in 1.loop corrections 
1202 1             # Include Ah in 1.loop corrections 
1203 1             # Include Hm in 1.loop corrections 
1301 1             # Include VG in 1.loop corrections 
1302 1             # Include VP in 1.loop corrections 
1303 1             # Include VZ in 1.loop corrections 
1304 1             # Include VWm in 1.loop corrections 
1401 1             # Include gG in 1.loop corrections 
1402 1             # Include gA in 1.loop corrections 
1403 1             # Include gZ in 1.loop corrections 
1404 1             # Include gWm in 1.loop corrections 
1405 1             # Include gWpC in 1.loop corrections 
1500 1               # Include Wave diagrams 1.loop corrections 
1501 1               # Include Penguin diagrams 1.loop corrections 
1502 1               # Include Box diagrams 1.loop corrections 

So, setting all 110X to zero SHOULD (I haven't tested it myself!) lead to a consistent spectrum file which can be used with the Vevacious model without fermions.

Best,
Florian

[Kdolev]

Hey Florian,

This worked very well, however, I would like to remove the gauge bosons as well. I can't just remove their loop contributions, since they contain some of the scalar contributions. Is there a way around this?