VLQcalc

a Python Module for Calculating Vector-like Quark Couplings

Contributors: Ali Can Canbay & Orhan Cakir

It is capable of: * Converting coupling constants between models VLQUFO $^{[1]}$ and VLQv4_UFO $^{[2]}$ prepared within the FeynRules $^{[3]}$ framework, * Calculating VLQ decay widths, * Computing coupling constants for width-to-mass ratio ($\Gamma/m$), * Generating MadGraph5 $^{[4]}$ input card.

By clicking on the 'launch binder' button above, the module can be run online with Binder $^{[5]}$.

Click here for the tutorial.

Installation:

Download the latest release, extract it, enter the extracted file, and run the following command via the console. console python setup.py install

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VLQ Class

It is defined in the submodule named model. python import VLQcalc.model as model

Creating a VLQ object: python vlq = model.VLQ( VLQ_type, FNS, LR )

| Parameter | Format | Values | Default Value | |-|-|:-:|:-:| |VLQ_type|string|X, T, B, Y|-| |FNS|integer|4, 5|4| |LR|bool|True, False|False|

• $m_{b}=0$ when FNS=5
• LR=False allows calculations with only left-handed couplings, while LR=True allows calculations with both left and right-handed couplings.
  

setMass method:

The mass is passed to the method as a single value or a list of values in integer or float data type in GeV unit. python vlq.setMass( 1000 ) vlq.setMAss( [1000,1500,2000] )

convertModel method:

It converts the couplings in VLQUFO and VLQv4_UFO models to each other.

python vlq.convertModel( Kappas, BRs, reverse )

| Parameter | Format | Values | Default Value | |-|-|:-:|:-:| |Kappas|float/integer or list|any|-| |BRs|float/integer or list|any|1| |reverse|bool|True, False|False|

• Kappas is
  • $\kappaQ$ where Q is X, T, B or Y for converting couplings from VLQUFO to VLQv4UFO.
  • given in the list as $[\kappaH, \kappaW, \kappaZ]$ for T and B, while it is only $\kappaW$ for X and Y when converting couplings from VLQv4UFO to VLQ_UFO.
• For T and B, the parameter named BRs is given in the list as [BR(Q→Hq), BR(Q→Wq), BR(Q→Zq)] where q represents the 3rd family quarks of the Standard Model. Only BR(Q→Wq) is specified for X and Y.
• When the reverse value is False, the conversion is from VLQUFO to VLQv4UFO; when True, it is from VLQv4UFO to VLQUFO.

calcDecay method:

It only works with the *VLQv4UFO** model. Converted couplings can be used for VLQ_UFO model*

For T and B: python decayH, decayW, decayZ, Gamma = vlq.calcDecay( Mass, Kappas, LR ) For X and Y: python decayW = vlq.calcDecay( Mass, Kappa, LR ) | Parameter | Format | Values | Default Value | |-|-|:-:|:-:| |Mass|float/integer or list|any|-| |Kappas|list|any|-| |Kappa|float/integer|any|-| |LR|bool|True, False|False|

calcRatioKappas method:

It is used to calculate the couplings according to the $\GammaQ/mQ$ ratio.
It only works with the *VLQv4UFO** model. Couplings can be converted to VLQ_UFO model after calculations are made according to this model.*

The modified Genetic Algorithm (modifiedGA) $^{[6]}$ is used to calculate couplings according to the $\GammaQ/mQ$ ratio.

python vlq.calcRatioKappas( BRs, Ratio )

• Ratio is $\GammaQ/mQ$ value.

MG5 Class

It is defined in the submodule named madgraph. python import VLQcalc.madgraph as madgraph

Creating a MG5 object: python mg5 = madgraph.MG5(VLQ, model) * model parameter can be VLQUFO or VLQv4_UFO in string format.

In the MG5 object, there are two different methods for entering a process: setProcess and addProcess methods, which take their parameters as strings, are used respectively to define the main process and additional processes. python mg5.setProcess( process ) mg5.addProcess( process )

MG5 object also have the properties in string format listed in the table below.

| Property | Values | Default Value | |-|-|:-:| |shower|OFF, pythia8, ...|OFF| |detector|OFF, Delphes, ...|OFF| |analysis|OFF, ExRoot, MadAnalysis, ...|OFF| |madspin|OFF, ON, onshell, full|OFF| |reweight|OFF, ON|OFF|

addInput method, which takes a string parameter, is used to define inputs that allow modifications to be made on simulation cards. After all definitions have been made, an MG5 input card can be generated using the createMG5Input method, which takes the output file name (in string format) as a parameter. python mg5.addInput( input ) mg5.createMG5Input( file_name )

When creating an input card, the processes defined in setProcess and addProcess are expanded to include both particles and antiparticles.

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References

1. M. Buchkremer, G. Cacciapaglia, A. Deandrea, and L. Panizzi. Model-independent framework for searches of top partners. Nuclear Physics B, 876(2):376–417, 2013.
2. B. Fuks and H. S. Shao. QCD next-to-leading-order predictions matched to parton showers for vector-like quark models. The European Physical Journal C, 77(2):1–21, 2017.
3. N. D. Christensen and C. Duhr. Feynrules–Feynman rules made easy. Computer Physics Communications,180(9):1614–1641, 2009.
4. J. Alwall, M. Herquet, F. Maltoni, O. Mattelaer, and T. Stelzer. Madgraph 5: going beyond. Journal of High Energy Physics, 2011(6):1–40, 2011.
5. Jupyter et al. Binder 2.0 - Reproducible, Interactive, Sharable Environments for Science at Scale. Proceedings of the 17th Python in Science Conference. 2018.
6. A. C. Canbay. modifiedGA (Version 0.1.0) [Computer software]. DOI: 10.5281/zenodo.12569505, GitHub: acanbay/modifiedGA