a Python Module for Calculating Vector-like Quark Couplings

Contributors: Ali Can Canbay & Orhan Cakir

It is capable of:

• Converting coupling constants between models VLQ_UFO $^{[1]}$ and VLQ_v4_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.

python setup.py install

It is defined in the submodule named model.

import VLQcalc.model as model

Creating a VLQ object:

vlq = model.VLQ( VLQ_type, FNS, LR )

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

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.

vlq.setMass( 1000 )
vlq.setMAss( [1000,1500,2000] )

It converts the couplings in VLQ_UFO and VLQ_v4_UFO models to each other.

vlq.convertModel( Kappas, BRs, reverse )

• Kappas is
  • $\kappa_Q$ where Q is X, T, B or Y for converting couplings from VLQ_UFO to VLQ_v4_UFO.
  • given in the list as $[\kappa_H, \kappa_W, \kappa_Z]$ for T and B, while it is only $\kappa_W$ for X and Y when converting couplings from VLQ_v4_UFO 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 VLQ_UFO to VLQ_v4_UFO; when True, it is from VLQ_v4_UFO to VLQ_UFO.

It only works with the VLQ_v4_UFO model. Converted couplings can be used for VLQ_UFO model

For T and B:

decayH, decayW, decayZ, Gamma = vlq.calcDecay( Mass, Kappas, LR )

For X and Y:

decayW = vlq.calcDecay( Mass, Kappa, LR )

It is used to calculate the couplings according to the $\Gamma_Q/m_Q$ ratio.
It only works with the VLQ_v4_UFO model. Couplings can be converted to VLQ_UFO model after calculations are made according to this model.

The modified Genetic Algorithm (mGA) $^{[5]}$ is used to calculate couplings according to the $\Gamma_Q/m_Q$ ratio.

vlq.calcRatioKappas( BRs, Ratio )

• Ratio is $\Gamma_Q/m_Q$ value.

It is defined in the submodule named madgraph.

import VLQcalc.madgraph as madgraph

Creating a MG5 object:

mg5 = madgraph.MG5(VLQ, model)

• model parameter can be VLQ_UFO or VLQ_v4_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.

mg5.setProcess( process )
mg5.addProcess( process )

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.

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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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