= Top-quark baryon number violation =

The model contains baryon-(and lepton)-number-violating (BNV) four-fermion interactions like tbμc, tbue, tτdu. These interactions for instance lead to the t→b̅c̅μ⁺ decay and ub→t̅e⁺ single top production in association with a single lepton.

Following [https://arxiv.org/abs/1107.3805 1107.3805]/[https://doi.org/10.1103/PhysRevD.85.016006, PRD85(2012)016006], the implemented mass-eigenstate operators take the form:
\\[[Image(operators-s-t.png)]]\\
The corresponding parameters are {{{aaa}}}, {{{bbb}}}, {{{ccc}}}, {{{ddd}}} and their primed analogues.
Suffixes of the type {{{IxJ}}} encode the generation indices {{{I}}} and {{{J}}} of the fermion in each of the currents.
An effective scale {{{Lambda}}} is introduced and set by default to 1 TeV.
Relations between the parameters above and those of the following gauge-eigenstate basis:
\\[[Image(operators-1-5.png)]]\\
are
\\[[Image(operators-relations.png)]]\\
where the various {{{V}}}'s are the rotations between mass- and gauge eigenstates.

To overcome !MadGraph limitations, the model introduces a very heavy fictitious mediator {{{X}}} which effectively generates the required four-fermion interactions. Its mass {{{MX}}} is set by default to 1 PeV and should be kept much higher than the energy scale of the considered process, so that computation do not depend on its exact value.

The decay {{{t > t~ ta+ u~ d~}}} and production {{{u d > t~ ta+}}} matrix elements computed by !MadGraph in {{{standalone_cpp}}} mode (for various combinations of {{{aaa3x1}}}, {{{bbb3x1}}}, {{{ccc1x3}}}, {{{ddd1x3}}}, {{{aaaprime3x3}}}, {{{bbbprime3x3}}}, {{{cccprime1x1}}}, {{{dddprime1x1}}} and at various phase-space point) have been validated against analytical computations (see [attachment:check_matrix_element.tar.gz]). 

UFO model: [attachment:bnv_mediator_ufo.tar.gz]

!FeynRules source files: [attachment:generate_model.tar.gz]

Please refer to: [https://arxiv.org/abs/1107.3805 1107.3805]/[https://doi.org/10.1103/PhysRevD.85.016006, PRD85(2012)016006]

Contact person: Gauthier Durieux

Changelog:
 - 2022-01-21: interference sign fixed (thanks to Reza Goldouzian)