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 ​1107.3805/​PRD85(2012)016006, the implemented mass-eigenstate operators take the form:

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:

are

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 check_matrix_element.tar.gz​).

UFO model: bnv_mediator_ufo.tar.gz​

FeynRules source files: generate_model.tar.gz​

Please refer to: ​1107.3805/​PRD85(2012)016006

Contact person: Gauthier Durieux

Changelog:

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