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, 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 BNV decay width of the top quark as well as the u d > t~ ta+ matrix element 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.

UFO model: bnv_mediator_ufo.tar.gz​

Please refer to: ​https://arxiv.org/abs/1107.3805

Contact person: Gauthier Durieux