in BLMSSM∗
Abstract
Applying the effective Lagrangian method, we study the Flavor Changing Neutral Current within the minimal supersymmetric extension of the standard model where baryon and lepton numbers are local gauge symmetries. Constraints on the parameters are investigated numerically with the experimental data on branching ratio of . Additionally, we present the corrections to direct CP-violation in and time-dependent CP-asymmetry in . With appropriate assumptions on parameters, we find the direct CP-violation is very small, while one-loop contributions to can be significant.
pacs:
12.60.Jv; 12.15.LkI Introduction
Since the Flavor Changing Neutral Current process(FCNC) originates only from loop diagrams, it is very sensitive to new physics beyond the Standard Model(SM). The updated average data of inclusive is PDG
(1) |
and the prediction of SM at next-next-to-leading order (NNLO) isBrSM1 ; BrSM2 ; BrSM3 ; BrSM4 ; BrSM5 ; BrSM6 ; BrSM7 ; BrSM8
(2) |
Though the deviation of SM prediction from experimental results has been almost eliminated in the past few years, it is helpful to constrain parameters of new physics.
The discovery of Higgs boson on Large Hadron Collider(LHC) makes SM the most successful theory in particle physics. Because of the hierarchy problem and missing of gravitational interaction, it is believed that SM is just an effective approximation of a more fundamental theory at higher scale. Among various extensions of SM, supersymmetric models have been studied for decades.
As the simplest extension, the Minimal Supersymmetric Standard Model(MSSM)MSSM solves the hierarchy problem as well as the instability of Higgs boson by introducing a superpartner for each SM particle. The Lightest Supersymmetric Particle (LSP) within this frmework also provides candidates of dark matter as Weakly Interacting Massive Particles (WIMPs). However the MSSM can not naturely generates tiny neutrino mass which is needed to explain the observation of neutrino oscillation. To acquire neutrino masses, heavy majorana neutrinos are introduced in the seesaw mechanism, which implies that the lepton numbers are broken. Besides, the baryon numbers are also expected to be broken because of the asymmetry of matter-antimatter in the universe. The authors of BLMSSM1 ; BLMSSM2 present the so called BLMSSM model in which the baryon and lepton number are local gauged and spontaneously broken at TeV scale. The experimental bounds on proton decay lifetime is the main motivation of great desert hypothesis. In BLMSSM, the proton decay can be avoid with discrete symmetry called matter parity and R-parityPR597-2015-1-30
To describe the symmetries of baryon and lepton numbers, gauge group is enlarged to . Then corrections to various observations can be induced from new gauge boson and exotic fields within this scenario. In ref. JHEP1411-119 , corrections to anomalous magnetic moment from one loop diagrams and two-loop Barr-Zee type diagrams are investigated with effective Lagrangian method. One-loop contributions to electric dipole moment in CP-Violating BLMSSM is presented in ref. EPJC-zhao-2017 . To account for the experimental data on Higgs, the authors of NPB-871-2013-223 study the signals of and with a 125 GeV Higgs. In this work, we use the branching ratio to constrain the parameters. Furthermore, we present the corrections to CP-Violation of due to new parameters introduced in this model.
Our presentation is organized as follows. In section II, we briefly introduce the construction of BLMSSM and the interactions we need for our caculation. After that, we present the one-loop corrections to branching ratio and CP-Violation with effective Lagrangian method in section III. Numerical results are discussed in section IV and the conclusions is given in section V.
II Introduction to BLMSSM
The BLMSSM is based on gauge symmetry . In order to cancel the anomalies of Baryon number(B), exotic quarks are introduced. Baryon number are broken spontaneously after Higgs superfields acquire nonzero vacuum expectation values(VEVs). To deal with the anomalies of Lepton number(L), exotic leptons are introduced, and are responsable for the breaking of lepton numberBLMSSM2 . The superfields which mediate the decay of exotic quarks are added in this model to avoid their stability.
Given the superfields above, one can construct the superpotential as
(3) |
where indicates the superpotential of MSSM, and
(4) |
The soft breaking terms are given by
(5) | |||||
The first term denotes the soft breaking terms of MSSM. To break the gauge symmetry from to electromagnetic symmetry , nonzero VEVs and are allocated to doublets and singlets .
(8) | |||||
(11) | |||||
(12) |
Here we take the notation and . After spontaneously breaking and unitary transformation from interactive eigenstate to mass eigenstate, one can extract the Feynman rules and mass spectrums in BLMSSM. The mass matrices of the particles that mediate the one-loop process can be found in ref. mass-matrice . The Feynman rules that we need can be extracted from the following terms, where all the repeated index of generation should be summed over.
(13) |
III One-loop corrections to from BLMSSM
The flavor transition process can be described by effective Hamiltonian at scale as follow hamiltonian :
(14) |
and the operators are given by ref. operators1 ; operators2 ; operators3 :
(15) |
Coefficients of these operators can be extracted from Feynman amplitudes that originate from considered diagrams. Actually only the Coefficients of and are needed if we adopt the branching ratio formula presented in ref. hamiltonian :
(16) | |||||
where the first term is SM prediction. The others come from new physics in which , , and indicate Wilson coefficients at electroweak scale. It is an advantage of this expression that we don’t have to evolve them down to hadronic scale as the effect of evolution has already been involved in the coefficients . The numerical values of these coefficients are given in table 1.

To obtain the New Physics corrections in BLMSSM, we investigate one-loop diagrams shown in Figure 1. Photons should be attached to all inner lines with electric charge to complete the diagrams of that contribute to and . Similarly, diagrams of can be completed with gluons attached to all the inner lines with color charge, and and originate from these process.
In details, we attach a photon to SM quark or charged Higgs in Figure 1.(a) to get a set of trigonal diagrams for , while gluon can only be attached to up-type quarks to form a specific diagram of . To give a complete correction originating from Figure 1.(a), contributions from all generations of and Higgs should be summed over. From the amplitudes of these diagrams, one can extract Wilson coefficients of electric- and chromomagnetic-dipole operators and at electroweak scale,
(17) |
where . The concrete expressions of relevant couplings are already given in previous section, and the form factors can be written as:
(18) |
where function is defined as:
(19) |
Corrections from all the other diagrams to and can be obtained similarly. In Figure 1.(b), the photon can only be attached to charged -1/3 squark . We present contributions from both neutralinos and baryon neutralinos at electroweak scale as
(20) |
(21) |
With the photon attached to the charged +2/3 squarks or chargino in Figure 1.(c), the contributions to Wilson coefficients read
(22) |
(23) |
The intermediate particles in Figure 1.(d) are the exotic quarks with charge -1/3 and superfield introduced in BLMSSM. The contributions from this diagram are
(24) |
Correspondingly, the corrections of exotic squarks with charge -1/3 and fermionic particle can be obtained from Figure 1.(e)
(25) |
(26) |
From Figure 1.(f), we obtain the corrections from gluinos in MSSM, the Wilson coefficients at are
(27) |
with
(28) |
The corrections to and at electroweak scale can be obtained by attaching the gluon to intermediate virtual particles with colors. For diagrams in Figure 1, the gluon can be attached to SM up-type quarks , squarks in MSSM , exotic quarks with charge -1/3 and its supersymmetric partners , as well as the gluinos . Wilson coefficients at electroweak scale can be formulated as:
(29) |
with the form factors listed below. As gluon can only be attached to intermediate fermion and in Figure 1.(a) and 1.(d), so the form factors have the same expressions. While in Figure 1.(b), 1.(c) and Figure 1.(e), the gluon can only be attached to scalar particles. Then form factors associated to these diagrams are the same. By summing over the contributions to Wilson coefficients when gluon attached to and , we get form factors of Figure 1.(f).
(30) |
The Wilson coefficients obtained above can also be used to direct CP-violation in and the time-dependent CP-asymmetry in . The direct CP-violation and CP-asymmetry are defined in hadronic scale ACP-def1 ; ACP-def2 ; ACP-def3 ; ACP-def4 ; ACP-def5
(31) | |||||
(32) |
where the photon energy cut in is taken as , and in is phase of mixing amplititude. Here we use the experimental data given in ref. 1010-1589 .
As the Wilson coefficients are calculated at electroweak scale , we need to evolve them down to hadronic scale with renormalization group equations.
(33) |
where the Wilson coefficients are constructed as
(34) |
To be convenient, we take the numerrical results of effective coefficients from SM at next-to-next-to-leading logarithmic(NNLL) level, . The evolving matrices involved in Eq.(33) are given as
(35) |
with anomalous dimension matrices
(44) |
and
(47) |
IV Numerical analysis
The consistency of SM prediction and experimental data on sets stringent constraint on new physics parameters. In this section, we discuss the numerical results of branching ratio with some assumptions. The SM inputs are given in Table 2. All the parameters with mass dimension are given in the unit GeV. To be concise, we omit all the unit GeV in this section. Other free parameters introduced in BLMSSM are set to be , , and to make sure the masses of new physics particles under experimental limitations.
As a new field introduced in BLMSSM, superfield interacts with exotic quarks. The coplings between and denoted by are given in Eq.4. From the analytical expressions, one can find the Wilson coefficients are sensitive to these couplings as well as coefficients of mass term of , which turns up in as and . We show the branching ratio varying with , , and in firgure 2. The dependency of is not listed as it is similar to .




In Figure 2.(a), one can find the branching ratio increases when raises up. The experimental limitations are denoted by the gray area, and we have taken . It can be seen in this figure that branching ratio reachs the upper limitations of experimental limitations when , then we get the constrain .
Similarly, we plot the branching ratio varying with in Figure 2.(b). By taking , which satisfies the limitations obtained in Figure 2.(a), and , we find the branching ratio rises very slowly when runs from 0.01 to 1.5. The whole curve lies in the gray area, which means the branching ratio satisfies the experimental constraint under our assumptions.
To investigate the trends of varying with , we take . We find from Figure 2.(c) that the branching ratio diminishes steeply with increasing of , and finally gets to the value of standard model. In Figure 2.(d), we plot the branching ratio varying with , where we take . With the upper limitations of experimental result, we get the constraints .


In Figure 3.(a), we present the branching ratio varying with , which is the coupling truns up in superpotential term . With , we find branching ratio decreases when gets larger. To consist with the experimental data, one has . Another interesting parameter is , which is defined as , where and are VEVs of and respectively. We plot branching ratio varying with in Figure 3.(b) with . To satisfy the experimental constraints, we have .
Additionally, we plot the direct CP-violation of and time-dependent CP-asymmetry of varying with and . Within the framework of SM, we have PRL-106-2011-141801 , and the average value of this observable is PDG . Within some uncertainty, the theoretical value is consistent with the experimental result. Compared with direct CP-violation of , there is significant deviation between SM prediction and experimental result of . The SM prediction of time-dependent CP-asymmetry in at LO level is given as skr-SM and the experimental result is PDG ; operators1 .
To investigate and numerically, some parameters are taken to be complex, and the area within experimental boundaries are filled to be gray in the presented figures. In Figure 4, we plot the dependency of parameters relevant to superfield . Under our assumptions of free parameters introduced in BLMSSM, we find that (solid line) are hardly affected by the change of . Though corrections from one-loop level are almost zero, the numerical results are consistent with experimental data.
As shown in Figure 4.(a), one-loop corrections to (dashed line) in BLMSSM can reach with appropriate inputs. By changing the free parameters, one finds can be as small as zero in Figure 4.(b). In Figure 4.(c), it can be seen that raise obviously with increasing of , and finally gets stable around zero. The varying with are given in Figure 4.(d). When raises up, we can see that decreases. Within the range of parameters and , we find is consistent with experimental data.
In Figure 5, we take into account the parameters and . When runs from 0.01 to 2.0, the time-dependent CP-asymmetry decrease from to . While for the increasing of , raises from to . Under our assumptions, we conclude that and affect apparently, and the numerical results of new physics correction are consistent with experimental data. However, the direct CP-violation of depends on and weakly, and the one-loop contributions from BLMSSM are very small.
The last Figure 6 illustrates the trend of and varying with . By taking and , we find that increases from to . The stays around zero within the range .







V Conclusions
As an interesting process of FCNC, we investigate the transition within the framework of BLMSSM. With effective Hamiltonian method, we present the Wilson coefficients extracted from amplitudes corresponding to the concerned one-loop diagrams. Based on the analytical expressions, constraints on parameters are given in the numerical section with the experimental data of branching ratio of . The direct CP-violation of in BLMSSM is very small, and depend on the free parameters weakly. However, the time-dependent CP-asymmetry in varies with and obviously. The contributions from new physics can reach under appropriate setup of the parameters.
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