Narrow Results

Hadronic form factors for the rare weak transitions Λ_b → Λ^(*) are calculated using a nonrelativistic quark model. The form factors are extracted in two ways. An analytic extraction using single-component wave functions (SCA) with the quark current being reduced to its nonrelativistic Pauli form is employed in the first method. In the second method, the form factors are extracted numerically using the full quark model wave function (MCN) with the full relativistic form of the quark current. Although there are differences between the two sets of form factors, both sets satisfy the relationships expected from the heavy quark effective theory (HQET). Differential decay rates, branching ratios (BRs) and forward–backward asymmetries (FBAs) are calculated for the dileptonic decays Λ_b → Λ^(*) ℓ⁺ ℓ^-, for transitions to both ground state and excited daughter baryons. Inclusion of the long distance contributions from charmonium resonances significantly enhances the decay rates. In the MCN model the Λ(1600) mode is the dominant mode in the μ channel when charmonium resonances are considered; the Λ(1520) mode is also found to have a comparable BR to that of the ground state in the μ channel.

Branching ratios, lepton forward–backward asymmetries, and lepton polarization asymmetries for the flavor-changing neutral current (FCNC) dileptonic decays of the ${\Lambda }_b$ baryon to the ground state and a number of excited state $\Lambda$ baryons are calculated using form factors extracted using wave functions from a constituent quark model. The SM branching ratios for the transition to the ground state calculated using these quark model form factors are consistent with the recent measurement reported by the LHCb collaboration. It is shown that the lepton polarization asymmetries are largely insensitive to the transition form factors and, therefore, may also be insensitive to the effects of QCD in the nonperturbative regime. These observables could therefore provide somewhat model independent ways of extracting various combinations of the Wilson coefficients.

The measurements of the top quark flavor changing neutral current interactions are one of the most important goals of the top quark physics program in the present and the future collider experiments. These measurements provide direct information on nonstandard interactions of the top quark. Within the framework of new physics beyond the Standard Model, these interactions can be defined by an effective Lagrangian. In this study, we have investigated the potential of the future $\mu p$ colliders on the top quark flavor changing neutral current interactions through the subprocesses $\gamma q\to t\to Wb$, where $q=u,c$. These subprocesses have been produced through the main reaction $\mu p\to \mu \gamma p\to \mu WbX$ at the LHC-$\mu p$, the FCC-$\mu p$ and the SPPC-$\mu p$. For the main reaction, the total cross-sections have been calculated as a function of the anomalous $tq\gamma$ couplings. In addition, sensitivities on $\mathrm{\text{BR}}(t\to q\gamma )$ at 95% Confidence Level have been calculated. We obtain that the best constraints on $\mathrm{\text{BR}}(t\to q\gamma )$ are at the order of $10^{-7}$ which is four orders of magnitude better than the LHC’s experimental results.

In this work, we overhaul previous studies of Flavor Changing Neutral Current processes in the context of the Reduced Minimal 3-3-1 (RM331) model. We sift the individual contributions from the CP-even scalars and the Z′ gauge boson using two different parametrizations schemes and compare our results with current measurements. In particular, studying the meson system we find the most stringent bounds in the literature on this model, namely and .

We study rare decays and in the framework of nonstandard neutrino interactions (NSIs). We calculate branching ratios of these decays. We explore the possibility for second generation of quarks in NSIs just like leptonic contribution in and . We study the dependence of on . We show that there exists a possibility for , also from this reaction and other two reactions, and . Three other processes, and are investigated with s quark in the loop for NSIs instead of d quark. Constraints on and are provided. We point out that constraints for both u and c quark are equal and similarly for d and s quarks the constraints are equal .

In this work, we present a Mathematica package Peng4BSM@LO which calculates the contributions to the Wilson Coefficients of certain effective operators originating from the one-loop penguin Feynman diagrams. Both vector and scalar external legs are considered. The key feature of our package is the ability to find the corresponding expressions in almost any New Physics model which extends the SM and has no flavor changing neutral current (FCNC) transitions at the tree level.

Processes τ→lγ, τ→lll with l = e, μ and μ(τ) →e (μ) γ are evaluated in the framework of a model based on the extended symmetry gauge SU(3)_c ⊗SU(3)_L ⊗U(1)_Y with a leptonic sector consisting of five triplets. Lepton flavor violating processes are allowed at tree level in this model through the new Z′ gauge boson. We obtained bounds for the mixing angles in the leptonic sector of the model, considering the experimental measurements of the processes from the BELLE and the BABAR collaborations.

The rare semileptonic $B\to K{\mu }^{+}{\mu }^{-}$ and $B\to \varphi {\mu }^{+}{\mu }^{-}$ decay modes mediated by the $b\to s{\mu }^{+}{\mu }^{-}$ transition are studied in this paper. We analyze observables such as the differential branching ratio, lepton polarization asymmetry and forward–backward asymmetry within the standard model in the low $q^2$ region. We then perform an analysis of the same modes within the 331 or $S{U}_C(3)\times S{U}_L(3)\times U_X(1)$ model in which a new heavy $Z^{\prime }$ boson contributes. The effects of the $Z^{\prime }$-mediated flavor-changing neutral current (FCNC) transitions on these modes are investigated by varying the mass $M_{Z^{\prime }}$ and the model parameter $\beta$. The new $Z^{\prime }$ couplings are constrained by flavor observables of $B_s-{\bar{B}}_s$ mixing and branching ratio of $B_s\to {\mu }^{+}{\mu }^{-}$. We find that for some values of these couplings, the observables are quite sensitive to $Z^{\prime }$ effects and deviations from Standard Model can be large.

We study the rare semileptonic $B\to \pi {\mu }^{+}{\mu }^{-}$ and $B\to \rho {\mu }^{+}{\mu }^{-}$ decay modes mediated by the quark level $b\to d{\mu }^{+}{\mu }^{-}$ transition in this paper. We analyze observables such as the differential branching ratio, lepton polarization asymmetry and forward–backward asymmetry within the standard model in the large hadronic recoil region. We then analyze these observables within the 331 or $S{U}_C(3)\times S{U}_L(3)\times U_X(1)$ model in which a new heavy $Z^{\prime }$ boson contributes. The effects of the $Z^{\prime }$-mediated flavor changing neutral current (FCNC) transitions on these modes are examined by varying the mass $M_{Z^{\prime }}$ and the model parameter $\beta$. The new $Z^{\prime }$ couplings are constrained by flavor observables of $B_d-{\bar{B}}_d$ mixing. For the obtained parameter space, we observe $Z^{\prime }$ sensitivities of our observables of interest and deviations from standard model can range from moderate to large depending on the $\beta$ value.

We calculate bounds for the branching ratio of the $B_s^0\to \tau e$ decay, for the first time, in the context of flavor changing neutral currents mediated by a $Z^{\prime }$ gauge boson, which can arise from five extended models. In this sense, by using experimental measurements on the $B\to X_s\gamma$ decay and the $B_s^0\to {\mu }^{+}{\mu }^{-}$ process, we look for constraints of the $Z^{\prime }bs$ coupling, where the more restrictive bound is offered by the last one. On the other hand, by employing the experimental restriction on the $\tau \to eeē$ decay, the strength of the $Z^{\prime }\tau e$ coupling is estimated. Our analysis is based on the more recent experimental results on searches for the $Z^{\prime }$ gauge boson in ATLAS and CMS detectors. In addition, we revisited the $B_s^0\to \tau \mu ,\mu e$ meson decays by using different approaches not previously reported. The strengths of the $Z^{\prime }\tau \mu$ and $Z^{\prime }\mu e$ couplings were estimated by employing experimental restrictions on the $\tau \to \mu \mu \bar{\mu }$ decay and the $\mu -e$ conversion rate, respectively. Thus, we predict the following upper bounds: $B_s^0\to \tau e\sim 10^{-6}$, $B_s^0\to \tau \mu \sim 10^{-6}$ and $B_s^0\to \mu e\sim 10^{-11}$.

We study the rare mesonic decays and for the search of new physics (NP) in the form of nonstandard neutrino interactions (NSIs). We calculate branching ratios (BRs) of these decays in the framework of NSIs. We try to explore the possibility for second and third generations of quarks in NSIs, exactly on the same footing as for leptonic case we have and . We show that there exist a possibility for and also from these reactions. Three other processes and are investigated with s and b quarks in the loop for NSIs instead of d quark only. Constraints on and (where q = s, b and l, l′ ≠ τ) are provided. We point out that constraints for u, c and t quarks are equal and similarly for d, s and b quarks the constraints are equal .