Looking for B→Xsℓ+ℓ− in a nonminimal universal extra dimensional model

Abstract

Non-vanishing boundary localised terms significantly modify the mass spectrum and various interactions among the Kaluza-Klein excited states of 5-Dimensional Universal Extra Dimensional scenario. In this scenario we compute the contributions of Kaluza-Klein excitations of gauge bosons and third generation quarks for the decay process B → X s + − incorporating next-to-leading order QCD corrections. We estimate branching ratio as well as ForwardBackward asymmetry associated with this decay process. Considering the constraints from some other b → s observables and electroweak precision data we show that significant amount of parameter space of this scenario has been able to explain the observed experimental data for this decay process. From our analysis we put lower limit on the size of the extra dimension by comparing our theoretical prediction for branching ratio with the corresponding experimental data. Depending on the values of free parameters of the present scenario, lower limit on the inverse of the radius of compactification (R −1 ) can be as high as ≥ 760 GeV.Even this value could slightly be higher if we project the upcoming measurement by Belle II experiment. Unfortunately, the Forward Backward asymmetry of this decay process would not provide any significant limit on R −1 in the present model. *In the present article, in order to serve our purposes we are particularly focused on an extension of SM with one flat space-like dimension (y) compactified on a circle S 1 of radius R. All the SM fields are allowed to propagate along the extra dimension y. This model is called as 5-dimensional (5D) Universal Extra Dimensional (UED) [20] scenario. The fields manifested on this manifold are usually defined in terms of towers of 4-Dimensional (4D) Kaluza-Klein (KK) states while the zero-mode of the KK-towers is designated as the corresponding 4D SM field. A discrete symmetry Z 2 (y ↔ −y) has been needed to generate chiral SM fermions in this scenario. Consequently, the extra dimension is defined as S 1 /Z 2 orbifold and eventually physical domain extends from y = 0 to y = πR. As a result, the y ↔ −y symmetry has been translated as a conserved parity which is known as KK-parity = (−1) n , where n is called the KK-number. This KK-number (n)is identified as discretised momentum along the y-direction. From the conservation of KK-parity the lightest Kaluza-Klein particle (LKP) with KK-number one (n = 1) cannot decay to a pair of SM particles and becomes absolutely stable. Hence, the LKP has been considered as a potential DM candidate in this scenario [21][22][23][24][25][26][27][28]. Furthermore, few variants of this model can address some other shortcomings of SM, for example, gauge coupling unifications [29][30][31], neutrino mass [32,33] and fermion mass hierarchy [34] etc.At the n th KK-level all the KK-state particles have the mass (m 2 + (nR −1 ) 2 ). Here, m is considered as the zero-mode mass (SM particle mass) which is very small with respect to R −1 . Therefore, this UED scenario contains almost degenerate mass...

The impact of nonminimal universal extra dimensional model on $$\Delta B=2$$ transitions

“…Therefore, if we compare our theoretical prediction with the current allowed ranges of the CKM parameters and elements of the UT then we can easily constrain the parameter space of this nmUED framework. Moreover, from our study we can also measure the lower limit on R −1 and compare the same with the results obtained from our previous analyses [53][54][55]. Similar kind of exercise was executed several years ago in UED framework [9] where the BLT parameters are zero.…”

“…In this section we overview the salient features of the nmUED scenario necessary for our current analysis. One can find detailed description of this scenario in [33][34][35][36][37][38][39][40][46][47][48][49][50][51][52][53][54][55][56]. In order to conserve the KK-parity, coefficients of boundary terms at both the boundary points (y = 0 and y = π R) are kept equal.…”

“…In this type of scenario, one can find an extensive study on DM in [44]. Action for 5D fermionic fields considering appropriate boundary localised kinetic term (BLKT) with coefficient r f [38,44,[53][54][55][56] can be written as…”

“…In the above action 5D four component Dirac spinors are represented by L (x, y) and R (x, y), which can be expressed in terms of two component spinors as [38,44,[53][54][55][56]]…”

“…In literature there exists number of phenomenological studies in this scenario. For example, bounds on the values of the coefficients of the BLTs have been obtained from the evaluation of electroweak observables [39,41], S, T and U parameters [37,42], DM relic density [43,44], production as well as decay of SM Higgs boson [45], collider study of LHC experiments [46][47][48][49][50][51], Z → bb [52], branching ratios of some rare decay processes of B-meson: e.g., B s → μ + μ − [53], B → X s γ [54] and B → X s + − [55], R D ( * ) anomalies [56][57][58], flavour changing rare top decay [59,60] and unitarity of scattering amplitudes containing KK-excitations [61].…”