Single Universal Extra Dimension Research Articles

Study of B s →φℓ + ℓ − decay in a single universal extra dimension model

Utilizing form factors calculated within the light-cone sum rules, we have evaluated the decay branching ratios of $B_s\to \phi\gamma$ and $B_s\to \phi \ell^+\ell^-$ in a single universal extra dimension model (UED), which is viewed as one of the alternative theories beyond the standard model (SM). For the decay $B_s \to \phi \ell^+\ell^-$, the dilepton invariant mass spectra, the forward-backward asymmetry, and double lepton polarization are also calculated. For each case, we compared the obtained results with predictions of the SM. In lower values of the compactification factor 1/R, the only parameter in this model, we see the considerable discrepancy between the UED and SM models. However, when 1/R increases, the results of UED tend to diminish and at $1/R = 1000 \mathrm{GeV}$, two models have approximately the same predictions. Compared with data from CDF of $B_s \to \phi \mu^+ \mu^-$, the 1/R tends to be larger than $350 \mathrm{GeV}$. We also note that the zero crossing point of the forward-backward asymmetry is become smaller, which will be an important plat to prob the contribution from the extra dimension model. The results obtained in this work will be very useful in searching new physics beyond SM. Moreover, the order of magnitude for branching ratios shows a possibility to study these channels at the Large Hadron Collider (LHC), CDF and the future super-B factory.

Investigation of the Λ b → Λℓ+ℓ− transition in universal extra dimension using form factors from full QCD

Using the related form factors from full QCD which recently are available, we provide a comprehensive analysis of the $\Lambda_b \rightarrow \Lambda \ell^+ \ell^-$ transition in universal extra dimension model in the presence of a single universal extra dimension called the Applequist-Cheng-Dobrescu model. In particular, we analyze some related observables like branching ratio, forward-backward asymmetry, double lepton polarization asymmetries and polarization of the $\Lambda$ baryon in terms of compactification radius and corresponding form factors. We present the sensitivity of these observables to the compactification parameter, 1/R up to 1/R=1000 GeV. We also compare the results with those obtained using the form factors from heavy quark effective theory as well as the SM predictions.

RareBsdecays toηandη′final states

We study exclusive ${B}_{s}$ decays to final states with $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$, induced by the rare $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ and $b\ensuremath{\rightarrow}s\ensuremath{\nu}\overline{\ensuremath{\nu}}$ transitions. Differential decay rates and total branching fractions are predicted in the standard model, adopting the flavor scheme for the description of the $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\eta}}^{\ensuremath{'}}$ mixing. We discuss the theoretical uncertainty related to the hadronic matrix elements. We also consider these decay modes in a new physics scenario with a single universal extra dimension, studying the dependence of branching ratios and decay distributions on the compactification scale ${R}^{\ensuremath{-}1}$ of the extra dimension.

Double-lepton polarization asymmetries and polarized forward backward asymmetries in the rareb→sℓ+ℓ−decays in a single universal extra dimension scenario

We study the double-lepton polarization asymmetries and single and double-lepton polarization forward-backward asymmetries of the rare $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ mode within the standard model and in the Appelquist-Cheng-Dobrescu model, which is a new physics scenario with a single universal extra dimension. In particular, we examine the sensitivity of the observables to the radius $R$ of the compactified extra dimension, which is the new parameter in this new physics model.

FCNCBsandΛbtransitions: Standard model versus a single universal extra dimension scenario

We study the flavor changing neutral current ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\phi}\ensuremath{\gamma}$, $\ensuremath{\phi}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ and ${\ensuremath{\Lambda}}_{b}\ensuremath{\rightarrow}\ensuremath{\Lambda}\ensuremath{\gamma}$, $\ensuremath{\Lambda}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ transitions in the standard model and in a scenario with a single universal extra dimension. In particular, we focus on the present knowledge of the hadronic uncertainties and on possible improvements. We discuss how the measurements of these modes can be used to constrain the new parameter involved in the extra-dimensional scenario, the radius $R$ of the extra dimension, completing the information available from $B$-factories. The rates of these $b\ensuremath{\rightarrow}s$ induced decays are within the reach of new experiments, such as LHCb.

Exclusive B→K1ℓ+ℓ- decay in model with single universal extra dimension

Decay rate and forward–backward asymmetries in B→K1l+l-, where K1 is the axial vector meson, are calculated in the universal extra dimension (UED) model. The dependence of these physical quantities on the compactification radius R, the only unknown parameter in UED model, is studied, and it is shown that the zero of the forward–backward asymmetry is sensitive to the UED model; therefore they can be a very useful tool to establish new physics predicted by the UED model. This work is briefly extended to B→K*l+l-.

Rare B decays in a single Universal Extra Dimension scenario

Exclusive rare B → K ( ∗ ) l + l − , B → K ( ∗ ) ν ν ¯ and B → K ∗ γ decays are studied within the Applequist-Cheng-Dobrescu model, an extension of the Standard Model in presence of universal extra dimensions. In the case of a single universal extra dimension compactified on a circle of radius R , we study the dependence of several observables on 1 / R , and discuss whether the hadronic uncertainty due to the form factors obscures or not such a dependence. We find that, using present data, it is possible in many cases to put a sensible lower bound to 1 / R , the most stringent one coming from B → K ∗ γ .

Λb→Λℓ+ℓ- decay in universal extra dimensions

We study the exclusive Λb→Λl+l- decay in the Appelquist, Chang, Dobrescu model with a single universal extra dimension. We investigate the sensitivity of the branching ratio, lepton polarization and forward–backward asymmetry $\mathcal{A}_{\text{FB}}$ to the compactification parameter 1/R. We obtain the result that the branching ratio for the Λb→Λl+l- (l=μ,τ) decay changes about 25% compared to the SM value when 1/R=250 GeV, and the zero position of the forward–backward asymmetry is shifted to the left compared to the SM result. Therefore, measurement of the branching ratio of Λb→Λl+l- decay and determination of the zero position of $\mathcal{A}_{\text{FB}}$ are very useful in looking for new physics in the framework of the UED models.

Spin effects in rareB→Xsτ+τ−andB→K(*)τ+τ−decays in a single universal extra dimension scenario

We study the branching fractions and the lepton polarization asymmetries of rare $B\ensuremath{\rightarrow}{X}_{s}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ and $B\ensuremath{\rightarrow}{K}^{(*)}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ modes within the standard model and in the Appelquist-Cheng-Dobrescu model, which is a New Physics scenario with a single universal extra dimension. In particular, we investigate the sensitivity of the observables to the radius $R$ of the compactified extra dimension, which is the only new parameter in this New Physics model. For the exclusive transitions we study the uncertainties due to the hadronic matrix elements using two set of form factors, finding that in many cases such uncertainties are small. In particular, we show that the ${\ensuremath{\tau}}^{\ensuremath{-}}$ polarization asymmetries become free of hadronic uncertainties if Large Energy relations for the form factors, valid for low momentum transfer to the lepton pair, are used. We also consider ${K}^{*}$ helicity fractions and their sensitivity to the compactification parameter.

ExclusiveB→K(*)ℓ+ℓ−,B→K(*)νν¯andB→K*γtransitions in a scenario with a single universal extra dimension

We analyze the exclusive rare $B \to K^{(*)} \ell^+ \ell^-$, $B \to K^{(*)} \nu \bar \nu$ and $B \to K^* \gamma$ decays in the Applequist-Cheng-Dobrescu model, which is an extension of the Standard Model in presence of universal extra dimensions. In particular, we consider the case of a single universal extra dimension. We study how spectra, branching fractions and asymmetries depend on the compactification parameter 1/R, and whether the hadronic uncertainty due to the form factors obscures or not such a dependence. We find that, using present data, it is possible in many cases to put a sensible lower bound to 1/R, the most stringent one coming from $B \to K^* \gamma$. We also study how improved experimental data can be used to establish stronger constraints to this model.

Universal extra dimensions andZ→bb¯

We study, at the one loop level, the dominant contributions from a single universal extra dimension to the process (Z\to b\bar{b}). By resorting to the gaugeless limit of the theory we explain why the result is expected to display a strong dependence on the mass of the top-quark, not identified in the early literature. A detailed calculation corroborates this expectation, giving rise to a lower bound for the compactification scale which is comparable to that obtained from the $\rho$ parameter. An estimate of the subleading corrections is furnished, together with a qualitative discussion on the difference between the present results and those derived previously for the non-universal case.