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Avirup Shaw
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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 $Brightarrow X_sell^+ell^-$ incorporating next-to-leading order QCD corrections. We estimate branching ratio as well as Forward Backward asymmetry associated with this decay process. Considering the constraints from some other $b to s$ 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 $geq 760$ 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.
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We estimate contributions from Kaluza-Klein excitations of third generation quarks and gauge bosons to the branching ratio of $Brightarrow X_sgamma$ decay process in 5-Dimensional Universal Extra Dimensional scenario with non-vanishing boundary localised terms. This model is conventionally known as non-minimal Universal Extra Dimensional model. We have derived the lower limit on the size of the extra dimension by comparing our theoretical estimation of the branching ratio which includes next-to-next-to leading order QCD corrections with its experimentally measured value. Coefficients of the boundary localised terms have also been constrained. 95 % C.L. lower limit on inverse of radius of compactification ($R^{-1}$) can be as large as 670 GeV for some choice of the value of coefficients of boundary localised terms.
In a scenario in which fourth generation fermions exist, we study effects of new physics on the differential decay width, forward-backward asymmetry $A_{text{FB}}$ and integrated branching ratio for $Bto X_s ell^+ ell^-$ decay with $(ell=e,mu)$. Prediction of the new physics on the mentioned quantities essentially differs from the Standard Model results, in certain regions of the parameter space, enhancement of new physics on the above mentioned physical quantities can yield values as large as two times of the SM predictions, whence present limits of experimental measurements of branching ratio is spanned, contraints of the new physics can be extracted. For the fourth generation CKM factor $V_{t^prime b}^ast V_{t^prime s}$ we use $pm 10^{-2}$ and $pm 10^{-3}$ ranges, take into consideration the possibility of a complex phase where it may bring sizable contributions, obtained no significant dependency on the imaginary part of the new CKM factor. For the above mentioned quantities with a new family, deviations from the SM are promising, can be used as a probe of new physics.
With the first data being recorded at Belle II, we are at the brink of a new era in quark flavour physics. The many exciting new opportunities for Belle~II include a full angular analysis of inclusive ${bar B to X_{s} , ell^+ell^-}$ which has the potential to reveal new physics, in particular by its interplay with the exclusive $b to s ell^+ell^-$ counterparts studied extensively at LHCb. In this paper, we present fully updated Standard Model predictions for all angular observables necessary for this endeavour. These predictions are tailored to Belle II and include an elaborate study of the treatment of collinear photons which become crucial when aiming for the highest precision. In addition, we present a phenomenological study of the potential for Belle II to reveal possible new physics in the inclusive decay channel, both in an independent manner and in combination with exclusive modes.
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.
Inspired by the recent experimental results which show deviations from the standard model (SM) predictions of $brightarrow s ell^+ell^-$ transitions, we study the $R$-parity violating minimal supersymmetric standard model (RPV-MSSM) extended by the inverse seesaw mechanisms. The trilinear $R$-parity violating terms together with the chiral mixings of sneutrinos induce the loop contributions to the $brightarrow s ell^+ell^-$ anomaly. We study the parameter space of the single-parameter scenario $C^{rm NP}_{9,mu}=-C^{rm NP}_{10,mu}=C_{rm V}$ and the double-parameter scenario $(C_{rm V},C_{rm U})$ respectively, constrained by other experimental data such as $B_s-bar{B}_s$ mixing, $Brightarrow X_s gamma$ decay, the lepton flavour violating decays, etc.. Both the single-parameter scenario and double-parameter scenario can resolve the long existed muon anomalous magnetic moment problem as well.
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