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Register a new userStudying the $brightarrow s ell^+ell^-$ Anomalies and $(g-2)_{mu}$ in RPV-MSSM Framework with Inverse Seesaw
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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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One of the fundamental predictions of the Standard Model is Lepton Flavour Universality. Any deviation from this prediction would indicate the existence of physics beyond the Standard Model. Recent LHCb measurements present a pattern of deviations from this prediction in rare B-meson decays. While not yet statistically significant (currently $2.2-2.6 sigma$), these measurements show an imbalance in the ratio of B-meson decays to a pair of muons in association with a Kaon and decays to a pair of electrons in association with a Kaon. If the measured deviations are indeed present in nature, new physics may mediate interactions involving a pair of same flavour leptons, a $b$- and an $s$-quark. We present the prospect for a search of new physics in this type of interactions at the LHC, in a process that involves an $s$-quark, and a final state with two leptons and a $b$-jet. The proposed search can improve the sensitivity to new physics in these processes by a factor of four compared to current searches with in the total dataset expected at the LHC.
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.
Ratios of branching fractions of semileptonic B decays, $(B to H mu mu)$ over $(B to H ee)$ with $H=K, K^*,X_s, K_0(1430), phi, ldots$ are sensitive probes of lepton universality. In the Standard Model, the underlying flavor changing neutral current process $brightarrow s ell ell$ is lepton flavor universal. However models with new flavor violating physics above the weak scale can give substantial non-universal contributions. The leading contributions from such new physics can be parametrized by effective dimension six operators involving left- or right-handed quarks. We show that in the double ratios $R_{X_s}/R_K$, $R_{K^*}/R_K$ and $R_phi/R_K$ the dependence on new physics coupling to left-handed quarks cancels out. Thus a measurement of any of these double ratios is a clean probe of flavor nonuniversal physics coupling to right-handed quarks. We also point out that the observables $R_{X_s}$, $R_{K^*}$, $R_{K_0(1430)}$ and $R_phi$ depend on the same combination of Wilson coefficients and therefore satisfy simple consistency relations.
We analyze the class of models with an extra $U(1)_X$ gauge symmetry that can account for the $b to s ell ell$ anomalies by modifying the Wilson coefficients $C_{9e}$ and $C_{9mu}$ from their standard model values. At the same time, these models generate appropriate quark mixing, and give rise to neutrino mixing via the Type-I seesaw mechanism. Apart from the gauge boson $Z$, these frugal models only have three right-handed neutrinos for the seesaw mechanism, an additional $SU(2)_L$ scalar doublet for quark mixing, and a SM-singlet scalar that breaks the $U(1)_X$ symmetry. This set-up identifies a class of leptonic symmetries, and necessitates non-zero but equal charges for the first two quark generations. If the quark mixing beyond the standard model were CKM-like, all these symmetries would be ruled out by the latest flavor constraints on Wilson coefficients and collider constraints on $Z$ parameters. However, we identify a single-parameter source of non-minimal flavor violation that allows a wider class of $U(1)_X$ symmetries to be compatible with all data. We show that the viable leptonic symmetries have to be of the form $L_e pm 3 L_mu - L_tau$ or $L_e - 3 L_mu + L_tau$, and determine the $(M_{Z^prime}, g_{Z^prime})$ parameter space that may be probed by the high-luminosity data at the LHC.
Recently the LHCb collaboration has confirmed the evidence for lepton flavour nonuniversality at the $3.1sigma$ level via an updated measurement of $R_K$. In this work we analyse this evidence within a model-independent approach. We make projections for future measurements which indicate that LHCb will be in the position to discover lepton nonuniversality with the Run 3 data in a single observable. We analyse other ratios based on our analysis of the present measurements of the ratios $R_{K^{(*)}}$ and analyse if they are able to differentiate between various new physics options within the effective field theory at present or in the near future. We also compare the present deviations in the ratios with NP indications in the angular observables of exclusive $b to s ellell$ transitions. Finally, we update our global analysis considering all $b to s ellell$ observables altogether, including a 20-parameter fit in connection of a Wilks test.
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