
Abbas, G., Celis, A., Li, X. Q., Lu, J., & Pich, A. (2015). Flavourchanging top decays in the aligned twoHiggsdoublet model. J. High Energy Phys., 06(6), 005–26pp.
Abstract: We perform a complete oneloop computation of the twobody flavourchanging top decays t > ch and t > cV (V = gamma, Z), within the aligned twoHiggsdoublet model. We evaluate the impact of the model parameters on the associated branching ratios, taking into account constraints from flavour data and measurements of the Higgs properties. Assuming that the 125 GeV Higgs corresponds to the lightest CPeven scalar of the CPconserving aligned twoHiggsdoublet model, we find that the rates for such flavourchanging top decays lie below the expected sensitivity of the future highluminosity phase of the LHC. Measurements of the Higgs signal strength in the diphoton channel are found to play an important role in limiting the size of the t > ch decay rate when the charged scalar of the model is light.



ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). A search for flavour changing neutral currents in topquark decays in pp collision data collected with the ATLAS detector at root s=7 TeV. J. High Energy Phys., 09(9), 139–37pp.
Abstract: A search for flavour changing neutral current (FCNC) processes in topquark decays by the ATLAS Collaboration is presented. Data collected from pp collisions at the LHC at a centreofmass energy of root s = 7 TeV during 2011, corresponding to an integrated luminosity of 2.1 fb(1), were used. A search was performed for topquark pairproduction events, with one top quark decaying through the t > Zq FCNC (q = u, c) channel, and the other through the Standard Model dominant mode t > Wb. Only the decays of the Z boson to charged leptons and leptonic Wboson decays were considered as signal. Consequently, the finalstate topology is characterised by the presence of three isolated charged leptons, at least two jets and missing transverse momentum from the undetected neutrino. No evidence for an FCNC signal was found. An upper limit on the t > Zq branching ratio of BR(t > Zq) < 0.73% is set at the 95% confidence level.



ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). Search for the decay Bs(0) > mu(+)mu() with the ATLAS detector. Phys. Lett. B, 713(45), 387–407.
Abstract: A blind analysis searching for the decay Bs(0) > mu(+)mu() has been performed using protonproton collisions at a centreofmass energy of 7 TeV recorded with the ATLAS detector at the LHC. With an integrated luminosity of 2.4 fb(1) no excess of events over the background expectation is found and an upper limit is set on the branching fraction BR(Bs(0) > mu(+)mu()) <2.2(1.9) x 10(8) at 95% (90%) confidence level.



Botella, F. J., Branco, G. C., & Nebot, M. (2012). The hunt for New Physics in the Flavour Sector with up vectorlike quarks. J. High Energy Phys., 12(12), 040–34pp.
Abstract: We analyse the possible presence of New Physics (NP) in the Flavour Sector and evaluate its potential for solving the tension between the experimental values of A(J/Psi KS) and Br(B+ > tau(+)v(tau)) with respect to the Standard Model (SM) expectations. Updated model independent analyses, where NP contributions are allowed in Bd(0) – (B) over bar (0)(d) and Bs(0) – (B) over bar (0)(s) transitions, suggest the need of New Physics in the bd sector. A detailed analysis of recent Flavour data is then presented in the framework of a simple extension of the SM, where a Q = 2/3 vectorlike isosinglet quark is added to the spectrum of the SM. Special emphasis is given to the implications of this model for correlations among various measurable quantities. We include constraints from all the relevant quark flavour sectors and give precise predictions for selected rare processes. We find important deviations from the SM in observables in the bd sector like the semileptonic asymmetry A(SL)(d), Bd(0) > mu(+)mu() and A(SL)(s) – A(SL)(d). Other potential places where NP can show up include A(J/Psi Phi), gamma, KL(0) > pi(0)v (v) over bar, t > Zq and D0 > mu(+)mu() among others. The experimental data favours in this model the existence of an up vectorlike quark with a mass below 600(1000) GeV at 1(2) sigma.



Chang, Q., Li, X. Q., & Yang, Y. D. (2011). The effects of a family nonuniversal Z ' boson on B > pi pi decays. Int. J. Mod. Phys. A, 26(78), 1273–1294.
Abstract: Motivated by the measured large branching ratio of (B) over bar (0) > pi(0)pi(0) (the socalled pi pi puzzle), we investigate the effects of a family nonuniversal Z' model on the treedominated B > pi pi decays. We find that the Z' coupling parameter zeta(LR)(d) similar to 0.05 with a nontrivial new weak phase phi(L)(d) similar to 50 degrees, which is relevant to the Z' contributions to the QCD penguin sector Delta C5, is needed to reconcile the observed discrepancy. Combined with the recent fitting results from B > pi K, pi K* and rho K decays, the Z' parameter spaces are severely reduced but still not excluded entirely, implying that both the “pi pi” and “pi K” puzzles could be accommodated simultaneously within such a family nonuniversal Z' model.



Hirsch, M., Joaquim, F. R., & Vicente, A. (2012). Constrained SUSY seesaws with a 125 GeV Higgs. J. High Energy Phys., 11(11), 105–33pp.
Abstract: Motivated by the ATLAS and CMS discovery of a Higgslike boson with a mass around 125 GeV, and by the need of explaining neutrino masses, we analyse the three canonical SUSY versions of the seesaw mechanism (type I, II and III) with CMSSM boundary conditions. In type II and III cases, SUSY particles are lighter than in the CMSSM (or the constrained type I seesaw), for the same set of input parameters at the universality scale. Thus, to explain m(h0) similar or equal to 125 GeV at low energies, one is forced into regions of parameter space with very large values of m(0), M1/2 or A(0). We compare the squark and gluino masses allowed by the ATLAS and CMS ranges for m(h0) (extracted from the 20112012 data), and discuss the possibility of distinguishing seesaw models in view of future results on SUSY searches. In particular, we briefly comment on the discovery potential of LHC upgrades, for squark/gluino mass ranges required by present Higgs mass constraints. A discrimination between different seesaw models cannot rely on the Higgs mass data alone, therefore we also take into account the MEG upper limit on BR(mu > e gamma) and show that, in some cases, this may help to restrict the SUSY parameter space, as well as to set complementary limits on the seesaw scale.



Hirsch, M., Kernreiter, T., Romao, J. C., & del Moral, A. V. (2010). Minimal supersymmetric inverse seesaw: neutrino masses, lepton flavour violation and LHC phenomenology. J. High Energy Phys., 01(1), 103–21pp.
Abstract: We study neutrino masses in the framework of the supersymmetric inverse seesaw model. Different from the nonsupersymmetric version a minimal realization with just one pair of singlets is sufficient to explain all neutrino data. We compute the neutrino mass matrix up to 1loop order and show how neutrino data can be described in terms of the model parameters. We then calculate rates for lepton flavour violating (LFV) processes, such as μ> e gamma and chargino decays to singlet scalar neutrinos. The latter decays are potentially observable at the LHC and show a characteristic decay pattern dictated by the same parameters which generate the observed large neutrino angles.



Li, X. Q., Lu, J., & Pich, A. (2014). Bs,d(0) > l(+)l() decays in the aligned twoHiggsdoublet model. J. High Energy Phys., 06(6), 022–39pp.
Abstract: The rare decays Bs,d(0) > l(+)l() are analyzed within the general framework of the aligned twoHiggs doublet model. We present a complete oneloop calculation of the relevant shortdistance Wilson coefficients, giving a detailed technical summary of our results and comparing them with previous calculations performed in particular limits or approximations. We investigate the impact of various model parameters on the branching ratios and study the phenomenological constraints imposed by present data.



Li, X. Q., Yang, Y. D., & Yuan, X. B. (2012). Anomalous tqZ coupling effects in rare B and Kmeson decays. J. High Energy Phys., 03(3), 018–22pp.
Abstract: As a topfactory, the LHC is performing a direct study of topquark anomalous FCNC couplings, which are, however, correlated closely with the rare B and Kmeson decays. In this paper, we study the effects of anomalous tqZ (with q = u, c) couplings in the rare decays Bs,Bd > mu(+)mu(), B > Xs nu(nu) over bar, B > K(*)nu(nu) over bar, K+ > pi(+)nu(nu) over bar, and KL > pi(0)nu(nu) over bar. With the uptodate experimental bounds on the branching ratios of these channels, constraints on the lefthanded anomalous couplings Xct(L), and Xut(L) are derived, respectively. With these lowenergy constraints taken into account, we find that, for real couplings Xct(L) and Xut(L), the indirect upper bounds on B(t > qZ) are much lower than that from the D0 collaboration, but are still compatible with the 5 sigma discovery potential of ATLAS with an integrated luminosity of 10 fb(1). With refined measurements to be available at the LHCb, the future superB factories, the NA62 at CERN, and the KOTO at JPARC, closer correlations between the t > qZ and the rare B and Kmeson decays are expected in the near future, which will be helpful for the searches of thu e topquark FCNC decays at the LHC.

