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Register a new userT-odd asymmetries in radiative top-quark decays
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We study the angular distribution of the charged lepton in the top-quark decay into a bottom quark and a W boson which subsequently decays into ell u_{ell}, when a hard gluon is radiated off. The absorptive part of the t to bWg decay amplitudes, which gives rise to T-odd asymmetries in the distribution, is calculated at the one-loop level in perturbative QCD. The asymmetries at a few percent level are predicted, which may be observable at future colliders.
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We revisit the effect of CP violating anomalous top-quark couplings in $tbar{t}$ production and decay. We consider $tbar{t}$ production through gluon fusion (and light $q{bar q}$ annihilation) followed by top-quark decay into $bW$ or $bell u$. We find explicit analytic expressions for all the triple products generated by the anomalous couplings that fully incorporate all spin correlations. Our results serve as a starting point for numerical simulations for the LHC.
We propose CP asymmetries based on triple product correlations in the decays sbottom_m -> top chargino_j with subsequent decays of top and chargino_j. For the subsequent chargino_j decay into a leptonic final state l^- u neutralino_1 we consider the three possible decay chains chargino_j -> l^- sneutrino -> l^- u neutralino_1, chargino_j -> slepton_n u -> l^- u neutralino_1 and chargino_j -> W^- neutralino_1 -> l^- u neutralino_1. We consider two classes of CP asymmetries. In the first class it must be possible to distinguish between different leptonic chargino_j decay chains, whereas in the second class this is not necessary. We consider also the 2-body decay chargino_j -> W^- neutralino_1, and we assume that the momentum of the W boson can be measured. Our framework is the minimal supersymmetric standard model with complex parameters. The proposed CP asymmetries are non-vanishing due to non-zero phases for the parameters mu and/or A_b. We present numerical results and estimate the observability of these CP asymmetries.
Top quark decays are of particular interest as a mean to test the standard model (SM) predictions, both for dominant (t -> b + W) and rare decays (t -> q + W, cV, cVV, c phi^{0}, bWZ). As the latter are highly suppressed, they become an excellent window to probe the predictions of thories beyond the SM. In particular, we evaluate the corrections from new physics to the CKM-suppressed SM top quark decay t -> q + W (q = d, s), both within the an effective model with right-handed currents and the MSSM. We also discuss the perspectives to probe those predictions at the ILC.
We identify the $T$-odd structure functions that appear in the description of polarized top quark decays in the sequential decay $t(uparrow) to X_b+W^+(to ell^+ + u_ell)$ (two structure functions) and the quasi-three-body decay $t(uparrow) to X_b+ ell^+ + u_ell$ (one structure function). A convenient measure of the magnitude of the $T$-odd structure functions is the contribution of the imaginary part Im $g_R$ of the right-chiral tensor coupling $g_R$ to the $T$-odd structure functions which we work out. Contrary to the case of QCD the NLO electroweak corrections to polarized top quark decays admit of absorptive one-loop vertex contributions. We analytically calculate the imaginary parts of the relevant four electroweak one-loop triangle vertex diagrams and determine their contributions to the $T$-odd helicity structure functions that appear in the description of polarized top quark decays.
We propose a novel strategy to test lepton flavor universality (LFU) in top decays, applicable to top pair production at colliders. Our proposal exploits information in kinematic distributions and mostly hinges on data-driven techniques, thus having very little dependence on our theoretical understanding of top pair production. Based on simplified models accommodating recent hints of LFU violation in charged current B meson decays, we show that existing LHC measurements already provide non-trivial information on the flavor structure and the mass scale of such new physics (NP). We also project that the measurements of LFU in top decays at the high-luminosity LHC could reach a precision at the percent level or below, improving the sensitivity to LFU violating NP in the top sector by more than an order of magnitude compared to existing approaches.
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