Gad Eilam

Supersymmetry-induced flavor-changing neutral-current top-quark processes at the CERN Large Hadron Collider

We systematically calculate various flavor-changing neutral-current top-quark processes induced by supersymmetry at the Large Hadron Collider, which include five decay modes and six production channels. To reveal the characteristics of these processes, we first compare the dependence of the rates for these channels on the relevant supersymmetric parameters, then we scan the whole parameter space to find their maximal rates, including all the direct and indirect current experimental constraints on the scharm-stop flavor mixings. We find that, under all these constraints, only a few channels, through cg->t at parton-level and t->ch, may be observable at the Large Hadron Collider.

Top-quark rare decay t→ch in R-parity-violating SUSY

The flavor-changing top-quark decay t --> ch, where h is the lightest CP-even Higgs boson in the minimal supersymmetric standard model, is examined in the R-parity-violating supersymmetric model. Within the existing bounds on the relevant R-parity-violating couplings, the branching fraction for t --> ch can be as large as about 10(-5) in some part of the parameter space

On the rate asymmetries in charged B-decays

Abstract We recalculate the rate asymmetries in rare B-decays on the quark level to order α s 2 , taking into account all gg intermediate states. In contrast to previous investigations, we find the total asymmetries to lie below 1%, except for b → d +( d d , s s ) where it is 4%. The asymmetry of differential rates reaches 3% in b → su u for large momentum transfer. The complete calculation is outlined and the infrared problems are analyzed. We comment on the decay B s →gg.

Scalar flavor changing neutral currents and rare top quark decays in a two Higgs doublet model 'for the top quark'

In the so called two Higgs doublet model for the top-quark (T2HDM), first suggested by Das and Kao, the top quark receives a special status, which endows it with a naturally large mass, and also potentially gives rise to large flavor changing neutral currents (FCNC) only in the up-quark sector. In this paper we calculate the branching ratio (BR) for the rare decays t → ch and h → t̄c (h is a neutral Higgs) in the T2HDM, at tree level and at 1-loop when it exceeds the tree-level. We compare our results to predictions from other versions of 2HDM’s and find that the scalar FCNC in the T2HDM can play a significant role in these decays. In particular, the 1-loop mediated decays can be significantly enhanced in the T2HDM compared to the 2HDM of types I and II, in some instances reaching BR ∼ 10−4 which is within the detectable level at the LHC.

Radiative Dileptonic Decays of B Mesons

Abstract We investigate the radiative dileptonic decays B s ( B d ) → γl + l − within the standard model. Using the constituent quark model, the branching ratios turn out to be around 5 × 10 −9 for B s → γμ + μ − and around 6 × 10 −10 for B d → γμ + μ − , with slightly larger values for B s ( B d ) → γe + e − . The differential rate as a function of the dilepton invariant mass is given. The possibility of using these processes to determine the decay constants of B s or B d is discussed.

Majorana neutrinos and lepton-number-violating signals in top-quark and W-boson rare decays

Abstract We discuss rare lepton-number-violating top-quark and W -boson four-body decays to final states containing a same-charge lepton pair, of the same or of different flavors: t → b W − l i + l j + and W + → J J ¯ ′ l i + l j + , where i ≠ j or i = j and J J ¯ ′ stands for two light jets originating from a u ¯ d or a c ¯ s pair. These Δ L = 2 decays are forbidden in the Standard Model and may be mediated by exchanges of Majorana neutrinos. We adopt a model independent approach for the Majorana neutrinos mixing pattern and calculate the branching ratios (BR) for these decays. We find, for example, that for O ( 1 ) mixings between heavy and light Majorana neutrinos (not likely but not ruled out) and if at least one of the heavy Majorana neutrinos has a mass of ≲ 100 GeV , then the BRs for these decays are: BR ( t → b l i + l j + W − ) ∼ 10 −4 and BR ( W + → l i + l j + J J ¯ ′ ) ∼ 10 −7 if m N ∼ 100 GeV and BR ( t → b l i + l j + J J ¯ ′ ) ∼ BR ( W + → l i + l j + J J ¯ ′ ) ∼ 0.01 if m N ≲ 50 GeV . Taking into account the present limits on the neutrino mixing parameters, we obtain more realistic values for these BRs: BR ( t → b l i + l j + W − ) ∼ 10 −6 and BR ( W + → l i + l j + J J ¯ ′ ) ∼ 10 −10 for m N ∼ 100 GeV and BR ( t → b l i + l j + J J ¯ ′ ) ∼ BR ( W + → l i + l j + J J ¯ ′ ) ∼ 10 −6 for m N ≲ 50 GeV .

Large CP asymmetries in B+/---> eta c( chi c0) pi +/- from the eta c( chi c0) width.

We study {ital CP} asymmetries in {ital B}{sup {plus_minus}}{r_arrow}{ital h}{pi}{sup {plus_minus}} decays, where the hadronic states {ital h}={rho}{rho}, {ital K{bar K}}{pi}, {pi}{sup +}{pi}{sup {minus}}{ital K}{sup +}{ital K}{sup {minus}}, etc., and {ital h}={pi}{sup +}{pi}{sup {minus}}, {ital K}{sup +}{ital K}{sup {minus}}, 2({pi}{sup +}{pi}{sup {minus}}), etc., are taken on the resonances {eta}{sub {ital c}} and {chi}{sub {ital c}0}, respectively. The relatively large {eta}{sub {ital c}} and {chi}{sub {ital c}0} decay widths, of about 10--15 MeV, provide the necessary absorptive phase in the interference between the resonance (going through {ital b}{r_arrow}{ital c{bar c}d}) and the background (through {ital b}{r_arrow}{ital u{bar u}d}) contributions to the amplitude. Large asymmetries of order 10% or more are likely in some modes.We study CP asymmetries in

Nonresonant Cabibbo suppressed decay B+/---> pi + pi - pi +/- and signal for CP violation.

B^{\pm}\to h\pi^{\pm}

Four generations and the decay K→πνν

decays, where the hadronic states

Charged Higgs boson effects in the production and decay of a heavy Majorana neutrino at the CERN LHC

h=\rho\rho, K\Kbar\pi