Alejandro Szynkman

New-physics contributions to the forward-backward asymmetry in B → K * μ + μ −

We study the forward-backward asymmetry (AFB) and the differential branching ratio (DBR) in B → K*μ+μ− in the presence of new physics (NP) with different Lorentz structures. We consider NP contributions from vector-axial vector (VA), scalarpseudoscalar (SP), and tensor (T) operators, as well as their combinations. We calculate the effects of these new Lorentz structures in the low-q2 and high-q2 regions, and explain their features through analytic approximations. We find two mechanisms that can give a significant deviation from the standard-model predictions, in the direction indicated by the recent measurement of AFB by the Belle experiment. They involve the addition of the following NP operators: (i) VA, or (ii) a combination of SP and T (slightly better than T alone). These two mechanisms can be distinguished through measurements of DBR in B → K*μ+μ− and AFB in B → Kμ+μ−.

Electroweak precision constraints on the Lee-Wick standard model

We perform an analysis of the electroweak precision observables in the Lee-Wick Standard Model. The most stringent restrictions come from the S and T parameters that receive important tree level and one loop contributions. In general the model predicts a large positive S and a negative T. To reproduce the electroweak data, if all the Lee-Wick masses are of the same order, the Lee-Wick scale is of order 5 TeV. We show that it is possible to find some regions in the parameter space with a fermionic state as light as 2.4-3.5 TeV, at the price of rising all the other masses to be larger than 5-8 TeV. To obtain a light Higgs with such heavy resonances a fine-tuning of order a few per cent, at least, is needed. We also propose a simple extension of the model including a fourth generation of Standard Model fermions with their Lee-Wick partners. We show that in this case it is possible to pass the electroweak constraints with Lee-Wick fermionic masses of order 0.4-1.5 TeV and Lee-Wick gauge masses of order 3 TeV.

CP violation in tau ---> K pi pi nu(tau)

We consider CP-violating effects in tau->K pi pi nu_tau, assuming that a charged Higgs boson provides a new amplitude that can interfere with the usual Standard Model amplitude. We consider four CP-odd observables -- the regular rate asymmetry, two modified rate asymmetries and a triple-product asymmetry. The regular rate asymmetry is expected to be small because it requires the interference of the new physics amplitude with the standard model amplitude containing the hadronic scalar form factor. The other CP asymmetries may be more promising in terms of their new physics reach. Numerical estimates indicate that the maximum obtainable values for the modified and triple-product asymmetries are on the order of a percent.

DIRECT TEST OF TIME REVERSAL INVARIANCE VIOLATION IN B-MESONS

In this letter we reinterpret and reanalyze the available data of the B-meson factories showing the existence of direct experimental evidence of time reversal invariance violation in B-mesons. This reinterpretation consists of using the available observables to define a new observable which, in a model-independent way and without assuming CPT invariance, compares a transition between a B0 and a here-defined Bα-state, with its time reversed transition. The observable then offers a direct way to probe time reversal invariance and it is therefore independent of any conclusion obtained from current experimental information on CP violation and CPT invariance. As far as we are concerned, this is the first direct evidence of time reversal invariance violation in B-mesons and also the first one obtained from decaying particles whose mean lifetime difference is negligible.

Testing explanations of the B → ϕ K * polarization puzzle

B{yields}{phi}K* (b{yields}s) is three separate decays, one for each polarization of the final-state vector mesons (one longitudinal, two transverse). It is observed that the fraction of transverse decays, f{sub T}, and the fraction of longitudinal decays, f{sub L}, are roughly equal: f{sub T}/f{sub L}{approx_equal}1, in opposition to the naive expectation that f{sub T}<<f{sub L}. If one requires a single explanation of all polarization puzzles, two possibilities remain within the standard model: penguin annihilation and rescattering. In this paper we examine the predictions of these two explanations for f{sub T}/f{sub L} in b{yields}d decays. In B{yields}{rho}{rho} decays, only B{sub d}{sup 0}{yields}{rho}{sup 0}{rho}{sup 0} can possibly exhibit a large f{sub T}/f{sub L}. In B decays related by U-spin, we find two promising possibilities: (i) B{sup +}{yields}K*{sup 0}{rho}{sup +} (b{yields}s) and B{sup +}{yields}K*{sup 0}K*{sup +} (b{yields}d) and (ii) B{sub s}{yields}K*{sup 0}K*{sup 0} (b{yields}s) and B{sub d}{sup 0}{yields}K*{sup 0}K*{sup 0} (b{yields}d). The measurement of f{sub T}/f{sub L} in these pairs of decays will allow us to test penguin annihilation and rescattering. Finally, it is possible to distinguish penguin annihilation from rescattering by performing a time-dependent angular analysis of B{sub d}{sup 0}{yields}K*{sup 0}K*{sup 0}.

CPviolation in supersymmetric theories:t˜2→t˜1τ−τ+

Supersymmetric (SUSY) theories include many new parameters, some of which are CP-violating. Assuming that SUSY is found at a future high-energy collider, we examine the decay stop2 -> stop1 tau- tau+ with an eye to obtaining information about the new CP phases. We show that there are two CP-violating asymmetries which can be large in some regions of the SUSY parameter space. These involve measuring one or both of the tau spins. These asymmetries are particularly sensitive to phi_At, the phase of the trilinear coupling A_t.

Study of Polarization in B ! V T Decays

In this paper, we examine

U-SPIN TESTS OF THE STANDARD MODEL AND NEW PHYSICS

B\ensuremath{\rightarrow}VT

Vertex displacements for acausal particles: testing the Lee-Wick standard model at the LHC

decays (

Final-state polarization in B s 0 decays

V