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A model-independent expression for the Dalitz plot of semileptonic decays of neutral kaons, K0l3, including radiative corrections to order (α/π)(q/M1), where q is the momentum transfer and M1 is the mass of the kaon, is presented. The model dependence of radiative corrections is kept in a general form within this approximation, which is suitable for model-independent experimental analyses. Expressions for bremsstrahlung radiative corrections are presented in two forms: one with the triple integral over the kinematical variables of the photon ready to be performed numerically and the other one in a fully analytical form. The final result is restricted to the so-called three-body region of the Dalitz plot and it is not compromised to fixing the values of the form factors at predetermined values. [ABSTRACT FROM AUTHOR]

We have shown that it is possible to formulate the consistent and probability-preserving description of the CP-symmetry-violating evolution of a system of decaying particles. This has been done within the framework of quantum mechanics of open systems. This approach allows the description of both the exponential decay and flavor oscillations. We have solved explicitly the Kossakowski-Lindblad master equation for a system of particles with violated CP symmetry and found the evolution of any observable bilinear in creation and annihilation operators. The choice of a concrete observable can be done by the proper choice of initial conditions for the system of differential equations. We have calculated the evolution as well as mean values of the observables most interesting from the physical point of view, and we have found their lowest order difference with the CP-preserved values. [ABSTRACT FROM AUTHOR]

We study the dependence on the charm quark mass of the leading-order low-energy constants of the ΔS = 1 effective Hamiltonian, with the aim of elucidating the role of the charm mass scale in the &#916I = 1/2 rule for K → ππ decay. To that purpose, finite-volume chiral perturbation theory predictions are matched to QCD simulations, performed in the quenched approximation with overlap fermions and mu = md = ms. Light quark masses range between a few MeV up to around one third of the physical strange mass, while charm masses range between mu and a few hundred MeV. Novel variance reduction techniques are used to obtain a signal for penguin contractions in correlation functions involving four-fermion operators. The important role played by the subtractions required to construct renormalized amplitudes for mc # mu is discussed in detail. We find evidence that the moderate enhancement of the ΔI= 1/2 amplitude previously found in the GIM limit mc = mu increases only slightly as mc abandons the light quark regime. Hints of a stronger enhancement for even higher values of mc are also found, but their confirmation requires a better understanding of the subtraction terms. [ABSTRACT FROM AUTHOR]

We present results for matrix elements of ΔS = 2 four-fermion operators arising generically in models of new physics. These are needed to constrain such models using the measured values of eK and ΔMK. We use lattice QCD with 2+1 flavors of improved staggered fermions on lattices generated by the MILC Collaboration. We extrapolate to the continuum from three lattice spacings ranging down to a ~ 0.045 fm. Total errors are ~5%-6%, arising primarily from our use of one-loop matching between lattice and continuum operators. For two of the matrix elements, our results disagree significantly from those obtained using different fermion discretizations. [ABSTRACT FROM AUTHOR]

The four-body contribution of the model-independent radiative corrections to the Dalitz plot of the semileptonic decays of neutral kaons are computed to order (α/π)(q/M1), where q is the momentum transfer and M1 is the kaon mass. The final result is presented in two forms. The first one is given in terms of the triple integration of the bremsstrahlung photon ready to be performed numerically; the second one is a fully analytical expression. This paper is organized to make it accessible and reliable in the analysis of the Dalitz plot of precision experiments involving kaons and is not compromised to fixing the form factors at predetermined values. As a byproduct, gathering together three- and four-body contributions of radiative corrections yields, through a least-squares fit to the measured kaon decay rates, the value fK0πâ?'+|Vus|=0.2168(3). [ABSTRACT FROM AUTHOR]