Calculation of epsilon'/epsilon

I shortly review the present status of the theoretical calculations of epsilon'/epsilon and the comparison with the present experimental results. I discuss the role of higher order chiral corrections and in general of non-factorizable contributions for the explanation of the Delta I = 1/2 selection rule and direct CP violation in kaon decays. Still lacking reliable lattice calculations, analytic methods and phenomenological approaches are helpful in understanding correlations among theoretical effects and the experimental data. Substantial progress from lattice QCD is expected in the coming years.Comment: 10 pages, Invited talk at the 9th Int. Symposium on Heavy Flavour Physics, Pasadena, CA, 10-13 September 2001 Comments added on Table

Computational complexity of μ calculation

The structured singular value μ measures the robustness of uncertain systems. Numerous researchers over the last decade have worked on developing efficient methods for computing μ. This paper considers the complexity of calculating μ with general mixed real/complex uncertainty in the framework of combinatorial complexity theory. In particular, it is proved that the μ recognition problem with either pure real or mixed real/complex uncertainty is NP-hard. This strongly suggests that it is futile to pursue exact methods for calculating μ of general systems with pure real or mixed uncertainty for other than small problems

Symplectic Calculation of Lyapunov Exponents

The Lyapunov exponents of a chaotic system quantify the exponential divergence of initially nearby trajectories. For Hamiltonian systems the exponents are related to the eigenvalues of a symplectic matrix. We make use of this fact to develop a new method for the calculation of Lyapunov exponents of such systems. Our approach avoids the renormalization and reorthogonalization of usual techniques. It is also easily extendible to damped systems. We apply our method to two examples of physical interest: a model system that describes the beam halo in charged particle beams and the driven van der Pol oscillator.Comment: 10 pages, uuencoded PostScript (figures included), LA-UR-94-216

Full major-shell calculation for states that were degenerate in a single-j-shell calculation

A full fp calculation is performed for states which were degenerate in a single-j-shell calculation in which isospin-zero two-body matrix elements were set to zero energy. Most of the splitting in a complete shell calculation (but not all) comes from the T=0 part of the interaction.Comment: 5 pages, RevTeX4. Submitted to Physical Review

Entanglement Entropy: A Perturbative Calculation

We provide a framework for a perturbative evaluation of the reduced density matrix. The method is based on a path integral in the analytically continued spacetime. It suggests an alternative to the holographic and `standard' replica trick calculations of entanglement entropy. We implement this method within solvable field theory examples to evaluate leading order corrections induced by small perturbations in the geometry of the background and entangling surface. Our findings are in accord with Solodukhin's formula for the universal term of entanglement entropy for four dimensional CFTs.Comment: 28 pages, 3 appendices, 5 figure

Faster Calculation of Superquadric Shapes

Nonparametric methods of calculating points on the curve produce the recently introduced superquadric objects at great savings in time

Lattice calculation of κ\kappa meson

We study the $\kappa$ meson in 2+1 flavor QCD with sufficiently light $u/d$ quarks. Using numerical simulation we measure the point-to-point $\kappa$ correlators in the "Asqtad" improved staggered fermion formulation. We analyze those correlators using the rooted staggered chiral perturbation theory (rS$\chi$PT), particular attention is paid to the bubble contribution. After chiral extrapolation, we obtain the physical $\kappa$ mass with $828\pm97$ MeV, which is within the recent experimental value $800\sim900$MeV. These numerical simulations are carried out with MILC 2+1 flavor gauge configurations at lattice spacing $a \approx 0.12$ fm.Comment: Accepted in Chinese Physics