23,699 research outputs found
Is it possible to Measure the Weak Phase of a Penguin Diagram?
The penguin amplitude receives contributions from internal ,
and -quarks. We show that it is impossible to measure the weak phase of any
of these penguin contributions without theoretical input. However, a single
assumption involving the hadronic parameters makes it possible to obtain the
weak phase and test for the presence of new physics in the
flavour-changing neutral current.Comment: 4 pages, latex, no figures, talk given by R. Sinha at the 3rd
International Conference on B Physics and CP Violation, Taipei, Taiwan,
December 3-7, 1999, to appear in the Proceeding
Parallel String Sample Sort
We discuss how string sorting algorithms can be parallelized on modern
multi-core shared memory machines. As a synthesis of the best sequential string
sorting algorithms and successful parallel sorting algorithms for atomic
objects, we propose string sample sort. The algorithm makes effective use of
the memory hierarchy, uses additional word level parallelism, and largely
avoids branch mispredictions. Additionally, we parallelize variants of multikey
quicksort and radix sort that are also useful in certain situations.Comment: 34 pages, 7 figures and 12 table
Angular Distribution and CP Asymmetries in the Decays B->K^-pi^+e^-e^+ and B->pi^-pi^+e^-e^+
The short-distance Hamiltonian describing b->s(d)e^-e^+ in the standard model
is used to obtain the decay spectrum of \bar{B}->K^-pi^+e^-e^+ and
\bar{B}->pi^-pi^+e^-e^+, assuming the Kpi and pipi systems to be the decay
products of K^* and rho respectively. Specific features calculated are (i)
angular distribution of K^- (or pi^-) in the K^-pi^+ (or pi^-pi^+)
centre-of-mass (c.m.) frame; (ii) angular distribution of e^- in the e^-e^+
c.m. frame; and (iii) the correlation between the meson and lepton planes. We
also derive CP-violating observables obtained by combining the above decays
with the conjugate processes B->K^+pi^-e^-e^+ and B->pi^-pi^+e^-e^+.Comment: 19 pages, REVTeX, no figures. Equations (2.19a), (2.19b), (5.5)-(5.7)
have been corrected; all results remain unchanged. These changes will appear
in an Erratum submitted to Phys. Rev.
Scattering in a varying mass PT symmetric double heterojunction
We observe that the reflection and transmission coefficients of a particle
within a double, PT symmetric heterojunction with spatially varying mass, show
interesting features, depending on the degree of non Hermiticity, although
there is no spontaneous breakdown of PT symmetry. The potential profile in the
intermediate layer is considered such that it has a non vanishing imaginary
part near the heterojunctions. Exact analytical solutions for the wave function
are obtained, and the reflection and transmission coefficients are plotted as a
function of energy, for both left as well as right incidence. As expected, the
spatial dependence on mass changes the nature of the scattering solutions
within the heterojunctions, and the space-time (PT) symmetry is responsible for
the left-right asymmetry in the reflection and transmission coefficients.
However, the non vanishing imaginary component of the potential near the
heterojunctions gives new and interesting results.Comment: 7 pages, 8 figure
Robust Emergent Activity in Dynamical Networks
We study the evolution of a random weighted network with complex nonlinear
dynamics at each node, whose activity may cease as a result of interactions
with other nodes. Starting from a knowledge of the micro-level behaviour at
each node, we develop a macroscopic description of the system in terms of the
statistical features of the subnetwork of active nodes. We find the asymptotic
characteristics of this subnetwork to be remarkably robust: the size of the
active set is independent of the total number of nodes in the network, and the
average degree of the active nodes is independent of both the network size and
its connectivity. These results suggest that very different networks evolve to
active subnetworks with the same characteristic features. This has strong
implications for dynamical networks observed in the natural world, notably the
existence of a characteristic range of links per species across ecological
systems.Comment: 4 pages, 5 figure
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