Σ-Λ Relative Parity and the Σ0→Λ0+γ+γ Decay

It is shown that the π0-pole term predicts a large difference by nearly two to three orders of magnitude for the branching ratio of the Σ0→Λ0+2γ decay mode, depending upon the value of the Σ-Λ relative parity. It is further argued that this difference is not masked, even if we include other diagrams. It is thus suggested that a study of the branching ratio of the Σ0→Λ0+2γ decay may serve to determine the Σ-Λ relative parity

The Chao Phraya delta : historical development, dynamics and challenges of Thailand's rice bowl

In Thailand, since the first epidemics in 1958, there has been a global upward trend in incidence of Dengue Hemorrhagic Fever (DHF), an acute and severe form of dengue virus infection, which remains a major public health concern. The dengue is due to an arbovirus mainly transmitted by #Aedes aegypti$, a mosquito living close to human communities. The intensity of the transmission (i.e. number of cases and speed of the spread of the disease) is dependant on the number of vectors, the serotype of the virus, the herd immunity and the environment. In the Central Plain of Thailand despite an apparent very homogenous environment (altitude, climate, type of agriculture) the incidence of DHF exhibits strong variations at the province and sub-province levels. A Geographical Information System using epidemiological data, as well as information about the land-use, demography, geography, climate has been built to identify indicators likely to help to describe areas and periods at risk for dengue transmission. A particular approach is focusing on the structure of the urban environment, the main field for dengue transmission. Different degrees and types of urbanisation appear to be linked to different intensities of dengue transmission. The main output of this study will be a method to describe areas at risk for high level of transmission and to forecast epidemic periods allowing a quick launch of dengue control activities. This study developed in the Central Plain of Thailand will be extended to other parts of the country and the same methods may be applied to similar environments in other countries where the dengue is endemic. (Résumé d'auteur

Asymmetry Parameter of Λ Decay and the Intermediate Boson of Weak Interactions

The magnitude of the pion asymmetry parameter α- of the Λ → p + π- decay has been determinted [1] to be greater than or equal to (0.73 ± 0.14). The sign of this parameter, however, is rather hard to find. The results of Boldt et al. [2] anf the preliminary results of Birge and Fowler [3] indicated a positive sign for α-. Recently, however, Birge and Fowler [4] have reported a negative sign for α-, contrary to their own preliminary [3] results. In this Letter we wish to point out that the negative sign of α-, provides a favorable argument for the conjecture that the V-A four-fermion interaction may be mediated by a vector boson

Non-factorizable contributions in hadronic weak decays of charm mesons

Two body decays of charm mesons are studied by describing their amplitude in terms of a sum of factorizable and non-factorizable ones. The former is estimated by using a naive factorization while the latter is calculated by using a hard pseudo-scalar-meson approximation. The hard pseudo-scalar-meson amplitude is given by a sum of the so-called equal-time commutator term and surface term which contains all possible pole contributions of various mesons, not only the ordinary $\{q\bar q\}$ but also four-quark $\{qq\bar q\bar q\}$, hybrid $\{q\bar qg\}$ and glue-balls. Naively factorized amplitudes for the spectator decays which lead to too big rates can interfere destructively with exotic meson pole amplitudes and the total amplitudes can reproduce their observed rates. The non-factorizable contributions can supply sufficiently large contributions to the color suppressed decays which are strongly suppressed in the naive factorization. A possible solution to the long standing puzzle that the ratio of decay rates for $D^0\to K^+K^-$ to $D^0\to \pi^+\pi^-$ is around 2.5 is given by different contributions of exotic meson poles.Comment: 22 pages, RevTe

Towards resolution of the scalar meson nonet enigma

By the application of a linear mass spectrum to a composite system of both the pseudoscalar and scalar meson nonets, we find three mass relations for the masses of the scalar states which suggest the $q\bar{q}$ assignment for the scalar meson nonet: $a_0(1320),$ $K_0^\ast (1430),$ $f_0(1500),$ $f_0'(980).$Comment: 16 pages, LaTe

Newly observed two-body decays of B mesons in a hybrid perspective

In consistency with the b --> c type of (quasi) two body decays, recently observed two body decays of B mesons are studied in a hybrid perspective in which their amplitude is given by a sum of factorizable and non-factorizable ones, and a role of the latter in these decays are discussed.Comment: 7 page

Radiative Kaon Decays K±→π±π0γK^\pm\to\pi^\pm\pi^0\gamma and Direct CP Violation

It is stressed that a measurement of the electric dipole amplitude for direct photon emission in \kpm decays through its interference with inner bremsstrahlung is important for differentiating among various models. Effects of amplitude CP violation in the radiative decays of the charged kaon are analyzed in the Standard Model in conjunction with the large $N_c$ approach. We point out that gluon and electromagnetic penguin contributions to the CP-violating asymmetry between the Dalitz plots of \kpm are of equal weight. The magnitude of CP asymmetry ranges from $2\times 10^{-6}$ to $1\times 10^{-5}$ when the photon energy in the kaon rest frame varies from 50 MeV to 170 MeV.Comment: Latex, 11 pages, ITP-SB-93-36, IP-ASTP-22-9

The Mixed Vector Current Correlator <0|T(V^3_\mu V^8_\nu )|0> To Two Loops in Chiral Perturbation Theory

The isospin-breaking correlator of the product of flavor octet vector currents, $V^3_\mu$ and $V^8_\nu$, $\Pi^{38}_{\mu\nu}(q^2)$ is computed to next-to-next- to-leading (two-loop) order in Chiral Perturbation Theory. Large corrections to both the magnitude and $q^2$-dependence of the one-loop result are found, and the reasons for the slow convergence of the chiral series for the correlator given. The two-loop expression involves a single ${\cal O}(q^6)$ counterterm, present also in the two-loop expressions for $\Pi^{33}_{\mu\nu}(q^2)$ and $\Pi^{88}_{\mu\nu}(q^2)$, which counterterm contributes a constant to the scalar correlator $\Pi^{38}(q^2)$. The feasibility of extracting the value of this counterterm from other sources is discussed. Analysis of the slope of the correlator with respect to $q^2$ using QCD sum rules is shown to suggest that, even to two-loop order, the chiral series for the correlator may not yet be well-converged.Comment: 32 pages, uses REVTEX and epsfig.sty with 7 uuencoded figures. Entire manuscript available as a ps file at http://www.physics.adelaide.edu.au/theory/home.html Also available via anonymous ftp at ftp://adelphi.adelaide.edu.au/pub/theory/ADP-95-27.T181.p

η→π0γγ\eta \to \pi^0 \gamma \gamma decay within unitarized chiral perturbation theory

We improve the calculations of the $\eta \to \pi^0 \gamma \gamma$ decay within the context of meson chiral lagrangians. We use a chiral unitary approach for the meson-meson interaction, thus generating the $a_0(980)$ resonance and fixing the longstanding sign ambiguity on its contribution. This also allows us to calculate the loops with one vector meson exchange, thus removing a former source of uncertainty. In addition we ensure the consistency of the approach with other processes. First, by using vector meson dominance couplings normalized to agree with radiative vector meson decays. And, second, by checking the consistency of the calculations with the related $\gamma \gamma \to \pi^0 \eta$ reaction. We find an $\eta \to \pi^0 \gamma \gamma$ decay width of $0.47\pm 0.10$ eV, in clear disagreement with published data but in remarkable agreement with the most recent measurement.Comment: 15 pages, 10 figures, published versio

Study of 3-prong Hadronic τ\tau Decays with Charged Kaons

Using a sample of 4.7/fb integrated luminosity accumulated with the CLEO-II detector at the Cornell Electron Storage Ring (CESR), we have measured the branching fractions of the tau lepton into $K^- h^+ \pi^- \nu_\tau$ and $K^- K^+ \pi^- \nu_\tau$ relative to $h^- h^+ h^- \nu_\tau; K^- h^+ \pi^- \pi^0\nu_\tau$ and $K^- K^+ \pi^- \pi^0\nu_\tau$ relative to $h^- h^+ h^- \pi^0 \nu_\tau$. The relative branching fractions are: (5.16+-0.20+-0.50)*$10^{-2}$, (1.52+-0.14+-0.29)*$10^{-2}$, (2.54+-0.44+-0.39)*$10^{-2}$ and $<0.0154$ at 95% C.L., respectively. Coupled with additional experimental information, we use our results to extract information on the structure of three-prong tau decays to charged kaons.Comment: 16 pages postscript file also available through http://w4.lns.cornell.edu/public/CLN