Radiative and leptonic decays of the pseudoscalar charmonium state ηc\eta_c

The radiative and leptonic decays of $\eta_c\to \gamma\gamma$ and $\eta_c\to l^+l^-$ are studied. For $\eta_c\to \gamma\gamma$ decay, the second-order electromagnetic tree-level diagram gives the leading contribution. The decay rate of $\eta_c\to \gamma\gamma$ is calculated, the prediction is in good agreement with the experimental data. For \eta_c\to l^+\l^-, both the tree and loop diagrams are calculated. The analysis shows that the loop contribution dominates, the contribution of tree diagram with $Z^0$ intermediate state can only modifies the decay rate by less than 1%. The prediction of the branching ratios of $\eta_c\to e^+e^-$ and $\mu^+\mu^-$ are very tiny within the standard model. The smallness of these predictions within the standard model makes the leptonic decays of $\eta_c$ sensitive to physics beyond the standard model. Measurement of the leptonic decay may give information of new physics.Comment: 9 pages, 4 figures, RevTex, small change, version to appear in Phys. Rev.

Captures of Hot and Warm Sterile Antineutrino Dark Matter on EC-decaying Ho-163 Nuclei

Capturing low-energy electron antineutrinos on radioactive Ho-163 nuclei, which decay into Dy-163 via electron capture (EC), is a noteworthy opportunity to detect relic sterile antineutrinos. Such hypothetical particles are more or less implied by current experimental and cosmological data, and they might be a part of hot dark matter or a candidate for warm dark matter in the Universe. Using the isotope Ho-163 as a target and assuming reasonable active-sterile antineutrino mixing angles, we calculate the capture rate of relic electron antineutrinos against the corresponding EC-decay background in the presence of sterile antineutrinos at the sub-eV or keV mass scale. We show that the signature of hot or warm sterile antineutrino dark matter should in principle be observable, provided the target is big enough and the energy resolution is good enough.Comment: 16 pages, 6 figures, more discussions and references added. To appear in JCA

Defects in the medial entorhinal cortex and dentate gyrus in the mouse model of Sanfilippo syndrome type B.

Sanfilippo syndrome type B (MPS IIIB) is characterized by profound mental retardation in childhood, dementia and death in late adolescence; it is caused by deficiency of α-N-acetylglucosaminidase and resulting lysosomal storage of heparan sulfate. A mouse model, generated by homologous recombination of the Naglu gene, was used to study pathological changes in the brain. We found earlier that neurons in the medial entorhinal cortex (MEC) and the dentate gyrus showed a number of secondary defects, including the presence of hyperphosphorylated tau (Ptau) detected with antibodies raised against Ptau in Alzheimer disease brain. By further use of immunohistochemistry, we now show staining in neurons of the same area for beta amyloid, extending the resemblance to Alzheimer disease. Ptau inclusions in the dentate gyrus of MPS IIIB mice were reduced in number when the mice were administered LiCl, a specific inhibitor of Gsk3β. Additional proteins found elevated in MEC include proteins involved in autophagy and the heparan sulfate proteoglycans, glypicans 1 and 5, the latter closely related to the primary defect. The level of secondary accumulations was associated with elevation of glypican, as seen by comparing brains of mice at different ages or with different mucopolysaccharide storage diseases. The MEC of an MPS IIIA mouse had the same intense immunostaining for glypican 1 and other markers as MPS IIIB, while MEC of MPS I and MPS II mice had weak staining, and MEC of an MPS VI mouse had no staining at all for the same proteins. A considerable amount of glypican was found in MEC of MPS IIIB mice outside of lysosomes. We propose that it is the extralysosomal glypican that would be harmful to neurons, because its heparan sulfate branches could potentiate the formation of Ptau and beta amyloid aggregates, which would be toxic as well as difficult to degrade

D^0-D^0bar mixing in \Upsilon(1S) \to D^0 D^0bar decay at Super-B

\Dz-\Dzb mixing and significant CP violation in the charm system may indicate the signature of new physics. In this study, we suggest that the coherent \DzDzb events from the decay of \Upsilon(1S) \to \Dz \Dzb can be used to measure both mixing parameters and CP violation in charm decays. The neutral $D$ mesons from $\Upsilon(1S)$ decay are strongly boosted, so that it will offer the possibility to measure the proper-time interval, $\Delta t$, between the fully-reconstructed \Dz and \Dzb. Both coherent and time-dependent information can be used to extract \Dz-\Dzb mixing parameters. The sensitivity of the measurement should be improved at B factories or super-B.Comment: 6 pages, 1 figure, this is the last version to appear in Phys. Rev.

Interdecadal variability of winter precipitation in Southeast China

Interdecadal variability of observed winter precipitation in Southeast China (1961–2010) is characterized by the first empirical orthogonal function of the three-monthly Standardized Precipitation Index (SPI) subjected to a 9-year running mean. For interdecadal time scales the dominating spatial modes represent monopole features involving the Arctic Oscillation (AO) and the sea surface temperature (SST) anomalies. Dynamic composite analysis (based on NCEP/NCAR reanalyzes) reveals the following results: (1) Interdecadal SPI-variations show a trend from a dryer state in the 1970s via an increase during the 1980s towards stabilization on wetter conditions commencing with the 1990s. (2) Increasing wetness in Southeast China is attributed to an abnormal anticyclone over south Japan, with northward transport of warm and humid air from the tropical Pacific to South China. (3) In mid-to-high latitudes the weakened southward flow of polar airmasses induces low-level warming over Eurasia due to stronger AO by warmer zonal temperature advection. This indicates that AO is attributed to the Southeast China precipitation increase influenced by circulation anomalies over the mid-to-high latitudes. (4) The abnormal moisture transport along the southwestern boundary of the abnormal anticyclone over south Japan is related to anomalous south-easterlies modulated by the SST anomalies over Western Pacific Ocean; a positive (negative) SST anomaly will strengthen (weaken) warm and humid air transport, leading to abundant (reduced) precipitation in Southeast China. That is both AO and SST anomalies determine the nonlinear trend observed in winter precipitation over Southeast China