Dark Energy and Fate of the Universe

We explore the ultimate fate of the Universe by using a divergence-free parametrization for dark energy $w(z)=w_0+w_a({\ln (2+z)\over 1+z}-\ln2)$. Unlike the CPL parametrization, this parametrization has well behaved, bounded behavior for both high redshifts and negative redshifts, and thus can genuinely cover many theoretical dark energy models. After constraining the parameter space of this parametrization by using the current cosmological observations, we find that, at the 95.4% confidence level, our Universe can still exist at least 16.7 Gyr before it ends in a big rip. Moreover, for the phantom energy dominated Universe, we find that a gravitationally bound system will be destroyed at a time $t \simeq P\sqrt{2|1+3w(-1)|}/[6\pi |1+w(-1)|]$, where $P$ is the period of a circular orbit around this system, before the big rip.Comment: 5 pages, 3 figures; typos corrected, publication version, Sci China-Phys Mech Astron, doi: 10.1007/s11433-012-4748-

Decadal changes of wind stress over the Southern Ocean associated with Antarctic ozone depletion

Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 20 (2007): 3395-3410, doi:10.1175/JCLI4195.1Using 40-yr ECMWF Re-Analysis (ERA-40) data and in situ observations, the positive trend of Southern Ocean surface wind stress during two recent decades is detected, and its close linkage with spring Antarctic ozone depletion is established. The spring Antarctic ozone depletion affects the Southern Hemisphere lower-stratospheric circulation in late spring/early summer. The positive feedback involves the strengthening and cooling of the polar vortex, the enhancement of meridional temperature gradients and the meridional and vertical potential vorticity gradients, the acceleration of the circumpolar westerlies, and the reduction of the upward wave flux. This feedback loop, together with the ozone-related photochemical interaction, leads to the upward tendency of lower-stratospheric zonal wind in austral summer. In addition, the stratosphere–troposphere coupling, facilitated by ozone-related dynamics and the Southern Annular Mode, cooperates to relay the zonal wind anomalies to the upper troposphere. The wave–mean flow interaction and the meridional circulation work together in the form of the Southern Annular Mode, which transfers anomalous wind signals downward to the surface, triggering a striking strengthening of surface wind stress over the Southern Ocean.This study was supported by MOST of China (Grant 2006CB403604) and Chinese Academy of Sciences (Grant KZSW2-YW-214) (for YXY and DXW) and W. Alan Clark Chair from Woods Hole Oceanographic Institution (for RXH)

MSSM Anatomy of the Polarization Puzzle in B --> phi K* Decays

We analyze the $B \to \phi K^{*}$ polarization puzzle in the Minimal Supersymmetric Standard Model (MSSM) including the neutral Higgs boson (NHB) contributions. To calculate the non-factorizable contributions to hadronic matrix elements of operators, we have used the QCD factorization framework to the $\alpha_s$ order. It is shown that the recent experimental results of the polarization fractions in $B\to \phi K^{*}$ decays, which are difficult to be explained in SM, could be explained in MSSM if there are flavor non-diagonal squark mass matrix elements of 2nd and 3rd generations, which also satisfy all relevant constraints from known experiments ($B\to X_s\gamma, B_s\to \mu^+\mu^-, B\to X_s \mu^+\mu^-, B\to X_s g, \Delta M_s$, etc.). We have shown in details that the experimental results can be accommodated with the flavor non-diagonal mass insertion of chirality RL, RL+LR, RR, or LL+ RR when the NHB contributions as well as $\mathcal{O}(\alpha_s)$ corrections of hadronic matrix elements of operators are included. However the branching ratios for the decay are smaller than the experimental measurements.Comment: 15 pages, 5 figures, minor revision and references adde

Horizontal eddy energy flux in the world oceans diagnosed from altimetry data

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 4 (2014): 5316, doi:10.1038/srep05316.During the propagation of coherent mesoscale eddies, they directly or indirectly induce many effects and interactions at different scales, implying eddies are actually serving as a kind of energy carrier or energy source for these eddy-related dynamic processes. To quantify this dynamically significant energy flow, the multi-year averaged horizontal eddy energy fluxes (EEFs) were estimated by using satellite altimetry data and a two-layer model based on hydrographic climatology. There is a strong net westward transport of eddy energy estimated at the mean value of ~13.3 GW north of 5°N and ~14.6 GW at the band 5°S ~ 44°S in the Southern Hemisphere. However, poleward of 44°S east-propagating eddies carry their energy eastward with an averaged net flux of ~3.2 GW. If confirmed, it would signify that geostrophic eddies not only contain the most of oceanic kinetic energy (KE), but also carry and spread a significant amount of energy with them.This study is supported by Grants XDA11010202, 2011CB403505, 2013CB430303; Projects 41306016, U1033002, 40976021 of NNSFC and LTOZZ1304

Connection between the decadal variability in the Southern Ocean circulation and the Southern Annular Mode

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 34 (2007): L16604, doi:10.1029/2007GL030526.Previous studies demonstrated the remarkable upward trend of the Southern Annular Mode (SAM) and Southern Ocean wind stress in association with anthropogenic forcing. An oceanic reanalysis data set is used to investigate the response of the circulation in the Southern Ocean to the decadal variability of SAM. Our results indicate the strengthening and the poleward shift of the northward Ekman velocity as well as the Ekman pumping rate, which led to a corresponding strengthening trend in the Deacon Cell. This strengthening, in turn, intensified the meridional density gradient and the tilting of the isopycnal surfaces. On the interannual time scale, the Antarctic Circumpolar Currents (ACC) transport exhibits a positive correlation with SAM index as seen separately in observations. However, there is no significant trend in the total transport of ACC. Possible reasons are discussed.This work was supported by the Chinese Academy of Sciences (Grant KZSW2-YW-214), the Natural Science Foundation of China (Grant 40640420557) and National Basic Research Program of China (Grant 2006CB403604) for X-Y. Yang and D. Wang, and by W. Alan Clark Chair from Woods Hole Oceanographic Institution for R.X. Huang

An update of the catalog of radial velocity standard stars from the APOGEE DR17

We present an updated catalog of 46,753 radial velocity (RV) standard stars selected from the APOGEE DR17. These stars cover the Northern and Southern Hemispheres almost evenly, with 62% being red giants and 38% being main-sequence stars. These RV standard stars are stable on a baseline longer than 200 days (54% longer than one year and 10% longer than five years) with a median stability better than 215 m s$^{-1}$. The average observation number of those stars are 5 and each observation is required to have spectral-to-noise-ratio (SNR) greater than 50 and RV measurement error smaller than 500 m s$^{-1}$. Based on the new APOGEE RV standard star catalog, we have checked the RV zero points (RVZPs) for current large-scale stellar spectroscopic surveys including RAVE, LAMOST, GALAH and Gaia. By carefully analysis, we estimate their mean RVZP to be $+0.149$ km s$^{-1}$, $+4.574$ km s$^{-1}$ (for LRS), $-0.031$ km s$^{-1}$ and $+0.014$ km s$^{-1}$, respectively, for the four surveys. In the RAVE, LAMOST (for MRS), GALAH and Gaia surveys, RVZP exhibits systematic trend with stellar parameters (mainly [Fe/H], $T_{\rm{eff}}$, log $g$, $G_{\rm{BP}}-G_{\rm{RP}}$ and $G_{\rm{RVS}}$). The corrections of those small but clear RVZPs are of vital importances for these massive spectroscopic surveys in various studies that require extremely high radial velocity accuracies.Comment: 10 pages, 7 figures, 2 tables, accepted by RAA; full table can be accessed from https://nadc.china-vo.org/res/r101244

Estimate of eddy energy generation/dissipation rate in the world ocean from altimetry data

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Ocean Dynamics 61 (2011): 525-541, doi:10.1007/s10236-011-0377-8.Assuming eddy kinetic energy is equally partitioned between the barotropic mode and the first baroclinic mode and using the weekly TOPEX/ERS merged data for the period of 1993~2007, the mean eddy kinetic energy and eddy available gravitational potential energy in the world oceans are estimated at 0.157 EJ and 0.224 EJ; the annual mean generation/dissipation rate of eddy kinetic energy and available gravitational potential energy in the world oceans is estimated at 0.203 TW. Scaling and data analysis indicate that eddy available gravitational potential energy and its generation/dissipation rate are larger than those of eddy kinetic energy. High rate of eddy energy generation/dissipation is primarily concentrated in eddy rich regions, such as the Antarctic Circumpolar Current and the western boundary current extensions. Outside of these regimes of intense current, the energy generation/dissipation rate is 2 to 4 orders of magnitude lower than the peak values; however, along the eastern boundaries and in the region where complicated topography and current interact the eddy energy generation/dissipation rate is several times larger than those in background.This study is supported by Grants KZCX1-YW-12-01, 40976010, 40776008