118515553
A Kaluza--Klein-like model of the gauge theory of gravity and its cosmological meaning
A new Kaluza--Klein-like (KK-like) model of the de Sitter gauge theory of gravity is constructed from the geometry related to the gauge-invariant expressions of the gravitational fields. The model reduces to general relativity with a cosmological constant Lambda when the spin tensor is equal to zero. Moreover, it is shown that among the R-2Lambda+betaS^{abc}S_{abc} models, where beta is a dimensionless parameter and S_{abc} denotes torsion, the KK-like model is the only one that may avert the big-bang singularity of the Robertson--Walker universe filled with a spin fluid.
118605165
$R+S^2$ theories of gravity without big-bang singularity
Abstract The R + S 2 theories of gravity, where S 2 denotes the quadratic torsion terms, are analyzed under three cases. In the first two cases, the matter fields are described by two different spin fluids which are not homogeneous and isotropic. In the third case, a homogeneous and isotropic torsion field is used. It is found that under all the three cases, the R + S 2 theories may avert the big-bang singularity of the Robertson–Walker universe, with three corresponding constraints on the parameters.
118553608
Monte Carlo simulation of HERD calorimeter
The High Energy cosmic-Radiation Detection (HERD) facility onboard China's Space Station is planned for operation starting around 2020 for about 10 years. It is designed as a next generation space facility focused on indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. The calorimeter plays an essential role in the main scientific objectives of HERD. A 3-D cubic calorimeter filled with high granularity crystals as active material is a very promising choice for the calorimeter. HERD is mainly composed of a 3-D calorimeter (CALO) surrounded by silicon trackers (TK) from all five sides except the bottom. CALO is made of 9261 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. Here the simulation results of the performance of CALO with GEANT4 and FLUKA are presented: 1) the total absorption CALO and its absorption depth for precise energy measurements (energy resolution: 1% for electrons and gammarays beyond 100 GeV, 20% for protons from 100 GeV to 1 PeV); 2) its granularity for particle identification (electron/proton separation power better than 10-5); 3) the homogenous geometry for detecting particles arriving from every unblocked direction for large effective geometrical factor (<3 m2sr for electron and diffuse gammarays, >2 m2sr for cosmic ray nuclei); 4) expected observational results such as gamma-ray line spectrum from dark matter annihilation and spectrum measurement of various cosmic ray chemical components.