17209312
THE EFFECT OF 4D EFFECTIVE COSMOLOGICAL CONSTANT ON THE STABILITY OF RANDALL–SUNDRUM SCENARIO
We study the Randall-Sundrum model with a small 4D effective cosmological constant on the brane, and drive a corrected radion potential following the Goldberger-Wise mechanism. We then discuss the effect of the 4D effective cosmological constant on the stability of the brane-system, and find that to quintessence determined by updated observation, the proper distance between the two branes required to solve the hierarchy problem can exist. However, during inflation, whether we can get a reasonable hierarchy scale is still uncertain.
119362091
Adiabatic gravitational perturbation during reheating
We study the possibilities of parametric amplification of the gravitational perturbation during reheating in single-held inflation models. Our result shows that there is no additional growth of the super-horizon modes beyond the usual predictions.
119108700
Cosmological CPT-violation, baryo/leptogenesis and CMB polarization
In this Letter we study the cosmological CPT-violation and its implications in baryo/leptogenesis and CMB polarization. We propose specifically a variant of the models of gravitational leptogenesis. By performing a global analysis with the Markov Chain Monte Carlo (MCMC) method, we find the current CMB polarization observations from the three-year WMAP (WMAP3) and the 2003 flight of BOOMERANG (B03) data provide a weak evidence for our model. However to verify and especially exclude this type of mechanism for baryo/leptogenesis with cosmological CPT-violation, the future measurements on CMB polarization from PLANCK and CMBpol are necessary.
118341482
Cosmic Ray Positrons from Cosmic Strings
We study the spectrum of cosmic ray positrons produced by a scaling distribution of non-superconducting cosmic strings. In this scenario, the positrons are produced from the jets which form from the cosmic string cusp annihilation process. The spectral shape is a robust feature of our scenario, and is in good agreement with the results from the recent PAMELA and ATIC experiments. In particular, the model predicts a sharp upper cutoff in the spectrum, and a flux which rises as the upper cutoff is approached. The energy at which the flux peaks is determined by the initial jet energy. The amplitude of the flux can be adjusted by changing the cosmic string tension and also depends on the cusp annihilation efficiency.
14998446
The FCNC top-squark decay as a probe of squark mixing
In supersymmetry (SUSY) the flavor mixing between top-squark (stop) and charm-squark (scharm) induces the flavor-changing neutral-current (FCNC) stop decay t̃1 → cχ̃1. Searching for this decay serves as a probe of soft SUSY breaking parameters. Focusing on the stop pair production followed by the FCNC decay of one stop and the charge-current decay of the other stop, we investigate the potential of detecting this FCNC stop decay at the Fermilab Tevatron, the CERN Large Hadron Collider (LHC) and the next-generation ee linear collider (LC). We find that this decay may not be accessible at the Tevatron, but could be observable at the LHC and the LC with high sensitivity for some part of parameter space. 14.80.Ly, 11.30.Hv Typeset using REVTEX
117037888
Global fitting analysis on cosmological models after BICEP2
Recently, BICEP2 collaboration has released their results on the measurements of the CMB polarizations. In the framework of the $\Lambda$CDM with a power law form of the scalar primordial power spectrum, this new measurement on the B-mode puts a tight constraint on tensor/scalar ratio $r=0.2^{+0.07}_{-0.05}~(1\sigma)$, which however is in tension with the Planck limit, $r<0.11$ (95% C.L.). In this paper, we consider various extensions of the $\Lambda$CDM model by introducing extra cosmological parameters such as the equation state of dark energy $w$, the curvature of the universe $\Omega_k$, the running of the scalar power spectrum index $\alpha_s$, the sum of the neutrino mass $\Sigma m_{\nu}$, the effective number of neutrinos $N_{eff}$, the tensor power spectrum index $n_{t}$, then perform the global fit to the BICEP2, Planck and also the SN and BAO data. Our results show the cosmological parameters $\alpha_s$ and $n_t$ are highly and directly correlated with the tensor/scalar ratio $r$. However indirectly the parameters $\Omega_k$ and $N_{eff}$ are also correlated with $r$. We will in this paper give the numerical values on the parameters introduced and show explicitly how the tension between the BICEP2 and Planck is effectively alleviated by the inclusion of the parameters $\Omega_k$, $\alpha_s$, $N_{eff}$ and $n_{t}$ separately.
118454051
Investigation of excited states in $^{18}$Ne via resonant elastic scattering of $^{17}$F+p and its astrophysical implication in the stellar reaction of $^{14}$O($\alpha$,$p$)$^{17}$F
Properties of proton resonances in $^{18}$Ne have been investigated efficiently by utilizing a technique of proton resonant elastic scattering with a $^{17}$F radioactive ion (RI) beam and a thick proton target. A 4.22~MeV/nucleon $^{17}$F RI beam was produced via a projectile-fragmentation reaction, and subsequently separated by a Radioactive Ion Beam Line in Lanzhou ({\tt RIBLL}). Energy spectra of the recoiled protons were measured by two sets of $\Delta$E-E silicon telescope at center-of-mass scattering angles of $\theta_{c.m.}$$\approx$175${^\circ}$$\pm$5${^\circ}$, $\theta_{c.m.}$$\approx$152${^\circ}$$\pm$8${^\circ}$, respectively. Several proton resonances in $^{18}$Ne were observed, and their resonant parameters have been determined by an $R$-matrix analysis of the differential cross sections in combination with the previous results. The resonant parameters are related to the reaction-rate calculation of the stellar $^{14}$O($\alpha$,$p$)$^{17}$F reaction, which was thought to be the breakout reaction from the hot CNO cycles into the $rp$-process in x-ray bursters. Here, $J^\pi$=(3$^-$, 2$^-$) are tentatively assigned to the 6.15-MeV state which was thought the key 1$^-$ state previously. In addition, a doublet structure at 7.05 MeV are tentatively identified, and its contribution to the resonant reaction rate of $^{14}$O($\alpha$,$p$)$^{17}$F could be enhanced by at least factors of about 4$\sim$6 in comparison with the previous estimation involving only a singlet. The present calculated resonant rates are much larger than those previous values, and it may imply that this breakout reaction could play a crucial role under x-ray bursters conditions.
117747714
Study on multifractal structure of the distribution fluctuation of secondary particles in the core region of EAS
The differences of space distributions and time profiles between the gamma-ray and proton induced shower particles are studied using Monte Carlo simulation data. The multifractal analysis is performed with the G-moment method for the distribution fluctuation of secondary particles near the core of showers induced by gamma-rays and protons. From the spectrum functions of gamma and proton events, it is seen that this method can be adopted as a basis for the gamma/proton separation. It is shown that the separation of gamma and proton can be achieved with a good efficiency in the energy region of 1-10TeV.
121510906
Results from the ARGO-YBJ test experiment
Abstract A resistive plate counters (RPCs) carpet of ∼50 m 2 has been put in operation in the Yangbajing Laboratory (Tibet, P.R. China) at 4300 m a.s.l., in order to study the RPCs performance at high altitude and the detector capability of imaging the EAS disc. This test has been performed in view of an enlarged use of RPCs for the ARGO-YBJ experiment. This experiment will be devoted to a wide range of fundamental issues in cosmic rays and astroparticle physics, including in particular γ-ray astronomy and γ-ray bursts physics at energies ⩾100 GeV. In this paper we present and discuss the procedures adopted to calibrate the detector and reconstruct the shower direction. Results concerning many shower features as the angular distribution, the density spectrum, the time profile of the shower front, are found well consistent with the expectation.
108549890
A fast Time‐of‐Flight detector also used as a tracker
We present a possible scheme for a fast Time‐of‐Flight detector which could also serve as part of the charged particle tracking system. The detector consists of scintillating fibers read out by newly developed microchannel plate photomultipliers. The performance of the detector in the experimental environment of the τ/charm factory was investigated by a detailed Monte Carlo simulation. The time and space resolutions of the detector are expected to be about 92 ps and 140 μm, respectively.
16277502
High altitude test of RPCs for the Argo YBJ experiment
Abstract A 50 m 2 RPC carpet was operated at the YanBaJin Cosmic Ray Laboratory (Tibet) located 4300 m a.s.l. The performance of RPCs in detecting Extensive Air Showers was studied. Efficiency and time-resolution measurements at the pressure and temperature conditions typical of high mountain laboratories, are reported.