118822877
Cosmological CPT violating effect on CMB polarization
A dark energy scalar (or a function of the Ricci scalar) coupled with the derivative to the matter fields will violate the CPT symmetry during the expansion of the Universe. This type of cosmological CPT violation helps to generate the baryon number asymmetry and gives rise to the rotation of the photon polarization which can be measured in the astrophysical and cosmological observations, especially the experiments of the cosmic microwave background radiation. In this paper, we derive the rotation angle in a fully general relativistic way and present the rotation formulas used for the cosmic microwave background data analysis. Our formulas include the corrections from the spatial fluctuations of the scalar field. We also estimate the magnitude of these corrections in a class of dynamical dark energy models for quintessential baryo/leptogenesis.
118693182
The high energy neutrino nuisance at a medium baseline reactor experiment
10 years from now medium baseline reactor experiments will attempt to determine the neutrino mass hierarchy from quantities associated to the Fourier transformed neutrino spectra. Recently Qian et al. have claimed that this goal may be impeded by the strong dependence of these quantities on the reactor neutrino flux and on slight variations of vertical bar Delta M-32(2)vertical bar. We demonstrate that this effect results from a spurious dependence of the quantities on the very high energy (8+ MeV) tail of the reactor neutrino spectrum. This dependence is spurious because the high energy tail depends upon decays of exotic isotopes and is insensitive to the mass hierarchy. An energy-dependent weight in the Fourier transform eliminates this spurious dependence without decreasing the chance of correctly determining the hierarchy. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
119071739
Gravitational leptogenesis and neutrino mass limit
Recently Davoudiasl et al. (hep-ph/0403019) have introduced a new type of interaction between the Ricci scalar R and the baryon current ${J}^{\ensuremath{\mu}},$ ${\ensuremath{\partial}}_{\ensuremath{\mu}}{\mathrm{RJ}}^{\ensuremath{\mu}}$ and proposed a mechanism for baryogenesis, the gravitational baryogenesis. Generally, however, ${\ensuremath{\partial}}_{\ensuremath{\mu}}R$ vanishes in the radiation-dominated era. In this paper we consider a generalized form of their interaction ${\ensuremath{\partial}}_{\ensuremath{\mu}}{f(R)J}^{\ensuremath{\mu}}$ and study again the possibility of gravitational baryo(lepto)genesis. Taking $f(R)\ensuremath{\sim}\mathrm{ln}R,$ we will show that ${\ensuremath{\partial}}_{\ensuremath{\mu}}f(R)\ensuremath{\sim}{\ensuremath{\partial}}_{\ensuremath{\mu}}R/R$ does not vanish and the required baryon number asymmetry can be naturally generated in the early universe.
119354521
Inflation in string inspired cosmology and suppression of CMB low multipoles
We construct a string-inspired nonsingular cosmological scenario in which an inflaton field is driven up the potential before the graceful exit by employing a low-energy string effective action with an orbifold compactification. This sets up an initial condition for the inflaton to lead to a sufficient number of e-foldings and to generate a nearly scale-invariant primordial density perturbation during slow-roll inflation. Our scenario provides an interesting possibility to explain a suppressed power spectrum at low multipoles due to the presence of the modulus-driven phase prior to slow-roll inflation and thus can leave a strong imprint of extra dimensions in observed CMB anisotropies.
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.
14959007
Gravity in a model of multi-branes alternated between Minkowski and AdS spacetime in the fifth dimension
We construct in this Letter a multi-brane model with Minkowski and AdS spacetime alternated in the fifth dimension and study the gravity on the brane of our universe. We will show that in this model there are both the graviton-like resonant state which generates the "quasi-localized gravity" and the resonant states of the massive KK mode. This model gives rise to gravity which deviates from the Newton gravitational potential at small and large scale which, however can be shown to be consistent with the observations in the absence of fine-tuning of the model parameters. (C) 2002 Elsevier Science B.V. All rights reserved.
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.
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.
18008677
Results from the ARGO-YBJ test experiment
Abstract An RPC carpet covering ∼ 104 m2 (ARGO-YBJ experiment) will be installed in the YangBaJing Laboratory (Tibet, P.R. China) at an altitude of 4300 m a.s.l.. A test-module of ∼ 50 m2 has been put in operation in this laboratory and about 106 air shower events have been collected. The carpet capability of reconstructing the shower features is presented.
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.
122356247
Automatic analysis of the emulsion chamber using the image scanner applied to the Tibet hybrid experiment
A new method of emulsion chamber analysis by using an image scanner is developed in order to process a large number of X-ray films used in the Tibet hybrid experiment which is carried out to observe primary proton spectrum in the PeV region. The experimental procedure in this method consists of multiple steps of processing the image of the X-ray films, i.e. the detection of cascade showers induced by high-energy γ-rays, the noise reduction, the spatial reconstruction of γ-families and their energy determination. The quality of the results obtained by the new method is compared with that obtained by the current manual method or Monte Carlo simulations. It is shown that sufficiently high quality of the emulsion chamber analysis is realized by the automatic method both in energy and geometrical resolution.