10 research outputs found

    Probing signatures of bounce inflation with current observations

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    The aim of this paper is to probe the features of the bouncing cosmology with the current observational data. Basing on bounce inflation model, with high derivative term, we propose a general parametrization of primordial power spectrum which includes the typical bouncing parameters, such as bouncing time-scale, and energy scale. By applying Markov Chain Monto Carlo analysis with current data combination of Planck 2015, BAO and JLA, we report the posterior probability distributions of the parameters. We find that, bouncing models can well explain CMB observations, especially the deficit and oscillation on large scale in TT power spectrum.Comment: 17 pages, 8 figure

    Confronting Inflation Models with the Coming Observations on Primordial Gravitational Waves

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    The recent observations from CMB have imposed a very stringent upper-limit on the tensor/scalar ratio rr of inflation models, r<0.064r < 0.064, which indicates that the primordial gravitational waves (PGW), even though possible to be detected, should have a power spectrum of a tiny amplitude. However, current experiments on PGW is ambitious to detect such a signal by improving the accuracy to an even higher level. Whatever their results are, it will give us much information about the early Universe, not only from the astrophysical side but also from the theoretical side, such as model building for the early Universe. In this paper, we are interested in analyzing what kind of inflation models can be favored by future observations, starting with a kind of general action offered by the effective field theory (EFT) approach. We show a general form of rr that can be reduced to various models, and more importantly, we show how the accuracy of future observations can put constraints on model parameters by plotting the contours in their parameter spaces.Comment: 19 pages, 9 figures with title changed and contents improve

    Eliminating polarization leakage effect for neutral hydrogen intensity mapping with deep learning

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    The neutral hydrogen (HI) intensity mapping (IM) survey is regarded as a promising approach for cosmic large-scale structure (LSS) studies. A major issue for the HI IM survey is to remove the bright foreground contamination. A key to successfully remove the bright foreground is to well control or eliminate the instrumental effects. In this work, we consider the instrumental effect of polarization leakage and use the U-Net approach, a deep learning-based foreground removal technique, to eliminate the polarization leakage effect. The thermal noise is assumed to be a subdominant factor compared with the polarization leakage for future HI IM surveys and ignored in this analysis. In this method, the principal component analysis (PCA) foreground subtraction is used as a preprocessing step for the U-Net foreground subtraction. Our results show that the additional U-Net processing could either remove the foreground residual after the conservative PCA subtraction or compensate for the signal loss caused by the aggressive PCA preprocessing. Finally, we test the robustness of the U-Net foreground subtraction technique and show that it is still reliable in the case of existing constraint error on HI fluctuation amplitude.Comment: 13 pages, 13 figures; accepted for publication in MNRA

    Detecting Primordial Gravitational Waves: a forecast study on optimizing frequency distribution of next generation ground-based CMB telescope

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    Probing primordial gravitational waves is one of the core scientific objectives of the next generation CMB polarization experiment. Integrating more detector modules on the focal plane and performing high accurate observations are the main directions of the next generation CMB polarization telescope, like CMB S4. Also, multi-band observation is required by foreground analysis and reduction, as it is understood that foregrounds have become the main obstacles of CMB polarization measurements. However, ground observation is limited by the atmospheric window and can be usually carried out in one or two bands, like what BICEP or Keck array have done in the south pole. In this paper, we forecast the sensitivity of tensor-to-scalar ratio r that may be achieved by a multi-frequency CMB polarization experiment, basing on which to provide guidance for further expanding frequency bands and optimize the focal plane of a telescope. At the same time, the realization of having two frequency bands in one atmospheric window is discussed. With fixed number of detectors, the simulation results show that, in order to get a good limit, more frequency bands are needed. Better constraints can be obtained when it includes at least three bands, i.e., one CMB channel (95 GHz) + one dust channel (high frequency) and one synchrotron channel (low frequency). For example, 41 + 95 + 220 GHz, which is better than only focusing around the CMB band, like 85 + 105 + 150 GHz, and 95 + 135 + 155 GHz, and this frequency combination is even better than the combination of 41 + 95 + 150 + 220 GHz. As CMB S4 plans to consider two frequency bands in each atmospheric window, and along this way, we find that one CMB band and more bands in synchrotron and dust channels are helpful, for example, 2 bands in lower frequency, 30 + 41 GHz, 2 bands in higher frequency, 220 + 270 GHz, i.e. 30 + 41 + 95 + 220 + 270 GHz, can get better constraints, and in this case, more detectors are asked to be assigned in the CMB channel

    Search for the doubly charmed baryon Ξcc+\it{\Xi}_{cc}^{+} in the Ξc+ππ+\it{\Xi}_{c}^{+} \pi^{-} \pi^{+} final state

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    A search for the doubly charmed baryon Ξcc+\it{\Xi}_{cc}^{+} is performed in the Ξc+ππ+\it{\Xi}_{c}^{+} \pi^{-} \pi^{+} invariant-mass spectrum, where the Ξc+\it{\Xi}_{c}^{+} baryon is reconstructed in the pKπ+p K^{-} \pi^{+} final state. The study uses proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 13TeV\mathrm{\,Te\kern -0.1em V}, corresponding to a total integrated luminosity of 5.4fb1\,\mathrm{fb}^{-1}. No significant signal is observed in the invariant-mass range of 3.4-3.8GeV/c2\mathrm{\,Ge\kern -0.1em V}/c^2. Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the Ξcc++(Ξc+pKπ+)π+\it{\Xi}_{cc}^{++} \rightarrow (\it{\Xi}_{c}^{+} \rightarrow p K^{-} \pi^{+}) \pi^{+} decay for different Ξcc+\it{\Xi}_{cc}^{+} mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25GeV/c\mathrm{\,Ge\kern -0.1em V}/c. The results from this search are combined with a previously published search for the Ξcc+Λc+Kπ+\it{\Xi}_{cc}^{+} \rightarrow \it{\Lambda}_{c}^{+} K^{-} \pi^{+} decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620MeV/c2\mathrm{\,Me\kern -0.1em V}/c^2, including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5-3.7GeV/c2\mathrm{\,Ge\kern -0.1em V}/c^2 mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties

    Search for the doubly charmed baryon Ξcc+ {\varXi}_{cc}^{+} in the Ξc+ππ+ {\varXi}_c^{+}{\pi}^{-}{\pi}^{+} final state

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    International audienceA search for the doubly charmed baryon Ξcc+ {\varXi}_{cc}^{+} is performed in the Ξc+ππ+ {\varXi}_c^{+}{\pi}^{-}{\pi}^{+} invariant-mass spectrum, where the Ξc+ {\varXi}_c^{+} baryon is reconstructed in the pK^{−}π+^{+} final state. The study uses proton-proton collision data collected with the LHCb detector at a centre- of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 5.4 fb1^{−1}. No significant signal is observed in the invariant-mass range of 3.4–3.8 GeV/c2^{2}. Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the Ξcc++ {\varXi}_{cc}^{++} → (Ξc+ {\varXi}_c^{+} → pK^{−}π+^{+}+^{+} decay for different Ξcc+ {\varXi}_{cc}^{+} mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25 GeV/c. The results from this search are combined with a previously published search for the Ξcc+ {\varXi}_{cc}^{+} Λc+ {\varLambda}_c^{+} K^{−}π+^{+} decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620 MeV/c2^{2}, including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5–3.7 GeV/c2^{2} mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.[graphic not available: see fulltext
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