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Inflation coupled to a Gauss-Bonnet term

Peng-Xu Jiang; Jian-Wei Hu; Zong-Kuan GuoSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The newly released Planck CMB data place tight constraints on slow-roll inflationary models. Some of commonly discussed inflationary potentials are disfavored due mainly to the large tensor-to-scalar ratio. In this paper we show that these potentials may be in good agreement with the Planck data when the inflaton has a non-minimal coupling to the Gauss-Bonnet term. Moreover, such a coupling violates the consistency relation between the tensor spectral index and tensor-to-scalar ratio. If the tensor spectral index is allowed to vary freely, the Planck constraints on the tensor-to-scalar ratio are slightly improved. |

Constraints on Cosmic Distance Duality Relation from Cosmological Observations

Meng-Zhen Lv; Jun-Qing XiaSubjects: Physics >> Nuclear Physics

In this paper, we use the model dependent method to revisit the constraint on the well-known cosmic distance duality relation (CDDR). By using the latest SNIa samples, such as Union2.1, JLA and SNLS, we find that the SNIa data alone can not constrain the cosmic opacity parameter?ε, which denotes the deviation from the CDDR,?dL=dA(1+z)2+ε, very well. The constraining power on?ε?from the luminosity distance indicator provided by SNIa and GRB is hardly to be improved at present. When we include other cosmological observations, such as the measurements of Hubble parameter, the baryon acoustic oscillations and the distance information from cosmic microwave background, we obtain the tightest constraint on the cosmic opacity parameter?ε, namely the 68\% C.L. limit:?ε=0.023±0.018. Furthermore, we also consider the evolution of?ε?as a function of?z?using two methods, the parametrization and the principle component analysis, and do not find the evidence for the deviation from zero. Finally, we simulate the future SNIa and Hubble measurements and find the mock data could give very tight constraint on the cosmic opacity?ε?and verify the CDDR at high significance |

Testing Einstein's Equivalence Principle With Gravitational Waves

Xue-Feng Wu; He Gao; Jun-Jie Wei; Xi-Long Fan; Peter M?esz?aros; Bing Zhang; Zi-Gao Dai; Shuang-Nan Zhang; Zong-Hong ZhuSubjects: Physics >> Nuclear Physics

A conservative constraint on the Einstein Equivalence Principle (EEP) can be obtained under the assumption that the observed time delay between correlated particles from astronomical sources is dominated by the gravitational fields through which they move. Current limits on the EEP are mainly based on the observed time delays of photons with different energies, and it is highly desirable to develop more accurate tests involving different types of particles. The detection by the advanced LIGO/VIRGO systems of gravitational waves (GWs) will provide attractive candidates for constraining the EEP, which would further extend the tested particle species to the gravitons, with potentially higher accuracy. Considering the capabilities of the advanced LIGO/VIRGO network and the source direction uncertainty, we show that the joint detection of GWs and electromagnetic signals can potentially probe the EEP to an accuracy of 10?11, which is several orders of magnitude tighter than previous limits. |

Cosmographic analysis from distance indicator and dynamical redshift drift

Ming-Jian Zhang; Hong Li; Jun-Qing XiaSubjects: Physics >> Nuclear Physics

Cosmography is a model-independent de 1. To ensure data in the convergence radius, y=z/(1+z) redshift was defined. However, discussions about the usefulness of y-redshift and the leading cause of the issue are commonly absent. In the present paper, we study the cosmography in both z and y redshift using the supernova and mock redshift drift data. By introducing the bias-variance tradeoff, we reveal that the large bias square between cosmography and Union2.1 supernova data is the "chief culprit" of convergence issue. Moreover, expansion up to higher order and introduction of the y-redshift both are not effective to reconcile this contradiction. Minimizing risk, it suggests that Taylor expansion up to the second term is a better choice for available supernova data. Forecast from future supernova data and redshift drift shows that redshift drift can give much tighter constraints on the cosmography. We also investigate the effect of convergence issue on the deceleration parameter and dark energy. It inspires us that dynamical observations including redshift drift can give more detailed information on cosmic evolution |

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