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Constraining the Lorentz invariance violation from the continuous spectra of short gamma-ray bursts

Zhe Chang; Xin Li; Hai-Nan Lin; Yu Sang; Ping Wang; Sai WangSubjects: Physics >> Nuclear Physics

In quantum gravity, a foamy structure of space-time leads to Lorentz invariance violation (LIV). As the most energetic astrophysical processes in the Universe, gamma-ray bursts (GRBs) provide an effective way to probe quantum gravity effects. We use continuous spectra of 20 short GRBs detected by the Swift satellite to give a conservative lower limit of quantum gravity energy scale MQG. Due to the LIV effect, photons with different energy have different velocities. This will lead to the delayed arrival of high energy photons relative to the low energy ones. Based on the fact that the LIV-induced time delay can't be longer than the duration of a GRB, we present the most conservative estimation of the quantum gravity energy scales from 20 short GRBs. The most strict constraint,MQG>5.05* 1014 GeV, is from GRB 140622A. |

Testing the isotropy of the Universe by using the JLA compilation of type-Ia supernovae

Hai-Nan Lin; Sai Wang; Zhe Chang; Xin LiSubjects: Physics >> Nuclear Physics

We probe the possible anisotropy of the Universe by using the JLA compilation of type-Ia supernovae. We apply the Markov Chain Monte Carlo (MCMC) method to constrain the amplitude and direction of anisotropy in three cosmological models. For the dipole-modulated?ΛCDM model, the anisotropic amplitude is consistent with zero at?68%?C.L., and has an upper bound?AD<1.98×10?3?at?95%?C.L. Regardless of much larger uncertainty, we find the dipole direction of JLA is amazingly opposite to that of Union2. Similar results are found for the dipole-modulated?wCDM and CPL models. Thus, the Universe is still well consistent with the isotropy according to the JLA compilation. |

Anisotropic inflation in Finsler spacetime

Xin Li; Sai Wang; Zhe ChangSubjects: Physics >> Nuclear Physics

We suggest the universe is Finslerian in the stage of inflation. The Finslerian background spacetime breaks rotational symmetry and induces parity violation. The primordial power spectrum is given for quantum fluctuation of the inflation field. It depends not only on the magnitude of wavenumber but also on the preferred direction. We derive the gravitational field equations in the perturbed Finslerian background spacetime, and obtain a conserved quantity outside the Hubble horizon. The angular correlation coefficients are presented in our anisotropic inflation model. The parity violation feature of Finslerian background spacetime requires that the anisotropic effect only appears in angular correlation coefficients if?l′=l+1. The numerical results of the angular correlation coefficients are given to describe the anisotropic effect. |

Subjects: Physics >> Nuclear Physics

We propose a Finsler spacetime scenario of the anisotropic universe. The Finslerian universe requires both the fine-structure constant and accelerating cosmic expansion have dipole structure, and the directions of these two dipoles are the same. Our numerical results show that the dipole direction of SnIa Hubble diagram locates at?(l,b)=(314.6?±20.3?,?11.5?±12.1?)?with magnitude?B=(?3.60±1.66)×10?2. And the dipole direction of the fine-structure constant locates at?(l,b)=(333.2?±8.8?,?12.7?±6.3?)?with magnitude?B=(0.97±0.21)×10?5. The angular separation between the two dipole directions is about?18.2?. |

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