In this paper, we study the anisotropy of cosmic acceleration the using Pantheon sample, which includes 1048 spectroscopically confirmed Type Ia supernovae (SNe Ia) covering the redshift range 0.01 < z < 2.3. In hemisphere comparison method, we find the dipole direction is (l = 37 ± 40 • , b = 33 ± 16 • ) with the maximum anisotropy level of δ = 0.136 +0.009 −0.005 . From the dipole fitting method, we find that the magnitude of anisotropy is A = (3.7 +2.5 −3.7 ) × 10 −4 , and the direction of the dipole (l = 329 •+101 • −28 • , b = 37 •+52 • −21 • ) in the galactic coordinate system. The result is weakly dependent on redshift from the redshift tomography analysis. The anisotropy is small and the isotropic cosmological model is an excellent approximation.

We present a mechanism of momentum relaxation in higher derivative gravity by adding linear scalar fields to the Gauss-Bonnet theory. We analytically computed all of the DC thermoelectric conductivities in this theory by adopting the method given by Donos and Gauntlett in [arXiv:1406.4742]. The results show that the DC electric conductivity is not a monotonic function of the effective impurity parameter β: in the small β limit, the DC conductivity is dominated by the coherent phase, while for larger β, pair creation contribution to the conductivity becomes dominant, signaling an incoherent phase. In addition, the DC heat conductivity is found independent of the Gauss-Bonnet coupling constant.

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Recent studies indicated that an anisotropic cosmic expansion may exist. In this paper, we use three data sets of type Ia supernovae (SNe Ia) to probe the isotropy of cosmic acceleration. For the Union2.1 data set, the direction and magnitude of the dipole are (l = 309., and A = (4.4 ± 5.0) × 10 −4 for dipole fitting and δ = 0.56, l = 141 • , b = −11 • for hemisphere comparison. For the JLA data set, no significant dipolar or quadrupolar deviation is found. We find previous works using (l, b, A) directly as fitting parameters may get improper results. We also explore the effects of anisotropic distributions of coordinates and redshifts on the results using Monte-Carlo simulations. We find that the anisotropic distribution of coordinates can cause dipole directions and make dipole magnitude larger. Anisotropic distribution of redshifts is found to have no significant effect on dipole fitting results.

Many astrophysics data show that our universe has a critical energy density, and 73% of it is dark energy, which drives the accelerating expansion of the universe. We consider the holographic dark energy in induced gravity by taking the Hubble scale, particle horizon and event horizon as the infrared cutoff. We find that only the event horizon can give accelerating expansion of our universe.