1303.6124 (Shuang-Nan Zhang)

Re-accelerating expansion of the universe revealed by supernovae Ia and {\it Planck} data    [PDF]

Shuang-Nan Zhang

The possibility that we are living in a fast expanding and underdensed local bubble has made many to debate if dark energy is needed to explain the apparent over-dimming of distant supernovae Ia (SNe Ia). Recently the {\it Planck} team has reported a lower value of Hubble constant and a larger matter density than known previously. Here we show that the lower Hubble constant is inconsistent with SNe Ia data, and the local bubble density is too low, unless it is also a global property of the universe at the present cosmic time. We suggest a new scenario that the universe expands at initially a low, then slightly higher, and finally much higher rate at present, corresponding to increasing Hubble constant with cosmic time. Therefore these data provide evidence for re-accelerating expansion of the universe, deviating from accelerating expansion described by the concordant cosmological model, but still not requiring preferred observers.

View original: http://arxiv.org/abs/1303.6124