14,798 research outputs found
Age Problem in Lemaitre-Tolman-Bondi Void Models
As is well known, one can explain the current cosmic acceleration by
considering an inhomogeneous and/or anisotropic universe (which violates the
cosmological principle), without invoking dark energy or modified gravity. The
well-known one of this kind of models is the so-called
Lema\^{\i}tre-Tolman-Bondi (LTB) void model, in which the universe is
spherically symmetric and radially inhomogeneous, and we are living in a
locally underdense void centered nearby our location. In the present work, we
test various LTB void models with some old high redshift objects (OHROs).
Obviously, the universe cannot be younger than its constituents. We find that
an unusually large (characterizing the size of the void) is required to
accommodate these OHROs in LTB void models. There is a serious tension between
this unusually large and the much smaller inferred from other
observations (e.g. SNIa, CMB and so on). However, if we instead consider the
lowest limit 1.7\,Gyr for the quasar APM 08279+5255 at redshift , this
tension could be greatly alleviated.Comment: 17 pages, 9 figures, revtex4; v2: discussions added, Phys. Lett. B in
press; v3: published versio
Complexity growth rates for AdS black holes in massive gravity and gravity
The "complexity = action" duality states that the quantum complexity is equal
to the action of the stationary AdS black holes within the Wheeler-DeWitt patch
at late time approximation. We compute the action growth rates of the neutral
and charged black holes in massive gravity and the neutral, charged and
Kerr-Newman black holes in gravity to test this conjecture. Besides, we
investigate the effects of the massive graviton terms, higher derivative terms
and the topology of the black hole horizon on the complexity growth rate.Comment: 11 pages, no figur
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