منابع مشابه
Cosmological acceleration from structure formation
We discuss the Buchert equations, which describe the average expansion of an inhomogeneous dust universe. In the limit of small perturbations, they reduce to the Friedmann-Robertson-Walker equations. However, when the universe is very inhomogeneous, the behaviour can be qualitatively different from the FRW case. In particular, the average expansion rate can accelerate even though the local expa...
متن کاملA Measure of Cosmological Acceleration
We propose quantifying the quantum gravitational back-reaction on inflation with an invariant measure of the local acceleration rather than the expansion rate. Our observable is suitable for models in which there is no scalar inflaton to provide a preferred velocity field with which to define the expansion. As an example, we use stochastic techniques to evaluate the local acceleration at one lo...
متن کاملCosmological Acceleration from Energy Influx
We discuss the cosmological evolution of a 3-brane Universe in the presence of energy influx from the bulk. We show that this influx can lead to accelerated expansion on the brane, depending on the equations of state of the bulk and brane matter. The absorption of non-relativistic bulk matter by the brane at an increasing rate leads to a small positive acceleration parameter during the era of m...
متن کاملCosmological acceleration from a gas of strings
In string gas cosmology, the extra dimensions of the underlying theory are kept at a microscopic scale by a gas of strings. In the matter-dominated era, however, dust pressure can lead to oscillations of the extra dimensions and to acceleration in the three visible dimensions, even with a vanishing cosmological term. We review the resulting oscillating expansion history, that provides an accept...
متن کاملCosmological Acceleration: Dark Energy or Modified Gravity?
The recently observed accelerating cosmological expansion or ”dark energy” may be either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity) without any constituent Dark Energy. Lowor high-curvature modifications of Einstein gravity are distinguished by the spacetime (Ricci) curvature of their vacua. If constituent Dark Energy does not exist, s...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
ژورنال
عنوان ژورنال: Physics-Uspekhi
سال: 2019
ISSN: 1063-7869,1468-4780
DOI: 10.3367/ufne.2018.10.038469