Related papers: A Mechanism for a small but nonzero cosmological c…
We are at a specific period of modern cosmology, during which the large increase of the amount of data leads to the idea that the determination of cosmological parameters has been achieved with a rather good precision. There is a large…
Perhaps the deepest mystery of our accelerating Universe in expansion is the existence of a tiny and rigid cosmological constant, $\Lambda$. Its size is many orders of magnitude below the expected one in the standard model of particle…
We suggest that the solution to the cosmological vacuum energy puzzle does not require any new field beyond the standard model, but rather can be explained as a result of the interaction of the infrared sector of the effective theory of…
Within present constraints on the observed smooth energy and its equation of state parameter, it is important to find out whether the smooth energy is static (cosmological constant) or dynamic (quintessence). The most dynamical quintessence…
Standard quantum field theory arguments predict an enormous cosmological constant. But what would this mean observationally? For a homogeneous universe the answer is clear, but if the universe is inhomogeneous at the Planck scale, the…
We show that the cosmological constant appears as a Lagrange multiplier if nature is described by a canonical noncommutative spacetime. It is thus an arbitrary parameter unrelated to the action and thus to vacuum fluctuations. The…
We start with a brief account of the latest analysis of the Oklo phenomenon providing the still most stringent constraint on time-variability of the fine- structure constant $\alpha$. Comparing this with the recent result from the…
We consider a flat cosmological model with a free massless scalar field and the cosmological constant $\Lambda$ in the framework of loop quantum cosmology. The scalar field plays the role of an intrinsic time. We apply the reduced phase…
In the era of precision cosmology, the cosmological constant $\Lambda$ gives quite an accurate description of the evolution of the Universe, but it is still plagued with the fine-tuning problem and the cosmic coincidence problem. In this…
We consider a wide class of four-dimensional effective field theories in which gravity is coupled to multiple four-forms and their dual scalar fields, with membrane sources charged under the corresponding three-form potentials. Four-form…
Why the cosmological constant $\Lambda$ observed today is so much smaller than the Planck scale or why the universe is accelerating at present? This is so-called the cosmological constant fine-tuning problem. In this paper, we find that…
We explore the effects of a positive cosmological constant on astrophysical and cosmological configurations described by a polytropic equation of state. We derive the conditions for equilibrium and stability of such configurations and…
We show that the combined minimal and non minimal interaction with the gravitational field may produce the generation of a cosmological constant without self-interaction of the scalar field. In the same vein we analyze the existence of…
We consider a cosmology with a non-compact nonlinear sigma model.The target space is of de-Sitter type and four scalar fields are introduced.The potential is absent but cosmological constant term $\Lambda$ is added. One of the scalar fields…
Self tuning is one of the few methods for dynamically cancelling a large cosmological constant and yet giving an accelerating universe. Its drawback is that it tends to screen all sources of energy density, including matter. We develop a…
Everpresent $\Lambda$ is a cosmological scenario in which the observed cosmological "constant" $\Lambda$ fluctuates between positive and negative values with a vanishing mean, and with a magnitude comparable to the critical density at any…
We present a simple cosmological model in which a single, non-minimally coupled scalar field with a quartic potential is responsible for both inflation at early times and acceleration at late times. Little or no fine tuning is needed to…
Perhaps standard effective field theory arguments are right, and vacuum fluctuations really do generate a huge cosmological constant. I show that if one does not assume homogeneity and an arrow of time at the Planck scale, a very large…
Cosmography is a model-independent phenomenological approach to observational cosmology, relying on Taylor series expansions of physical quantities as a function of the cosmological redshift or other analogous variables. A recent work…
In no--scale supergravity global symmetries protect local supersymmetry and a zero value for the cosmological constant. We consider the breakdown of these symmetries and present a minimal SUGRA model motivated by the multiple point…