19 research outputs found
A tachyonic scalar field with mutually interacting components
We investigate the tachyonic cosmological potential in two
different cases of the quasi-exponential expansion of universe and discuss
various forms of interaction between the two components---matter and the
cosmological constant--- of the tachyonic scalar field, which leads to the
viable solutions of their respective energy densities. The distinction among
the interaction forms is shown to appear in the diagnostic. Further,
the role of the high- and low-redshift observations of the Hubble parameter is
discussed to determine the proportionality constants and hence the correct form
of matter--cosmological constant interaction.Comment: 14 page
Interacting new agegraphic Phantom model of dark energy in non-flat universe
In this paper we consider the new agegraphic model of interacting dark energy
in non-flat universe. We show that the interacting agegraphic dark energy can
be described by a phantom scalar field. Then we show this phantomic description
of the agegraphic dark energy and reconstruct the potential of the phantom
scalar field.Comment: 8 pages, no figur
Cosmological constraints from galaxy clustering
In this manuscript I review the mathematics and physics that underpins recent
work using the clustering of galaxies to derive cosmological model constraints.
I start by describing the basic concepts, and gradually move on to some of the
complexities involved in analysing galaxy redshift surveys, focusing on the 2dF
Galaxy Redshift Survey (2dFGRS) and the Sloan Digital Sky survey (SDSS).
Difficulties within such an analysis, particularly dealing with redshift space
distortions and galaxy bias are highlighted. I then describe current
observations of the CMB fluctuation power spectrum, and consider the importance
of measurements of the clustering of galaxies in light of recent experiments.
Finally, I provide an example joint analysis of the latest CMB and large-scale
structure data, leading to a set of parameter constraints.Comment: 30 pages, 13 figures. Lecture given at Third Aegean Summer School,
The invisible universe: Dark matter and Dark energ
Agegraphic dark energy as a quintessence
Recently, a dark energy model characterized by the age of the universe,
dubbed ``agegraphic dark energy'', was proposed by Cai. In this paper, a
connection between the quintessence scalar-field and the agegraphic dark energy
is established, and accordingly, the potential of the agegraphic quintessence
field is constructed.Comment: 9 pages, 3 figures; accepted by Eur. Phys. J.
Broad spectrum element-specific X-ray imaging
In this article element-specific mapping using a broad-spectrum laboratory based X-ray source is reported. Element-specific and element-exempt images of silver nitrate and di-hydrated barium chloride have been obtained from raw images collected either side of the K-edges for silver and barium. The informed positioning of filters between the source and sample narrowed the X-ray spectra, thereby enhancing the final images. For barium, samples with a barium area density of less than 8×10−5 g mm−2 have been analysed. The system used here can be employed for mapping the distribution of elements from the middle of the second row transition metals to the light lanthanides