2,183 research outputs found
Cosmological constant and late transient acceleration of the universe in the Horava-Witten Heterotic M-Theory on S^{1}/Z_{2}
Orbifold branes are studied in the framework of the 11-dimensional
Horava-Witten heterotic M-Theory. It is found that the effective cosmological
constant can be easily lowered to its current observational value by the
mechanism of large extra dimensions. The domination of this constant over the
evolution of the universe is only temporarily. Due to the interaction of the
bulk and the branes, the universe will be in its decelerating expansion phase
again in the future, whereby all problems connected with a far future de Sitter
universe are resolved.Comment: latex4 file, one figure. Version to be published in Physics Letters
Effect of sea quarks on the single-spin asymmetries in polarized pp collisions at RHIC
We calculate the single-spin asymmetries of
bosons produced in polarized pp collisions with the valence part of the up and
down quark helicity distributions modeled by the light-cone
quark-spectator-diquark model while the sea part helicity distributions of the
up and down quarks treated as parametrization. Comparing our results with those
from experimental data at RHIC, we find that the helicity distributions of sea
quarks play an important role in the determination of the shapes of
. It is shown that is sensitive to , while to intuitively. The experimental
data of the polarized structure functions and the sum of helicities are also
important to constrain the sizes of quark helicity distributions both for the
sea part and the valence part of the nucleon.Comment: 19 latex pages, 5 figures, final version for publicatio
Cosmological Implications of 5-dimensional Brans-Dicke Theory
The five dimensional Brans-Dicke theory naturally provides two scalar fields
by the Killing reduction mechanism. These two scalar fields could account for
the accelerated expansion of the universe. We test this model and constrain its
parameter by using the type Ia supernova (SN Ia) data. We find that the best
fit value of the 5-dimensional Brans-Dicke coupling contant is .
This result is also consistent with other observations such as the baryon
acoustic oscillation (BAO).Comment: 5 pages, 4 figures, PLB accepte
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