90 research outputs found
Analog geometry in an expanding fluid from AdS/CFT perspective
The dynamics of an expanding hadron fluid at temperatures below the chiral
transition is studied in the framework of AdS/CFT correspondence. We establish
a correspondence between the asymptotic AdS geometry in the 4+1-dimensional
bulk with the analog spacetime geometry on its 3+1 dimensional boundary with
the background fluid undergoing a spherical Bjorken type expansion. The analog
metric tensor on the boundary depends locally on the soft pion dispersion
relation and the four-velocity of the fluid. The AdS/CFT correspondence
provides a relation between the pion velocity and the critical temperature of
the chiral phase transition.Comment: 16 pages, 2 figures, revised to match the published version, relation
to static solutions clarified, the section on de Sitter boundary removed,
results unchange
Self-gravitating bosons at nonzero temperature
A system of charged bosons at finite temperature and chemical potential is
studied in a general-relativistic framework. We assume that the boson fields
interact only gravitationally. At sufficiently low temperature the system
exists in two phases: the gas and the condensate. By studying the condensation
process numerically we determine the critical temperature at which the
condensate emerges. As the temperature decreases, the system eventually settles
down in the ground state of a cold boson star.Comment: 21 pages, 11 figures included, revised, to appear in Nucl. Phys.
Vacuum fluctuations in a supersymmetric model in FRW spacetime
We study a noninteracting supersymmetric model in an expanding FRW spacetime.
A soft supersymmetry breaking induces a nonzero contribution to the vacuum
energy density. A short distance cutoff of the order of Planck length provides
a scale for the vacuum energy density comparable with the observed cosmological
constant. Assuming the presence of a dark energy substance in addition to the
vacuum fluctuations of the field an effective equation of state is derived in a
selfconsistent approach. The effective equation of state is sensitive to the
choice of the cut-off but no fine tuning is needed.Comment: 19 pages, accepted for publication in Phys. Rev.
Cosmological tachyon condensation
We consider the prospects for dark matter/energy unification in k-essence
type theories. General mappings are established between the k-essence scalar
field, the hydrodynamic and braneworld descriptions. We develop an extension of
the general relativistic dust model that incorporates the effects of both
pressure and the associated acoustic horizon. Applying this to a tachyon model,
we show that this inhomogeneous "variable Chaplygin gas" does evolve into a
mixed system containing cold dark matter like gravitational condensate in
significant quantities. Our methods can be applied to any dark energy model as
well as to mixtures of dark energy and traditional dark matter.Comment: 22 pages, 3 figures, title changed, typos corrected, accepted in
Phys. Rev.
Numerical Calculation of Hubble Hierarchy Parameters and Observational Parameters of Inflation
We present results obtained by a software we developed for computing
observational cosmological inflation parameters: the scalar spectral index
() and the tensor-to-scalar ratio () for a standard single field and
tachyon inflation, as well as for a tachyon inflation in the second
Randall-Sundrum model with an additional radion field. The calculated numerical
values of observational parameters are compared with the latest results of
observations obtained by the Planck Collaboration. The program is written in
C/C++. The \textit{GNU Scientific Library} is used for some of the numerical
computations and R language is used for data analysis and plots.Comment: 8 pages, 5 figures, based on talk presented at The 10th Jubilee
Conference of the Balkan Physical Union (BPU10), 26-30 August 2018 (Sofia,
Bulgaria
Inflationary RSII Model with a Matter in the Bulk and Exponential Potential of Tachyon Field
In this paper we study a tachyon cosmological model based on dynamics of a
3-brane in the second Randall-Sundrum (RSII) model extended to include matter
in the bulk. The presence of matter in the bulk changes warp factor which leads
to modification of inflationary dynamics. The additional brane behaves
effectively as a tachyon. We calculate numerically observation parameters of
inflation: the scalar spectral index () and the tensor-to-scalar ratio
() for the exponential potential of tachyon field.Comment: 9 pages, 1 figure, will be published in the Special Issue of Facta
Universitatis, Series: Physics, Chemistry and Technology devoted to the
SEENET-MTP Balkan Workshop BSW2018 (3-14 June 2018
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