426 research outputs found
Thermodynamics of AdS planar black holes and holography
A large AdS Schwarzschild black hole can be approximated by an AdS planar
black hole. However, the temperature of a planar black hole is not well defined
due to the translational invariance of the horizon. We propose to fix this
arbitrariness by imposing the entropy area law. Furthermore, using the AdS/CFT
holography, we propose a relationship between the temperatures of an AdS planar
and large AdS Schwarzschild black holes.Comment: 13 pages, clarifying comments added, typos corrected, published in
JHE
Chaplygin Gas Cosmology - Unification of Dark Matter and Dark Energy
The models that unify dark matter and dark energy based upon the Chaplygin
gas fail owing to the suppression of structure formation by the adiabatic speed
of sound. Including string theory effects, in particular the Kalb-Ramond field,
we show how nonadiabatic perturbations allow a successful structure formation.Comment: 7 pages, presented by N. B. at IRGAC 2006, Barcelona, 11-15 July
2006, typos corrected, concluding paragraph slightly expanded, final version,
accepted in J. Phys. A, special issu
Primordial perturbations and inflation in holographic cosmology
We consider an inflationary scenario in the holographic braneworld with a
cosmological fluid occupying the 3+1 dimensional brane located at the
holographic boundary of an asymptotic ADS bulk. The contribution of the
boundary conformal field can be represented as a modification of Einstein's
equations on the boundary. Using these effective Einstein equations we
calculate the cosmological perturbations and derive the corresponding power
spectra assuming a general -essence type of inflaton. We find that the
braneworld scenario affects the scalar power spectrum only in the speed of
sound dependence on the slow-roll parameters whereas there is no change in the
tensor power spectrum. This implies that the changes in the spectral indices
appear at the second order in the slow-roll parameter expansion.Comment: v2: 19 pages, 1 figure. Appendices and references added. Accepted in
PR
Does an educative approach work? A reflective case study of how two Australian higher education Enabling programs support students and staff uphold a responsible culture of academic integrity
Introduction
Enabling education programs, otherwise known as Foundation Studies or Preparatory programs, provide pathways for students typically under-represented in higher education. Students in Enabling programs often face distinct challenges in their induction to academic culture which can implicate them in cases of misconduct. This case study addresses a gap in the enabling literature reporting on how a culture of academic integrity can be developed for students and staff in these programs through an educative approach.
Case description
This paper outlines how an educative approach to academic integrity is implemented within the Enabling programs of two Australian universities.
Discussion and reflection
This case study reflects upon an approach which makes specific reference to the key elements of ‘support’, ‘approach’ and ‘responsibility’ as highlighted in Bretag and Mahmud’s seminal paper. The paper reports a reduction in misconduct cases at the two institutions suggesting a positive correlation between the interventions and students’ understanding of ethical academic practice. This study reflects upon practitioner experiences with academic integrity investigations to evaluate the effectiveness of this approach.
Conclusions
The authors show that it is possible to ensure academic integrity practices and values are upheld within a supportive learning environment appropriate to a students’ level of study
Constraints on Exotic Matter for An Emergent Universe
We study a composition of normal and exotic matter which is required for a
flat Emergent Universe scenario permitted by the equation of state
(EOS)() and predict the range of the permissible values
for the parameters and to explore a physically viable cosmological
model. The permitted values of the parameters are determined taking into
account the data obtained from observations, a model independent BAO
peak parameter and CMB shift parameter (WMAP7 data). It is found that although
can be very close to zero, most of the observations favours a small and
negative . As a consequence, the effective Equation of State parameter for
this class of Emergent Universe solutions remains negative always. We also
compared the magnitude () vs. redshift() curve obtained in the
model with that obtained from the union compilation data. According to our
analysis the class of Emergent Universe solutions considered here is not ruled
out by the observations.Comment: 6 pages, 7 figures, 1 tabl
Emergent Universe from A Composition of Matter, Exotic Matter and Dark Energy
A specific class of flat Emergent Universe (EU) is considered and its
viability is tested in view of the recent observations. Model parameters are
constrained from Stern data for Hubble Parameter and Redshift ( vs. )
and from a model independent measurement of BAO peak parameter. It is noted
that a composition of Exotic matter, dust and dark energy, capable of producing
an EU, can not be ruled out with present data. Evolution of other relevant
cosmological parameters, viz. density parameter (), effective equation
of state (EOS) parameter () are also shown.Comment: 5 pages, 5 figures (accepted in MNRAS
Dieterici gas as a Unified Model for Dark Matter and Dark Energy
The dominance of dark energy in the universe has necessitated the
introduction of a repulsive gravity source to make q0 negative. The models for
dark energy range from a simple lambda-term to quintessence, Chaplygin gas,
etc. We look at the possibility of how change of behaviour of missing energy
density, from DM to DE, may be determined by the change in the equation of
state of a background fluid instead of a form of potential. The question of
cosmic acceleration can be discussed within the framework of theories which do
not necessarily include scalar fields.Comment: 9 pages, 38 equation
Gravitating Global k-monopole
A gravitating global k-monopole produces a tiny gravitational field outside
the core in addition to a solid angular deficit in the k-field theory. As a new
feature, the gravitational field can be attractive or repulsive depending on
the non-canonical kinetic term.Comment: 9 pages, 2 figures, references added, typos corrected, accepted by
Class. Quantum Gra
Matter Power Spectrum for the Generalized Chaplygin Gas Model: The Newtonian Approach
We model the cosmic medium as the mixture of a generalized Chaplygin gas and
a pressureless matter component. Within a neo-Newtonian approach (in which,
different from standard Newtonian cosmology, the pressure enters the
homogeneous and isotropic background dynamics) we compute the matter power
spectrum. The 2dFGRS data are used to discriminate between unified models of
the dark sector (a purely baryonic matter component of roughly 5 percent of the
total energy content and roughly 95 percent generalized Chaplygin gas) and
different models, for which there is separate dark matter, in addition to that
accounted for by the generalized Chaplygin gas. Leaving the corresponding
density parameters free, we find that the unified models are strongly
disfavored. On the other hand, using unified model priors, the observational
data are also well described, in particular for small and large values of the
generalized Chaplygin gas parameter . The latter result is in agreement
with a recent, more qualitative but fully relativistic, perturbation analysis
in Gorini et al.Comment: Latex file, 17 pages, 29 figures in eps forma
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