337 research outputs found
Black String Perturbations in RS1 Model
We present a general formalism for black string perturbations in
Randall-Sundrum 1 model (RS1). First, we derive the master equation for the
electric part of the Weyl tensor . Solving the master equation
using the gradient expansion method, we give the effective Teukolsky equation
on the brane at low energy. It is useful to estimate gravitational waves
emitted by perturbed rotating black strings. We also argue the effect of the
Gregory-Laflamme instability on the brane using our formalism.Comment: 14 pages, Based on a talk presented at ACRGR4, the 4th Australasian
Conference on General Relativity and Gravitation, Monash University,
Melbourne, January 2004. To appear in the proceedings, in General Relativity
and Gravitatio
Branes, Instantons, And Taub-NUT Spaces
ALE and Taub-NUT (or ALF) hyper-Kahler four-manifolds can be naturally
constructed as hyper-Kahler quotients. In the ALE case, this construction has
long been understood in terms of D-branes; here we give a D-brane derivation in
the Taub-NUT case. Likewise, instantons on ALE spaces and on Taub-NUT spaces
have ADHM-like constructions related to hyper-Kahler quotients. Here we refine
the analysis in the Taub-NUT case by making use of a D-brane probe, and give an
application to M-theory.Comment: 63 p
Quantum magneto-oscillations in a two-dimensional Fermi liquid
Quantum magneto-oscillations provide a powerfull tool for quantifying
Fermi-liquid parameters of metals. In particular, the quasiparticle effective
mass and spin susceptibility are extracted from the experiment using the
Lifshitz-Kosevich formula, derived under the assumption that the properties of
the system in a non-zero magnetic field are determined uniquely by the
zero-field Fermi-liquid state. This assumption is valid in 3D but, generally
speaking, erroneous in 2D where the Lifshitz-Kosevich formula may be applied
only if the oscillations are strongly damped by thermal smearing and disorder.
In this work, the effects of interactions and disorder on the amplitude of
magneto-oscillations in 2D are studied. It is found that the effective mass
diverges logarithmically with decreasing temperature signaling a deviation from
the Fermi-liquid behavior. It is also shown that the quasiparticle lifetime due
to inelastic interactions does not enter the oscillation amplitude, although
these interactions do renormalize the effective mass. This result provides a
generalization of the Fowler-Prange theorem formulated originally for the
electron-phonon interaction.Comment: 4 pages, 1 figur
The holographic superconductors in higher-dimensional AdS soliton
We explore the behaviors of the holographic superconductors at zero
temperature for a charged scalar field coupled to a Maxwell field in
higher-dimensional AdS soliton spacetime via analytical way. In the probe
limit, we obtain the critical chemical potentials increase linearly as a total
dimension grows up. We find that the critical exponent for condensation
operator is obtained as 1/2 independently of , and the charge density is
linearly related to the chemical potential near the critical point.
Furthermore, we consider a slightly generalized setup the
Einstein-Power-Maxwell field theory, and find that the critical exponent for
condensation operator is given as in terms of a power parameter
of the Power-Maxwell field, and the charge density is proportional to the
chemical potential to the power of .Comment: LaTeX, 16 pages, 5 figures, typos corrected, one reference added,
version to appear in European Physical Journal
Introduction to Holographic Superconductors
These lectures give an introduction to the theory of holographic
superconductors. These are superconductors that have a dual gravitational
description using gauge/gravity duality. After introducing a suitable
gravitational theory, we discuss its properties in various regimes: the probe
limit, the effects of backreaction, the zero temperature limit, and the
addition of magnetic fields. Using the gauge/gravity dictionary, these
properties reproduce many of the standard features of superconductors. Some
familiarity with gauge/gravity duality is assumed. A list of open problems is
included at the end.Comment: 34 pages, 10 figures, to appear in the proceedings of the 5th Aegean
Summer School, "From Gravity to Thermal Gauge Theories: the AdS/CFT
Correspondence"; v2: references adde
Black Holes in Higher-Dimensional Gravity
These lectures review some of the recent progress in uncovering the phase
structure of black hole solutions in higher-dimensional vacuum Einstein
gravity. The two classes on which we focus are Kaluza-Klein black holes, i.e.
static solutions with an event horizon in asymptotically flat spaces with
compact directions, and stationary solutions with an event horizon in
asymptotically flat space. Highlights include the recently constructed
multi-black hole configurations on the cylinder and thin rotating black rings
in dimensions higher than five. The phase diagram that is emerging for each of
the two classes will be discussed, including an intriguing connection that
relates the phase structure of Kaluza-Klein black holes with that of
asymptotically flat rotating black holes.Comment: latex, 49 pages, 5 figures. Lectures to appear in the proceedings of
the Fourth Aegean Summer School, Mytiline, Lesvos, Greece, September 17-22,
200
Basic epidemiology of wellbeing among children and adolescents: a cross-sectional population level study
Wellbeing and mental health are fundamental rights of children and adolescents essential for sustainable development. Understanding the epidemiology of child and adolescent wellbeing is essential to informing population health approaches to improving wellbeing and preventing mental illness. The present study estimated the prevalence of wellbeing and how wellbeing indicators were distributed across social and economic groups. This study used data from the 2019 Wellbeing and Engagement Collection; an annual census conducted in South Australian schools that measures self-reported wellbeing in students aged 8-18 years (n = 75,966). We estimated the prevalence (n, %) of low, medium and high wellbeing across five outcomes: life satisfaction, optimism, sadness, worries and happiness, overall and stratified by gender, age, language background, socio-economic position and geographical remoteness. The prevalence of low wellbeing on each indicator was: happiness 13%, optimism 16%, life satisfaction 22%, sadness 16% and worries 25%. The prevalence of low wellbeing increased with age, particularly for females. For example, 22.5% of females aged 8-10 years had high levels of worries compared to 43.6% of 15 to 18-year old females. Socioeconomic inequality in wellbeing was evident on all indicators, with 19.5% of children in the most disadvantaged communities having high levels of sadness compared to 12.5% of children in the most advantaged communities. Many children and adolescents experience low wellbeing on one or more indicators (40.7%). The scale of this problem warrants a population-level preventative health response, in addition to a clinical, individual-level responses to acute mental health needs. Universal school-based programs that support social and emotional wellbeing have a role to play in this response but need to be supported by universal and targeted responses from outside of the education system.Tess Gregory, Alanna Sincovich, Mary Brushe, Amy Finlay-Jones, Luke R.Collier, Blair Grace ... et al
Deviation From \Lambda CDM With Cosmic Strings Networks
In this work, we consider a network of cosmic strings to explain possible
deviation from \Lambda CDM behaviour. We use different observational data to
constrain the model and show that a small but non zero contribution from the
string network is allowed by the observational data which can result in a
reasonable departure from \Lambda CDM evolution. But by calculating the
Bayesian Evidence, we show that the present data still strongly favour the
concordance \Lambda CDM model irrespective of the choice of the prior.Comment: 15 Pages, Latex Style, 4 eps figures, Revised Version, Accepted for
publication in European Physical Journal
Using the past to constrain the future: how the palaeorecord can improve estimates of global warming
Climate sensitivity is defined as the change in global mean equilibrium
temperature after a doubling of atmospheric CO2 concentration and provides a
simple measure of global warming. An early estimate of climate sensitivity,
1.5-4.5{\deg}C, has changed little subsequently, including the latest
assessment by the Intergovernmental Panel on Climate Change.
The persistence of such large uncertainties in this simple measure casts
doubt on our understanding of the mechanisms of climate change and our ability
to predict the response of the climate system to future perturbations. This has
motivated continued attempts to constrain the range with climate data, alone or
in conjunction with models. The majority of studies use data from the
instrumental period (post-1850) but recent work has made use of information
about the large climate changes experienced in the geological past.
In this review, we first outline approaches that estimate climate sensitivity
using instrumental climate observations and then summarise attempts to use the
record of climate change on geological timescales. We examine the limitations
of these studies and suggest ways in which the power of the palaeoclimate
record could be better used to reduce uncertainties in our predictions of
climate sensitivity.Comment: The final, definitive version of this paper has been published in
Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All
rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso
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