3,378 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
Electronic phase diagram of the layered cobalt oxide system, LixCoO2 (0.0 <= x <= 1.0)
Here we report the magnetic properties of the layered cobalt oxide system,
LixCoO2, in the whole range of Li composition, 0 <= x <= 1. Based on
dc-magnetic susceptibility data, combined with results of 59Co-NMR/NQR
observations, the electronic phase diagram of LixCoO2 has been established. As
in the related material NaxCoO2, a magnetic critical point is found to exist
between x = 0.35 and 0.40, which separates a Pauli-paramagnetic and a
Curie-Weiss metals. In the Pauli-paramagnetic regime (x <= 0.35), the
antiferromagnetic spin correlations systematically increase with decreasing x.
Nevertheless, CoO2, the x = 0 end member is a non-correlated metal in the whole
temperature range studied. In the Curie-Weiss regime (x >= 0.40), on the other
hand, various phase transitions are observed. For x = 0.40, a susceptibility
hump is seen at 30 K, suggesting the onset of static AF order. A magnetic jump,
which is likely to be triggered by charge ordering, is clearly observed at Tt =
175 K in samples with x = 0.50 (= 1/2) and 0.67 (= 2/3), while only a tiny kink
appears at T = 210 K in the sample with an intermediate Li composition, x =
0.60. Thus, the phase diagram of the LixCoO2 system is complex, and the
electronic properties are sensitively influenced by the Li content (x).Comment: 29 pages, 1 table, 9 figure
Lorentz Violating Inflation
We explore the impact of Lorentz violation on the inflationary scenario. More
precisely, we study the inflationary scenario in the scalar-vector-tensor
theory where the vector is constrained to be unit and time like. It turns out
that the Lorentz violating vector affects the dynamics of the chaotic
inflationary model and divides the inflationary stage into two parts; the
Lorentz violating stage and the standard slow roll stage. We show that the
universe is expanding as an exact de Sitter spacetime in the Lorentz violating
stage although the inflaton field is rolling down the potential. Much more
interestingly, we find exact Lorentz violating inflationary solutions in the
absence of the inflaton potential. In this case, the inflation is completely
associated with the Lorentz violation. We also mention some consequences of
Lorentz violating inflation which can be tested by observations.Comment: 7 pages, 1 figur
Low energy effective action on a self-gravitating D-brane
Recently the study of braneworld on the self-gravitating D-brane has been
initiated and derived the gravitational equation on the brane by holographic
and geometrical projection methods. Surprisingly, in common with these two
methods, the matter on the brane cannot be the source of the gravity on the
brane at leading order. In this paper we will propose the low energy effective
action on the D-brane coupled with gravity which derives the same results.Comment: 8 pages, minor corrections, accepted for publication in Physical
Review
Cosmological constant and gravitational theory on D-brane
In a toy model we derive the gravitational equation on a self-gravitating
curved D-brane. The effective theory on the brane is drastically changed from
the ordinal Einstein equation. The net cosmological constant on the brane
depends on a tuning between the brane tension and the brane charges. Moreover,
non-zero matter stress tensor exists if the net cosmological constant is not
zero. This fact indicates a direct connection between matters on the brane and
the dark energy.Comment: 6 pages, minor corrections, accepted for publication in Physical
Review
Measurement of electron correlations in LixCoO2 (x=0.0 - 0.35) using 59Co nuclear magnetic resonance and nuclear quadrupole resonance techniques
CoO2 is the parent compound for the superconductor NaxCoO2\cdot1.3H2O and was
widely believed to be a Mott insulator. We performed 59Co nuclear magnetic
resonance (NMR) and nuclear quadrupole resonance (NQR) studies on LixCoO2 (x =
0.35, 0.25, 0.12, and 0.0) to uncover the electronic state and spin
correlations in this series of compounds which was recently obtained through
electrochemical de-intercalation of Li from pristine LiCoO2. We find that
although the antiferromagnetic spin correlations systematically increase with
decreasing Li-content (x), the end member, CoO2 is a non-correlated metal that
well satisfies the Korringa relation for a Fermi liquid. Thus, CoO2 is not
simply located at the limit of x->0 for AxCoO2 (A = Li, Na) compounds. The
disappearance of the electron correlations in CoO2 is due to the three
dimensionality of the compound which is in contrast to the highly two
dimensional structure of AxCoO2.Comment: 4pages, 4figures, to be published in Phys.Rev.B. Rapid
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