654 research outputs found
Clinical events after deferral of LAD revascularization following physiological coronary assessment
Stable two--brane models with bulk tachyon matter
We explore the possibility of constructing stable, warped two--brane models
which solve the hierarchy problem, with a bulk non--canonical scalar field
(tachyon matter) as the source term in the action. Among our examples are two
models--one with a warp factor (denoted as ) which differs
from that of the standard Randall--Sundrum by the addition of a quadratic piece
in the and another, where the warping is super-exponential. We
investigate the issue of resolution of hierarchy and perform a stability
analysis by obtaining the effective inter-brane potentials, in each case. Our
analysis reveals that there does exist stable values of the modulus consistent
with hierarchy resolution in both the models. Thus, these models, in which the
bulk scalar field generates the geometry and also ensures stability, provide
viable alternatives to the standard Randall--Sundrum two-brane scenario.Comment: Final version published in Int. Jr. Mod. Phys
Universal near-horizon conformal structure and black hole entropy
It is shown that a massless scalar probe reveals a universal near-horizon
conformal structure for a wide class of black holes, including the BTZ. The
central charge of the corresponding Virasoro algebra contains information about
the black hole. With a suitable quantization condition on the central charge,
the CFT associated with the black hole in our approach is consistent with the
recent observation of Witten, where the dual theory for the BTZ in the AdS/CFT
framework has been identified with the construction of Frenkel, Lepowsky and
Meurman. This CFT admits the Fischer-Griess monster group as its symmetry. The
logarithm of the dimension of a specific representation of the monster group
has been identified by Witten as the entropy of the BTZ black hole. Our
algebraic approach shows that a wide class of black holes share the same
near-horizon conformal structure as that for the BTZ. With a suitable
quantization condition, the CFT's for all these black holes in our formalism
can be identified with the FLM model, although not through the AdS/CFT
correspondence. The corresponding entropy for the BTZ provides a lower bound
for the entropy of this entire class of black holes.Comment: References updated, text rearrange
The ischaemic constellation: an alternative to the ischaemic cascadeâimplications for the validation of new ischaemic tests
The ischaemic cascade is the concept that progressive myocardial oxygen supplyâdemand mismatch causes a consistent sequence of events, starting with metabolic alterations and followed sequentially by myocardial perfusion abnormalities, wall motion abnormalities, ECG changes, and angina. This concept would suggest that investigations that detect expressions of ischaemia earlier in the cascade should be more sensitive tests of ischaemia than those that detect expressions appearing later in the cascade. However, careful review of the studies on which the ischaemic cascade is based suggests that the ischaemic cascade concept may be less well supported by the literature than assumed. In this review we explore this, discuss an alternative method for conceptualising ischaemia, and discuss the potential implications of this new approach to clinical studies and clinical practice
Cosmic optical activity from an inhomogeneous Kalb-Ramond field
The effects of introducing a harmonic spatial inhomogeneity into the
Kalb-Ramond field, interacting with the Maxwell field according to a
`string-inspired' proposal made in earlier work are investigated. We examine in
particular the effects on the polarization of synchrotron radiation from
cosmologically distant (i.e. of redshift greater than 2) galaxies, as well as
the relation between the electric and magnetic components of the radiation
field. The rotation of the polarization plane of linearly polarized radiation
is seen to acquire an additional contribution proportional to the square of the
frequency of the dual Kalb-Ramond axion wave, assuming that it is far smaller
compared to the frequency of the radiation field.Comment: 9 pages, Revtex, no figure
Estimating phase transition of perturbed J1-J2 Heisenberg quantum chain in mixtures of ground and first excited states
We show that the nearest neighbour entanglement in a mixture of ground and
first excited states - the subjacent state - of the J1-J2 Heisenberg quantum
spin chain can be used as an order parameter to detect the phase transition of
the chain from a gapless spin fluid to a gapped dimer phase. We study the
effectiveness of the order parameter for varying relative mixing probabilities
between the ground and first excited states in the subjacent state for
different system sizes, and extrapolate the results to the thermodynamic limit.
We observe that the nearest neighbour concurrence can play a role of a good
order parameter even if the system is in the ground state, but with a small
probability of leaking into the first excited state. Moreover, we apply the
order parameter of the subjacent state to investigate the response to
introduction of anisotropy and of glassy disorder on the phase diagram of the
model, and analyse the corresponding finite-size scale exponents and the
emergent tricritical point.Comment: 14 pages, 9 figure
Scale Factor Duality and the Energy Condition Inequalities
We demonstrate, by a simple analysis, that cosmological line elements related
by scale factor duality also exhibit a duality with respect to the
conservation/violation of the Weak Energy Condition (WEC) by the matter that
acts as the source in the one-loop beta function equations for the metric
coupling written explicitly in the form of the Einstein equations. Furthermore,
a study of specific pairs of line elements (obtained via O(d,d)
transformations) hints at a possible generalisation of the above duality w.r.t.
WEC for the case of O(d,d) related spacetimes. Consequences and extensions
thereof are also pointed out.Comment: 16 pages, RevTex, no figure
Kerr-type nonlinear baths enhance cooling in quantum refrigerators
We study the self-contained three-qubit quantum refrigerator, with a
three-body interaction enabling cooling of the target qubit, in presence of
baths composed of anharmonic quantum oscillators with Kerr-type nonlinearity.
We show that such baths, locally connected to the three qubits, opens up the
opportunity to implement superior steady-state cooling compared to using
harmonic oscillator baths, aiding in access to the free energy required for
empowering the refrigerator function autonomously. We find that in spite of
providing significant primacy in steady-state cooling, such anharmonic baths do
not impart much edge over using harmonic oscillator baths if one targets
transient cooling. However, we gain access to steady-state cooling in the
parameter region where only transient cooling could be achieved by using
harmonic baths. Subsequently, we also study the scaling of steady-state cooling
advantage and the minimum attainable temperature for varying levels of
anharmonicity present in the bath oscillators. Finally, we analyse heat
currents and coefficients of performance of quantum refrigerators using bath
modes involving Kerr-type nonlinearity, and present a comparison with the case
of using bosonic baths made of simple harmonic oscillators. On the way, we
derive the decay rates in the Gorini-Kossakowski-Sudarshan-Lindblad quantum
master equation for Kerr-type anharmonic oscillator baths.Comment: 10 pages, 5 figure
A novel braneworld model with a bulk scalar field
We consider a new braneworld model with a bulk scalar field coupled to
gravity. The bulk scalar action is inspired by the proposed low energy
effective action around the tachyon vacuum. A class of warped geometries
representing solutions of this Einstein-scalar system for a specific scalar
potential is found. The geometry is non singular with a decaying warp factor
and a negative Ricci curvature. The solution of the hierarchy problem is
obtained using this type of warping. Though qualitatively similar to the usual
Randall--Sundrum I model there are interesting quantitative differences.
Additionally, in the RS-II set up the graviton zero mode as well as spin half
massless fermions are found to be localised on the brane.Comment: 14 pages, 4 figures, replaced with corrections in the solution of
hierarchy proble
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