18,359 research outputs found
Macroscopic Anisotropy and Symmetry Breaking in the Pyrochlore Antiferromagnet GdTiO}
In the Heisenberg antiferromagnet , the exchange interactions
are geometrically frustrated by the pyrochlore lattice structure. This ESR
study reveals a strong temperature dependent anisotropy with respect to a [111]
body diagonal below a temperature K, despite the spin only nature of
the ion. Anisotropy and symmetry breaking can nevertheless appear
through the superexchange interaction. The presence of short range planar
correlation restricted to specific Kagom\'{e} planes is sufficient to explain
the two ESR modes studied in this work.Comment: 4 pages, 5 figure
Optical bistability in sideband output modes induced by squeezed vacuum
We consider two-level atoms in a ring cavity interacting with a broadband
squeezed vacuum centered at frequency and an input monochromatic
driving field at frequency . We show that, besides the central mode
(at \o), many other {\em sideband modes} are produced at the output, with
frequencies shifted from by multiples of .
Here we analyze the optical bistability of the two nearest sideband modes, one
red-shifted and the other blue-shifted.Comment: Replaced with final published versio
Entanglement Capacity of Nonlocal Hamiltonians : A Geometric Approach
We develop a geometric approach to quantify the capability of creating
entanglement for a general physical interaction acting on two qubits. We use
the entanglement measure proposed by us for -qubit pure states (PRA
\textbf{77}, 062334 (2008)). Our procedure reproduces the earlier results (PRL
\textbf{87}, 137901 (2001)). The geometric method has the distinct advantage
that it gives an experimental way to monitor the process of optimizing
entanglement production.Comment: 8 pages, 1 figure
Sound Velocity Anomaly at the Mott Transition: application to organic conductors and V2O3
Close to the Mott transition, lattice degrees of freedom react to the
softening of electron degrees of freedom. This results in a change of lattice
spacing, a diverging compressibility and a critical anomaly of the sound
velocity. These effects are investigated within a simple model, in the
framework of dynamical mean-field theory. The results compare favorably to
recent experiments on the layered organic \kappa-(BEDT-TTF)_2Cu[N(CN)_2]Cl
conductor . We predict that effects of a similar magnitude are expected for
V2O3, despite the much larger value of the elastic modulus of this material.Comment: New discussion of the relation between the sound-velocity and the
compressibility has been adde
Cosmological solutions of massive gravity on de Sitter
In the framework of the recently proposed models of massive gravity, defined
with respect to a de Sitter reference metric, we obtain new homogeneous and
isotropic solutions for arbitrary cosmological matter and arbitrary spatial
curvature. These solutions can be classified into three branches. In the first
two, the massive gravity terms behave like a cosmological constant. In the
third branch, the massive gravity effects can be described by a time evolving
effective fluid with rather remarkable features, including the property to
behave as a cosmological constant at late time.Comment: 6 pages, 1 figure; discussion extended, a few references added,
improved analysis in Section
Interacting Spin-2 Fields
We construct consistent theories of multiple interacting spin-2 fields in
arbitrary spacetime dimensions using a vielbein formulation. We show that these
theories have the additional primary constraints needed to eliminate potential
ghosts, to all orders in the fields, and to all orders beyond any decoupling
limit. We postulate that the number of spin-2 fields interacting at a single
vertex is limited by the number of spacetime dimensions. We then show that, for
the case of two spin-2 fields, the vielbein theory is equivalent to the
recently proposed theories of ghost-free massive gravity and bi-metric gravity.
The vielbein formulation greatly simplifies the proof that these theories have
an extra primary constraint which eliminates the Boulware-Deser ghost.Comment: 42 pages, 3 figures. v3 alternative argument using constrained
spatial vielbeins has been removed (see footnote 3
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