9,115 research outputs found
The Weyl tensor two-point function in de Sitter spacetime
We present an expression for the Weyl-Weyl two-point function in de Sitter
spacetime, based on a recently calculated covariant graviton two-point function
with one gauge parameter. We find that the Weyl-Weyl two-point function falls
off with distance like r^{-4}, where r is spacelike coordinate separation
between the two points.Comment: 9 pages, no figure
Stability of Massive Cosmological Gravitons
We analyze the physics of massive spin 2 fields in (A)dS backgrounds and
exhibit that: The theory is stable only for masses m^2 >= 2\Lambda/3, where the
conserved energy associated with the background timelike Killing vector is
positive, while the instability for m^2<2\Lambda/3 is traceable to the helicity
0 energy. The stable, unitary, partially massless theory at m^2=2\Lambda/3
describes 4 propagating degrees of freedom, corresponding to helicities
(+/-2,+/-1) but contains no 0 helicity excitation.Comment: 13 pages, LaTeX, version to appear in Phys. Lett.
How entangled can two couples get?
We describe a pure state of four qubits whose single-qubit density matrices
are all maximally mixed and whose average entanglement as a system of two pairs
of qubits appears to be maximal.Comment: 9 pages. Note added about the robustness of the entanglement in the
four-qubit state described in the paper. Version to be published in Phys.
Lett.
Group quantization of parametrized systems II. Pasting Hilbert spaces
The method of group quantization described in the preceeding paper I is
extended so that it becomes applicable to some parametrized systems that do not
admit a global transversal surface. A simple completely solvable toy system is
studied that admits a pair of maximal transversal surfaces intersecting all
orbits. The corresponding two quantum mechanics are constructed. The similarity
of the canonical group actions in the classical phase spaces on the one hand
and in the quantum Hilbert spaces on the other hand suggests how the two
Hilbert spaces are to be pasted together. The resulting quantum theory is
checked to be equivalent to that constructed directly by means of Dirac's
operator constraint method. The complete system of partial Hamiltonians for any
of the two transversal surfaces is chosen and the quantum Schr\"{o}dinger or
Heisenberg pictures of time evolution are constructed.Comment: 35 pages, latex, no figure
Electronic structure and the Fermi surface of UTGa_{5} (T=Fe, Co, Rh)
The relativistic energy-band calculations have been carried out for
UFeGa_{5}, UCoGa_{5} and URhGa_{5} under the assumption that 5f-electrons are
itinerant. A hybridization between the U 5f state and Ga 4p state occurs in the
vicinity of the Fermi level. The Fermi surface of UCoGa_{5} is quite similar to
that of URhGa_{5}, which are all small in size and closed in topology.
UFeGa_{5} has the quasi-two-dimensional Fermi surface which looks like a
lattice structure.Comment: 2 pages, 3 figures, LT23auth.cls, elsart.cls. submitted to conference
LT2
Do static sources outside a Schwarzschild black hole radiate?
We show that static sources coupled to a massless scalar field in
Schwarzschild spacetime give rise to emission and absorption of zero-energy
particles due to the presence of Hawking radiation. This is in complete analogy
with the description of the bremsstrahlung by a uniformly accelerated charge
from the coaccelerated observers' point of view. The response rate of the
source is found to coincide with that in Minkowski spacetime as a function of
its proper acceleration. This result may be viewed as restoration of the
equivalence principle by the Hawking effect.Comment: 13 page
SO(4) Invariant States in Quantum Cosmology
The phenomenon of linearisation instability is identified in models of
quantum cosmology that are perturbations of mini-superspace models. In
particular, constraints that are second order in the perturbations must be
imposed on wave functions calculated in such models. It is shown explicitly
that in the case of a model which is a perturbation of the mini-superspace
which has spatial sections these constraints imply that any wave
functions calculated in this model must be SO(4) invariant. (This replaces the
previous corrupted version.)Comment: 15 page
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