187,587 research outputs found
Gauge Theory of Gravity Requires Massive Torsion Field
One of the greatest unsolved issues of the physics of this century is to find
a quantum field theory of gravity. According to a vast amount of literature
unification of quantum field theory and gravitation requires a gauge theory of
gravity which includes torsion and an associated spin field. Various models
including either massive or massless torsion fields have been suggested. We
present arguments for a massive torsion field, where the probable rest mass of
the corresponding spin three gauge boson is the Planck mass.Comment: 3 pages, Revte
Separable states to distribute entanglement
It was shown that two distant particles can be entangled by sending a third
particle never entangled with the other two [T. S. Cubitt et al., Phys. Rev.
Lett. 91, 037902 (2003)]. In this paper, we investigate a class of three-qubit
separable states to distribute entanglement by the same way, and calculate the
maximal amount of entanglement which two particles of separable states in the
class can have after applying the way.Comment: 4 pages, no figures, Revised argumen
Large-N Yang-Mills Theory as Classical Mechanics
To formulate two-dimensional Yang-Mills theory with adjoint matter fields in
the large-N limit as classical mechanics, we derive a Poisson algebra for the
color-invariant observables involving adjoint matter fields. We showed
rigorously in J. Math. Phys. 40, 1870 (1999) that different quantum orderings
of the observables produce essentially the same Poisson algebra. Here we
explain, in a less precise but more pedagogical manner, the crucial topological
graphical observations underlying the formal proof.Comment: 8 pages, 3 eps figues, LaTeX2.09, aipproc macros needed; conference
proceeding of MRST '99 (10-12 May, 1999, Carleton University, Canada
A Lie Algebra for Closed Strings, Spin Chains and Gauge Theories
We consider quantum dynamical systems whose degrees of freedom are described
by matrices, in the planar limit . Examples are
gauge theoires and the M(atrix)-theory of strings. States invariant under U(N)
are `closed strings', modelled by traces of products of matrices. We have
discovered that the U(N)-invariant opertors acting on both open and closed
string states form a remarkable new Lie algebra which we will call the heterix
algebra. (The simplest special case, with one degree of freedom, is an
extension of the Virasoro algebra by the infinite-dimensional general linear
algebra.) Furthermore, these operators acting on closed string states only form
a quotient algebra of the heterix algebra. We will call this quotient algebra
the cyclix algebra. We express the Hamiltonian of some gauge field theories
(like those with adjoint matter fields and dimensionally reduced pure QCD
models) as elements of this Lie algebra. Finally, we apply this cyclix algebra
to establish an isomorphism between certain planar matrix models and quantum
spin chain systems. Thus we obtain some matrix models solvable in the planar
limit; e.g., matrix models associated with the Ising model, the XYZ model,
models satisfying the Dolan-Grady condition and the chiral Potts model. Thus
our cyclix Lie algebra described the dynamical symmetries of quantum spin chain
systems, large-N gauge field theories, and the M(atrix)-theory of strings.Comment: 52 pages, 8 eps figures, LaTeX2.09; this is the published versio
Ultra-dense phosphorus in germanium delta-doped layers
Phosphorus (P) in germanium (Ge) delta-doped layers are fabricated in
ultra-high vacuum by adsorption of phosphine molecules onto an atomically flat
clean Ge(001) surface followed by thermal incorporation of P into the lattice
and epitaxial Ge overgrowth by molecular beam epitaxy. Structural and
electrical characterizations show that P atoms are confined, with minimal
diffusion, into an ultra-narrow 2-nm-wide layer with an electrically-active
sheet carrier concentration of 4x10^13 cm-2 at 4.2 K. These results open up the
possibility of ultra-narrow source/drain regions with unprecedented carrier
densities for Ge n-channel field effect transistors
Ferromagnetism below 10 K in Mn doped BiTe
Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This
material has the BiTe structure, which is made from the stacking of two
Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure
analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an
equal amount of TeBi anti-site occupancy in the Bi2Te3 blocks. These TeBi
anti-site defects greatly enhance the Mn solubility. This is demonstrated by
comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the
solubility is limited to x = 0.067, while the latter has xmax = 0.125. The
magnetism in [Bi1-xMnx]Te changes little with x, while that for
[Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x >
0.067. Magnetic hysteresis and the anomalous Hall Effect are observed for the
ferromagnetic samples.Comment: Accepted for publication in Phys. Rev.
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