1,713,400 research outputs found
Reproducing spin lattice models in strongly coupled atom-cavity systems
In an array of coupled cavities where the cavities are doped with an atomic
V-system, and the two excited levels couple to cavity photons of different
polarizations, we show how to construct various spin models employed in
characterizing phenomena in condensed matter physics, such as the spin-1/2
Ising, XX, Heisenberg, and XXZ models. The ability to construct networks of
arbitrary geometry also allows for the simulation of topological effects. By
tuning the number of excitations present, the dimension of the spin to be
simulated can be controlled, and mixtures of different spin types produced. The
facility of single-site addressing, the use of only the natural hopping photon
dynamics without external fields, and the recent experimental advances towards
strong coupling, makes the prospect of using these arrays as efficient quantum
simulators promising.Comment: 4 pages, 3 figures. v3: References adde
Theory of Polar Corrections to Donor Binding
We calculate the optical phonon correction to the binding energy of electrons
to donors in cubic materials. Previous theories calculated the Rydberg energy
reduced by the effective mass and the static dielectric function. They omitted
an important energy term from the long-range polarization of the ionized donor,
which vanishes for the neutral donor. They also omitted the donor-phonon
interaction. Including these terms yields a new formula for the donor binding
energy
A polarised QCD condensate: nu p elastic scattering as a probe of U_A(1) dynamics
U_A(1) dynamics have the potential to induce a polarised condensate inside a
nucleon. The formation of this condensate is related to the realisation of
U_A(1) symmetry breaking by tunneling processes such as instantons. If it is
present, the polarised condensate induces a term in g_1 which has support only
at x=0. Tunneling processes then induce a net transfer of ``spin'' from finite
x to x=0. The polarised condensate may be measured by comparing the
flavour-singlet axial charges which are extracted from polarised deep inelastic
and nu p elastic scattering experiments.Comment: 13 pages LaTeX, Section 3 improved to include discussion of the 3
flavour quark instanton interaction; to appear in Mod. Phys. Lett.
Relating Green's Functions in Axial and Lorentz Gauges using Finite Field-Dependent BRS Transformations
We use finite field-dependent BRS transformations (FFBRS) to connect the
Green functions in a set of two otherwise unrelated gauge choices. We choose
the Lorentz and the axial gauges as examples. We show how the Green functions
in axial gauge can be written as a series in terms of those in Lorentz gauges.
Our method also applies to operator Green's functions. We show that this
process involves another set of related FFBRS transfomations that is derivable
from infinitesimal FBRS. We suggest possible applications.Comment: 20 pages, LaTex, Section 4 expanded, typos corrected; last 2
references modified; (this) revised version to appear in J. Math. Phy
Quantization of the First-Order Two-Dimensional Einstein-Hilbert Action
A canonical analysis of the first-order two-dimensional Einstein-Hilbert
action has shown it to have no physical degrees of freedom and to possess an
unusual gauge symmetry with a symmetric field acting as a gauge
function. Some consequences of this symmetry are explored. The action is
quantized and it is shown that all loop diagrams beyond one-loop order vanish.
Furthermore, explicit calculation of the one-loop two-point function shows that
it too vanishes, with the contribution of the ghost loop cancelling that of the
``graviton'' loop
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