30,807 research outputs found
Onset of -nuclear binding in a pionless EFT approach
and bound states are explored in stochastic
variational method (SVM) calculations within a pionless effective field theory
(EFT) approach at leading order. The theoretical input consists of regulated
and contact terms, and a regulated energy dependent contact
term derived from coupled-channel models of the nucleon
resonance plus a regulated contact term. A self consistency procedure
is applied to deal with the energy dependence of the subthreshold
input, resulting in a weak dependence of the calculated -nuclear binding
energies on the EFT regulator. It is found, in terms of the scattering
length , that the onset of binding \eta\,^3He requires a minimal
value of Re close to 1 fm, yielding then a few MeV binding
in \eta\,^4He. The onset of binding \eta\,^4He requires a lower value of
Re, but exceeding 0.7 fm.Comment: v4 consists of the published Physics Letters B version [31] plus
Erratum ([30], Appendix A here); main results and conclusions remain intac
Energy dynamics in a simulation of LAPD turbulence
Energy dynamics calculations in a 3D fluid simulation of drift wave
turbulence in the linear Large Plasma Device (LAPD) [W. Gekelman et al., Rev.
Sci. Inst. 62, 2875 (1991)] illuminate processes that drive and dissipate the
turbulence. These calculations reveal that a nonlinear instability dominates
the injection of energy into the turbulence by overtaking the linear drift wave
instability that dominates when fluctuations about the equilibrium are small.
The nonlinear instability drives flute-like () density
fluctuations using free energy from the background density gradient. Through
nonlinear axial wavenumber transfer to fluctuations, the
nonlinear instability accesses the adiabatic response, which provides the
requisite energy transfer channel from density to potential fluctuations as
well as the phase shift that causes instability. The turbulence characteristics
in the simulations agree remarkably well with experiment. When the nonlinear
instability is artificially removed from the system through suppressing
modes, the turbulence develops a coherent frequency spectrum
which is inconsistent with experimental data
Quantum Lattice Fluctuations and Luminescence in C_60
We consider luminescence in photo-excited neutral C_60 using the
Su-Schrieffer-Heeger model applied to a single C_60 molecule. To calculate the
luminescence we use a collective coordinate method where our collective
coordinate resembles the displacement of the carbon atoms of the Hg(8) phonon
mode and extrapolates between the ground state "dimerisation" and the exciton
polaron. There is good agreement for the existing luminescence peak spacing and
fair agreement for the relative intensity. We predict the existence of further
peaks not yet resolved in experiment. PACS Numbers : 78.65.Hc, 74.70.Kn,
36.90+
Topological entropy of realistic quantum Hall wave functions
The entanglement entropy of the incompressible states of a realistic quantum
Hall system are studied by direct diagonalization. The subdominant term to the
area law, the topological entanglement entropy, which is believed to carry
information about topologic order in the ground state, was extracted for
filling factors 1/3, 1/5 and 5/2. The results for 1/3 and 1/5 are consistent
with the topological entanglement entropy for the Laughlin wave function. The
5/2 state exhibits a topological entanglement entropy consistent with the
Moore-Read wave function.Comment: 6 pages, 6 figures; improved computations and graphics; added
reference
Quasi-Adiabatic Continuation in Gapped Spin and Fermion Systems: Goldstone's Theorem and Flux Periodicity
We apply the technique of quasi-adiabatic continuation to study systems with
continuous symmetries. We first derive a general form of Goldstone's theorem
applicable to gapped nonrelativistic systems with continuous symmetries. We
then show that for a fermionic system with a spin gap, it is possible to insert
-flux into a cylinder with only exponentially small change in the energy
of the system, a scenario which covers several physically interesting cases
such as an s-wave superconductor or a resonating valence bond state.Comment: 19 pages, 2 figures, final version in press at JSTA
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