34,247 research outputs found
Nonlinear Zeno dynamics due to atomic interactions in Bose-Einstein condensate
We show that nonlinear interactions induce both the Zeno and anti-Zeno
effects in the generalised Bose-Josephson model (with the on-site interactions
and the second-order tunneling) describing Bose-Einstein condensate in
double-well trap subject to particle removal from one of the wells. We find
that the on-site interactions induce \textit{only} the Zeno effect, which
appears at long evolution times, whereas the second-order tunneling leads to a
strong decay of the atomic population at short evolution times, reminiscent of
the anti-Zeno effect, and destroys the nonlinear Zeno effect due to the on-site
interactions at long times.Comment: 8 pages, 3 figures. Physica B, DOI: 10.1016/j.physb.2014.08.00
The spectra of mixed He-He droplets
The diffusion Monte Carlo technique is used to calculate and analyze the
excitation spectrum of He atoms bound to a cluster of He atoms, by
using a previously determined optimum filling of single-fermion orbits with
well defined orbital angular momentum , spin and parity quantum numbers.
The study concentrates on the energies and shapes of the three kinds of states
for which the fermionic part of the wave function is a single Slater
determinant: maximum or maximum states within a given orbit, and fully
polarized clusters. The picture that emerges is that of systems with strong
shell effects whose binding and excitation energies are essentially determined
over configuration at fixed number of particles and spin, i.e., by the monopole
properties of an effective Hamiltonian.Comment: 14 pages, 15 figure
The Phase-Space Density Profiles of Cold Dark Matter Halos
We examine the coarse-grained phase-space density profiles of a set of
recent, high-resolution simulations of galaxy-sized Cold Dark Matter (CDM)
halos. Over two and a half decades in radius the phase-space density closely
follows a power-law, , with . This behaviour matches the self-similar solution obtained by
Bertschinger for secondary infall in a uniformly expanding universe. On the
other hand, the density profile corresponding to Bertschinger's solution (a
power-law of slope ) differs significantly from the density
profiles of CDM halos. We show that isotropic mass distributions with power-law
phase-space density profiles form a one-parameter family of structures
controlled by , the ratio of the velocity dispersion to the peak
circular velocity. For one recovers the power-law
solution . For larger than some critical
value, , solutions become non-physical, leading to negative
densities near the center. The critical solution, , has
the narrowest phase-space density distribution compatible with the power-law
phase-space density stratification constraint. Over three decades in radius the
critical solution is indistinguishable from an NFW profile. Our results thus
suggest that the NFW profile is the result of a hierarchical assembly process
that preserves the phase-space stratification of Bertschinger's infall model
but which ``mixes'' the system maximally, perhaps as a result of repeated
merging.Comment: 16 pages, 4 figures; submitted to The Astrophysical Journa
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