23,183 research outputs found
Matter wave soliton bouncer
Dynamics of a matter wave soliton bouncing on the reflecting surface (atomic
mirror) under the effect of gravity has been studied by analytical and
numerical means. The analytical description is based on the variational
approach. Resonant oscillations of the soliton's center of mass and width,
induced by appropriate modulation of the atomic scattering length and the slope
of the linear potential are analyzed. In numerical experiments we observe the
Fermi type acceleration of the soliton when the vertical position of the
reflecting surface is periodically varied in time. Analytical predictions are
compared with the results of numerical simulations of the Gross-Pitaevskii
equation and qualitative agreement between them is found.Comment: 8 pages, 5 figure
Conformality Lost
We consider zero-temperature transitions from conformal to non-conformal
phases in quantum theories. We argue that there are three generic mechanisms
for the loss of conformality in any number of dimensions: (i) fixed point goes
to zero coupling, (ii) fixed point runs off to infinite coupling, or (iii) an
IR fixed point annihilates with a UV fixed point and they both disappear into
the complex plane. We give both relativistic and non-relativistic examples of
the last case in various dimensions and show that the critical behavior of the
mass gap behaves similarly to the correlation length in the finite temperature
Berezinskii-Kosterlitz-Thouless (BKT) phase transition in two dimensions, xi ~
exp(c/|T-T_c|^{1/2}). We speculate that the chiral phase transition in QCD at
large number of fermion flavors belongs to this universality class, and attempt
to identify the UV fixed point that annihilates with the Banks-Zaks fixed point
at the lower end of the conformal window.Comment: 30 pages, 6 figures; v2: typos fixed, references adde
Destruction of valence-bond order in a sawtooth chain with a Dzyaloshinskii-Moriya term
A small value of the spin gap in quantum antiferromagnets with strong
frustration makes them susceptible to nominally small deviations from the ideal
Heisenberg model. One of such perturbations, the anisotropic
Dzyaloshinskii-Moriya interaction, is an important perturbation for the
kagome antiferromagnet, one of the current candidates for a quantum-disordered
ground state. We study the influence of the DM term in a related
one-dimensional system, the sawtooth chain that has valence-bond order in its
ground state. Through a combination of analytical and numerical methods, we
show that a relatively weak DM coupling, , is sufficient to destroy the
valence-bond order, close the spin gap, and turn the system into a Luttinger
liquid with algebraic spin correlations. A similar mechanism may be at work in
the kagome antiferromagnet.Comment: 11 pages. References added. Revisions made as requested by referee
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