8,489 research outputs found
Destruction of Long-range Order by Quenching the Hopping Range in One Dimension
We study the dynamics in a one dimensional hard-core Bose gas with power-law
hopping after an abrupt reduction of the hopping range using the time-dependent
density-matrix renormalization group (t-DMRG) and bosonization techniques. In
particular, we focus on the destruction of the Bose-Einstein condensate (BEC),
which is present in the initial state in the thermodynamic limit. We argue that
this type of quench is akin to a sudden reduction in the effective
dimensionality of the system (from to ). We identify two
regimes in the evolution of the BEC fraction. For short times the decay of the
BEC fraction is Gaussian while for intermediate to long times, it is well
described by a stretched exponential with an exponent that depends on the
initial effective dimensionality of the system. These results are potentially
relevant for cold trapped-ion experiments which can simulate an equivalent of
hard-core bosons, i.e. spins, with tunable long-range interactions.Comment: 8 pages, 7 figures, accepted for publication in Phys. Rev.
Necesidad y morfología: la forma racional
Abstracts aceptados sin presentacion / Accepted abstracts without presentatio
El crecimiento económico argentino en perspectiva histórica
Nuevos enfoques en la historia económica de España y de América Latina.
Homenaje a Robert W. Fogel y Douglas C. North, Premios Nobel de Economía 1993Editada en la Universidad Carlos IIIPublicad
Faddeev-Jackiw approach to gauge theories and ineffective constraints
The general conditions for the applicability of the Faddeev-Jackiw approach
to gauge theories are studied. When the constraints are effective a new proof
in the Lagrangian framework of the equivalence between this method and the
Dirac approach is given. We find, however, that the two methods may give
different descriptions for the reduced phase space when ineffective constraints
are present. In some cases the Faddeev-Jackiw approach may lose some
constraints or some equations of motion. We believe that this inequivalence can
be related to the failure of the Dirac conjecture (that says that the Dirac
Hamiltonian can be enlarged to an Extended Hamiltonian including all first
class constraints, without changes in the dynamics) and we suggest that when
the Dirac conjecture fails the Faddeev-Jackiw approach fails to give the
correct dynamics. Finally we present some examples that illustrate this
inequivalence.Comment: 21 pages, Latex. To be published in Int. J. Mod. Phys.
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