16,424 research outputs found
Vortex macroscopic superpositions in ultracold bosons in a double-well potential
We study macroscopic superpositions in the orbital rather than the spatial
degrees of freedom, in a three-dimensional double-well system. We show that the
ensuing dynamics of interacting excited ultracold bosons, which in general
requires at least eight single-particle modes and Fock
vectors, is described by a surprisingly small set of many-body states. An
initial state with half the atoms in each well, and purposely excited in one of
them, gives rise to the tunneling of axisymmetric and transverse vortex
structures. We show that transverse vortices tunnel orders of magnitude faster
than axisymmetric ones and are therefore more experimentally accessible. The
tunneling process generates macroscopic superpositions only distinguishable by
their orbital properties and within experimentally realistic times.Comment: 9 pages, 6 figure
Particle density and non-local kinetic energy density functional for two-dimensional harmonically confined Fermi vapors
We evaluate analytically some ground state properties of two-dimensional
harmonically confined Fermi vapors with isotropy and for an arbitrary number of
closed shells. We first derive a differential form of the virial theorem and an
expression for the kinetic energy density in terms of the fermion particle
density and its low-order derivatives. These results allow an explicit
differential equation to be obtained for the particle density. The equation is
third-order, linear and homogeneous. We also obtain a relation between the
turning points of kinetic energy and particle densities, and an expression of
the non-local kinetic energy density functional.Comment: 7 pages, 2 figure
A Unified Theory of Matter Genesis: Asymmetric Freeze-In
We propose a unified theory of dark matter (DM) genesis and baryogenesis. It
explains the observed link between the DM density and the baryon density, and
is fully testable by a combination of collider experiments and precision tests.
Our theory utilises the "thermal freeze-in" mechanism of DM production,
generating particle anti-particle asymmetries in decays from visible to hidden
sectors. Calculable, linked, asymmetries in baryon number and DM number are
produced by the feeble interaction mediating between the two sectors, while the
out-of-equilibrium condition necessary for baryogenesis is provided by the
different temperatures of the visible and hidden sectors. An illustrative model
is presented where the visible sector is the MSSM, with the relevant CP
violation arising from phases in the gaugino and Higgsino masses, and both
asymmetries are generated at temperatures of order 100 GeV. Experimental
signals of this mechanism can be spectacular, including: long-lived metastable
states late decaying at the LHC; apparent baryon-number or lepton-number
violating signatures associated with these highly displaced vertices; EDM
signals correlated with the observed decay lifetimes and within reach of
planned experiments; and a prediction for the mass of the dark matter particle
that is sensitive to the spectrum of the visible sector and the nature of the
electroweak phase transition.Comment: LaTeX, 22 pages, 6 figure
Volume change of bulk metals and metal clusters due to spin-polarization
The stabilized jellium model (SJM) provides us a method to calculate the
volume changes of different simple metals as a function of the spin
polarization, , of the delocalized valence electrons. Our calculations
show that for bulk metals, the equilibrium Wigner-Seitz (WS) radius, , is always a n increasing function of the polarization i.e., the
volume of a bulk metal always increases as increases, and the rate of
increasing is higher for higher electron density metals. Using the SJM along
with the local spin density approximation, we have also calculated the
equilibrium WS radius, , of spherical jellium clusters, at
which the pressure on the cluster with given numbers of total electrons, ,
and their spin configuration vanishes. Our calculations f or Cs, Na,
and Al clusters show that as a function of behaves
differently depending on whether corresponds to a closed-shell or an
open-shell cluster. For a closed-shell cluster, it is an increasing function of
over the whole range , whereas in open-shell clusters
it has a decreasing behavior over the range , where
is a polarization that the cluster has a configuration consistent
with Hund's first rule. The resu lts show that for all neutral clusters with
ground state spin configuration, , the inequality always holds (self-compression) but, at some
polarization , the inequality changes the direction
(self-expansion). However, the inequality
always holds and the equality is achieved in the limit .Comment: 7 pages, RevTex, 10 figure
Big Bang Synthesis of Nuclear Dark Matter
We investigate the physics of dark matter models featuring composite bound
states carrying a large conserved dark "nucleon" number. The properties of
sufficiently large dark nuclei may obey simple scaling laws, and we find that
this scaling can determine the number distribution of nuclei resulting from Big
Bang Dark Nucleosynthesis. For plausible models of asymmetric dark matter, dark
nuclei of large nucleon number, e.g. > 10^8, may be synthesised, with the
number distribution taking one of two characteristic forms. If
small-nucleon-number fusions are sufficiently fast, the distribution of dark
nuclei takes on a logarithmically-peaked, universal form, independent of many
details of the initial conditions and small-number interactions. In the case of
a substantial bottleneck to nucleosynthesis for small dark nuclei, we find the
surprising result that even larger nuclei, with size >> 10^8, are often finally
synthesised, again with a simple number distribution. We briefly discuss the
constraints arising from the novel dark sector energetics, and the extended set
of (often parametrically light) dark sector states that can occur in complete
models of nuclear dark matter. The physics of the coherent enhancement of
direct detection signals, the nature of the accompanying dark-sector form
factors, and the possible modifications to astrophysical processes are
discussed in detail in a companion paper.Comment: 27 pages, 5 figures, v3; minor additional comments - matches
published versio
Tunneling, self-trapping and manipulation of higher modes of a BEC in a double well
We consider an atomic Bose-Einstein condensate trapped in a symmetric
one-dimensional double well potential in the four-mode approximation and show
that the semiclassical dynamics of the two ground state modes can be strongly
influenced by a macroscopic occupation of the two excited modes. In particular,
the addition of the two excited modes already unveils features related to the
effect of dissipation on the condensate. In general, we find a rich dynamics
that includes Rabi oscillations, a mixed Josephson-Rabi regime, self-trapping,
chaotic behavior, and the existence of fixed points. We investigate how the
dynamics of the atoms in the excited modes can be manipulated by controlling
the atomic populations of the ground states.Comment: 12 pages, 5 figure
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