11,581 research outputs found
Integral equation for inhomogeneous condensed bosons generalizing the Gross-Pitaevskii differential equation
We give here the derivation of a Gross-Pitaevskii--type equation for
inhomogeneous condensed bosons. Instead of the original Gross-Pitaevskii
differential equation, we obtain an integral equation that implies less
restrictive assumptions than are made in the very recent study of Pieri and
Strinati [Phys. Rev. Lett. 91 (2003) 030401]. In particular, the Thomas-Fermi
approximation and the restriction to small spatial variations of the order
parameter invoked in their study are avoided.Comment: Phys. Rev. A (accepted
Sharp crossover from composite fermionization to phase separation in mesoscopic mixtures of ultracold bosons
We show that a two-component mixture of a few repulsively interacting
ultracold atoms in a one-dimensional trap possesses very different quantum
regimes and that the crossover between them can be induced by tuning the
interactions in one of the species. In the composite fermionization regime,
where the interactions between both components are large, none of the species
show large occupation of any natural orbital. Our results show that by
increasing the interaction in one of the species, one can reach the
phase-separated regime. In this regime, the weakly interacting component stays
at the center of the trap and becomes almost fully phase coherent, while the
strongly interacting component is displaced to the edges of the trap. The
crossover is sharp, as observed in the in the energy and the in the largest
occupation of a natural orbital of the weakly interacting species. Such a
transition is a purely mesoscopic effect which disappears for large atom
numbers.Comment: 5 pages, 3 figure
Quantum correlations and spatial localization in one-dimensional ultracold bosonic mixtures
We present the complete phase diagram for one-dimensional binary mixtures of
bosonic ultracold atomic gases in a harmonic trap. We obtain exact results with
direct numerical diagonalization for small number of atoms, which permits us to
quantify quantum many-body correlations. The quantum Monte Carlo method is used
to calculate energies and density profiles for larger system sizes. We study
the system properties for a wide range of interaction parameters. For the
extreme values of these parameters, different correlation limits can be
identified, where the correlations are either weak or strong. We investigate in
detail how the correlation evolve between the limits. For balanced mixtures in
the number of atoms in each species, the transition between the different
limits involves sophisticated changes in the one- and two-body correlations.
Particularly, we quantify the entanglement between the two components by means
of the von Neumann entropy. We show that the limits equally exist when the
number of atoms is increased, for balanced mixtures. Also, the changes in the
correlations along the transitions among these limits are qualitatively
similar. We also show that, for imbalanced mixtures, the same limits with
similar transitions exist. Finally, for strongly imbalanced systems, only two
limits survive, i.e., a miscible limit and a phase-separated one, resembling
those expected with a mean-field approach.Comment: 18 pages, 8 figure
Information entropy and nucleon correlations in nuclei
The information entropies in coordinate and momentum spaces and their sum
(, , ) are evaluated for many nuclei using "experimental"
densities or/and momentum distributions. The results are compared with the
harmonic oscillator model and with the short-range correlated distributions. It
is found that depends strongly on and does not depend very much
on the model. The behaviour of is opposite. The various cases we consider
can be classified according to either the quantity of the experimental data we
use or by the values of , i.e., the increase of the quality of the density
and of the momentum distributions leads to an increase of the values of . In
all cases, apart from the linear relation , the linear relation
also holds. V is the mean volume of the nucleus. If is
considered as an ensemble entropy, a relation between or and the
ensemble volume can be found. Finally, comparing different electron scattering
experiments for the same nucleus, it is found that the larger the momentum
transfer ranges, the larger the information entropy is. It is concluded that
could be used to compare different experiments for the same nucleus and to
choose the most reliable one.Comment: 14 pages, 4 figures, 2 table
A Brief Review on Dark Matter Annihilation Explanation for Excesses in Cosmic Ray
Recently data from PAMELA, ATIC, FERMI-LAT and HESS show that there are
excesses in the cosmic ray energy spectrum. PAMELA observed excesses
only in , but not in anti-proton spectrum. ATIC, FERMI-LAT and HESS
observed excesses in spectrum, but the detailed shapes are different
which requires future experimental observations to pin down the correct data
set. Nevertheless a lot of efforts have been made to explain the observed
excesses, and also why PAMELA only observed excesses in but not
in anti-proton. In this brief review we discuss one of the most popular
mechanisms to explain the data, the dark matter annihilation. It has long been
known that about 23% of our universe is made of relic dark matter. If the relic
dark matter was thermally produced, the annihilation rate is constrained
resulting in the need of a large boost factor to explain the data. We will
discuss in detail how a large boost factor can be obtained by the Sommerfeld
and Briet-Wigner enhancement mechanisms. Some implications for particle physics
model buildings will also be discussed.Comment: 22 pages, 6 figures. Several typoes corrected and some references
added. Published in Mod. Phys. Lett. A, Vol. 24, No. 27 (2009) pp. 2139-216
A topological charge selection rule for phase singularities
We present an study of the dynamics and decay pattern of phase singularities
due to the action of a system with a discrete rotational symmetry of finite
order. A topological charge conservation rule is identified. The role played by
the underlying symmetry is emphasized. An effective model describing the short
range dynamics of the vortex clusters has been designed. A method to engineer
any desired configuration of clusters of phase singularities is proposed. Its
flexibility to create and control clusters of vortices is discussed.Comment: 4 pages, 3 figure
Confining Flux Tubes in a Current Algebra Approach
We describe flux tubes and their interactions in a low energy sigma model
induced by flavor symmetry breaking in
QCD. Unlike standard QCD, this model allows gauge confinement to
manifest itself in the low energy theory, which has unscreened spinor color
sources and global flux tubes. We construct the flux tubes and show how
they mediate the confinement of spinor sources. We further examine the flux
tubes' quantum stability, spectrum and interactions. We find that flux tubes
are Alice strings, despite ambiguities in defining parallel transport.
Furthermore, twisted loops of flux tube support skyrmion number, just as gauged
Alice strings form loops that support monopole charge. This model, while
phenomenologically nonviable, thus affords a perspective on both the dynamics
of confinement and on subtleties which arise for global Alice strings.Comment: 29 pages (REVTEX) plus 6 figures, two corrections in the final
section and added reference
Energy gaps in quantum first-order mean-field-like transitions: The problems that quantum annealing cannot solve
We study first-order quantum phase transitions in models where the mean-field
traitment is exact, and the exponentially fast closure of the energy gap with
the system size at the transition. We consider exactly solvable ferromagnetic
models, and show that they reduce to the Grover problem in a particular limit.
We compute the coefficient in the exponential closure of the gap using an
instantonic approach, and discuss the (dire) consequences for quantum
annealing.Comment: 6 pages, 3 figure
Power, norms and institutional change in the European Union: the protection of the free movement of goods
How do institutions of the European Union change? Using an institutionalist approach, this article highlights the interplay between power, cognitive limits, and the normative order that underpins institutional settings and assesses their impact upon the process of institutional change. Empirical evidence from recent attempts to reinforce the protection of the free movement of goods in the EU suggests that, under conditions of uncertainty, actors with ambiguous preferences assess attempts at institutional change on the basis of the historically defined normative order which holds a given institutional structure together. Hence, path dependent and incremental change occurs even when more ambitious and functionally superior proposals are on offer
Higgs bosons near 125 GeV in the NMSSM with constraints at the GUT scale
We study the NMSSM with universal Susy breaking terms (besides the Higgs
sector) at the GUT scale. Within this constrained parameter space, it is not
difficult to find a Higgs boson with a mass of about 125 GeV and an enhanced
cross section in the diphoton channel. An additional lighter Higgs boson with
reduced couplings and a mass <123 GeV is potentially observable at the LHC. The
NMSSM-specific Yukawa couplings lambda and kappa are relatively large and
tan(beta) is small, such that lambda, kappa and the top Yukawa coupling are of
order 1 at the GUT scale. The lightest stop can be as light as 105 GeV, and the
fine-tuning is modest. WMAP constraints can be satisfied by a dominantly
higgsino-like LSP with substantial bino, wino and singlino admixtures and a
mass of ~60-90 GeV, which would potentially be detectable by XENON100.Comment: 20 pages, 14 figure
- âŠ