1,038 research outputs found
Higher-order mutual coherence of optical and matter waves
We use an operational approach to discuss ways to measure the higher-order
cross-correlations between optical and matter-wave fields. We pay particular
attention to the fact that atomic fields actually consist of composite
particles that can easily be separated into their basic constituents by a
detection process such as photoionization. In the case of bosonic fields, that
we specifically consider here, this leads to the appearance in the detection
signal of exchange contributions due to both the composite bosonic field and
its individual fermionic constituents. We also show how time-gated counting
schemes allow to isolate specific contributions to the signal, in particular
involving different orderings of the Schr\"odinger and Maxwell fields.Comment: 11 pages, 2 figure
Formulation and constraints on decaying dark matter with finite mass daughter particles
Decaying dark matter cosmological models have been proposed to remedy the
overproduction problem at small scales in the standard cold dark matter
paradigm. We consider a decaying dark matter model in which one CDM mother
particle decays into two daughter particles, with arbitrary masses. A complete
set of Boltzmann equations of dark matter particles is derived which is
necessary to calculate the evolutions of their energy densities and their
density perturbations. By comparing the expansion history of the universe in
this model and the free-streaming scale of daughter particles with astronomical
observational data, we give constraints on the lifetime of the mother particle,
, and the mass ratio between the daughter and the mother particles
. From the distance to the last scattering surface of the
cosmic microwave background, we obtain 30 Gyr in the massless
limit of daughter particles and, on the other hand, we obtain
0.97 in the limit . The free-streaming constraint
tightens the bound on the mass ratio as for .Comment: 20 pages, 7 figure
Input-output theory for fermions in an atom cavity
We generalize the quantum optical input-output theory developed for optical
cavities to ultracold fermionic atoms confined in a trapping potential, which
forms an "atom cavity". In order to account for the Pauli exclusion principle,
quantum Langevin equations for all cavity modes are derived. The dissipative
part of these multi-mode Langevin equations includes a coupling between cavity
modes. We also derive a set of boundary conditions for the Fermi field that
relate the output fields to the input fields and the field radiated by the
cavity. Starting from a constant uniform current of fermions incident on one
side of the cavity, we use the boundary conditions to calculate the occupation
numbers and current density for the fermions that are reflected and transmitted
by the cavity
Liouville Correlation Functions from Four-dimensional Gauge Theories
We conjecture an expression for the Liouville theory conformal blocks and
correlation functions on a Riemann surface of genus g and n punctures as the
Nekrasov partition function of a certain class of N=2 SCFTs recently defined by
one of the authors. We conduct extensive tests of the conjecture at genus 0,1.Comment: 32 pages, 8 figures; v2: minor corrections, published versio
Mirror Dark Matter and Core Density of Galaxies
We present a particle physics realization of a recent suggestion by Spergel
and Steinhardt that collisional but dissipationless dark matter may resolve the
core density problem in dark matter-dominated galaxies such as the dwarf
galaxies. The realization is the asymmetric mirror universe model introduced to
explain the neutrino puzzles and the microlensing anomaly. The mirror baryons
are the dark matter particles with the desired properties. The time scales are
right for resolution of the core density problem and formation of mirror stars
(MACHOs observed in microlensing experiments). The mass of the region
homogenized by Silk damping is between a dwarf and a large galaxy.Comment: 9 pages, LaTex. The present version shows that atomic scattering
inherent in the mirror model can solve the core density problem without the
need for an extra U(1) discussed in the original version; all conclusions are
unchanged. This version is accepted for publication in Phys. Rev.
Level-Spacing Distributions and the Bessel Kernel
The level spacing distributions which arise when one rescales the Laguerre or
Jacobi ensembles of hermitian matrices is studied. These distributions are
expressible in terms of a Fredholm determinant of an integral operator whose
kernel is expressible in terms of Bessel functions of order . We derive
a system of partial differential equations associated with the logarithmic
derivative of this Fredholm determinant when the underlying domain is a union
of intervals. In the case of a single interval this Fredholm determinant is a
Painleve tau function.Comment: 18 pages, resubmitted to make postscript compatible, no changes to
manuscript conten
The Relational Power of Education: The immeasurability of knowledge, value and meaning
Recognizing the challenge of adequate evaluation in
higher education, this essay introduces some of the critical,
alternative-seeking conversation about educational measurement.
The thesis is that knowledge, value, and meaning emerge in the
relational dynamics of education, thus requiring complex
approaches to evaluation, utilizing relational criteria. The method
of the essay is to analyse two educational case studies Ă Ă Ă ĂÂą a travel
seminar and a classroom course Ă Ă Ă ĂÂą in dialogue with educational
literature and a process-relational philosophy of education.
Building from this analysis, the essay concludes with proposals for
relational criteria of evaluation: relations with self, community and
culture, difference, earth, and social structures
Mirror Matter as Self Interacting Dark Matter
It has been argued that the observed core density profile of galaxies is
inconsistent with having a dark matter particle that is collisionless and
alternative dark matter candidates which are self interacting may explain
observations better. One new class of self interacting dark matter that has
been proposed in the context mirror universe models of particle physics is the
mirror hydrogen atom whose stability is guaranteed by the conservation of
mirror baryon number. We show that the effective transport cross section for
mirror hydrogen atoms, has the right order of magnitude for solving the
``cuspy'' halo problem. Furthermore, the suppression of dissipation effects for
mirror atoms due to higher mirror mass scale prevents the mirror halo matter
from collapsing into a disk strengthening the argument for mirror matter as
galactic dark matter.Comment: 6 pages; some references adde
Momentum state engineering and control in Bose-Einstein condensates
We demonstrate theoretically the use of genetic learning algorithms to
coherently control the dynamics of a Bose-Einstein condensate. We consider
specifically the situation of a condensate in an optical lattice formed by two
counterpropagating laser beams. The frequency detuning between the lasers acts
as a control parameter that can be used to precisely manipulate the condensate
even in the presence of a significant mean-field energy. We illustrate this
procedure in the coherent acceleration of a condensate and in the preparation
of a superposition of prescribed relative phase.Comment: 9 pages incl. 6 PostScript figures (.eps), LaTeX using RevTeX,
submitted to Phys. Rev. A, incl. small modifications, some references adde
Theory of output coupling for trapped fermionic atoms
We develop a dynamic theory of output coupling, for fermionic atoms initially
confined in a magnetic trap. We consider an exactly soluble one-dimensional
model, with a spatially localized delta-type coupling between the atoms in the
trap and a continuum of free-particle external modes. Two important special
cases are considered for the confinement potential: the infinite box and the
harmonic oscillator. We establish that in both cases a bound state of the
coupled system appears for any value of the coupling constant, implying that
the trap population does not vanish in the infinite-time limit. For weak
coupling, the energy spectrum of the outgoing beam exhibits peaks corresponding
to the initially occupied energy levels in the trap; the height of these peaks
increases with the energy. As the coupling gets stronger, the energy spectrum
is displaced towards dressed energies of the fermions in the trap. The
corresponding dressed states result from the coupling between the unperturbed
fermionic states in the trap, mediated by the coupling between these states and
the continuum. In the strong-coupling limit, there is a reinforcement of the
lowest-energy dressed mode, which contributes to the energy spectrum of the
outgoing beam more strongly than the other modes. This effect is especially
pronounced for the one-dimensional box, which indicates that the efficiency of
the mode-reinforcement mechanism depends on the steepness of the confinement
potential. In this case, a quasi-monochromatic anti-bunched atomic beam is
obtained. Results for a bosonic sample are also shown for comparison.Comment: 16 pages, 7 figures, added discussion on time-dependent spectral
distribution and corresponding figur
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