3,887 research outputs found
Green's Functions and the Adiabatic Hyperspherical Method
We address the few-body problem using the adiabatic hyperspherical
representation. A general form for the hyperangular Green's function in
-dimensions is derived. The resulting Lippmann-Schwinger equation is solved
for the case of three-particles with s-wave zero-range interactions. Identical
particle symmetry is incorporated in a general and intuitive way. Complete
semi-analytic expressions for the nonadiabatic channel couplings are derived.
Finally, a model to describe the atom-loss due to three-body recombination for
a three-component fermi-gas of Li atoms is presented.Comment: 14 pages, 8 figures, 2 table
Invariant submanifold for series arrays of Josephson junctions
We study the nonlinear dynamics of series arrays of Josephson junctions in
the large-N limit, where N is the number of junctions in the array. The
junctions are assumed to be identical, overdamped, driven by a constant bias
current and globally coupled through a common load. Previous simulations of
such arrays revealed that their dynamics are remarkably simple, hinting at the
presence of some hidden symmetry or other structure. These observations were
later explained by the discovery of (N - 3) constants of motion, each choice of
which confines the resulting flow in phase space to a low-dimensional invariant
manifold. Here we show that the dimensionality can be reduced further by
restricting attention to a special family of states recently identified by Ott
and Antonsen. In geometric terms, the Ott-Antonsen ansatz corresponds to an
invariant submanifold of dimension one less than that found earlier. We derive
and analyze the flow on this submanifold for two special cases: an array with
purely resistive loading and another with resistive-inductive-capacitive
loading. Our results recover (and in some instances improve) earlier findings
based on linearization arguments.Comment: 10 pages, 6 figure
Reconstructing a Z' Lagrangian using the LHC and low-energy data
We study the potential of the LHC and future low-energy experiments to
precisely measure the underlying model parameters of a new Z' boson. We
emphasize the complimentary information obtained from both on- and off-peak LHC
dilepton data, from the future Q-weak measurement of the weak charge of the
proton, and from a proposed measurement of parity violation in low-energy
Moller scattering. We demonstrate the importance of off-peak LHC data and
Q-weak for removing sign degeneracies between Z' couplings that occur if only
on-peak LHC data is studied. A future precision measurement of low-energy
Moller scattering can resolve a scaling degeneracy between quark and lepton
couplings that remains after analyzing LHC dilepton data, permitting an
extraction of the individual Z' couplings rather than combinations of them. We
study how precisely Z' properties can be extracted for LHC integrated
luminosities ranging from a few inverse femtobarns to super-LHC values of an
inverse attobarn. For the several example cases studied with M_Z'=1.5 TeV, we
find that coupling combinations can be determined with relative uncertainties
reaching 30% with 30 fb^-1 of integrated luminosity, while 50% is possible with
10 fb^-1. With SLHC luminosities of 1 ab^-1, we find that products of quark and
lepton couplings can be probed to 10%.Comment: 36 pages, 17 figure
KMOS view of the Galactic Centre I. Young stars are centrally concentrated
The Galactic centre hosts a crowded, dense nuclear star cluster with a
half-light radius of 4 pc. Most of the stars in the Galactic centre are cool
late-type stars, but there are also >100 hot early-type stars in the central
parsec of the Milky Way. These stars are only 3-8 Myr old. Our knowledge of the
number and distribution of early-type stars in the Galactic centre is
incomplete. Only a few spectroscopic observations have been made beyond a
projected distance of 0.5 pc of the Galactic centre. The distribution and
kinematics of early-type stars are essential to understand the formation and
growth of the nuclear star cluster. We cover the central >4pc^2 of the Galactic
centre using the integral-field spectrograph KMOS. We extracted more than 1,000
spectra from individual stars and identified early-type stars based on their
spectra. Our data set contains 114 bright early-type stars: 6 have narrow
emission lines, 23 are Wolf-Rayet stars, 9 stars have featureless spectra, and
76 are O/B type stars. Our wide-field spectroscopic data confirm that the
distribution of young stars is compact, with 90% of the young stars identified
within 0.5 pc of the nucleus. We identify 24 new O/B stars primarily at large
radii. We estimate photometric masses of the O/B stars and show that the total
mass in the young population is >12,000M_sun. The O/B stars all appear to be
bound to the Milky Way nuclear star cluster, while less than 30% belong to the
clockwise rotating disk. The central concentration of the early-type stars is a
strong argument that they have formed in situ. A large part of the young O/B
stars is not on the disk, which either means that the early-type stars did not
all form on the same disk or that the disk is dissolving rapidly. [abridged]Comment: 27 pages, 17 figures, matches journal version: Corrected typos,
corrected Notes in Table B.
Cloning, sequencing, and characterization of the hexahydro-1,3,5-trinitro-1,3,5-triazine degradation gene cluster from Rhodococcus rhodochrous
Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a high explosive which presents an environmental hazard as a major land and groundwater contaminant. Rhodococcus rhodochrous strain 11Y was isolated from explosive contaminated land and is capable of degrading RDX when provided as the sole source of nitrogen for growth. Products of RDX degradation in resting-cell incubations were analyzed and found to include nitrite, formaldehyde, and formate. No ammonium was excreted into the medium, and no dead-end metabolites were observed. The gene responsible for the degradation of RDX in strain 11Y is a constitutively expressed cytochrome P450-like gene, xpLA, which is found in a gene cluster with an adrenodoxin reductase homologue, xplB. The cytochrome P450 also has a flavodoxin domain at the N terminus. This study is the first to present a gene which has been identified as being responsible for RDX biodegradation. The mechanism of action of XplA on RDX is thought to involve initial denitration followed by spontaneous ring cleavage and mineralization
Efimov states embedded in the three-body continuum
We consider a multichannel generalization of the Fermi pseudopotential to
model low-energy atom-atom interactions near a magnetically tunable Feshbach
resonance, and calculate the adiabatic hyperspherical potential curves for a
system of three such interacting atoms. In particular, our model suggests the
existence of a series of quasi-bound Efimov states attached to excited
three-body thresholds, far above open channel collision energies. We discuss
the conditions under which such states may be supported, and identify which
interaction parameters limit the lifetime of these states. We speculate that it
may be possible to observe these states using spectroscopic methods, perhaps
allowing for the measurement of multiple Efimov resonances for the first time.Comment: 4 pages 3 figure
Dimer-dimer collisions at finite energies in two-component Fermi gases
We introduce a major theoretical generalization of existing techniques for
handling the three-body problem that accurately describes the interactions
among four fermionic atoms. Application to a two-component Fermi gas accurately
determines dimer-dimer scattering parameters at finite energies and can give
deeper insight into the corresponding many-body phenomena. To account for
finite temperature effects, we calculate the energy-dependent complex
dimer-dimer scattering length, which includes contributions from elastic and
inelastic collisions. Our results indicate that strong finite-energy effects
and dimer dissociation are crucial for understanding the physics in the
strongly interacting regime for typical experimental conditions. While our
results for dimer-dimer relaxation are consistent with experiment, they confirm
only partially a previously published theoretical result.Comment: 4.1 pages, 3 figures, revised text. Supplemental material provided: 2
pages, 2 figure
Conveyor belt clock synchronization
A protocol for synchronizing distant clocks is proposed that does not rely on
the arrival times of the signals which are exchanged, and an optical
implementation based on coherent-state pulses is described. This protocol is
not limited by any dispersion that may be present in the propagation medium
through which the light signals are exchanged. Possible improvements deriving
from the use of quantum-mechanical effects are also addressed.Comment: 8 pages, 7 figure
Cosmological Histories for the New Variables
Histories and measures for quantum cosmology are investigated through a
quantization of the Bianchi IX cosmology using path integral techniques. The
result, derived in the context of Ashtekar variables, is compared with earlier
work. A non-trivial correction to the measure is found, which may dominate the
classical potential for universes on the Planck scale.Comment: 14, CGPG-94/2-
- …