19,666 research outputs found
Monte Carlo Evaluation of Non-Abelian Statistics
We develop a general framework to (numerically) study adiabatic braiding of
quasiholes in fractional quantum Hall systems. Specifically, we investigate the
Moore-Read (MR) state at filling factor, a known candidate for
non-Abelian statistics, which appears to actually occur in nature. The
non-Abelian statistics of MR quasiholes is demonstrated explicitly for the
first time, confirming the results predicted by conformal field theories.Comment: 4 pages, 4 figure
Fano-Kondo effect in a two-level system with triple quantum dots: shot noise characteristics
We theoretically compare transport properties of Fano-Kondo effect with those
of Fano effect. We focus on shot noise characteristics of a triple quantum dot
(QD) system in the Fano-Kondo region at zero temperature, and discuss the
effect of strong electric correlation in QDs. We found that the modulation of
the Fano dip is strongly affected by the on-site Coulomb interaction in QDs.Comment: 4 pages, 6figure
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Wavefunctions and counting formulas for quasiholes of clustered quantum Hall states on a sphere
The quasiholes of the Read-Rezayi clustered quantum Hall states are
considered, for any number of particles and quasiholes on a sphere, and for any
degree k of clustering. A set of trial wavefunctions, that are zero-energy
eigenstates of a k+1-body interaction, and so are symmetric polynomials that
vanish when any k+1 particle coordinates are equal, is obtained explicitly and
proved to be both complete and linearly independent. Formulas for the number of
states are obtained, without the use of (but in agreement with) conformal field
theory, and extended to give the number of states for each angular momentum. An
interesting recursive structure emerges in the states that relates those for k
to those for k-1. It is pointed out that the same numbers of zero-energy states
can be proved to occur in certain one-dimensional models that have recently
been obtained as limits of the two-dimensional k+1-body interaction
Hamiltonians, using results from the combinatorial literature.Comment: 9 pages. v2: minor corrections; additional references; note added on
connection with one-dimensional Hamiltonians of recent interes
The case for a cold dark matter cusp in Draco
We use a new mass modelling method, GravSphere, to measure the central dark
matter density profile of the Draco dwarf spheroidal galaxy. Draco's star
formation shut down long ago, making it a prime candidate for hosting a
'pristine' dark matter cusp, unaffected by stellar feedback during galaxy
formation. We first test GravSphere on a suite of tidally stripped mock
'Draco'-like dwarfs. We show that we are able to correctly infer the dark
matter density profile of both cusped and cored mocks within our 95% confidence
intervals. While we obtain only a weak inference on the logarithmic slope of
these density profiles, we are able to obtain a robust inference of the
amplitude of the inner dark matter density at 150pc, . We show that, combined with constraints on the density profile at larger
radii, this is sufficient to distinguish a Cold Dark Matter
(CDM) cusp that has from alternative dark matter models
that have lower inner densities. We then apply GravSphere to the real Draco
data. We find that Draco has an inner dark matter density of , consistent with a CDM cusp. Using a velocity independent
SIDM model, calibrated on SIDM cosmological simulations, we show that
Draco's high central density gives an upper bound on the SIDM cross section of
at 99% confidence. We conclude that
the inner density of nearby dwarf galaxies like Draco provides a new and
competitive probe of dark matter models.Comment: 19 pages, 11 Figures. Final version accepted for publication in MNRA
Recommended from our members
Geometrical Comparison of Conventional and Gerotor-Type Positive Displacement Screw Machines
Signatures of the Milky Way's Dark Disk in Current and Future Experiments
In hierarchical structure formation models of disk galaxies, a dark matter
disk forms as massive satellites are preferentially dragged into the disk-plane
where they dissolve. Here, we quantify the importance of this dark disk for
direct and indirect dark matter detection. The low velocity of the dark disk
with respect to the Earth enhances detection rates in direct detection
experiments at low recoil energy. For WIMP masses M_{WIMP} >~ 50 GeV, the
detection rate increases by up to a factor of 3 in the 5 - 20 keV recoil energy
range. Comparing this with rates at higher energy is sensitive to M_{WIMP},
providing stronger mass constraints particularly for M_{WIMP}>~100 GeV. The
annual modulation signal is significantly boosted by the dark disk and the
modulation phase is shifted by ~3 weeks relative to the dark halo. The
variation of the observed phase with recoil energy determines M_{WIMP}, once
the dark disk properties are fixed by future astronomical surveys. The low
velocity of the particles in the dark disk with respect to the solar system
significantly enhances the capture rate of WIMPs in the Sun, leading to an
increased flux of neutrinos from the Sun which could be detected in current and
future neutrino telescopes. The dark disk contribution to the muon flux from
neutrino back conversion at the Earth is increased by a factor of ~5 compared
to the SHM, for rho_d/rho_h=0.5.Comment: 5 pages, 7 figures, To appear in the proceedings of Identification of
Dark Matter 2008 (IDM2008), Stockholm, 18-22 August 2008; corrected one
referenc
Dark matter heats up in dwarf galaxies
Gravitational potential fluctuations driven by bursty star formation can
kinematically 'heat up' dark matter at the centres of dwarf galaxies. A key
prediction of such models is that, at a fixed dark matter halo mass, dwarfs
with a higher stellar mass will have a lower central dark matter density. We
use stellar kinematics and HI gas rotation curves to infer the inner dark
matter densities of eight dwarf spheroidal and eight dwarf irregular galaxies
with a wide range of star formation histories. For all galaxies, we estimate
the dark matter density at a common radius of 150pc, . We find that our sample of dwarfs falls into two
distinct classes. Those that stopped forming stars over 6Gyrs ago favour
central densities , consistent with cold dark matter cusps, while those with more
extended star formation favour , consistent with shallower dark matter cores. Using
abundance matching to infer pre-infall halo masses, , we show that
this dichotomy is in excellent agreement with models in which dark matter is
heated up by bursty star formation. In particular, we find that steadily decreases with increasing stellar mass-to-halo
mass ratio, . Our results suggest that, to leading order, dark
matter is a cold, collisionless, fluid that can be kinematically 'heated up'
and moved around.Comment: 22 pages, 10 Figures. Final version accepted for publication in MNRA
The stellar mass-halo mass relation of isolated field dwarfs: a critical test of CDM at the edge of galaxy formation
We fit the rotation curves of isolated dwarf galaxies to directly measure the
stellar mass-halo mass relation () over the mass range . By accounting for cusp-core
transformations due to stellar feedback, we find a monotonic relation with
little scatter. Such monotonicity implies that abundance matching should yield
a similar if the cosmological model is correct. Using the 'field
galaxy' stellar mass function from the Sloan Digital Sky Survey (SDSS) and the
halo mass function from the Cold Dark Matter Bolshoi simulation, we
find remarkable agreement between the two. This holds down to M, and to M if we
assume a power law extrapolation of the SDSS stellar mass function below M.
However, if instead of SDSS we use the stellar mass function of nearby galaxy
groups, then the agreement is poor. This occurs because the group stellar mass
function is shallower than that of the field below M,
recovering the familiar 'missing satellites' and 'too big to fail' problems.
Our result demonstrates that both problems are confined to group environments
and must, therefore, owe to 'galaxy formation physics' rather than exotic
cosmology.
Finally, we repeat our analysis for a Warm Dark Matter cosmology,
finding that it fails at 68% confidence for a thermal relic mass of keV, and keV if we use the power law extrapolation
of SDSS. We conclude by making a number of predictions for future surveys based
on these results.Comment: 22 pages; 2 Tables; 10 Figures. This is the version accepted for
publication in MNRAS. Key changes: (i) added substantially more information
on the surveys used to measure the stellar mass functions; (ii) added tests
of the robustness of our results. Results and conclusions unchanged from
previously. Minor typos corrected from previous versio
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