43,037 research outputs found
Getting the astrophysics and particle physics of dark matter out of next-generation direct detection experiments
The next decade will bring massive new data sets from experiments of the
direct detection of weakly interacting massive particle (WIMP) dark matter. The
primary goal of these experiments is to identify and characterize the
dark-matter particle species. However, mapping the data sets to the
particle-physics properties of dark matter is complicated not only by the
considerable uncertainties in the dark-matter model, but by its poorly
constrained local distribution function (the "astrophysics" of dark matter). In
this Letter, I propose a shift in how to do direct-detection data analysis. I
show that by treating the astrophysical and particle physics uncertainties of
dark matter on equal footing, and by incorporating a combination of data sets
into the analysis, one may recover both the particle physics and astrophysics
of dark matter. Not only does such an approach yield more accurate estimates of
dark-matter properties, but may illuminate how dark matter coevolves with
galaxies.Comment: 4 pages, 4 figures, replaced to match version accepted by Phys. Rev.
Decoherence-free quantum-information processing using dipole-coupled qubits
We propose a quantum-information processor that consists of decoherence-free
logical qubits encoded into arrays of dipole-coupled qubits. High-fidelity
single-qubit operations are performed deterministically within a
decoherence-free subsystem without leakage via global addressing of bichromatic
laser fields. Two-qubit operations are realized locally with four physical
qubits, and between separated logical qubits using linear optics. We show how
to prepare cluster states using this method. We include all
non-nearest-neighbor effects in our calculations, and we assume the qubits are
not located in the Dicke limit. Although our proposal is general to any system
of dipole-coupled qubits, throughout the paper we use nitrogen-vacancy (NV)
centers in diamond as an experimental context for our theoretical results.Comment: 7 pages, 5 figure
Capture of dark matter by the Solar System. Simple estimates
We consider the capture of galactic dark matter by the Solar System, due to
the gravitational three-body interaction of the Sun, a planet, and a dark
matter particle. Simple estimates are presented for the capture cross-section,
as well as for density and velocity distribution of captured dark matter
particles close to the Earth.Comment: 5 page
A simple model of unbounded evolutionary versatility as a largest-scale trend in organismal evolution
The idea that there are any large-scale trends in the evolution of biological organisms is highly controversial. It is commonly believed, for example, that there is a large-scale trend in evolution towards increasing complexity, but empirical and theoretical arguments undermine this belief. Natural selection results in organisms that are well adapted to their local environments, but it is not clear how local adaptation can produce a global trend. In this paper, I present a simple computational model, in which local adaptation to a randomly changing environment results in a global trend towards increasing evolutionary versatility. In this model, for evolutionary versatility to increase without bound, the environment must be highly dynamic. The model also shows that unbounded evolutionary versatility implies an accelerating evolutionary pace. I believe that unbounded increase in evolutionary versatility is a large-scale trend in evolution. I discuss some of the testable predictions about organismal evolution that are suggested by the model
On a generalized quantum SWAP gate
The SWAP gate plays a central role in network designs for qubit quantum computation. However, there has been a view to generalize qubit quantum computing to higher dimensional quantum systems. In this paper we construct a generalized SWAP gate using only instances of the generalized controlled-NOT gate to cyclically permute the states of d qudits for d prime
Enhanced tidal stripping of satellites in the galactic halo from dark matter self-interactions
We investigate the effects of self-interacting dark matter (SIDM) on the
tidal stripping and evaporation of satellite galaxies in a Milky Way-like host.
We use a suite of five zoom-in, dark-matter-only simulations, two with
velocity-independent SIDM cross sections, two with velocity-dependent SIDM
cross sections, and one cold dark matter simulation for comparison. After
carefully assigning stellar mass to satellites at infall, we find that stars
are stripped at a higher rate in SIDM than in CDM. In contrast, the total bound
dark matter mass loss rate is minimally affected, with subhalo evaporation
having negligible effects on satellites for viable SIDM models. Centrally
located stars in SIDM haloes disperse out to larger radii as cores grow.
Consequently, the half-light radius of satellites increases, stars become more
vulnerable to tidal stripping, and the stellar mass function is suppressed. We
find that the ratio of core radius to tidal radius accurately predicts the
relative strength of enhanced SIDM stellar stripping. Velocity-independent SIDM
models show a modest increase in the stellar stripping effect with satellite
mass, whereas velocity-dependent SIDM models show a large increase in this
effect towards lower masses, making observations of ultra-faint dwarfs prime
targets for distinguishing between and constraining SIDM models. Due to small
cores in the largest satellites of velocity-dependent SIDM, no identifiable
imprint is left on the all-sky properties of the stellar halo. While our
results focus on SIDM, the main physical mechanism of enhanced tidal stripping
of stars apply similarly to satellites with cores formed via other means.Comment: 19 pages, 18 figures, Accepted by MNRA
Mapping the allowed parameter space for decaying dark matter models
I consider constraints on a phenomenological decaying-dark-matter model, in
which two weakly-interacting massive particle (WIMP) species have a small mass
splitting, and in which the heavier particle decays to the lighter particle and
a massless particle on cosmological timescales. The decay parameter space is
parameterized by , the speed of the lighter particle in the center-of-mass
frame of the heavier particle prior to decay, and the decay time . Since
I consider the case in which dark-matter halos have formed before there has
been significant decay, I focus on the effects of decay in already-formed
halos. I show that the parameter space may be constrained by
observed properties of dark-matter halos. I highlight which set of observations
is likely to yield the cleanest constraints on parameter space, and
calculate the constraints in those cases in which the effect of decay on the
observables can be calculated without N-body simulations of decaying dark
matter. I show that for km s, the z=0 galaxy
cluster mass function and halo mass-concentration relation constrain 40 Gyr, and that precise constraints on for smaller will
require N-body simulations.Comment: 14 pages, 5 figures, references added, replaced to match version
published in Phys. Rev.
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