3,534 research outputs found
Spectral gap for random-to-random shuffling on linear extensions
In this paper, we propose a new Markov chain which generalizes
random-to-random shuffling on permutations to random-to-random shuffling on
linear extensions of a finite poset of size . We conjecture that the second
largest eigenvalue of the transition matrix is bounded above by
with equality when the poset is disconnected. This Markov
chain provides a way to sample the linear extensions of the poset with a
relaxation time bounded above by and a mixing time of . We conjecture that the mixing time is in fact as for the
usual random-to-random shuffling.Comment: 16 pages, 10 figures; v2: typos fixed plus extra information in
figures; v3: added explicit conjecture 2.2 + Section 3.6 on the diameter of
the Markov Chain as evidence + misc minor improvements; v4: fixed
bibliograph
Effective Theories of Gamma-ray Lines from Dark Matter Annihilation
We explore theories of dark matter in which dark matter annihilations produce
mono-energetic gamma rays ("lines") in the context of effective field theory,
which captures the physics for cases in which the particles mediating the
interaction are somewhat heavier than the dark matter particle itself. Building
on earlier work, we explore the generic signature resulting from SU(2)xU(1)
gauge invariance that two (or more) lines are generically expected, and
determine the expected relative intensities, including the possibility of
interference between operators.Comment: 11 pages, 0 figure
Facile fabrication of lateral nanowire wrap-gate devices with improved performance
We present a simple fabrication technique for lateral nanowire wrap-gate
devices with high capacitive coupling and field-effect mobility. Our process
uses e-beam lithography with a single resist-spinning step, and does not
require chemical etching. We measure, in the temperature range 1.5-250 K, a
subthreshold slope of 5-54 mV/decade and mobility of 2800-2500 --
significantly larger than previously reported lateral wrap-gate devices. At
depletion, the barrier height due to the gated region is proportional to
applied wrap-gate voltage.Comment: 3 pages, 3 figure
Simulating a single qubit channel using a mixed state environment
We analyze the class of single qubit channels with the environment modeled by
a one-qubit mixed state. The set of affine transformations for this class of
channels is computed analytically, employing the canonical form for the
two-qubit unitary operator. We demonstrate that, 3/8 of the generalized
depolarizing channels can be simulated by the one-qubit mixed state environment
by explicitly obtaining the shape of the volume occupied by this class of
channels within the tetrahedron representing the generalized depolarizing
channels. Further, as a special case, we show that the two-Pauli Channel cannot
be simulated by a one-qubit mixed state environment.Comment: Published version with minor change
Collisions of Jets of Particles from Active Galactic Nuclei with Neutralino Dark Matter
We examine the possibility that energetic Standard Model particles contained
in the jets produced by active galactic nuclei (AGN) may scatter off of the
dark matter halo which is expected to surround the AGN. In particular, if there
are nearby states in the dark sector which can appear resonantly in the
scattering, the cross section can be enhanced and a distinctive edge feature in
the energy spectrum may appear. We examine bounds on supersymmetric models
which may be obtained from the Fermi Gamma-ray Space Telescope observation of
the nearby AGN Centaurus A.Comment: 20 pages, 9 figures; v2: version published in JCA
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