288 research outputs found
Bulk Majorons at Colliders
Lepton number violation may arise via the spontaneous breakdown of a global
symmetry. In extra dimensions, spontaneous lepton number violation in the bulk
implies the existence of a Goldstone boson, the majoron J^(0), as well as an
accompanying tower of Kaluza-Klein (KK) excitations, J^(n). Even if the
zero-mode majoron is very weakly interacting, so that detection in low-energy
processes is difficult, the sum over the tower of KK modes may partially
compensate in processes of relevance at high-energy colliders. Here we consider
the inclusive differential and total cross sections for e^- e^- --> W^- W^- J,
where J represents a sum over KK modes. We show that allowed parameter choices
exist for which this process may be accessible to a TeV-scale electron
collider.Comment: 11 pages LaTeX, 3 eps figures (references added
Finding the Needles in the Haystacks: High-Fidelity Models of the Modern and Archean Solar System for Simulating Exoplanet Observations
We present two state-of-the-art models of the solar system, one corresponding
to the present day and one to the Archean Eon 3.5 billion years ago. Each model
contains spatial and spectral information for the star, the planets, and the
interplanetary dust, extending to 50 AU from the sun and covering the
wavelength range 0.3 to 2.5 micron. In addition, we created a spectral image
cube representative of the astronomical backgrounds that will be seen behind
deep observations of extrasolar planetary systems, including galaxies and Milky
Way stars. These models are intended as inputs to high-fidelity simulations of
direct observations of exoplanetary systems using telescopes equipped with
high-contrast capability. They will help improve the realism of observation and
instrument parameters that are required inputs to statistical observatory yield
calculations, as well as guide development of post-processing algorithms for
telescopes capable of directly imaging Earth-like planets.Comment: Accepted for publication in PAS
Brane decay of a (4+n)-dimensional rotating black hole: spin-0 particles
In this work, we study the `scalar channel' of the emission of Hawking
radiation from a (4+n)-dimensional, rotating black hole on the brane. We
numerically solve both the radial and angular part of the equation of motion
for the scalar field, and determine the exact values of the absorption
probability and of the spheroidal harmonics, respectively. With these, we
calculate the particle, energy and angular momentum emission rates, as well as
the angular variation in the flux and power spectra -- a distinctive feature of
emission during the spin-down phase of the life of the produced black hole. Our
analysis is free from any approximations, with our results being valid for
arbitrarily large values of the energy of the emitted particle, angular
momentum of the black hole and dimensionality of spacetime. We finally compute
the total emissivities for the number of particles, energy and angular momentum
and compare their relative behaviour for different values of the parameters of
the theory.Comment: 24 pages, 13 figure
Inducing Metallicity in Graphene Nanoribbons via Zero-Mode Superlattices
The design and fabrication of robust metallic states in graphene nanoribbons
(GNRs) is a significant challenge since lateral quantum confinement and
many-electron interactions tend to induce electronic band gaps when graphene is
patterned at nanometer length scales. Recent developments in bottom-up
synthesis have enabled the design and characterization of atomically-precise
GNRs, but strategies for realizing GNR metallicity have been elusive. Here we
demonstrate a general technique for inducing metallicity in GNRs by inserting a
symmetric superlattice of zero-energy modes into otherwise semiconducting GNRs.
We verify the resulting metallicity using scanning tunneling spectroscopy as
well as first-principles density-functional theory and tight binding
calculations. Our results reveal that the metallic bandwidth in GNRs can be
tuned over a wide range by controlling the overlap of zero-mode wavefunctions
through intentional sublattice symmetry-breaking.Comment: The first three authors listed contributed equall
Topological Band Engineering of Graphene Nanoribbons
Topological insulators (TIs) are an emerging class of materials that host
highly robust in-gap surface/interface states while maintaining an insulating
bulk. While most notable scientific advancements in this field have been
focused on TIs and related topological crystalline insulators in 2D and 3D,
more recent theoretical work has predicted the existence of 1D
symmetry-protected topological phases in graphene nanoribbons (GNRs). The
topological phase of these laterally-confined, semiconducting strips of
graphene is determined by their width, edge shape, and the terminating unit
cell, and is characterized by a Z2 invariant (similar to 1D solitonic systems).
Interfaces between topologically distinct GNRs characterized by different Z2
are predicted to support half-filled in-gap localized electronic states which
can, in principle, be utilized as a tool for material engineering. Here we
present the rational design and experimental realization of a
topologically-engineered GNR superlattice that hosts a 1D array of such states,
thus generating otherwise inaccessible electronic structure. This strategy also
enables new end states to be engineered directly into the termini of the 1D GNR
superlattice. Atomically-precise topological GNR superlattices were synthesized
from molecular precursors on a Au(111) surface under ultra-high vacuum (UHV)
conditions and characterized by low temperature scanning tunneling microscopy
(STM) and spectroscopy (STS). Our experimental results and first-principles
calculations reveal that the frontier band structure of these GNR superlattices
is defined purely by the coupling between adjacent topological interface
states. This novel manifestation of 1D topological phases presents an entirely
new route to band engineering in 1D materials based on precise control of their
electronic topology, and is a promising platform for future studies of 1D
quantum spin physics.Comment: Contains main manuscript and supplemental informatio
Balancing Detection and Eradication for Control of Epidemics: Sudden Oak Death in Mixed-Species Stands
Culling of infected individuals is a widely used measure for the control of several plant and animal pathogens but culling first requires detection of often cryptically-infected hosts. In this paper, we address the problem of how to allocate resources between detection and culling when the budget for disease management is limited. The results are generic but we motivate the problem for the control of a botanical epidemic in a natural ecosystem: sudden oak death in mixed evergreen forests in coastal California, in which species composition is generally dominated by a spreader species (bay laurel) and a second host species (coast live oak) that is an epidemiological dead-end in that it does not transmit infection but which is frequently a target for preservation. Using a combination of an epidemiological model for two host species with a common pathogen together with optimal control theory we address the problem of how to balance the allocation of resources for detection and epidemic control in order to preserve both host species in the ecosystem. Contrary to simple expectations our results show that an intermediate level of detection is optimal. Low levels of detection, characteristic of low effort expended on searching and detection of diseased trees, and high detection levels, exemplified by the deployment of large amounts of resources to identify diseased trees, fail to bring the epidemic under control. Importantly, we show that a slight change in the balance between the resources allocated to detection and those allocated to control may lead to drastic inefficiencies in control strategies. The results hold when quarantine is introduced to reduce the ingress of infected material into the region of interest
Discerning Noncommutative Extra Dimensions
Experimental limits on the violation of four-dimensional Lorentz invariance
imply that noncommutativity among ordinary spacetime dimensions must be small.
Noncommutativity among extra, compactified spatial dimensions, however, is far
less constrained and may have discernable collider signatures. Here we study
the experimental consequences of noncommutative QED in six dimensions, with
noncommutativity restricted to a TeV-scale bulk. Assuming the orbifold T^2/Z_2,
we construct the effective four-dimensional theory and study interactions
unique to the noncommutative case. New vertices involving the Kaluza-Klein (KK)
excitations of the photon yield order 100% corrections to the pair production
and to the decays of some of the lighter modes. We show that these effects are
difficult to resolve at the LHC, but are likely within the reach of a future
Very Large Hadron Collider (VLHC).Comment: 20 pages LaTeX, 8 eps figures (minor revisions, version to appear in
Phys. Rev. D
The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII): towards the first flight
The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is a balloon-borne, far-infrared
direct detection interferometer with a baseline of 8 m and two collectors of 50 cm. It is designed to study
galactic clustered star formation by providing spatially-resolved spectroscopy of nearby star clusters. It is being
assembled and tested at NASA Goddard Space Flight Center for a first flight in Fall 2016. We report on recent
progress concerning the pointing control system and discuss the overall status of the project as it gets ready forits commissioning flight
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