2,445 research outputs found
Ultraviolet modifications of dispersion relations in effective field theory
The existence of a fundamental ultraviolet scale, such as the Planck scale,
may lead to modifications of the dispersion relations for particles at high
energies, in some scenarios of quantum gravity. We apply effective field theory
to this problem and identify dimension 5 operators that do not mix with
dimensions 3 and 4 and lead to cubic modifications of dispersion relations for
scalars, fermions, and vector particles. Further we show that, for electrons,
photons and light quarks, clock comparison experiments bound these operators at
10^{-5}/Mpl.Comment: Version to appear in Phys.Rev.Let
Matter in Toy Dynamical Geometries
One of the objectives of theories describing quantum dynamical geometry is to
compute expectation values of geometrical observables. The results of such
computations can be affected by whether or not matter is taken into account. It
is thus important to understand to what extent and to what effect matter can
affect dynamical geometries. Using a simple model, it is shown that matter can
effectively mold a geometry into an isotropic configuration. Implications for
"atomistic" models of quantum geometry are briefly discussed.Comment: 8 pages, 1 figure, paper presented at DICE 200
Space as a low-temperature regime of graphs
I define a statistical model of graphs in which 2-dimensional spaces arise at
low temperature. The configurations are given by graphs with a fixed number of
edges and the Hamiltonian is a simple, local function of the graphs.
Simulations show that there is a transition between a low-temperature regime in
which the graphs form triangulations of 2-dimensional surfaces and a
high-temperature regime, where the surfaces disappear. I use data for the
specific heat and other observables to discuss whether this is a phase
transition. The surface states are analyzed with regard to topology and
defects.Comment: 22 pages, 12 figures; v3: published version; J.Stat.Phys. 201
Curved geometry and Graphs
Quantum Graphity is an approach to quantum gravity based on a background
independent formulation of condensed matter systems on graphs. We summarize
recent results obtained on the notion of emergent geometry from the point of
view of a particle hopping on the graph. We discuss the role of connectivity in
emergent Lorentzian perturbations in a curved background and the Bose--Hubbard
(BH) model defined on graphs with particular symmetries.Comment: are welcome. 4pp, 2 fig. Proceedings of Loops'11 Conference, Madri
The impact of mixing across the polar vortex edge on Match ozone loss estimates
The Match method for quantification of polar chemical ozone loss is investigated mainly with respect to the impact of mixing across the vortex edge onto this estimate. We show for the winter 2002/03 that significant mixing across the vortex edge occurred and was accurately modeled by the Chemical Lagrangian Model of the Stratosphere. Observations of inert tracers and ozone in-situ from HAGAR on the Geophysica aircraft and sondes and also remote from MIPAS on ENVISAT were reproduced well. The model even reproduced a small vortex remnant that was isolated until June 2003 and was observed in-situ by a balloon-borne whole air sampler. We use this CLaMS simulation to quantify the impact of cross vortex edge mixing on the results of the Match method. It is shown that a time integration of the determined vortex average ozone loss rates as performed in Match results in larger ozone loss than the polar vortex average ozone loss in CLaMS. Also, the determination of the Match ozone loss rates can be influenced by mixing. This is especially important below 430 K, where ozone outside the vortex is lower than inside and the vortex boundary is not a strong transport barrier. This effect and further sampling effects cause an offset between vortex average ozone loss rates derived from Match and deduced from CLaMS with an even sampling for the entire vortex. Both, the time-integration of ozone loss and the determination of ozone loss rates for Match are evaluated using the winter 2002/03 CLaMS simulation. These impacts can explain the differences between CLaMS and Match column ozone loss. While the investigated effects somewhat reduce the apparent discrepancy in January ozone loss rates, a discrepancy between simulations and Match remains. However, its contribution to the accumulated ozone loss over the winter is not large
Quantum Geometry Phenomenology: Angle and Semiclassical States
The phenomenology for the deep spatial geometry of loop quantum gravity is
discussed. In the context of a simple model of an atom of space, it is shown
how purely combinatorial structures can affect observations. The angle operator
is used to develop a model of angular corrections to local, continuum
flat-space 3-geometries. The physical effects involve neither breaking of local
Lorentz invariance nor Planck scale suppression, but rather reply on only the
combinatorics of SU(2) recouping theory. Bhabha scattering is discussed as an
example of how the effects might be observationally accessible.Comment: 5 pages, slightly extended version of the contribution to the
Loops'11 conference proceeding
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Synthesis of organic biaryl and aryl silyl ether linkers for surface functionalization of silicon semiconductors
Functional organic materials for use in inorganic semiconductor applications is of high scientific interest due to the need for flexible, conductive materials that can be utilized in solar energy applications. Herein is described a synthetic route for a new variant of biphenylene linker called 2Ldm-OTf-bpA, which can be used as a building block for future conductive oligophenylene materials in semiconductor devices. With unique ortho-functionalized dimethoxy handles and para-functionalization via triflate and bromo groups, this linker can be chemically modified at the bromo position to attach to silicon semiconductor surfaces. Additionally, a synthetic route for 1-LdSihex₃-OTf is presented which utilizes the modular synthon 1Ld-OH-OTf that can be synthetically modified to generate many variations of small molecules, which can be used to control the steric spacing of molecules on surfaces during functionalization. Conversely, the triflate group can be utilized as a synthetic modification point for future studies of molecular wire growth on silicon surfaces. These molecular wires will be the foundation of future studies for developing a hybrid molecular/materials (HMM) layer on Si(111). These surfaces can then act as anchor points for catalysts for the production of solar fuels conversion such as H₂ from water or the reduction of CO₂ to methanolChemistr
Charging and coagulation of dust in protoplanetary plasma environments
Combining a particle-particle, particle-cluster and cluster-cluster
agglomeration model with an aggregate charging model, the coagulation and
charging of dust particles in various plasma environments relevant for
proto-planetary disks have been investigated. The results show that charged
aggregates tend to grow by adding small particles and clusters to larger
particles and clusters, leading to greater sizes and masses as compared to
neutral aggregates, for the same number of monomers in the aggregate. In
addition, aggregates coagulating in a Lorentzian plasma (containing a larger
fraction of high-energy plasma particles) are more massive and larger than
aggregates coagulating in a Maxwellian plasma, for the same plasma densities
and characteristic temperature. Comparisons of the grain structure, utilizing
the compactness factor, {\phi}{\sigma}, demonstrate that a Lorentzian plasma
environment results in fluffier aggregates, with small {\phi}{\sigma}, which
exhibit a narrow compactness factor distribution. Neutral aggregates are more
compact, with larger {\phi}{\sigma}, and exhibit a larger variation in
fluffiness. Measurement of the compactness factor of large populations of
aggregates is shown to provide information on the disk parameters that were
present during aggregation
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