So you think your theory is better than Einstein's theory of General Relativity?
In our paper, we calculated how much information about gravity the next generation of cosmology surveys will yield, and what types of theories will be subject to the most scrutiny. If you think that your theory is better than Einstein's theory of General Relativity (GR), you might soon know just how right (or wrong) you are.
GR has been well tested in dense local regions, like our solar system. The next generation of surveys will open the way to precision tests of GR on larger, cosmological scales. They will allow us to trace the evolution of galaxy clustering and gravitational potentials through multiple epochs -- the cosmological equivalent of tomography. This will offer an exciting opportunity to test the validity of Einstein's equations of GR which set the relations between the Newtonian potential, matter inhomogeneities and curvature perturbations.
The tools that we developed in this study allowed us to forecast the power of such surveys to detect and constrain departures from GR on cosmological scales. Our analysis is model independent and determines how many parameters describing deviations from GR can be constrained, as well as
the redshifts and scales on which data is most sensitive to the departures. Reversely, this analysis can be used in survey design to focus the experiment on the region in time and space for which some theory makes a specific prediction.
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BKR1138
Discovery of a new quasicrystal, Sc12Zn88
Icosahedral quasicrystals, discovered 25 years ago by Dan Schectman,
literally transformed the science of crystallography. These materials
manifest long-range positional and orientational order, but lack the
periodic translational order of crystalline solids. Although they form,
almost readily, in a wide variety of ternary and quaternary metallic
alloys, examples of stable binary icosahedral quasicrystals are quite
rare. Indeed, it has been nearly a decade since the discovery of the
only known stable binary icosahedral phases in Cd-Yb and Cd-Ca by A.P.
Tsai’s group in Japan.
In the ___ issue of Physical Review B this month, a group of researchers
at DOE’s Ames Laboratory reported on the discovery of millimeter-sized,
facetted grains of the icosahedral phase in the Sc-Zn binary system
using a novel approach…. solution-growth. Although the Sc-Zn system has
been associated with quasicrystal formation in ternary and quaternary
alloys for some time, the binary “parent” icosahedral phase in the Sc-Zn
system had eluded detection. Using high-energy x-rays from the Advanced
Photon Source at Argonne National Laboratory, the Ames group confirmed
that the facetted grains were, in fact, icosahedral quasicrystals with
crystallographic symmetries that reflect their external growth habits.
The discovery of this new binary quasicrystal by solution-growth renews
the hope that other binary quasicrystals are lurking out there, waiting
to be uncovered.
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BB11094
Direct visualization of exotic electron crystals in graphene
In conventional solids, atoms or molecules "freeze" at well defined
positions, thus forming a lattice. However, electrons, one of the
smallest constituents of atoms, may also solidify and form a so-called
Wigner crystal. The magnetic field can enhance this tendency of
crystallization, and even more exotic solids may be found, with bubbles
containing two or more electrons per lattice site.
The recent discovery of graphene, a two-dimensional material where the
electrons live at the surface, has raised the hope to "see" electrons at
work. In contrast to conventional two-dimensional electron gases, that
are buried in a semiconductor, the electrons in graphene are directly
accessible, e.g., by a scanning tunneling microscope. Thus graphene
yields the promising prospect to directly observe exotic electronic-solid phases.
The article studies in detail the local density of
states -- a density map at a fixed energy -- of high-field electron
crystals in graphene. They calculated the density patterns for the
Wigner and bubble crystals and found that the local density of states
exhibits a scaling relation: it is possible to infer the behavior of a
complex bubble-crystal, by knowing the behavior of a Wigner-crystal.
These density patterns may find and experimental verification in future
spectroscopic measurements.
