16,311 research outputs found
Electrically detected interferometry of Majorana fermions in a topological insulator
We show how a chiral Dirac fermion (a massless electron or hole) can be
converted into a pair of neutral chiral Majorana fermions (a particle equal to
its own antiparticle). These two types of fermions exist on the metallic
surface of a topological insulator, respectively, at a magnetic domain wall and
at a magnet-superconductor interface. Interferometry of Majorana fermions is a
key operation in topological quantum computation, but the detection is
problematic since these particles have no charge. The Dirac-Majorana converter
enables electrical detection of the interferometric signal.Comment: 4 pages, 2 figure
Three-dimensional topologically gauged N=6 ABJM type theories
In this paper we construct the conformal supergravity in three
dimensions from a set of Chern-Simons-like terms one for each of the graviton,
gravitino, and R-symmetry gauge field and then couple this theory to the
superconformal ABJM theory. In a first step part of the coupled
Lagrangian for this topologically gauged ABJM theory is derived by demanding
that all terms of third and second order in covariant derivatives cancel in the
supersymmtry variation of the Lagrangian. To achieve this the transformation
rules of the two separate sectors must be augmented by new terms. In a second
step we analyze all terms in that are of first order in covariant
derivatives. The cancelation of these terms require additional terms in the
transformation rules as well as a number of new terms in the Lagrangian. As a
final step we check that all remaining terms in which are bilinear
in fermions cancel which means that the presented Lagrangian and transformation
rules constitute the complete answer. In particular we find in the last step
new terms in the scalar potential containing either one or no structure
constant. The non-derivative higher fermion terms in that have not
yet been completely analyzed are briefly discussed.Comment: 26 pages, v.2 minor corrections, comment on relation to chiral
gravity added
Quantum memory for non-stationary light fields based on controlled reversible inhomogeneous broadening
We propose a new method for efficient storage and recall of non-stationary
light fields, e.g. single photon time-bin qubits, in optically dense atomic
ensembles. Our approach to quantum memory is based on controlled, reversible,
inhomogeneous broadening. We briefly discuss experimental realizations of our
proposal.Comment: 4 page
Light-cone analysis of ungauged and topologically gauged BLG theories
We consider three-dimensional maximally superconformal
Bagger-Lambert-Gustavsson (BLG) theory and its topologically gauged version
(constructed recently in arXiv:0809.4478 [hep-th]) in the light-cone gauge.
After eliminating the entire Chern-Simons gauge field, the ungauged BLG theory
looks more conventional and, apart from the order of the interaction terms,
resembles N=4 super-Yang-Mills theory in four dimensions. The light-cone
superspace version of the BLG theory is given to quadratic and quartic order
and some problems with constructing the sixth order interaction terms are
discussed. In the topologically gauged case, we analyze the field equations
related to the three Chern-Simons type terms of N=8 conformal supergravity and
discuss some of the special features of this theory and its couplings to BLG.Comment: 22 pages; v2 some typos correcte
Heat capacity mapping mission project HCM-051
There are no author-identified significant results in this report
An almost isotropic cosmic microwave temperature does not imply an almost isotropic universe
In this letter we will show that, contrary to what is widely believed, an
almost isotropic cosmic microwave background (CMB) temperature does not imply
that the universe is ``close to a Friedmann-Lemaitre universe''. There are two
important manifestations of anisotropy in the geometry of the universe, (i) the
anisotropy in the overall expansion, and (ii) the intrinsic anisotropy of the
gravitational field, described by the Weyl curvature tensor, although the
former usually receives more attention than the latter in the astrophysical
literature. Here we consider a class of spatially homogeneous models for which
the anisotropy of the CMB temperature is within the current observational
limits but whose Weyl curvature is not negligible, i.e. these models are not
close to isotropy even though the CMB temperature is almost isotropic.Comment: 5 pages (AASTeX, aaspp4.sty), submitted to Astrophysical Journal
Letter
Rotational states in deformed nuclei: An analytic approach
The consequences of the spontaneous breaking of rotational symmetry are
investigated in a field theory model for deformed nuclei, based on simple
separable interactions. The crucial role of the Ward-Takahashi identities to
describe the rotational states is emphasized. We show explicitly how the rotor
picture emerges from the isoscalar Goldstone modes, and how the two-rotor model
emerges from the isovector scissors modes. As an application of the formalism,
we discuss the M1 sum rules in deformed nuclei, and make connection to
empirical information.Comment: 19 pages, 9 figure
The nature of z ~ 2.3 Lyman-alpha emitters
We study the multi-wavelength properties of a set of 171 Ly-alpha emitting
candidates at redshift z = 2.25 found in the COSMOS field, with the aim of
understanding the underlying stellar populations in the galaxies. We especially
seek to understand what the dust contents, ages and stellar masses of the
galaxies are, and how they relate to similar properties of Ly-alpha emitters at
other redshifts. The candidates here are shown to have different properties
from those of Ly-alpha emitters found at higher redshift, by fitting the
spectral energy distributions (SEDs) using a Monte-Carlo Markov-Chain technique
and including nebular emission in the spectra. The stellar masses, and possibly
the dust contents, are higher, with stellar masses in the range log M_* = 8.5 -
11.0 M_sun and A_V = 0.0 - 2.5 mag. Young population ages are well constrained,
but the ages of older populations are typically unconstrained. In 15% of the
galaxies only a single, young population of stars is observed. We show that the
Ly-alpha fluxes of the best fit galaxies are correlated with their dust
properties, with higher dust extinction in Ly-alpha faint galaxies. Testing for
whether results derived from a light-weighted stack of objects correlate to
those found when fitting individual objects we see that stellar masses are
robust to stacking, but ages and especially dust extinctions are derived
incorrectly from stacks. We conclude that the stellar properties of Ly-alpha
emitters at z = 2.25 are different from those at higher redshift and that they
are diverse. Ly-alpha selection appears to be tracing systematically different
galaxies at different redshifts.Comment: 15 pages, 11 figures, 8 tables, accepted in A&A. Table 6 available in
full from the author
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