3,106 research outputs found
Multi-galileons, solitons and Derrick's theorem
The field theory Galilean symmetry, which was introduced in the context of
modified gravity, gives a neat way to construct Lorentz-covariant theories of a
scalar field, such that the equations of motion contain at most second-order
derivatives. Here we extend the analysis to an arbitrary number of scalars, and
examine the restrictions imposed by an internal symmetry, focussing in
particular on SU(N) and SO(N). This therefore extends the possible gradient
terms that may be used to stabilise topological objects such as sigma model
lumps.Comment: 7 pages, 1 figure. Minor change to order of reference
Cross-Correlation analysis of WMAP and EGRET in Wavelet Space
We cross correlate the Wilkinson Microwave Anisotropy Probe (WMAP) first year
data and the diffuse gamma-ray intensity maps from the Energetic Gamma Ray
Experiment Telescope (EGRET) using spherical wavelet approaches. Correlations
at 99.7% significance level have been detected, at scales around
in the WMAP foreground cleaned W-band and Q-band maps, based on data from
regions that are outside the most conservative WMAP foreground mask; no
significant correlation is found with the Tegmark cleaned map. The detected
correlation is most likely of Galactic origin, and thus can help us probing the
origins of possible Galactic foreground residuals and ultimately removing them
from measured microwave sky maps.Comment: 4 pages, 7 figures; accepted for publication in ApJ
Phase Diagrams of Bi1-xSbx Thin Films with Different Growth Orientations
A closed-form model is developed to evaluate the band-edge shift caused by
quantum confinement for a two-dimensional non-parabolic carrier-pocket. Based
on this model, the symmetries and the band-shifts of different carrier-pockets
are evaluated for BiSb thin films that are grown along different crystalline
axes. The phase diagrams for the BiSb thin film systems with different growth
orientations are calculated and analyzed
Observation of Zeeman effect in topological surface state with distinct material dependence
The helical Dirac fermions on the surface of topological insulators host
novel relativistic quantum phenomena in solids. Manipulating spins of
topological surface state (TSS) represents an essential step towards exploring
the theoretically predicted exotic states related to time reversal symmetry
(TRS) breaking via magnetism or magnetic field. Understanding Zeeman effect of
TSS and determining its g-factor are pivotal for such manipulations in the
latter form of TRS breaking. Here, we report those direct experimental
observations in Bi2Se3 and Sb2Te2Se by spectroscopic imaging scanning tunneling
microscopy. The Zeeman shifting of zero mode Landau level is identified
unambiguously by judiciously excluding the extrinsic influences associated with
the non-linearity in the TSS band dispersion and the spatially varying
potential. The g-factors of TSS in Bi2Se3 and Sb2Te2Se are determined to be 18
and -6, respectively. This remarkable material dependence opens a new route to
control the spins in the TSS.Comment: main text: 17 pages, 4 figures; supplementary: 15 pages, 7 figure
Exploring the Latest Union2 SNIa Dataset by Using Model-Independent Parametrization Methods
We explore the cosmological consequences of the recently released Union2
sample of 557 Type Ia supernovae (SNIa). Combining this latest SNIa dataset
with the Cosmic microwave background (CMB) anisotropy data from the Wilkinson
Microwave Anisotropy Probe 7 year (WMAP7) observations and the baryon acoustic
oscillation (BAO) results from the Sloan Digital Sky Survey (SDSS) Data Release
7 (DR7), we measure the dark energy density function as a free function of redshift. Two
model-independent parametrization methods (the binned parametrization and the
polynomial interpolation parametrization) are used in this paper. By using the
statistic and the Bayesian information criterion, we find that the
current observational data are still too limited to distinguish which
parametrization method is better, and a simple model has advantage in fitting
observational data than a complicated model. Moreover, it is found that all
these parametrizations demonstrate that the Union2 dataset is still consistent
with a cosmological constant at 1 confidence level. Therefore, the
Union2 dataset is different from the Constitution SNIa dataset, which more
favors a dynamical dark energy.Comment: 11 pages, 8 figures, 2 tables, accepted for publication in PR
Quantum control by von Neumann measurements
A general scheme is presented for controlling quantum systems using evolution
driven by non-selective von Neumann measurements, with or without an additional
tailored electromagnetic field. As an example, a 2-level quantum system
controlled by non-selective quantum measurements is considered. The control
goal is to find optimal system observables such that consecutive non-selective
measurement of these observables transforms the system from a given initial
state into a state which maximizes the expected value of a target operator (the
objective). A complete analytical solution is found including explicit
expressions for the optimal measured observables and for the maximal objective
value given any target operator, any initial system density matrix, and any
number of measurements. As an illustration, upper bounds on measurement-induced
population transfer between the ground and the excited states for any number of
measurements are found. The anti-Zeno effect is recovered in the limit of an
infinite number of measurements. In this limit the system becomes completely
controllable. The results establish the degree of control attainable by a
finite number of measurements
Dilaton Black Holes in de Sitter or Anti-de Sitter Universe
Poletti and Wiltshire have shown that, with the exception of a pure
cosmological constant, the solution of a dilaton black hole in the background
of de Sitter or anti-de Sitter universe, does not exist in the presence of one
Liouville-type dilaton potential. Here with the combination of three
Liouville-type dilaton potentials, we obtain the dilaton black hole solutions
in the background of de Sitter or anti-de Sitter universe.Comment: 13 pages,to appear in Phys. Rev.
Landau-Zener-St\"uckelberg Spectroscopy of a Superconducting Flux Qubit
We proposed a new method to measure the energy spectrum of a superconducting
flux qubit. Different from the conventional frequency spectroscopy, a short
triangle pulse is used to drive the qubit through the anticrossing and
generates Landau-Zener-St\"uckelberg interference patterns, from which the
information of the energy spectrum can be extracted. Without installing
microwave lines one can simplify the experimental setup and reduce the unwanted
effects of noise. Moreover, the method can be applied to other quantum systems,
opening the possibility of calibrating and manipulating qubits with linear
pulses.Comment: 7 pages, 5 figure
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