13,729 research outputs found
Further refinements of the Heinz inequality
The celebrated Heinz inequality asserts that for , A,B\in \+, every unitarily invariant norm
and . In this paper, we present several
improvement of the Heinz inequality by using the convexity of the function
, some integration techniques
and various refinements of the Hermite--Hadamard inequality. In the setting of
matrices we prove that \begin{eqnarray*}
&&\hspace{-0.5cm}\left|\left|\left|A^{\frac{\alpha+\beta}{2}}XB^{1-\frac{\alpha+\beta}{2}}+A^{1-\frac{\alpha+\beta}{2}}XB^{\frac{\alpha+\beta}{2}}\right|\right|\right|\leq\frac{1}{|\beta-\alpha|}
\left|\left|\left|\int_{\alpha}^{\beta}\left(A^{\nu}XB^{1-\nu}+A^{1-\nu}XB^{\nu}\right)d\nu\right|\right|\right|\nonumber\\
&&\qquad\qquad\leq
\frac{1}{2}\left|\left|\left|A^{\alpha}XB^{1-\alpha}+A^{1-\alpha}XB^{\alpha}+A^{\beta}XB^{1-\beta}+A^{1-\beta}XB^{\beta}\right|\right|\right|\,,
\end{eqnarray*} for real numbers .Comment: 15 pages, to appear in Linear Algebra Appl. (LAA
Impact of internal bremsstrahlung on the detection of gamma-rays from neutralinos
We present a detailed study of the effect of internal bremsstrahlung photons
in the context of the minimal supersymmetric standard models and their impact
on gamma-ray dark matter annihilation searches. We find that although this
effect has to be included for the correct evaluation of fluxes of high energy
photons from neutralino annihilation, its contribution is relevant only in
models and at energies where the lines contribution is dominant over the
secondary photons. Therefore, we find that the most optimistic supersymmetric
scenarios for dark matter detection do not change significantly when including
the internal bremsstrahlung. As an example, we review the gamma-ray dark matter
detection prospects of the Draco dwarf spheroidal galaxy for the MAGIC
stereoscopic system and the CTA project. Though the flux of high energy photons
is enhanced by an order of magnitude in some regions of the parameter space,
the expected fluxes are still much below the sensitivity of the instruments.Comment: 5 pages, twocolumn format, 3 figures:3 references added, accepted as
Brief Report in PR
Spatial sampling of the thermospheric vertical wind field at auroral latitudes
Results are presented from two nights of bistatic Doppler measurements of neutral thermospheric winds using Fabry!Perot spectrometers at Mawson and Davis stations in Antarctica. A scanning Doppler imager (SDI) at Mawson and a narrow-field Fabry-Perot spectrometer (FPS) at Davis have been used to estimate the vertical wind at three locations along the great circle joining the two stations, in addition to the vertical wind routinely observed above each station. These data were obtained from observations of the 630.0 nm airglow line of atomic oxygen, at a nominal altitude of 240 km. Low!resolution all-sky images produced by the Mawson SDI have been used to relate disturbances in the measured vertical wind field to auroral activity and divergence in the horizontal wind field. Correlated vertical wind responses were observed on a range of horizontal scales from ~150 to 480 km. In general, the behavior of the vertical wind was in agreement with earlier studies, with strong upward winds observed poleward of the optical aurora and sustained, though weak, downward winds observed early in the night. The relation between vertical wind and horizontal divergence was seen to follow the general trend predicted by Burnside et al. (1981), whereby upward vertical winds were associated with positive divergence and vice versa; however, a scale height approximately 3–4 times greater than that modeled by NRLMSISE-00 was required to best fit the data using this relation
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