15,815 research outputs found

### Search for CP-violation in Positronium Decay

CP-violation in the quark sector has been well established over the last
decade, but has not been observed in the lepton sector. We search for
CP-violating decay processes in positronium, using the angular correlation of
(\vec{S}\cdot\vec{k_{1}})(\vec{S}\cdot\vec{k_{1}}\times\vec{k_{2}}), where
\vec{S} is the the positronium spin and \vec{k_{1}}, \vec{k_{2}} are the
directions of the positronium decay photons. To a sensitivity of
2.2\times10^{-3}, no CP-violation has been found, which is at the level of the
CP-violation amplitude in the K meson. A 90% confidence interval of the
CP-violation parameter (C_{CP}) was determined to be -0.0023 < C_{CP} < 0.0049.
This result is a factor 7 more strict than that of the previous experiment

### Study of unstable particle through the spectral function in O(4) $\phi^4$ theory

We test application of the maximum entropy method to decompose the states
contributing to the unstable $\sigma$ correlation function through the spectral
function in the four dimensional O(4) $\phi^4$ theory. Reliable results are
obtained for the $\sigma$ mass and two-particle $\pi\pi$ state energy using
only the $\sigma$ correlation function. We also find that the property of the
$\sigma$ particle is different between the unstable ($m_{\sigma}/m_{\pi}>2$)
and stable ($m_{\sigma}/m_{\pi}<2$) cases.Comment: Lattice2002(spectrum), 3 page

### Effect of the shape anisotropy on the magnetic configuration of (Ga,Mn)As and its evolution with temperature

We study the effect of the shape anisotropy on the magnetic domain
configurations of a ferromagnetic semiconductor (Ga,Mn)As/GaAs(001) epitaxial
wire as a function of temperature. Using magnetoresistance measurements, we
deduce the magnetic configurations and estimate the relative strength of the
shape anisotropy compared with the intrinsic anisotropies. Since the intrinsic
anisotropy is found to show a stronger temperature dependence than the shape
anisotropy, the effect of the shape anisotropy on the magnetic domain
configuration is relatively enhanced with increasing temperature. This
information about the shape anisotropy provides a practical means of designing
nanostructured spin electronic devices using (Ga,Mn)As.Comment: 4 pages, 4 figures, to appear in J. Appl. Phy

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