10,505 research outputs found

### Solar Neutrino Oscillation Parameters after KamLAND

We explore the impact of the data from the KamLAND experiment in constraining
neutrino mass and mixing angles involved in solar neutrino oscillations. In
particular we discuss the precision with which we can determine the the mass
squared difference $\Delta m^2_{solar}$ and the mixing angle $\theta_{solar}$
from combined solar and KamLAND data. We show that the precision with which
\Delta m^_{solar} can be determined improves drastically with the KamLAND
data but the sensitivity of KamLAND to the mixing angle is not as good. We
study the effect of enhanced statistics in KamLAND as well as reduced
systematics in improving the precision. We also show the effect of the SNO salt
data in improving the precision. Finally we discuss how a dedicated reactor
experiment with a baseline of 70 km can improve the $\theta_{solar}$
sensitivity by a large amount.Comment: Talk given at 4th International Conference on Nonaccelerator New
Physics (NANP 03), Dubna, Russia, 23-28 Jun 200

### The dominant spin relaxation mechanism in compound organic semiconductors

Despite the recent interest in "organic spintronics", the dominant spin
relaxation mechanism of electrons or holes in an organic compound semiconductor
has not been conclusively identified. There have been sporadic suggestions that
it might be hyperfine interaction caused by background nuclear spins, but no
confirmatory evidence to support this has ever been presented. Here, we report
the electric-field dependence of the spin diffusion length in an organic
spin-valve structure consisting of an Alq3 spacer layer, and argue that this
data, as well as available data on the temperature dependence of this length,
contradict the notion that hyperfine interactions relax spin. Instead, they
suggest that the Elliott-Yafet mechanism, arising from spin-orbit interaction,
is more likely the dominant spin relaxing mechanism.Comment: Accepted for publication in Physical Review

### Displaced Higgs production in type III seesaw

We point out that the type III seesaw mechanism introducing fermion triplets
predicts peculiar Higgs boson signatures of displaced vertices with two b jets
and one or two charged particles which can be cleanly identified. In a
supersymmetric theory, the scalar partner of the fermion triplet contains a
neutral dark matter candidate which is almost degenerate with its charged
components. A Higgs boson can be produced together with such a dark matter
triplet in the cascade decay chain of a strongly produced squark or gluino.
When the next lightest supersymmetric particle (NLSP) is bino/wino-like, there
appears a Higgs boson associated with two charged tracks of a charged lepton
and a heavy charged scalar at a displacement larger than about 1 mm. The
corresponding production cross-section is about 0.5 fb for the squark/gluino
mass of 1 TeV. In the case of the stau NLSP, it decays mainly to a Higgs boson
and a heavy charged scalar whose decay length is larger than 0.1 mm for the
stau NLSP mixing with the left-handed stau smaller than 0.3. As this process
can have a large cascade production $\sim 2$ pb for the squark/gluino mass
$\sim 1$ TeV, one may be able to probe it at the early stage of the LHC
experiment.Comment: 10 pages, 5 figure

### Entangling capacities of noisy two-qubit Hamiltonians

We show that intrinsic fluctuations in system control parameters impose
limits on the ability of two-qubit (exchange) Hamiltonians to generate
entanglement starting from mixed initial states. We find three classes for
Gaussian and Laplacian fluctuations. For the Ising and XYZ models there are
qualitatively distinct sharp entanglement-generation transitions, while the
class of Heisenberg, XY, and XXZ Hamiltonians is capable of generating
entanglement for any finite noise level. Our findings imply that exchange
Hamiltonians are surprisingly robust in their ability to generate entanglement
in the presence of noise, thus potentially reducing the need for quantum error
correction.Comment: 5 pages, incl. 2 figures. replaced with published versio

### Effect of silica colloids on the rheology of viscoelastic gels formed by the surfactant cetyl trimethylammonium tosylate

The effects of the addition of sub-micrometer sized colloidal silica spheres
on the linear and nonlinear rheology of semi-dilute solutions of a viscoelastic
gel are studied. For a 1.4 wt.% solution of the surfactant CTAT, a peak in the
zero shear rate viscosity $\eta_{\circ}$ is observed at approximately equal
weight percents of silica and CTAT. This peak shifts to lower silica
concentrations on increasing either the CTAT concentration or the surface
charge on silica and disappears when the CTAT concentration is increased to
2.6wt%. The increases in $\eta_{\circ}$ and the high frequency plateau modulus
G$_{\circ}$ on the introduction of SiO$_{2}$ are explained by considering the
increasingly entangled wormlike micelles that are formed due to the enhanced
screening of the electrostatic interactions. The observed decrease in the
values of G$_{\circ}$ and $\eta_{\circ}$ at higher concentrations of silica
particles is explained in terms of the formation of surfactant bilayers due to
the adsorption of the positively charged cetyl trimethylammonium to the
negatively charged silica.Comment: 28 pages, includes 8 eps and 2 png figures; accepted for publication
in Jl. Colloid Interface Sc

### Dynamical Behaviour in the Nonlinear Rheology of Surfactant Solutions

Several surfactant molecules self-assemble in solution to form long, flexible
wormlike micelles which get entangled with each other, leading to viscoelastic
gel phases. We discuss our recent work on the rheology of such a gel formed in
the dilute aqueous solutions of a surfactant CTAT. In the linear rheology
regime, the storage modulus $G^{\prime}(\omega)$ and loss modulus
$G^{\prime\prime}(\omega)$ have been measured over a wide frequency range. In
the nonlinear regime, the shear stress $\sigma$ shows a plateau as a function
of the shear rate $\dot\gamma$ above a certain cutoff shear rate
$\dot\gamma_c$. Under controlled shear rate conditions in the plateau regime,
the shear stress and the first normal stress difference show oscillatory
time-dependence. The analysis of the measured time series of shear stress and
normal stress has been done using several methods incorporating state space
reconstruction by embedding of time delay vectors.The analysis shows the
existence of a finite correlation dimension and a positive Lyapunov exponent,
unambiguously implying that the dynamics of the observed mechanical instability
can be described by that of a dynamical system with a strange attractor of
dimension varying from 2.4 to 2.9.Comment: 12 pages, includes 7 eps figure

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