97 research outputs found
Quantum Efficiency of Charge Qubit Measurements Using a Single Electron Transistor
The quantum efficiency, which characterizes the quality of information gain
against information loss, is an important figure of merit for any realistic
quantum detectors in the gradual process of collapsing the state being
measured. In this work we consider the problem of solid-state charge qubit
measurements with a single-electron-transistor (SET). We analyze two models:
one corresponds to a strong response SET, and the other is a tunable one in
response strength. We find that the response strength would essentially bound
the quantum efficiency, making the detector non-quantum-limited. Quantum
limited measurements, however, can be achieved in the limits of strong response
and asymmetric tunneling. The present study is also associated with appropriate
justifications for the measurement and backaction-dephasing rates, which were
usually evaluated in controversial methods.Comment: 10 pages, 2 figure
Correlated Hybrid Fluctuations from Inflation with Thermal Dissipation
We investigate the primordial scalar perturbations in the thermal dissipative
inflation where the radiation component (thermal bath) persists and the density
fluctuations are thermally originated. The perturbation generated in this model
is hybrid, i.e. it consists of both adiabatic and isocurvature components. We
calculate the fractional power ratio () and the correlation coefficient
() between the adiabatic and the isocurvature perturbations at the
commencing of the radiation regime. Since the adiabatic/isocurvature
decomposition of hybrid perturbations generally is gauge-dependent at
super-horizon scales when there is substantial energy exchange between the
inflaton and the thermal bath, we carefully perform a proper decomposition of
the perturbations. We find that the adiabatic and the isocurvature
perturbations are correlated, even though the fluctuations of the radiation
component is considered uncorrelated with that of the inflaton. We also show
that both and depend mainly on the ratio between the
dissipation coefficient and the Hubble parameter during inflation.
The correlation is positive () for strong dissipation cases
where , and is negative for weak dissipation instances where
. Moreover, and in this model are not
independent of each other. The predicted relation between and
is consistent with the WMAP observation. Other testable predictions are also
discussed.Comment: 18 pages using revtex4, accepted for publication in PR
Weak gravitational lensing
In this brief review I consider the advances made in weak gravitational
lensing over the last 8 years, concentrating on the large scales - cosmic
shear. I outline the theoretical developments, observational status, and the
challenges which cosmic shear must overcome to realise its full potential.
Finally I consider the prospects for probing Dark Energy and extra-dimensional
gravity theories with future experiments.Comment: 6 pages. Short version of invited review at Moriond Cosmology 200
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
Observation of Scaling Violations in Scaled Momentum Distributions at HERA
Charged particle production has been measured in deep inelastic scattering
(DIS) events over a large range of and using the ZEUS detector. The
evolution of the scaled momentum, , with in the range 10 to 1280
, has been investigated in the current fragmentation region of the Breit
frame. The results show clear evidence, in a single experiment, for scaling
violations in scaled momenta as a function of .Comment: 21 pages including 4 figures, to be published in Physics Letters B.
Two references adde
Cold Plus Hot Dark Matter Cosmology in the Light of Solar and Atmospheric Neutrino Oscillations
We explore the implications of possible neutrino oscillations, as indicated
by the solar and atmospheric neutrino experiments, for the cold plus hot dark
matter scenario of large scale structure formation. We find that there are
essentially three distinct schemes that can accommodate the oscillation data
and which also allow for dark matter neutrinos. These include (i) three nearly
degenerate (in mass) neutrinos, (ii) non-degenerate masses with in
the eV range, and (iii) nearly degenerate pair (in the eV
range), with the additional possibility that the electron neutrino is
cosmologically significant. The last two schemes invoke a `sterile' neutrino
which is light (< or ~ eV). We discuss the implications of these schemes for
and oscillation, and find
that scheme (ii) in particular, predicts them to be in the observable range. As
far as structure formation is concerned, we compare the one neutrino flavor
case with a variety of other possibilities, including two and three degenerate
neutrino flavors. We show, both analytically and numerically, the effects of
these neutrino mass scenarios on the amplitude of cosmological density
fluctuations. With a Hubble constant of 50 km s Mpc, a spectral
index of unity, and , the two and three flavor
scenarios fit the observational data marginally better than the single flavor
scheme. However, taking account of the uncertainties in these parameters, we
show that it is premature to pick a clear winner.Comment: 1 LaTEX file plus 1 uuencoded Z-compressed tar file with 3 postscript
figure
An Observational Overview of Solar Flares
We present an overview of solar flares and associated phenomena, drawing upon
a wide range of observational data primarily from the RHESSI era. Following an
introductory discussion and overview of the status of observational
capabilities, the article is split into topical sections which deal with
different areas of flare phenomena (footpoints and ribbons, coronal sources,
relationship to coronal mass ejections) and their interconnections. We also
discuss flare soft X-ray spectroscopy and the energetics of the process. The
emphasis is to describe the observations from multiple points of view, while
bearing in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is far from
complete, so we conclude with a brief discussion of models, and a list of
missing but important observations.Comment: This is an article for a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Observation of Events with an Energetic Forward Neutron in Deep Inelastic Scattering at HERA
In deep inelastic neutral current scattering of positrons and protons at the center of mass energy of 300 GeV, we observe, with the ZEUS detector, events with a high energy neutron produced at very small scattering angles with respect to the proton direction. The events constitute a fixed fraction of the deep inelastic, neutral current event sample independent of Bjorken x and Q2 in the range 3 · 10-4 \u3c xBJ \u3c 6 · 10-3 and 10 \u3c Q2 \u3c 100 GeV2
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