745 research outputs found
Entangled qutrits violate local realism stronger than qubits - an analytical proof
In Kaszlikowski [Phys. Rev. Lett. {\bf 85}, 4418 (2000)], it has been shown
numerically that the violation of local realism for two maximally entangled
-dimensional () quantum objects is stronger than for two maximally
entangled qubits and grows with . In this paper we present the analytical
proof of this fact for N=3.Comment: 5 page
A Bayesian view of the current status of dark matter direct searches
Bayesian statistical methods offer a simple and consistent framework for
incorporating uncertainties into a multi-parameter inference problem. In this
work we apply these methods to a selection of current direct dark matter
searches. We consider the simplest scenario of spin-independent elastic WIMP
scattering, and infer the WIMP mass and cross-section from the experimental
data with the essential systematic uncertainties folded into the analysis. We
find that when uncertainties in the scintillation efficiency of Xenon100 have
been accounted for, the resulting exclusion limit is not sufficiently
constraining to rule out the CoGeNT preferred parameter region, contrary to
previous claims. In the same vein, we also investigate the impact of
astrophysical uncertainties on the preferred WIMP parameters. We find that
within the class of smooth and isotropic WIMP velocity distributions, it is
difficult to reconcile the DAMA and the CoGeNT preferred regions by tweaking
the astrophysics parameters alone. If we demand compatibility between these
experiments, then the inference process naturally concludes that a high value
for the sodium quenching factor for DAMA is preferred.Comment: 37 pages, 14 figures and 7 tables. Replacement for matching the
version accepted for publicatio
Degree of entanglement for two qubits
In this paper, we present a measure to quantify the degree of entanglement
for two qubits in a pure state.Comment: 5 page
Scalar Multiplet Dark Matter
We perform a systematic study of the phenomenology associated to models where
the dark matter consists in the neutral component of a scalar SU(2)_L n-uplet,
up to n=7. If one includes only the pure gauge induced annihilation
cross-sections it is known that such particles provide good dark matter
candidates, leading to the observed dark matter relic abundance for a
particular value of their mass around the TeV scale. We show that these values
actually become ranges of values -which we determine- if one takes into account
the annihilations induced by the various scalar couplings appearing in these
models. This leads to predictions for both direct and indirect detection
signatures as a function of the dark matter mass within these ranges. Both can
be largely enhanced by the quartic coupling contributions. We also explain how,
if one adds right-handed neutrinos to the scalar doublet case, the results of
this analysis allow to have altogether a viable dark matter candidate,
successful generation of neutrino masses, and leptogenesis in a particularly
minimal way with all new physics at the TeV scale.Comment: 43 pages, 20 figure
operator for canonical quantum gravity
We study the properties of operator on the kinematical
Hilbert space for canonical quantum gravity. Its complete spectrum
with respect to the spin network basis is obtained. It turns out that
is diagonalized in this basis, and it is a well defined
self-adjoint operator on . The same conclusions are also tenable on
the SU(2) gauge invariant Hilbert space with the gauge invariant spin network
basis.Comment: 10 pages, minor modefication, reference update
Chern-Simons Term for BF Theory and Gravity as a Generalized Topological Field Theory in Four Dimensions
A direct relation between two types of topological field theories,
Chern-Simons theory and BF theory, is presented by using ``Generalized
Differential Calculus'', which extends an ordinary p-form to an ordered pair of
p and (p+1)-form. We first establish the generalized Chern-Weil homomormism for
generalized curvature invariant polynomials in general even dimensional
manifolds, and then show that BF gauge theory can be obtained from the action
which is the generalized second Chern class with gauge group G. Particularly
when G is taken as SL(2,C) in four dimensions, general relativity with
cosmological constant can be derived by constraining the topological BF theory.Comment: Improved abstract and introduction with 11 references added. Accepted
for publication in Physical Review
The Structure of Nanoscale Polaron Correlations in La1.2Sr1.8Mn2O7
A system of strongly-interacting electron-lattice polarons can exhibit charge
and orbital order at sufficiently high polaron concentrations. In this study,
the structure of short-range polaron correlations in the layered colossal
magnetoresistive perovskite manganite, La1.2Sr1.8Mn2O7, has been determined by
a crystallographic analysis of broad satellite maxima observed in diffuse X-ray
and neutron scattering data. The resulting q=(0.3,0,1) modulation is a
longitudinal octahedral-stretch mode, consistent with an incommensurate
Jahn-Teller-coupled charge-density-wave fluctuations, that implies an unusual
orbital-stripe pattern parallel to the directions.Comment: Reformatted with RevTe
Work function changes in the double layered manganite La1.2Sr1.8Mn2O7
We have investigated the behaviour of the work function of La1.2Sr1.8Mn2O7 as
a function of temperature by means of photoemission. We found a decrease of 55
+/- 10 meV in going from 60 K to just above the Curie temperature (125 K) of
the sample. Above T_C the work function appears to be roughly constant. Our
results are exactly opposite to the work function changes calculated from the
double-exchange model by Furukawa, but are consistent with other measurements.
The disagreement with double-exchange can be explained using a general
thermodynamic relation valid for second order transitions and including the
extra processes involved in the manganites besides double-exchange interaction.Comment: 6 pages, 4 figures included in tex
Effects of decoherence and errors on Bell-inequality violation
We study optimal conditions for violation of the Clauser-Horne-Shimony-Holt
form of the Bell inequality in the presence of decoherence and measurement
errors. We obtain all detector configurations providing the maximal Bell
inequality violation for a general (pure or mixed) state. We consider local
decoherence which includes energy relaxation at the zero temperature and
arbitrary dephasing. Conditions for the maximal Bell-inequality violation in
the presence of decoherence are analyzed both analytically and numerically for
the general case and for a number of important special cases. Combined effects
of measurement errors and decoherence are also discussed.Comment: 18 pages, 5 figure
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
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