6,015 research outputs found
Rigorous QCD Predictions for Decays of P-Wave Quarkonia
Rigorous QCD predictions for decay rates of the P-wave states of heavy
quarkonia are presented. They are based on a new factorization theorem which is
valid to leading order in the heavy quark velocity and to all orders in the
running coupling constant of QCD. The decay rates for all four P states into
light hadronic or electromagnetic final states are expressed in terms of two
phenomenological parameters, whose coefficients are perturbatively calculable.
Logarithms of the binding energy encountered in previous perturbative
calculations of P-wave decays are factored into a phenomenological parameter
that is related to the probability for the heavy quark-antiquark pair to be in
a color-octet S-wave state. Applying these predictions to charmonium, we use
measured decay rates for the \chione and \chitwo to predict the decay rates
of the \chizero and .Comment: 13 page
Hadronic Annihilation Decay Rates of P-wave Heavy Quarkonia with Both Relativistic and QCD Radiative Corrections
Hadronic annihilation decay rates of P-wave heavy quarkonia are given to
next-to-leading order in both and . They include ten
nonperturbative parameters, which can be rigorously defined as the matrix
elements of color-singlet and color-octet operators in NRQCD. We expect these
papameters will be determined from lattice calculations in future.Comment: 5 Pages RevTex. The paper is withdraw
Minimal Flavour Violation with hierarchical squark masses
In a supersymmetric model with hierarchical squark masses we analyze a
pattern of flavour symmetry breaking centered on the special role of the top
Yukawa coupling and, by extension, of the full Yukawa couplings for the up-type
quarks. For sufficiently heavy squarks of the first and second generation this
leads to effective Minimal Flavour Violation of the Flavour Changing Neutral
Current amplitudes. For this to happen we determine the bounds on the masses of
the heavy squarks with QCD corrections taken into account, properly including
previously neglected effects. We believe that the view presented in this paper
altogether strengthens the case for hierarchical sfermions.Comment: 13 pages, 1 figure. v2: an equation correcte
Continuous-Variable Quantum Computing in Optical Time-Frequency Modes using Quantum Memories
We develop a scheme for time-frequency encoded continuous-variable
cluster-state quantum computing using quantum memories. In particular, we
propose a method to produce, manipulate and measure 2D cluster states in a
single spatial mode by exploiting the intrinsic time-frequency selectivity of
Raman quantum memories. Time-frequency encoding enables the scheme to be
extremely compact, requiring a number of memories that is a linear function of
only the number of different frequencies in which the computational state is
encoded, independent of its temporal duration. We therefore show that quantum
memories can be a powerful component for scalable photonic quantum information
processing architectures.Comment: 5 pages, 6 figures, and supplementary information. Updated to be
consistent with published versio
Quantum Correlations from the Conditional Statistics of Incomplete Data
We study, in theory and experiment, the quantum properties of correlated
light fields measured with click-counting detectors providing incomplete
information on the photon statistics. We establish a correlation parameter for
the conditional statistics, and we derive the corresponding nonclassicality
criteria for detecting conditional quantum correlations. Classical bounds for
Pearson's correlation parameter are formulated that allow us, once they are
violated, to determine nonclassical correlations via the joint statistics. On
the one hand, we demonstrate nonclassical correlations in terms of the joint
click statistics of light produced by a parametric down conversion source. On
the other hand, we verify quantum correlations of a heralded, split
single-photon state via the conditional click statistics together with a
generalization to higher-order moments. We discuss the performance of the
presented nonclassicality criteria to successfully discern joint and
conditional quantum correlations. Remarkably, our results are obtained without
making any assumptions on the response function, quantum efficiency, and
dark-count rate of the photodetectors
Experimental quantum computing without entanglement
Entanglement is widely believed to lie at the heart of the advantages offered
by a quantum computer. This belief is supported by the discovery that a
noiseless (pure) state quantum computer must generate a large amount of
entanglement in order to offer any speed up over a classical computer. However,
deterministic quantum computation with one pure qubit (DQC1), which employs
noisy (mixed) states, is an efficient model that generates at most a marginal
amount of entanglement. Although this model cannot implement any arbitrary
algorithm it can efficiently solve a range of problems of significant
importance to the scientific community. Here we experimentally implement a
first-order case of a key DQC1 algorithm and explicitly characterise the
non-classical correlations generated. Our results show that while there is no
entanglement the algorithm does give rise to other non-classical correlations,
which we quantify using the quantum discord - a stronger measure of
non-classical correlations that includes entanglement as a subset. Our results
suggest that discord could replace entanglement as a necessary resource for a
quantum computational speed-up. Furthermore, DQC1 is far less resource
intensive than universal quantum computing and our implementation in a scalable
architecture highlights the model as a practical short-term goal.Comment: 5 pages, 4 figure
Expressive Stream Reasoning with Laser
An increasing number of use cases require a timely extraction of non-trivial
knowledge from semantically annotated data streams, especially on the Web and
for the Internet of Things (IoT). Often, this extraction requires expressive
reasoning, which is challenging to compute on large streams. We propose Laser,
a new reasoner that supports a pragmatic, non-trivial fragment of the logic
LARS which extends Answer Set Programming (ASP) for streams. At its core, Laser
implements a novel evaluation procedure which annotates formulae to avoid the
re-computation of duplicates at multiple time points. This procedure, combined
with a judicious implementation of the LARS operators, is responsible for
significantly better runtimes than the ones of other state-of-the-art systems
like C-SPARQL and CQELS, or an implementation of LARS which runs on the ASP
solver Clingo. This enables the application of expressive logic-based reasoning
to large streams and opens the door to a wider range of stream reasoning use
cases.Comment: 19 pages, 5 figures. Extended version of accepted paper at ISWC 201
Quasiparticles in Neon using the Faddeev Random Phase Approximation
The spectral function of the closed-shell Neon atom is computed by expanding
the electron self-energy through a set of Faddeev equations. This method
describes the coupling of single-particle degrees of freedom with correlated
two-electron, two-hole, and electron-hole pairs. The excitation spectra are
obtained using the Random Phase Approximation, rather than the Tamm-Dancoff
framework employed in the third-order algebraic diagrammatic contruction
[ADC(3)] method. The difference between these two approaches is studied, as
well as the interplay between ladder and ring diagrams in the self-energy.
Satisfactory results are obtained for the ionization energies as well as the
energy of the ground state with the Faddeev-RPA scheme that is also appropriate
for the high-density electron gas.Comment: Revised manuscript. The working equations of the Faddeev-RPA method
are included in the Appendi
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