8,323,408 research outputs found
Moments of semileptonic B decay distributions in the 1/m_b expansion
We report the OPE-based predictions for a number of lepton energy and
hadronic mass moments in the inclusive semileptonic B -> X_c \ell\nu decays
with a lower cut on the charged lepton energy. We rely on the direct OPE
approach where no expansion in the charm mass is employed and the theoretical
input is a limited set of underlying OPE parameters including m_b and m_c. A
Wilsonian treatment with a `hard' cutoff is applied using running low-scale
masses m_Q(\mu) and kinetic expectation value \mu_\pi^2(\mu). This leaves for
perturbative corrections only genuinely short-distance effects and makes them
numerically small. Predictions are also given for the modified hadronic moments
of the kinematic variable \cal N_X^2 which is a combination of M_X^2 and E_X.
Measurement of such moments would allow a more reliable extraction of
higher-order nonperturbative heavy quark parameters from experiment.Comment: 16 pages, LaTeX, three figure
Electron Scattering on 3He - a Playground to Test Nuclear Dynamics
The big spectrum of electron induced processes on 3He is illustrated by
several examples based on Faddeev calculations with modern nucleon-nucleon and
three-nucleon forces as well as exchange currents. The kinematical region is
restricted to a mostly nonrelativistic one where the three-nucleon c.m. energy
is below the pion production threshold and the three-momentum of the virtual
photon is sufficiently below the nucleon mass. Comparisons with available data
are shown and cases of agreement and disagreement are found. It is argued that
new and precise data are needed to systematically check the present day
dynamical ingredients.Comment: 27 pages, 24 figure
Signatures of Chiral Dynamics in Low Energy Compton Scattering off the Nucleon
We present a projector formalism which allows to define dynamical
polarizabilities of the nucleon from a multipole expansion of the nucleon
Compton amplitudes. We give predictions for the energy dependence of these
dynamical polarizabilities both from dispersion theory and from
leading-one-loop chiral effective field theory. Based on the good agreement
between the two theoretical frameworks, we conclude that the energy dependence
of the dynamical polarizabilities is dominated by chiral dynamics, except in
those multipole channels where the first nucleon resonance Delta(1232) can be
excited. Both the dispersion theory framework and a chiral effective field
theory with explicit Delta(1232) degrees of freedom lead to a very good
description of the available low energy proton Compton data. We discuss the
sensitivity of the proton Compton cross section to dynamical polarizabilities
of different multipole content and present a fit of the static electric and
magnetic dipole polarizabilities from low-energy Compton data up to omega=170
MeV, finding alpha_E=(11.04+-1.36)*10^(-4) fm^3, beta_M =(2.76-+1.36)*10^(-4)
fm^3.Comment: 43 pages, 13 figure
Transport of a quantum degenerate heteronuclear Bose-Fermi mixture in a harmonic trap
We report on the transport of mixed quantum degenerate gases of bosonic 87Rb
and fermionic 40K in a harmonic potential provided by a modified QUIC trap. The
samples are transported over a distance of 6 mm to the geometric center of the
anti-Helmholtz coils of the QUIC trap. This transport mechanism was implemented
by a small modification of the QUIC trap and is free of losses and heating. It
allows all experiments using QUIC traps to use the highly homogeneous magnetic
fields that can be created in the center of a QUIC trap and improves the
optical access to the atoms, e.g., for experiments with optical lattices. This
mechanism may be cascaded to cover even larger distances for applications with
quantum degenerate samples.Comment: 7 pages, 8 figure
The Experimental Status of the Standard Electroweak Model at the End of the LEP-SLC Era
A method is proposed to calculate the confidence level for agreement of data
with the Standard Model (SM) by combining information from direct and indirect
Higgs Boson searches. Good agreement with the SM is found for
GeV using the observables most sensitive to : and . In
particular, quantum corrections, as predicted by the SM, are observed with a
statistical significance of forty-four standard deviations. However, apparent
deviations from the SM of 3.7 and 2.8 are found for the Z and right-handed Zb couplings respectively. The
maximum confidence level for agreement with the SM of the entire data set
considered is for GeV. The reason why
confidence levels about an order of magnitude higher than this have been
claimed for global fits to similar data sets is explained.Comment: 47 pages, 8 figures, 24 tables. An in-depth study of statistical
issues related to the comparison of precision EW data to the S
Geometric Phase in Entangled Bipartite Systems
The geometric phase (GP) for bipartite systems in transverse external
magnetic fields is investigated in this paper. Two different situations have
been studied. We first consider two non-interacting particles. The results show
that because of entanglement, the geometric phase is very different from that
of the non-entangled case. When the initial state is a Werner state, the
geometric phase is, in general, zero and moreover the singularity of the
geometric phase may appear with a proper evolution time. We next study the
geometric phase when intra-couplings appear and choose Werner states as the
initial states to entail this discussion. The results show that unlike our
first case, the absolute value of the GP is not zero, and attains its maximum
when the rescaled coupling constant is less than 1. The effect of
inhomogeneity of the magnetic field is also discussed.Comment: 5 pages and to be published in Euro. Phys. J.
Experimental local realism tests without fair sampling assumption
Following the theoretical suggestion of Ref. [1,2], we present experimental
results addressed to test restricted families of local realistic models, but
without relying on the fair sampling assumption
Geometric Phase of a qubit interacting with a squeezed-thermal bath
We study the geometric phase of an open two-level quantum system under the
influence of a squeezed, thermal environment for both non-dissipative as well
as dissipative system-environment interactions. In the non-dissipative case,
squeezing is found to have a similar influence as temperature, of suppressing
geometric phase, while in the dissipative case, squeezing tends to counteract
the suppressive influence of temperature in certain regimes. Thus, an
interesting feature that emerges from our work is the contrast in the interplay
between squeezing and thermal effects in non-dissipative and dissipative
interactions. This can be useful for the practical implementation of geometric
quantum information processing. By interpreting the open quantum effects as
noisy channels, we make the connection between geometric phase and quantum
noise processes familiar from quantum information theory.Comment: Accepted for publication in Eur. Phys. J. D; slightly abridged
version of v2; 10 pages, 12 figure
On kaonic hydrogen. Quantum field theoretic and relativistic covariant approach
We study kaonic hydrogen, the bound K^-p state A_(Kp). Within a quantum field
theoretic and relativistic covariant approach we derive the energy level
displacement of the ground state of kaonic hydrogen in terms of the amplitude
of K^-p scattering for arbitrary relative momenta. The amplitude of low-energy
K^-p scattering near threshold is defined by the contributions of three
resonances Lambda(1405), Lambda(1800) and Sigma^0(1750) and a smooth elastic
background. The amplitudes of inelastic channels of low-energy K^-p scattering
fit experimental data on near threshold behaviour of the cross sections and the
experimental data by the DEAR Collaboration. We use the soft-pion technique
(leading order in Chiral Perturbation Theory) for the calculation of the
partial width of the radiative decay of pionic hydrogen A_(pi p) -> n + gamma
and the Panofsky ratio. The theoretical prediction for the Panofsky ratio
agrees well with experimental data. We apply the soft-kaon technique (leading
order in Chiral Perturbation Theory) to the calculation of the partial widths
of radiative decays of kaonic hydrogen A_(Kp) -> Lambda^0 + gamma and A_(Kp) ->
Sigma^0 + gamma. We show that the contribution of these decays to the width of
the energy level of the ground state of kaonic hydrogen is less than 1%.Comment: 33 pages, 1 figure, latex, References are adde
Helicity amplitudes and electromagnetic decays of hyperon resonances
We present results for the helicity amplitudes of the lowest-lying hyperon
resonances Y*, computed within the framework of the Bonn constituent-quark
model, which is based on the Bethe-Salpeter approach. The seven parameters
entering the model were fitted to the best known baryon masses. Accordingly,
the results for the helicity amplitudes are genuine predictions. Some hyperon
resonances are seen to couple more strongly to a virtual photon with finite Q^2
than to a real photon. Other Y*'s, such as the S_{01}(1670) Lambda resonance or
the S_{11}(1620) Sigma resonance, couple very strongly to real photons. We
present a qualitative argument for predicting the behaviour of the helicity
asymmetries of baryon resonances at high Q^2.Comment: 20 pages, 26 figures, uses svjour.cls style, submitted to the
European Physical Journal
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