8,962 research outputs found
Structure of the -meson and diamagnetism of the nucleon
The structure of the meson and the diamagnetism of the nucleon are
shown to be topics which are closely related to each other. Arguments are found
that the meson couples to two photons via its non-strange
structure component. This ansatz leads to a quantitative explanation of the
-channel component of the difference of electromagnetic polarizabilities,
(\alpha-\beta)^t(\alpha-\beta)^t_{p,n}=(5\alpha_e g_{\pi MM})/(6\pi^2 m^2_\sigma
f_\pi)=15.310^{-4}{\rm fm}^3(\alpha-\beta)^t_p=15.1\pm 1.3(\alpha-\beta)^t_n=14.8\pm 2.7\pi\pi\sigma(\alpha-\beta)^t_{p,n}=14\pm 2$, what also is in agreement with
the experimental results.Comment: Contribution made by Martin Schumacher to the International Workshop
on the Physics of Excited Baryons, 12 - 15 Oct. 2005, Tallahasse, Florida US
Surface roughness and interfacial slip boundary condition for quartz crystal microbalances
The response of a quartz crystal microbalance (QCM) is considered using a wave equation for the substrate and the Navier-Stokes equations for a finite liquid layer under a slip boundary condition. It is shown that when the slip length to shear wave penetration depth is small, the first order effect of slip is only present in the frequency response. Importantly, in this approximation the frequency response satisfies an additivity relation with a net response equal to a Kanazawa liquid term plus an additional Sauerbrey "rigid" liquid mass. For the slip length to result in an enhanced frequency decrease compared to a no-slip boundary condition, it is shown that the slip length must be negative so that the slip plane is located on the liquid side of the interface. It is argued that the physical application of such a negative slip length could be to the liquid phase response of a QCM with a completely wetted rough surface. Effectively, the model recovers the starting assumption of additivity used in the trapped mass model for the liquid phase response of a QCM having a rough surface. When applying the slip boundary condition to the rough surface problem, slip is not at a molecular level, but is a formal hydrodynamic boundary condition which relates the response of the QCM to that expected from a QCM with a smooth surface. Finally, possible interpretations of the results in terms of acoustic reflectivity are developed and the potential limitations of the additivity result should vapour trapping occur are discussed
Relativistic corrections to the electromagnetic polarizabilities of compound systems
The low-energy amplitude of Compton scattering on the bound state of two
charged particles of arbitrary masses, charges and spins is calculated. A case
in which the bound state exists due to electromagnetic interaction (QED) is
considered. The term, proportional to , is obtained taking into
account the first relativistic correction. It is shown that the complete result
for this correction differs essentially from the commonly used term
, proportional to the r.m.s. charge radius of the system. We
propose that the same situation can take place in the more complicated case of
hadrons.Comment: 19 pages, LaTe
Quantum privacy and quantum coherence
We derive a simple relation between a quantum channel's capacity to convey
coherent (quantum) information and its usefulness for quantum cryptography.Comment: 6 pages RevTex; two short comments added 7 October 199
Perturbative expansions for the fidelities and spatially correlated dissipation of quantum bits
We construct generally applicable short-time perturbative expansions for some
fidelities, such as the input-output fidelity, the entanglement fidelity, and
the average fidelity. Successive terms of these expansions yield characteristic
times for the damping of the fidelities involving successive powers of the
Hamiltonian. The second-order results, which represent the damping rates of the
fidelities, are extensively discussed. As an interesting application of these
expansions, we use them to study the spatially-correlated dissipation of
quantum bits. Spatial correlations in the dissipation are described by a
correlation function. Explicit conditions are derived for independent
decoherence and for collective decoherence.Comment: Minor changes in discussion
Entanglement transmission and generation under channel uncertainty: Universal quantum channel coding
We determine the optimal rates of universal quantum codes for entanglement
transmission and generation under channel uncertainty. In the simplest scenario
the sender and receiver are provided merely with the information that the
channel they use belongs to a given set of channels, so that they are forced to
use quantum codes that are reliable for the whole set of channels. This is
precisely the quantum analog of the compound channel coding problem. We
determine the entanglement transmission and entanglement-generating capacities
of compound quantum channels and show that they are equal. Moreover, we
investigate two variants of that basic scenario, namely the cases of informed
decoder or informed encoder, and derive corresponding capacity results.Comment: 45 pages, no figures. Section 6.2 rewritten due to an error in
equation (72) of the old version. Added table of contents, added section
'Conclusions and further remarks'. Accepted for publication in
'Communications in Mathematical Physics
Incoherent pion photoproduction on the deuteron in the first resonance region
Incoherent pion photoproduction on the deuteron is studied in the first
resonance region. The unpolarized cross section, the beam asymmetry, and the
vector and tensor target asymmetries are calculated in the framework of a
diagrammatic approach. Pole diagrams and one-loop diagrams with scattering
in the final state are taken into account. An elementary operator for pion
photoproduction on the nucleon is taken in various on-shell forms and
calculated using the SAID and MAID multipole analyses. Model dependence of the
obtained results is discussed in some detail. A comparison with predictions of
other works is given. Although a reasonable description of many available
experimental data on the unpolarized total and differential cross sections and
photon asymmetry has been achieved, in some cases a significant disagreement
between the theory and experiment has been found. Invoking known information on
the reactions and we predict the total
photoabsorption cross section for deuterium. We find that our values strongly
overestimate experimental data in the vicinity of the peak.Comment: 22 pages, 23 figure
Visible compression of commuting mixed states
We analyze the problem of quantum data compression of commuting density
operators in the visible case. We show that the lower bound for the compression
factor given by the Levitin--Holevo function is reached by providing an
explicit protocol.Comment: 7 pages, no figure
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