11,283,555 research outputs found
Monte Carlo simulation for radiative kaon decays
For high precision measurements of K decays, the presence of radiated photons
cannot be neglected. The Monte Carlo simulations must include the radiative
corrections in order to compute the correct event counting and efficiency
calculations. In this paper we briefly describe a method for simulating such
decays.Comment: 11 pages, 1 figur
Robust and fragile Werner states in the collective dephasing
We investigate the concurrence and Bell violation of the standard Werner
state or Werner-like states in the presence of collective dephasing. It is
shown that the standard Werner state and certain kinds of Werner-like states
are robust against the collective dephasing, and some kinds of Werner-like
states is fragile and becomes completely disentangled in a finite-time. The
threshold time of complete disentanglement of the fragile Werner-like states is
given. The influence of external driving field on the finite-time
disentanglement of the standard Werner state or Werner-like states is
discussed. Furthermore, we present a simple method to control the stationary
state entanglement and Bell violation of two qubits. Finally, we show that the
theoretical calculations of fidelity based on the initial Werner state
assumption well agree with previous experimental results.Comment: 7 pages, 6 figures, 1 table, RevTex4, Accepted by EPJ
Creating Ioffe-Pritchard micro-traps from permanent magnetic film with in-plane magnetization
We present designs for Ioffe-Pritchard type magnetic traps using planar
patterns of hard magnetic material. Two samples with different pattern designs
were produced by spark erosion of 40 m thick FePt foil. The pattern on the
first sample yields calculated axial and radial trap frequencies of 51 Hz and
6.8 kHz, respectively. For the second sample the calculated frequencies are 34
Hz and 11 kHz. The structures were used successfully as a magneto-optical trap
for Rb and loaded as a magnetic trap. A third design, based on
lithographically patterned 250 nm thick FePt film on a Si substrate, yields an
array of 19 traps with calculated axial and radial trap frequencies of 1.5 kHz
and 110 kHz, respectively.Comment: 8 pages, 5 figures Revised and accepted for EPJD, improved picture
Non-Minimal Coupling to a Lorentz-Violating Background and Topological Implications
The non-minimal coupling of fermions to a background responsible for the
breaking of Lorentz symmetry is introduced in Dirac's equation; the
non-relativistic regime is contemplated, and the Pauli's equation is used to
show how an Aharonov-Casher phase may appear as a natural consequence of the
Lorentz violation, once the particle is placed in a region where there is an
electric field. Different ways of implementing the Lorentz breaking are
presented and, in each case, we show how to relate the Aharonov-Casher phase to
the particular components of the background vector or tensor that realises the
violation of Lorentz symmetry.Comment: 8 pages, added references, no figure
Eikonal representation in the momentum-transfer space
By means of empirical fits to the differential cross section data on pp and
p(bar)p elastic scattering, above 10 GeV (center-of-mass energy), we determine
the eikonal in the momentum - transfer space (q^2- space). We make use of a
numerical method and a novel semi-analytical method, through which the
uncertainties from the fit parameters can be propagated up to the eikonal in
the - space. A systematic study of the effect of the experimental
information at large values of the momentum transfer is developed and discussed
in detail. We present statistical evidence that the imaginary part of the
eikonal changes sign in the q^2- space and that the position of the zero
decreases as the energy increases; after the position of the zero, the eikonal
presents a minimum and then goes to zero through negative values. We discuss
the applicability of our results in the phenomenological context, outlining
some connections with nonperturbative QCD. A short review and a critical
discussion on the main results concerning "model-independent" analyses are also
presented.Comment: 18 pages, 17 figures, 4 tables, svjour.cls. Revised discussion on the
proton's electromagnetic form factor and references added. To appear in Eur.
Phys. J.
Covariant canonical quantization of fields and Bohmian mechanics
We propose a manifestly covariant canonical method of field quantization
based on the classical De Donder-Weyl covariant canonical formulation of field
theory. Owing to covariance, the space and time arguments of fields are treated
on an equal footing. To achieve both covariance and consistency with standard
noncovariant canonical quantization of fields in Minkowski spacetime, it is
necessary to adopt a covariant Bohmian formulation of quantum field theory. A
preferred foliation of spacetime emerges dynamically owing to a purely quantum
effect. The application to a simple time-reparametrization invariant system and
quantum gravity is discussed and compared with the conventional noncovariant
Wheeler-DeWitt approach.Comment: 17 pages, revised, to appear in Eur. Phys. J.
Full separability criterion for tripartite quantum systems
In this paper, an intuitive approach is employed to generalize the full
separability criterion of tripartite quantum states of qubits to the
higher-dimensional systems (Phys. Rev. A \textbf{72}, 022333 (2005)). A
distinct characteristic of the present generalization is that less restrictive
conditions are needed to characterize the properties of full separability.
Furthermore, the formulation for pure states can be conveniently extended to
the case of mixed states by utilizing the kronecker product approximate
technique. As applications, we give the analytic approximation of the criterion
for weakly mixed tripartite quantum states and investigate the full
separability of some weakly mixed states.Comment: 5 pages. To be published in Europ. J.
Flavor changing neutral currents from lepton and B decays in the two Higgs doublet model
Constraints on the whole spectrum of lepton flavor violating vertices are
shown in the context of the standard two Higgs doublet model. The vertex
involving the mixing is much more constrained than the others, and
the decays proportional to such vertex are usually very supressed. On the other
hand, bounds on the quark sector are obtained from leptonic decays of the
mesons and from . We emphasize that
although the mixing restricts severely the
mixing vertex, the upper bound for this vertex could still give a sizeable
contribution to the decay respect to the standard
model contribution, from which we see that such vertex could still play a role
in the phenomenology.Comment: 9 pages, 2 figures, LaTeX2e. Minor typos corrected. References added
and corrected. Introduction change
Anisotropic field dependence of the magnetic transition in Cu2Te2O5Br2
We present the results of measurements of the thermal conductivity of
Cu2Te2O5Br2, a compound where tetrahedra of Cu^{2+} ions carrying S=1/2 spins
form chains along the c-axis of the tetragonal crystal structure. The thermal
conductivity kappa was measured along both the c- and the a-direction as a
function of temperature between 3 and 300 K and in external magnetic fields H
up to 69 kOe, oriented both parallel and perpendicular to the c-axis. Distinct
features of kappa(T) were observed in the vicinity of T_N=11.4 K in zero
magnetic field. These features are unaltered in external fields which are
parallel to the c-axis, but are more pronounced when a field is applied
perpendicularly to the c-axis. The transition temperature increases upon
enhancing the external field, but only if the field is oriented along the
a-axis.Comment: 5 pages, 3 figure
Josephson oscillation of a superfluid Fermi gas
Using the complete numerical solution of a time-dependent three-dimensional
mean-field model we study the Josephson oscillation of a superfluid Fermi gas
(SFG) at zero temperature formed in a combined axially-symmetric harmonic plus
one-dimensional periodic optical-lattice (OL) potentials after displacing the
harmonic trap along the axial OL axis. We study the dependence of Josephson
frequency on the strength of the OL potential. The Josephson frequency
decreases with increasing strength as found in the experiment of Cataliotti et
al. [Science 293 (2001) 843] for a Bose-Einstein condensate and of the
experiment of Pezze et al. [Phys. Rev. Lett. 93 (2004) 120401] for an ideal
Fermi gas. We demonstrate a breakdown of Josephson oscillation in the SFG for a
large displacement of the harmonic trap. These features of Josephson
oscillation of a SFG can be tested experimentally.Comment: 7 pages, 10 figure
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