4,692 research outputs found
Beam polarization effects on top-pair production at the ILC
Full one-loop electroweak-corrections for an
process associated with sequential decay are
discussed. At the one-loop level, the spin-polarization effects of the initial
electron and positron beams are included in the total and differential cross
sections. A narrow-width approximation is used to treat the top-quark
production and decay while including full spin correlations between them. We
observed that the radiative corrections due to the weak interaction have a
large polarization dependence on both the total and differential cross
sections. Therefore, experimental observables that depend on angular
distributions such as the forward-backward asymmetry of the top production
angle must be treated carefully including radiative corrections. We also
observed that the energy distribution of bottom quarks is majorly affected by
the radiative corrections.Comment: 15 pages, 8 figure
Population of individual Ne 1s<sup>-1</sup>np Rydberg states measured across the 1s ionization threshold and the evolution of shake-up into shake-down
Hyperbolic Deformation Applied to S = 1 Spin Chains - Scaling Relation in Excitation Energy -
We investigate excitation energies of hyperbolically deformed S = 1 spin
chains, which are specified by the local energy scale f_j^{~} = \cosh j
\lambda, where j is the lattice index and \lambda is the deformation parameter.
The elementary excitation is well described by a quasiparticle hopping model,
which is also expressed in the form of hyperbolic deformation. It is possible
to estimate the excitation gap \Delta in the uniform limit \lambda \rightarrow
0, by means of a finite size scaling with respect to the system size N and the
deformation parameter \lambda.Comment: 5 pages, 4 figure
Topological classification of vortex-core structures of spin-1 Bose-Einstein condensates
We classify vortex-core structures according to the topology of the order
parameter space. By developing a method to characterize how the order parameter
changes inside the vortex core. We apply this method to the spin-1
Bose-Einstein condensates and show that the vortex-core structures are
classified by winding numbers that are locally defined in the core region. We
also show that a vortex-core structure with a nontrivial winding number can be
stabilized under a negative quadratic Zeeman effect.Comment: 16 pages, 6 figure
Spin Driven Jahn-Teller Distortion in a Pyrochlore system
The ground-state properties of the spin-1 antiferromagnetic Heisenberg model
on the corner-sharing tetrahedra, pyrochlore lattice, is investigated. By
breaking up each spin into a pair of 1/2-spins, the problem is reduced to the
equivalent one of the spin-1/2 tetrahedral network in analogy with the valence
bond solid state in one dimension. The twofold degeneracy of the spin-singlets
of a tetrahedron is lifted by a Jahn-Teller mechanism, leading to a cubic to
tetragonal structural transition. It is proposed that the present mechanism is
responsible for the phase transition observed in the spin-1 spinel compounds
ZnVO and MgVO.Comment: 4 pages, 3 eps figures, REVTeX, to appear in Phys. Rev. Let
Full Counting Statistics of Charge Transfer in Coulomb Blockade Systems
Full counting statistics (FCS) of charge transfer in mesoscopic systems has
recently become a subject of significant interest, since it proves to reveal an
important information about the system which can be hardly assessed by other
means. While the previous research mostly addressed the FCS of non- interacting
systems, the present paper deals with the FCS in the limit of strong
interaction. In this Coulomb blockade limit the electron dynamics is known to
be governed by a master equation. We develop a general scheme to evaluate the
FCS in such case, this being the main result of the work presented. We
illustrate the scheme, by applying it to concrete systems. For generic case of
a single resonant level we establish the equivalence of scattering and master
equation approach to FCS. Further we study a single Coulomb blockade island
with two and three leads attached and compare the FCS in this case with our
recent results concerning an open dot either with two and three terminals. We
demonstrate that Coulomb interaction suppresses the relative probabilities of
large current fluctuations.Comment: 17 pages, 16 figure
T-cell cytotoxicity in the absence of viral protein synthesis in target cells
CYTOTOXIC T cells lyse only those virus infected target cells in vitro which express, in addition to the viral antigen(s), those K or D region products of the major histocompati-bility complex (MHC) which were present during anti-viral sensitisation in vivo. This 'associative recogniton' by cytotoxic T cells could reflect the interaction of two T-cell receptors with specificity for target K or D gene products and independently for the viral antigen, or one receptor with specificity for virally altered K or D region products (see ref. 1 and refs therein). There are various ways that the MHC antigens could be altered, including 'modification from within', where the virus modifies host protein synthesis by interfering with transcription2, translation or post-translational glycosylation; or 'modification from without' where enzymic or chemical alteration of cell membrane proteins are induced by virus activity at the cell surface. In this report we show that inactivated Sendai virus or isolated Sendai virus envelopes can serve to modify a cell and make it a specific target for Sendai-immune T-cell killing, thus excluding the possibility of 'modification from within' in this system
Multiphoton transitions in a macroscopic quantum two-state system
We have observed multiphoton transitions between two macroscopic
quantum-mechanical superposition states formed by two opposite circulating
currents in a superconducting loop with three Josephson junctions. Resonant
peaks and dips of up to three-photon transitions were observed in spectroscopic
measurements when the system was irradiated with a strong RF-photon field. The
widths of the multiphoton absorption dips are shown to scale with the Bessel
functions in agreement with theoretical predictions derived from the Bloch
equation or from a spin-boson model.Comment: 4 pages, 3 figure
Resonance structures in the multichannel quantum defect theory for the photofragmentation processes involving one closed and many open channels
The transformation introduced by Giusti-Suzor and Fano and extended by
Lecomte and Ueda for the study of resonance structures in the multichannel
quantum defect theory (MQDT) is used to reformulate MQDT into the forms having
one-to-one correspondence with those in Fano's configuration mixing (CM) theory
of resonance for the photofragmentation processes involving one closed and many
open channels. The reformulation thus allows MQDT to have the full power of the
CM theory, still keeping its own strengths such as the fundamental description
of resonance phenomena without an assumption of the presence of a discrete
state as in CM.Comment: 7 page
Fano effect in a ring-dot system with tunable coupling
Transport measurements are presented on a quantum ring that is tunnel-coupled
to a quantum dot. When the dot is in the Coulomb blockade regime, but strongly
coupled to the open ring, Fano line shapes are observed in the current through
the ring, when the electron number in the dot changes by one. The symmetry of
the Fano resonances is found to depend on the magnetic flux penetrating the
area of the ring and on the strength of the ring-dot coupling. At temperatures
above T=0.65 K the Fano effect disappears while the Aharonov-Bohm interference
in the ring persists up to T=4.2 K. Good agreement is found between these
experimental observations and a single channel scattering matrix model
including decoherence in the dot.Comment: 9 pages, 6 figure
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