Antiferromagnetic s-d exchange coupling in GaMnAs

Measurements of coherent electron spin dynamics in Ga1-xMnxAs/Al0.4Ga0.6As quantum wells with 0.0006%相似文献   

Information capacity gain by time-division multiplexing in three-dimensional integral imaging

We evaluate improvements in information capacity gained by use of time-division multiplexing (TDM) in three-dimensional integral imaging (II) systems. This analysis supports the motivation for two TDM methods in II [Opt. Lett. 27, 324 (2002); 1144 (2002)] that we previously developed.     

Chiral order and fluctuations in multi-flavour QCD

Multi-flavour chiral perturbation theory (PT) may exhibit instabilities due to vacuum fluctuations of sea pairs. Keeping the fluctuations small would require a very precise fine tuning of the low-energy constants and to , . A small deviation from these critical values - like the one suggested by the phenomenology of OZI-rule violation in the scalar channel - is amplified by huge numerical factors inducing large effects of vacuum fluctuations. This would lead in particular to a strong N_f dependence of chiral symmetry breaking (SB) and a suppression of the multi-flavour chiral order parameters. A simple resummation is shown to cure the instability of PT, but it modifies the standard expressions of some O(p ² ) and O(p ⁴ ) low-energy parameters in terms of observables. On the other hand, for r= m _s /m > 15, the two-flavour condensate is not suppressed, due to the contribution induced by massive vacuum pairs. Thanks to the latter, the standard two-flavour PT is protected from multi-flavour instabilities and could provide a well-defined expansion scheme in powers of non-strange quark masses. Received: 31 July 2002 / Revised version: 6 November 2002 / Published online: 15 January 2003 RID="a" ID="a" e-mail: sdg@hep.phys.soton.ac.uk RID="b" ID="b" e-mail: luca.girlanda@pd.infn.it ^* Present address: ECT^*, Villa Tambosi, Strada delle Tabarelle 286, 38050 Trento, Italy RID="c" ID="c" e-mail: stern@ipno.in2p3.fr     

Search for the lepton family number violating process nu(mu)e(-) --> mu(-)nu(e)

The NuTeV experiment at Fermilab has used a sign-selected neutrino beam to perform a search for the lepton number violating process nu(mu)e(-)-->mu(-)nu(e), and to measure the cross section of the standard model inverse muon decay process nu(mu)e(-)-->mu(-)nu(e). NuTeV measures the inverse muon decay asymptotic cross-section slope sigma/E to be (13.8 +/- 1.2 +/- 1.4) x 10(-42) cm(2)/GeV. The experiment also observes no evidence for lepton number violation and places one of the most restrictive limits on the cross-section ratio sigma(nu(mu)e(-)-->mu(-)nu(e))/sigma(nu(mu)e(-)-->mu(-)nu(e)) < or = 1.7% at 90% C.L. for V-A couplings and < or = 0.6% for scalar couplings.     

Nonperturbative field-theoretical model of leptonic weak interactions

Acta physica Academiae Scientiarum Hungaricae - In this work the problem of the four-leptonic weak processes is studied in the theory with an intermediate vectorW-meson. Neglecting 1.m lept., 2....     

Review of the KL → μ+μ− puzzle

It is recalled that the conventional mechanisms for weak and electromagnetic interactions and for observed particles lead via, unitarity and CPT, to a predicted value for the branching ratio of K_L → μ⁺μ^? in contradiction with the experimental upper limit. We review the models suggested as a solution to this puzzle which introduce new particles and/or new interactions; the models which preserve CP invariance appear unattractive or seem dubious from the experimental point of view; the models which incorporate large CP violations, predict an anomalously large value for the (K_S → μ⁺μ^?)-branching ratio which requires experimental confirmation.     

Light cone and mass shells

We propose a hypothesis which generalizes the notion of duality to off-mass-shell current matrix elements. The hypothesis, referred to as strong light-cone dominance, is formulated in terms of the light-cone sum rules, which reflect causality and the light-cone structure of current commutators: We postulate that these sum rules are saturated quasilocally by individual resonance peaks, in a similar manner as duality requires resonances to saturate the FESR for the hadronic on-shell amplitudes. This reconstitutes scaling in an average sense in regions where the leading light-cone singularity does not dominate. In coordinate space this hypothesis implies that the leading light-cone singularity regulates (tames) the entire light-cone expansion in a neighbourhood of the surface of the light-cone, whose extension is of the order of an inverse mass difference between consecutive resonances. We investigate the hypothesis of strong light-cone dominance in the framework of narrow resonance models for the vertex and show that the leading light-cone singularity indeed normalizes the single particle contributions by means of a relation of the Drell-Yan-West type. A simple Veneziano-like vertex model is exhibited, which is strongly light-cone dominated. Furthermore, we show how to exploitthe hypothesis in a rather model-independent way. We present some applications to the non-forward four-point function and show in particular that strong light-cone dominancerequires scaling for exclusive electroproduction processes like $\text{γ}{}^1\text{+}\text{N}\text{→ π +}\text{N}$.     

On complements in lattices with covering properties

Dedicated to the memory of Herbert Gross     

Colour Plasma Displays by UV-Excited Phosphors A Review

Though intense work on the development of a full colour flat TV display panel based on gas discharges has produced considerable progress over the last 10 years no practicable technological solutions have been found [1–2]. Of the different approaches the alternating current (ac) discharge has been proved suitable for the alphanumerical and graphical display technique and the direct current (dc) discharge for colour TV panels. To reach such aims as improved optical efficiency, colour gamut and increased life time as well as simpler manufacturing technology and more effective addressing for reducing costs, long-term basic research in the field of gas discharges and phosphors and the development of special technologies is necessary [3–8]. The present review is an attempt to give a survey of this situation. In Chap. 1 the trends of development, general problems of colour, display types and TV are dealt with, and in Chap. 2 and 3 the literature on dc and ac-display panels is reviewed.