Size effects on polaritons in thin crystals with perfect interference spectra

Size effects on polaritons in thin plane parallel CdS and CdSe crystals are discussed. For samples not thinner than 0.1 μm the measurements of transmittance and reflectance show the size quantization of the mechanical exciton dispersion and a shift of the resonance frequency of the exciton to the high-energy side with decreasing thickness. However no evidence for the alteration of the oscillator strength or other parameters has been obtained. This conclusion is in conflict with the recently published data taken on CdS samples. The stability of the polariton dispersion in our case is supported by the theoretical study of reflectance ignoring the effects of the finiteness of the exciton radius.     

D s lifetime,m b,m c and |V cb | in the heavy quark expansion

Zeitschrift für Physik C Particles and Fields - We present some straightforward applications of the QCD heavy quark expansion, stated in previous papers [1–3], to the inclusive widths of...     

Magnetic-field-effects on photoluminescence polarization in type II GaAs/AlAs superlattices

Optical orientation and alignment in the presence of a magnetic field have been applied to study the fine structure of excitons in type II GaAs/AlAs superlattices. We have developed a theory of polarized photoluminescence taking into account the anisotropic exchange splitting of the radiative excitonic doublet. The observed effects of the longitudinal and transverse magnetic fields on the polarization of the exciton emission unambiguously confirm that the actual symmetry of the exciton is lower that D_2d and that there exist two classes of excitons with opposite signs of the anisotropic exchange splitting.     

Picosecond luminescence studies of vertical transport in short-period superlattices

Photoluminescence studies with ps-time resolution are reported for three different types of GaAs-AlGaAs microstructures: (i) a short-period superlattice, (ii) a superlattice, where an enlarged well is introduced into the center, and, (iii) a superlattice, where this well is separated from the superlattice by enlarged barriers. Exciting the samples by a mode-locked Ar⁺ laser very high sensitivity is achieved by an electro-optical cross-correlation technique using a gain modulated Si avalanche photodiode as a detector. From the data obtained we are able to determine the relevant parameters of vertical transport and nonradiative recombination in the respective structures.     

Gluonic enhancements in non-spectator beauty decays—an inclusive mirage though an exclusive possibility

It has been claimed that gluon emission can raise weak annihilation contributions to heavy quark decays by powers of (m_Q/μ_had), the ratio of the heavy quark mass to a light hadron mass scale. We show that such powerlike enhancements of annihilation, interference and other preasymptotic effects do not arise for fully inclusive transitions, only for partial rates. The leading corrections are then logarithmic; even so they are crucial for determining the impact of these effects. We establish a non-trivial relation between euclidean renormalization and real decay processes in Minkowski space. Phenomenological consequences are briefly discussed, e.g. we expect the B_d and B⁻ lifetimes to differ by only a few percent with interference being the maon driving force. The (hybrid) log corrections are essential for the degree of interference by effectively cancelling non-leading terms in a 1/N_c expansion.     

Algebraic construction of static axially symmetric self-dual gauge fields for an arbitrary group

It is suggested that the Higgs and the Yukawa couplings of the standard model possess two global U(1)-symmetries: independent chiral rotations of quarks and leptons. The model requires the existence of two axions, one of which (massive) does not interact with leptons, whereas the second one interacts both with leptons and quarks.     

Moments of semileptonic B decay distributionsin 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 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 and a kinetic expectation value . 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 which is a combination of M_X² and E_X. The measurement of such moments would allow a more reliable extraction to be made of higher-order non-perturbative heavy quark parameters from experiment.Received: 13 January 2004, Published online: 3 March 2004N. Uraltsev: On leave of absence from St. Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg 188300, Russia.