Challenges for extended technicolour theories

We develop the dialectic between extended technicolour theories and phenomenological constraints on rare processes. The natural suppression of flavour-changing neutral currents and CP-violating processes which can occur in models with elementary scalars is not a general feature of naïve extended technicolour (ETC) models. We study the extent to which naïve ETC estimates must in fact be suppressed in order to be compatible with the phenomenology of such rare processes. We emphasize the potential significance of the exchanges of neutral flavour-changing bosons and find that the strongest constraints arise from considering the combination of the D₁⁰-D₂⁰ and K₁⁰-K₂⁰ systems. CP-violating effects in ETC models must be severely suppressed if they are to be compatible with the observational facts. We point to several rare processes whose further experimental study is of particular concern to ETC theories.     

Vacuum alignment by broken gauge interactions

We study the problem of vacuum alignment by the extended technicolour (ETC)forces which have been invoked to give mass to ordinary fermions (quarks and leptons) in technicolour theories. We find that the ETC interactions prefer to align the vacuum in such a way as to give the maximum possible mass to the ordinary fermions. We show that the P⁰, P³, P^+-, P₈⁰, P₈³, and P₈^+- pseudo-Goldstone bosons in one technifamily ETC models cannot acquire any mass from ETC interactions alone. Finally, we point out that the Pati-Salam unification which has been invoked to give mass to the P⁰ and P³ implies a remaining discrete degeneracy of the vacuum.     

On pseudo-Goldstone boson masses from broken gauge interactions

We investigate the effects of extended technicolour interactions on the masses of pseudo-Goldstone bosons in one-technifamily models. We find that the P⁰ and P³ cannot acquire any masses from ETC, while the P^± only acquire contributions of order g_Wg_ETC (?5 GeV). This removes a major source of uncertainty in the masses of these particles.     

Technicolour

The ideas of Technicolour or Dynamical Symmetry Breaking for the weak interactions are reviewed. The need for technicolour is established because of the gauge hierarchy problem. The obvious phenomenological consequences are explored with emphasis on the possible existence of light (less than 100 GeV) scalar particles. The extended technicolour or sideways generalizations of technicolour are discussed. The relations between technicolour and grand unified theories, groups breaking themselves and vacuum alignment are also explored. Finally there is a discussion of technicolour and the possible composite structure of quarks and leptons.     

SO(10) v ×SO(10) H grand unified-extended technicolour models

We discuss a recently proposedSO(10) _v ×SO(10) _H grand unified-extended technicolour model. Because proton decay is probably too fast in this model, we study the other possible models based onSO(10) _v ×SO(10) _H . As a result of this analysis only a few of these models could possibly be realistic, they would be slight modifications of that previously proposed. None of them predicts the expected value forΛ _TC, it must be adjusted by introducing another mass scale. In these models ordinary fermion masses tend to be too small.     

Supersymmetry and tensor coupling in

We study a possible explanation of the tensor currents in the weak radiative decay which was suggested recently by Bolotov et al. [Phys. Lett. B 243 (1990) 308] and Poblaguev [Phys. Lett. B 238 (1990) 108]. It can be shown that the supersymmetric particles can produce a tensor coupling at order (10⁻⁴−10⁻⁵)G_F which is 2–3 orders of magnitude smaller than the estimates extracted from the experimental data. A reliable calculation of the hadronic matrix element is done. The importance of a precision measurement of the tensor coupling in this decay is discussed as well as the possible relevance of the technicolour models.     

Grand unification at the subcomponent level

The Casalbuoni-Gatto subcomponent model of quarks and leptons is generalized allowing for an arbitrary number of subcomponents. It is shown that there are only a limited number of cases where the subcolour can be embedded in a semi-simple grand unification scheme. The most interesting models lead to an SU(7) ? SU(7) grand unification at the subcomponent level. In one of them there is also a natural place for a hypercolour (technicolour) group SU(2)_hc.     

Minimal composite Higgs systems

Extending to technicolour models recent results on the chiral, large N_c limit of QCD, we argue that minimal composite Higgs systems must contain an η like Higgs particle, whose peculiar properties follow from current algebra and large N arguments only. By contrast, the usual scalar Higgs is a model-independent entity without clear experimental signature.     

Magnetic spin excitations in Mn doped GaAs: a model study

We provide a quantitative theoretical model study of the dynamical magnetic properties of optimally annealed Ga_{1− x} Mn _x As. This model has already been shown to reproduce accurately the Curie temperatures for Ga_{1− x} Mn _x As. Here we show that the calculated spin stiffness are in excellent agreement with those which were obtained from ab-initio based studies. In addition, an overall good agreement is also found with available experimental data. We have also evaluated the magnon density of states and the typical density of states from which the“mobility edge”, separating the extended from localized magnon states, was determined. The power of the model lies in its ability to be generalized for a broad class of diluted magnetic semiconductor materials, thus it bridges the gap between first principle calculations and model based studies.     

On the equivalence of the Skyrme-Witten model and large-N c quark models

We review the equivalence of the two-flavor Skyrme-Witten model and the two-flavor large-N _c quark model. The claimed equivalence for three flavorsbetween these two models is shown to be incorrectly given in the literature, and the properly equivalent extended three-flavor large-N _c quark model is constructed and discussed.Dedicated to Professor Fritz Rohrlich on his 70th birthday.     

A convenient band-gap interpolation technique and an improved band line-up model for InGaAlAs on InP

The band-gap energy and the band line-up of InGaAlAs quaternary compound material on InP are essential information for the theoretical study of physical properties and the design of optoelectronics devices operating in the long-wavelength communication window. The band-gap interpolation of In_1−x−y Ga _x Al _y As on InP is known to be a challenging task due to the observed discrepancy of experimental results arising from the bowing effect. Besides, the band line-up results of In_1−x−y Ga _x Al _y As on InP based on previously reported models have limited success by far. In this work, we propose an interpolation solution using the single-variable surface bowing estimation interpolation method for the fitting of experimentally measured In_1−x−y Ga _x Al _y As band-gap data with various degree of bowing using the same set of input parameters. The suggested solution provides an easier and more physically interpretable way to determine not only lattice matched, but also strained band-gap energy of In_1−x−y Ga _x Al _y As on InP based on the experimental results. Interpolated results from this convenient method show a more favourable match to multiple independent experiment data sets measured under different temperature conditions as compared to those obtained from the commonly used weighted-sum approach. On top of that, extended framework of the model-solid theory for the band line-up of In_1−x−y Ga _x Al _y As/InP heterostructure is proposed. Our model-solid theory band line-up result using the proposed extended framework has shown an improved accuracy over those without the extension. In contrast to some previously reported works, it is worth noting that the band line-up result based on our proposed extended model-solid theory has also shown to be more accurate than those given by Harrison’s model.     

Effective Hubbard model for Zn-doped CuO2 plane

In the framework of the cell-perturbation method for the original p-d model an effective two-band Hubbard model for the CuO₂ plane with Zn impurities is derived. Zn impurities are modelled by Wannir oxygen one-hole states at vacant Cu sites. The model is based on the results of band structure calculations carried out within the local-density approximation. Further reduction to an extended t-J model shows a large ferromagnetic superexchange interaction between the Cu spin with the nearest virtual oxygen spin in the Zn cell. Received 17 November 1998     

The solid–liquid interface energy of organic crystals

A simple thermodynamic model, originally developed for metals based on the Gibbs–Thomson equation and related considerations for homogeneous nucleation, has been extended to predict the solid–liquid interface energy γ_sl of organic crystals. The model predictions correspond to available experimental and other theoretical results for 38 organic crystals. Copyright © 2007 John Wiley & Sons, Ltd.     

The SURF model and the curvature effect for PBX 9502

SURF is a high explosive burn model based on the ignition & growth concept of hot-spot reaction. For the TATB based explosive PBX 9502, the model has been calibrated to shock-to-detonation transition experiments. To apply the SURF model for propagating detonation waves, the rate has to be extended to a higher pressure regime than is sampled by shock initiation experiments. The experimentally measured curvature effect – detonation speed as a function of front curvature or D _n(κ) – provides the appropriate data for calibrating the propagation regime. The calibration to the curvature effect is based on the ODEs for the reaction zone profile of a detonation wave in conjunction with a shooting algorithm to determine the rate model parameters, for a given κ, needed to obtain a specified detonation speed. A complication for calibrating PBX 9502 rate models arises from the kink in the experimentally measured D _n(κ) curve. This results from the fast and slow reactions that TATB exhibits. To account for this, we use an extension of the SURF model that utilises a sequence of two reactions. The first, with a fast rate, is due to molecular decomposition and is described by the original SURF formulation. The second, with a slow rate, is due to carbon clustering and is used to contribute additional energy from the formation of carbon bonds. The wave profile equations are generalised to the SURF-plus model. Model parameters are then determined for the propagation regime to fit the curvature effect data. The extended model is applicable to both the shock initiation regime and the propagating detonation wave regime.     

Coherent motion of a hole in the copper-oxygen planes of high-temperature superconductors

The dispersion relation for the coherent propagation of a hole moving in a two-dimensional (CuO₂) _N system is discussed. The (CuO_2)N planes constitute the most important structural element in the high-T _c superconducting materials. The system is described by the Kondo-Heisenberg Hamiltonian, which is a simplified version of the extended Hubbard or Emery model. The calculations are based on the introduction of a trial wave function in the unitary space of the Cu spins and the O degrees of freedom. They generalize an approach recently proposed for the coherent motion of a hole in thet-J model. The propagation is mainly determined by the spin-fluctuation part of the superexchange between the copper spins. Minor contributions to the coherent hole motion are due to an effective tunneling of the hole to second and third nearest neighbors along spiral paths in the (CuO₂) _N plane. This mechanism can be considered as the analogue of a mechanism for coherent hole motion in thet-J model first discussed by Trugman. For the dispersion relation a cosine-band-like form is found similar to that for thet-J model. The band width, however, is somewhat increased. Except for this difference, our results seem to support the point of view of Zhang and Rice, who have claimed that there exists a one-to-one mapping between the low-lying states of the two-band model and the effectivet-J model.     

Particle mass limits in minimal and nonminimal supersymmetric models

A review of the Higgs and neutralino sector of supersymmetric models is presented. This includes the upper limit on the mass of the lightest Higgs boson in the minimal supersymmetric standard model, as well as models based on the standard model gauge groupSU(2) _L xU(l) _Y with extended Higgs sectors. We then discuss the Higgs sector of left-right supersymmetric models, which conserveR-parity as a consequence of gauge invariance, and present a calculable upper bound on the mass of the lightest Higgs boson in these models. We also discuss the neutralino sector of general supersymmetric models based on the SM gauge group. We show that, as a consequence of gauge coupling unification, an upper bound on the mass of the lightest neutralino as a function of the gluino mass can be obtained.     

Pseudoscalar Higgs bosons at the LHC: production and decays into electroweak gauge bosons revisited

We analyse and compute, within a number of standard model (SM) extensions, the cross sections σ _A→VV′ for the production of a heavy neutral pseudoscalar Higgs-boson/spin-zero resonance at the LHC and its subsequent decays into electroweak gauge bosons. For comparison we calculate also the corresponding cross sections for a heavy scalar. The SM extensions we consider include a type-II two-Higgs doublet model (2HDM), a 2HDM with four chiral fermion generations, the minimal supersymmetric extension of the SM (MSSM), and top-colour assisted technicolour models. Presently available phenomenological constraints on the parameters of these models are taken into account. We find that, with the exception of the MSSM, these models permit the LHC cross sections σ _A→VV′ to be of observable size. That is, a pseudoscalar resonance may be observable, if it exists, at the LHC in its decays into electroweak gauge bosons, in particular in WW and γ γ final states.     

两种扩展Harper模型的波包动力学

本文通过二次矩M₂(t)和概率分布W_n(t)数值地研究了两种扩展Harper模型的波包动力学,得到了这两种模型中各个相、各条临界线以及三相点的波包扩散情况.对于第一种扩展Harper模型,发现两个金属相中波包是弹道扩散的,在绝缘体相中波包不扩散,而在三相点以及各条临界线上波包是反常扩散的.同时,发现金属相—金属相转变的临界线上的波包动力学行为与金属相—绝缘体相转变的临界线上的相同,但三相点的动力学行为与各临 关键词： 金属绝缘体转变 扩展Harper模型 波包动力学     

Search for light technimesons

The light neutral colour-singlet spin-zero bosons P⁰ and P³ expected in contemporary extended technicolour theories have some small induced flavour-changing couplings, even in monophagic theories where their couplings are mainly flavour-diagonal. Their non-observation in K⁺ decay means that $\text{m}{}_{\mathrm{<mtext>P</mtext>}}\text{0,3 ? 350}\text{MeV}$, leading one to expect direct quark-lepton transitions mediating K_L0 → μe decay close to the present experimental upper limit. In the absence of some as yet unknown suppression mechanisms, eitherP⁰ and P³ should be observed in bottom decays with a branching ratio approaching 100% (which may already be experimentally excluded) and/or they should be observed in charm decays with branching ratios ? 1% and/or the decay K⁰_L → μe should be detected within an order of magnitude of the present upper limit.     

Level structure of 99Rh at high spins

High spins states in ⁹⁹Rh were populated via the ⁶⁶Zn(³⁷Cl, 2p2n)⁹⁹Rh reaction at an incident beam energy of 130 MeV. Seventeen new transitions have been observed in the present study and the level scheme has now been extended up to a spin of J∼ 25ħ and an excitation energy of about E _x∼ 10 MeV. The observation of a positive parity E2 cascade based on the 9/2⁺ isomeric level is suggestive of collective behaviour in this nucleus up to high spins. Spherical shell model (within restricted model space) and Cranked shell model calculations were performed to obtain an insight into the observed level structure. The new collective band observed up to a spin of J∼ 25ħ is suggested to be based on (πg _9/2 ³) ⊗ (νg _7/2 ²) quasi-particle excitations. Received: 12 July 1999 / Revised version: 14 September 1999