QT-Symmetry and Weak Pseudo-Hermiticity

For an invertible (bounded) linear operator Q acting in a Hilbert space ${\cal H}$, we consider the consequences of the QT-symmetry of a non-Hermitian Hamiltonian $H:{\cal H}\to{\cal H}$ where T is the time-reversal operator. If H is symmetric in the sense that ${\cal T} H^\dagger {\cal T}=H$, then QT-symmetry is equivalent to Q^{-1}-weak-pseudo-Hermiticity. But in general this equivalence does not hold. We show this using some specific examples. Among these is a large class of non-PT-symmetric Hamiltonians that share the spectral properties of PT-symmetric Hamiltonians.Comment: Extended published version, includes a new section giving a new exactly solvable class of bosonic non-PT-symmetric and non-Hermitian Hamiltonians with a real spectrum, 10 page

Two-dimensional model of dynamical fermion mass generation in strongly coupled gauge theories

We generalize the $N_F=2$ Schwinger model on the lattice by adding a charged scalar field. In this so-called $\chi U\phi_2$ model the scalar field shields the fermion charge, and a neutral fermion, acquiring mass dynamically, is present in the spectrum. We study numerically the mass of this fermion at various large fixed values of the gauge coupling by varying the effective four-fermion coupling, and find an indication that its scaling behavior is the same as that of the fermion mass in the chiral Gross-Neveu model. This suggests that the $\chi U\phi_2$ model is in the same universality class as the Gross-Neveu model, and thus renormalizable and asymptotic free at arbitrary strong gauge coupling.Comment: 18 pages, LaTeX2e, requires packages rotating.sty and curves.sty from CTA

The effects of a magnetic barrier and a nonmagnetic spacer in tunnel structures

The spin-polarized transport is investigated in a new type of magnetic tunnel junction which consists of two ferromagnetic electrodes separated by a magnetic barrier and a nonmagnetic metallic spacer. Based on the transfer matrix method and the nearly-free-electron-approximation the dependence of the tunnel magnetoresistance (TMR) and electron-spin polarization on the nonmagnetic layer thickness and the applied bias voltage are studied theoretically. The TMR and spin polarization show an oscillatory behavior as a function of the spacer thickness and the bias voltage. The oscillations originate from the quantum well states in the spacer, while the existence of the magnetic barrier gives rise to a strong spin polarization and high values of the TMR. Our results may be useful for the development of spin electronic devices based on coherent transport.Comment: 15 pages, 5 figure

Shape-Function Effects and Split Matching in B-> Xs l+ l-

We derive the triply differential spectrum for the inclusive rare decay B -> Xs l+ l- in the shape function region, in which Xs is jet-like with $mX^2 \lesssim mb \Lambda_QCD$. Experimental cuts make this a relevant region. The perturbative and non-perturbative parts of the matrix elements can be defined with the Soft-Collinear Effective Theory, which is used to incorporate alphas corrections consistently. We show that, with a suitable power counting for the dilepton invariant mass, the same universal jet and shape functions appear as in B-> Xs gamma and B-> Xu l nu decays. Parts of the usual alphas(m_b) corrections go into the jet function at a lower scale, and parts go into the non-perturbative shape function. For B -> Xs l+ l-, the perturbative series in alphas are of a different character above and below mu=mb. We introduce a ``split matching'' method that allows the series in these regions to be treated independently.Comment: 33 pages; journal versio

The flavour singlet mesons in QCD

We study the flavour singlet mesons from first principles using lattice QCD. We explore the splitting between flavour singlet and non-singlet for vector and axial mesons as well as the more commonly studied cases of the scalar and pseudoscalar mesons.Comment: 12 pages, LATEX, 4 ps figure

Quantum informatics with plasmonic metamaterials

Surface polaritons at a meta-material interface are proposed as qubits. The SP fields are shown to have low losses, subwavelength confinement and can demonstrate very small modal volume. These important properties are used to demonstatre interesting applications in quantum information, i.e., coherent control of weak fields and large Kerr nonlinearity at the low photon level

Simple generalizations of Anti-de Sitter space-time

We consider new cosmological solutions which generalize the cosmological patch of the Anti-de Sitter (AdS) space-time, allowing for fluids with equations of state such that $w\neq -1$. We use them to derive the associated full manifolds. We find that these solutions can all be embedded in flat five-dimensional space-time with $--+++$ signature, revealing deformed hyperboloids. The topology and causal-structure of these spaces is therefore unchanged, and closed time-like curves are identified, before a covering space is considered. However the structure of Killing vector fields is entirely different and so we may expect a different structure of Killing horizons in these solutions.Comment: 6 Pages, 5 Figures, Corrections and additions made for publication in Journal of Classical and Quantum Gravit

Standard Model CP violation in Polarised b->d l^+ l^-

In the standard model, we study CP violating rate asymmetries in the decay b->d l^+ l^- when one of the leptons is polarised. We find an asymmetry of (5 -- 15)% in the polarised decay spectrum which is comparable to known results for the unpolarised case. In the kinematic region separating the rho-omega and $c \bar c$ resonances, which is also theoretically cleanest, the polarised contribution to the asymmetry is larger than the unpolarised results. In order to observe a 3 sigma signal for direct CP violation in the polarised spectrum, assuming 100% efficiency, about 10^10 $B \bar B$ pairs are required at a B factory. Our results indicate an asymmetric contribution from the individual polarisation states to the unpolarised CP asymmetry. Taking advantage of this, one can attribute any new physics to be most sensitive to a specific polarisation state.Comment: 23 pages, one reference adde

Damage identification in a concrete beam using curvature difference ratio

Previous studies utilising changes in mode shape or curvature to locate damage rely on the fact that the greatest change occurs around the defect. However, in concrete beams this fact is undermined due to the nature of the defect as distributed multi-site cracks. In addition, differences in mode shape and curvature as ways to locate the damage is unstable because of occurrence of modal nodes and inflection points. In this paper, one interesting solution to this problem is being tested by establishing a new non-dimensional expression designated the 'Curvature Difference Ratio (CDR)'. This parameter exploits the ratio of differences in curvature of a specific mode shape for a damaged stage and another reference stage. The expression CDR is reasonably used to locate the damage and estimate the dynamic bending stiffness in a successively loaded 6m concrete beam. Results obtained by the proposed technique are tested and validated with a case study results done by Ren and De Roeck [1] also by Maeck and De Roeck [2]. Another contribution of this work is that relating changes in vibration properties to the design bending moment at beam sections as defined in Eurocode 2 specifications [3]. Linking between a beam section condition and the change in vibration data will help to give a better comprehension on the beam condition than the applied load

Towards a Model-Independent Analysis of Rare BB Decays

Motivated by the experimental accessibility of rare $B$ decays in the ongoing and planned experiments, we propose to undertake a model-independent analysis of the inclusive decay rates and distributions in the processes \bgamaxs~ and \Bsell ~($B=B^\pm$ or $B^0_d$). We show how measurements of the decay rates and distributions in these processes would allow us to extract the magnitude and sign of the dominant Wilson coefficients of the magnetic moment operator \mb \bar{s}_L \sigma_{\mu \nu} b_R F^{\mu \nu } and the four-fermion operators $(\bar{s}_L \gamma_\mu b_L)(\bar{\ell} \gamma^{\mu} \ell)$ and $(\bar{s}_L \gamma_\mu b_L)(\bar{\ell} \gamma^{\mu}\gamma^5 \ell)$. Non-standard-model effects could thus manifest themselves at low energy in rare $B$ decays through the Wilson coefficient having values distinctly different from their standard-model counterparts. We illustrate this possibility using the examples of the two-doublet Higgs models and the minimal supersymmetric models. The dilepton invariant mass spectrum and the forward-backward asymmetry of $\ell^+$ in the centre-of-mass system of the dilepton pair in the decay \Bsell ~are also worked out for the standard model and some representative solutions for the other two models.Comment: LaTeX, 36 pages, 11 figures appended after \end{document} as uu-encoded and compressed .eps files, uses epsf, CERN-TH.7346/9