Quantum constraint algebra for a closed bosonic string in a gravitational and dilaton background

We derive the quantum constraint algebra for a closed bosonic string moving in a gravitational and dilaton background to first order in '. The hamiltonian approach is used to directly compute the quantum constraint commutators and calculate the c-and q-number anomalies that arise at the quantum level. The requirement that the algebra preserves the conformal invariance leads to the known background field equations.     

Remarks on global anomalies in RCFT orientifolds

We check the list of supersymmetric standard model orientifold spectra of Dijkstra, Huiszoon and Schellekens for the presence of global anomalies, using probe branes. Absence of global anomalies is found to impose strong constraints, but in nearly all cases they are automatically satisfied by the solutions to the tadpole cancellation conditions.     

On the induced cosmological term in quantum gravity

Tadpole diagrams where zero-momentum gravitons couple to massive matter loops lead to divergences which are not a consequence of infinite momentum integrals, but of the masslessness of the gravitons. It is shown that there exists no definition of these diagrams consistent with the Ward identities. They can be eliminated by an appropriate gauge choice, but then the BRS symmetry is spontaneously broken. Also in the scalar-tensor, conformally invariant formulation of quantum gravity, the tadpole problem does survive. The tadpole diagrams can, however, be cancelled by a cosmological counter-term. In that case, the Ward identities are satisfied.     

Local grand unification in the heterotic landscape

We consider the possibility that the unification of the electroweak interactions and the strong force arises from string theory, at energies significantly lower than the string scale. As a tool, an effective grand unified field theory in six dimensions is derived from an anisotropic orbifold compactification of the heterotic string. It is explicitly shown that all anomalies cancel in the model, though anomalous Abelian gauge symmetries are present locally at the boundary singularities. In the supersymmetric vacuum additional interactions arise from higher‐dimensional operators. We develop methods that relate the couplings of the effective theory to the location of the vacuum, and find that unbroken discrete symmetries play an important role for the phenomenology of orbifold models. An efficient algorithm for the calculation of the superpotential to arbitrary order is developed, based on symmetry arguments. We furthermore present a correspondence between bulk fields of the orbifold model in six dimensions, and the moduli fields that arise from compactifying four internal dimensions on a manifold with non‐trivial gauge background.     

Tadpole resummations in string theory

While R–R tadpoles should be canceled for consistency, string models with broken supersymmetry generally have uncanceled NS–NS tadpoles. Their presence signals that the background does not solve the field equations, so that these models are in “wrong” vacua. In this Letter we investigate, with reference to some prototype examples, whether the true values of physical quantities can be recovered resumming the NS–NS tadpoles, hence by an approach that is related to the analysis based on String Field Theory by open–closed duality. We show that, indeed, the positive classical vacuum energy of a Dp-brane of the bosonic string is exactly canceled by the negative contribution arising from tree-level tadpole resummation, in complete agreement with Sen's conjecture on open-string tachyon condensation and with the consequent analysis based on String Field Theory. We also show that the vanishing classical vacuum energy of the SO(8192) unoriented bosonic open-string theory does not receive any tree-level corrections from the tadpole resummation. This result is consistent with the fact that this (unstable) configuration is free from tadpoles of massless closed-string modes, although there is a tadpole of the closed string tachyon. The application of this method to superstring models with broken supersymmetry is also discussed.     

A comment on discrete Kalb–Ramond field on orientifold and rank reduction

We show that the rank reduction of the gauge group on orientifolds in presence of non-vanishing discrete Kalb–Ramond field can be explained by the presence of an induced field strength in a non-trivial bundle on the branes. This field strength is also necessary for the tadpole cancellation and the number of branes is left unchanged by the presence of the discrete Kalb–Ramond background. We moreover give a derivation of the normalization of the Möbius amplitude in presence of a non-vanishing Kalb–Ramond field from first principles.     

Anomalies of the products of vertex functions in the superstring theories

We obtain the two-dimensional anomalous transforms of the products of several vertex functions (of Neveu-Schwarz sector) in the path integral formulation of closed superstrings: type II super and heterotic strings. The products of vertex functions are free from local anomalies except for Weyl anomalies. In the presence of background fields this kind of Weyl anomalies leads to interaction terms in the background field equations of motion, which are derived by the requirement of the cancellation of Weyl anomalies.     

Loop-corrected string field equations from world-sheet Weyl invariance

We investigate short distance singularities inside the Polyakov path integral in an arbitrary closed bosonic string background due to vertex operators and small handles or holes. The latter are represented in terms of handle or hole operators, which we construct explicitly. The requirement of global Weyl invariance generates loop-corrected equations of motion for the string modes including tadpole terms and self-energy corrections. The relation to theS-matrix and superstrings are discussed briefly.     

基于自洽场理论两亲高分子自组装的研究

运用扩展的自洽场和密度泛函理论(SCF/DFT),研究ABC蝌蚪形两亲高分子在稀溶剂中的自组装形态,其中蝌蚪形两亲高分子由线形嵌段共聚物链AB嫁接到球形纳米颗粒C上构成.与以往研究的线形ABC两亲高分子相比,蝌蚪形两亲高分子的自组装形态有着很大的不同.在粒子亲溶剂,嵌段共聚物疏溶剂时,各组分间弱分凝条件下,蝌蚪形两亲高分子自组装成胶球状形貌;在强分凝条件下,随着嵌段共聚物疏溶剂性的增强,两亲高分子的自组织态由胶球状转变成四角、三角状形貌,其中嵌段B主要分布在各角上.通过改变各组分间的相互作用,在嵌段A亲溶剂,嵌段B和粒子疏溶剂时,粒子呈平行棒状或小方块状分布在胶球中.     

Gauge group of gravity,spinors, and anomalies

A discussion is given of the gravitational anomalies that arise from coupling Weyl spinors to gravity, treating the metric, the soldering form, and the connection as independent dynamical variables. This system is strictly analogous to Weyl spinors coupled to Yang-Mills fields and a nonlinear sigma model. The larger gauge group of this formulation is seen to lie at the root of the equivalence between Einstein and Lorentz anomalies.On leave of absence from SISSA, Trieste, Italy.     

Half-magnetization plateau stabilized by structural distortion in the antiferromagnetic heisenberg model on a pyrochlore lattice

Magnetization plateaus, visible as anomalies in magnetic susceptibility at low temperatures, are one of the hallmarks of frustrated magnetism. We show how an extremely robust half-magnetization plateau can arise from coupling between spin and lattice degrees of freedom in a pyrochlore antiferromagnet and develop a detailed symmetry of analysis of the simplest possible scenario for such a plateau state. The application of this theory to the spinel oxides CdCr2O4 and HgCr2O4, where a robust half-magnetization plateau has been observed, is discussed.     

红外吸收峰的强度与反常吸收现象

红外光谱测量有时需要在强的背景信号下得到弱的样品吸收峰,如在大量溶剂中测量溶质的红外光谱.理论上,只要某一组分在背景样品和待测样品的含量(分子个数)完全一致,则该组分的光谱信号就不会出现在最终的红外光谱图上.而实际测量时结果并非总如此.本文在测量聚苯乙烯及硬脂酸的“基线”时发现,在样品吸收较强的峰位(吸光度A＞1.0)...     

Density-Dependence of Quark Mass in Scaling Chiral Lagrangian

We calculate the quark mass in dense medium at one-loop order for an effective chiral Lagrangian supplemented by the scale anomaly of QCD. It is found that the tadpole diagram corrections lead to the decreasing mass of quark with density, while the effect of radiative corrections is opposite to that of the tadpole diagrams.     

Type IIB orientifolds,D‐brane instantons and the LARGE volume scenario

This review article is concerned with three topics important for the construction of four‐dimensional models of particle physics in the context of type II String Theories. Special emphasis is put on a consistent presentation of these topics as well as on highlighting their interconnections. The first of the three topics deals with the tadpole cancellation conditions and the cancellation of chiral anomalies for type IIB orientifolds with orientifold three‐ and seven‐planes. The second topic is related to non‐perturbative effects originating from D‐brane instantons. In particular, in the presence of a realistic particle physics sector, a chiral zero‐mode constraint for contribution of instantons to the superpotential arises. The third topic is about moduli stabilisation in type IIB string compactifications. Two scenarios, the KKLT and Large Volume Scenario, are reviewed and a model for the latter scenario with the chiral zero‐mode constraint taken into account is presented.     

What is preferred about the preferred basis?

I introduce and review the most recent and most promising model of state vector reduction, that of Ghirardi, Rimini, Weber, and Pearle. This model requires the specification of a reduction basis. At least two questions therefore arise: Are there physical reasons to choose one basis rather than another? Does the choice made lead to any undesirable consequences? I argue that there arephysical reasons to choose from a certain class of reduction bases (a class which includes the choice made by the authors mentioned above), and that such a choice does not lead to problems, contra an argument by Albert and Vaidman.     

Decaying warm dark matter and neutrino masses

Neutrino masses may arise from spontaneous breaking of ungauged lepton number. Because of quantum gravity effects the associated Goldstone boson - the majoron - will pick up a mass. We determine the lifetime and mass required by cosmic microwave background observations so that the massive majoron provides the observed dark matter of the Universe. The majoron decaying dark matter scenario fits nicely in models where neutrino masses arise via the seesaw mechanism, and may lead to other possible cosmological implications.     

Spectral anomalies in supercontinuum focused waves

The diffraction-induced spectral anomalies in the focal plane of an apertured spherical wave with supercontinuum flat-top power spectrum are investigated. Coherent broadband radiation (also incoherent white light) demonstrates a strong blue shift in the vicinity of the optical axis, and discrete spectral gaps with overall red shift arise out of this central region. Unlike narrow-band light, the spectral switch effect fades away with ultra-broad spectra.     

Superspace analysis of local Lorentz and gauge anomalies in the heterotic string theory

Local Lorentz and gauge anomalies in the sigma model describing the propagation of the heterotic string in an arbitrary background field are discussed in the superspace formulation. An expression for these anomalies is written down in terms of the superfields, and is shown to cancel against an anomalous variation of the antisymmetric tensor field. World-sheet supersymmetry is manifest throughout this analysis.     

THE TOPOLOSICAL ORIGINS OF GAUGE ANOMALIES

In addition to the recent discovery that the Chern-Simons secondary classes are the topological origins generating special unitary gauge group anomalies, it is shown that some special orthogonal gauge group anomalies can also be generated, from the Pontrjagin and the Euler secondary classes. The common differential geometrical and topological background are explained as well.