Angle-resolved photoemission spectra in the cuprates from the d-density wave theory

Angle-resolved photoemission spectra present two challenges for the d-density wave (DDW) theory of the pseudogap state of the cuprates: (1) hole pockets near $(\pi/2,\pi/2)$ are not observed, in apparent contradiction with the assumption of translational symmetry breaking, and (2) there are no well-defined quasiparticles at the {\it antinodal} points, in contradiction with the predictions of mean-field theory of this broken symmetry state. Here, we show how these puzzles can be resolved.Comment: 4 pages, 3 eps figures, RevTex

Spin-spin Correlation lengths of Bilayer Antiferromagnets

The spin-spin correlation length and the static structure factor for bilayer antiferromagnets, such as YBa$_2$Cu$_3$O$_{6}$, are calculated using field theoretical and numerical methods. It is shown that these quantities can be directly measured in neutron scattering experiments using energy integrated two-axis scan despite the strong intensity modulation perpendicular to the layers. Our calculations show that the correlation length of the bilayer antiferromagnet diverges considerably more rapidly, as the temperature tends to zero, than the correlation length of the corresponding single layer antiferromagnet typified by La$_2$CuO$_4$. This rapid divergence may have important consequences with respect to magnetic fluctuations of the doped superconductors.Comment: This paper supersedes cond-mat/9703138 and contains numerical simulation results to compare against analytical results. 6 pages, 2 postscript figures (embedded), uses EuroPhys.sty and EuroMac

Meron-Cluster Solution of Fermion and Other Sign Problems

Numerical simulations of numerous quantum systems suffer from the notorious sign problem. Important examples include QCD and other field theories at non-zero chemical potential, at non-zero vacuum angle, or with an odd number of flavors, as well as the Hubbard model for high-temperature superconductivity and quantum antiferromagnets in an external magnetic field. In all these cases standard simulation algorithms require an exponentially large statistics in large space-time volumes and are thus impossible to use in practice. Meron-cluster algorithms realize a general strategy to solve severe sign problems but must be constructed for each individual case. They lead to a complete solution of the sign problem in several of the above cases.Comment: 15 pages,LATTICE9

The effects of magnetic field on the d-density wave order in the cuprates

We consider the effects of a perpendicular magnetic field on the d-density wave order and conclude that if the pseudogap phase in the cuprates is due to this order, then it is highly insensitive to the magnetic field in the underdoped regime, while its sensitivity increases as the gap vanishes in the overdoped regime. This appears to be consistent with the available experiments and can be tested further in neutron scattering experiments. We also investigate the nature of the de Haas- van Alphen effect in the ordered state and discuss the possibility of observing it.Comment: 5 pages, 4 eps figures, RevTex4. Corrected a silly but important typo in the abstrac

B2B Collaboration : Economic Value and Investment in Technology

To collaborate with partners a company must reengineer its business processes for information and knowledge sharing, and for operations coordination. Digital technologies have proven very effective in supporting such collaborations. Companies may collaborate vertically with their suppliers and customers, or they may collaborate horizontally with other manufacturers. The benefits of collaboration would obviously depend upon how the partners, together, extract economic value from the market. This value would be different in different demand and/or cost scenarios. The decision to invest in collaboration technologies, on the other hand, is usually made by individual companies. There is clearly a tradeoff between the capabilities a company may create through investment in digital technology, and the market benefits it may obtain from collaborating with partners. In this paper we explore (1) how markets can be leveraged to create economic values in collaboration, and (2) how optimal investment (in technology) can be made using these collaboration values

African Nazarites : a comparative religious ethnography of Rastafari and Ibandla lamaNazaretha

Deux mouvements théologiques et culturels actuellement en croissance rapide suscitent un intérêt mondial, Ibandla lamaNazaretha et les Rastafari. Fondé par le Zulu prédicateur Isaiah Shembe pendant les années 1910, Ibandla lamaNazaretha prend son origine d’une église hiérarchique célébrant dans des temples extérieurs dans la province de KwaZulu-Natal et inclut maintenant un certain nombre de factions regroupées autour de la péninsule de l’Afrique du Sud. Le groupe des Rastafari, quant à lui, né en Jamaïque, a commencé comme une idéologie à plusieurs têtes qui a fleuri dans des zones éparses de l’île des Caraïbes. Il découle des interprétations d’une prophétie généralement attribuée à Marcus Garvey, concernant un roi devant être couronné en Afrique (circa 1920), et qui fut appliquée aux années 1930, avec le couronnement de Ras Tafari Makonnen comme Haile Selassie I, 225e empereur d’Éthiopie. Les adhérents et sympathisants de ces deux mouvements se comptent en dizaines de millions et ils exercent plusieurs types d’influences, tant aux niveaux politique, théologique, social que culturel, en particulier en Afrique et dans les Caraïbes aujourd’hui. Cette thèse soutient que les deux, Ibandla lamaNazaretha et les Rastafari, perpétuent un amalgame entre le « Naziréat » de l’Ancien Testament (Nombres 6:1-8) et le « Nazaréen » de l’évangile de Matthieu (2:23), à travers la dévotion à un seigneur contemporain: Haile Selassie I dans le cas du mouvement Rastafari et Isaiah Shembe dans le cas du mouvement Ibandla lamaNazaretha. Dans ce cadre théologique, à la fois les Rastafari et Ibandla lamaNazaretha ont réanimé les anciens rites de purification judaïques du naziréat jusque-là disparus, et les ont également adaptés, dans le contexte du messianisme, aux préoccupations postcoloniales de l’autochtonie. Grâce à la persistance de l’autochtonie, l’influence des idéaux indiens de résistance non-violente, et l’appropriation des différents thèmes bibliques, les deux mouvements africains noirs ont habilité avec succès leurs membres « dépossédés ». Ils l’ont fait par la création de communautés liminales, alors que des modes de vie agraires et auto-suffisants s’épanouissent en dehors des auspices d’une élite dominante : une herméneutique du nazaritisme unifie les diverses racines hybrides africaines, judaïques, chrétiennes, indiennes, et européennes.Two rapidly growing theological and cultural movements currently sparking global interest are Rastafari and Ibandla lamaNazaretha. Founded by the Zulu preacher Isaiah Shembe during the 1910s, Ibandla lamaNazaretha originated as a hierarchical church order that worships at outdoor temples in the province of KwaZulu-Natal and currently comprises a number of splinter groups centralized around the Southern African peninsula. Rastafari, however, born in Jamaica, commenced as a multi-headed ideology that blossomed in scattered pockets across the Caribbean island and stemmed from the interpretations of a prophecy generally attributed to Marcus Garvey about a king to be crowned in Africa (circa 1920) as applied to the 1930 coronation of Ras Tafari Makonnen as Haile Selassie I, 225th Emperor of Ethiopia. Today, Ibandla lamaNazaretha and Rastafari comprise adherents and sympathizers numbering in the tens of millions and their presences connote varying degrees of political, theological, social, and cultural influence, especially in Africa and the Caribbean today. This dissertation argues that both Ibandla lamaNazaretha and Rastafari perpetuate a conflation between the “Nazirite” from the Old Testament (Numbers 6:1-8) and the “Nazorean” of Matthew 2:23 through the hailing of a contemporaneous saviour: i.e. Haile Selassie I for Rastafari and Isaiah Shembe for Ibandla lamaNazaretha. Within this theological framework, both Rastafari and Ibandla lamaNazaretha have provided renewed life to the long defunct Ancient Judaic purification rites of the Nazirite, but have also adapted them in the context of messianism for the benefits of Africanness and the postcolonial concerns of indigeneity. Thus, through the persistence of indigeneity, the influence of Indian ideals of peaceful resistance, and the appropriation of various biblical themes, both Black African movements have successfully empowered the dispossessed by creating liminal communities wherein expressions of agrarian self-reliance flourish outside the auspices of a subjugating elite; a hermeneutic of naziritism unifies the discernable African, Judaic, Christian, Indian, and European hybridic roots