Anomaly Inflow on Orientifold Planes

We examine some six-dimensional orientifold models with $N = 1$ supersymmetry, which can be realised as intersecting 7-branes and 7-planes. These models are studied in the light of recent work showing that orientifold planes carry anomalous gravitational couplings on their world-volume. We show that gravitational anomalies can be locally cancelled by these new couplings at every point in the internal space, under the assumption that the anomaly residing on orientifold planes is distributed in a particular way among brane-plane and plane-plane intersections.Comment: harvmac, 12 pages (b); Some changes in wording, in order to convey more accurately what is being done; no changes in computations or formula

BPS Nature of 3-String Junctions

We study BPS-saturated classical solutions for the world-sheet theory of a D-string in the presence of a point charge. These solutions are interpreted as describing planar 3-string junctions, which arise because the original D-string is deformed by the presence of the inserted charge. We compute the angles of the junctions and show that the vector sum of string tensions is zero, confirming a conjecture of Schwarz that such configurations are BPS states.Comment: 7 pages, harvmac (b), 3 figure

Brane Constructions, Fractional Branes and Anti-deSitter Domain Walls

Compactifications of type IIB string theory on AdS5 x X5, where X5 is an Einstein space, can have one-fourth or half maximal supersymmetry for certain choices of X5. Some of these theories admit exotic domain walls arising from 5-branes wrapping 2-cycles in X5. We explore the relationship among these domain walls, fractional branes and branes stretched on intervals. World-volume fluxes in the wrapped branes play an important role in the analysis. We draw some parallels between the AdS background with exotic domain walls and N=1 supersymmetric MQCD, and identify other extended objects on the AdS side in the dual brane construction. The process of brane creation is used to give an alternate derivation of the relationship between fractional branes and branes on intervals.Comment: harvmac, 34 pages (b), 8 figures; Reference adde

Noncommutative Tachyons

When unstable Dp-branes in type II string theory are placed in a B-field, the resulting tachyonic world-volume theory becomes noncommutative. We argue that for large noncommutativity parameter, condensation of the tachyon as a noncommutative soliton leads to new decay modes of the Dp-brane into (p-2)-brane configurations, which we interpret as suitably smeared BPS D(p-1)-branes. Some of these configurations are metastable. We discuss various generalizations of this decay process.Comment: 15 pages, harvmac (b

A Note on Low-Dimensional String Compactifications

We study supersymmetric compactifications of type II strings on eightfolds to two dimensions. It is demonstrated that the type IIB string on an eightfold is free of gravitational anomalies. T-duality requires that this theory when further compactified on a circle must have a vacuum momentum; this is explicitly shown to be present and to have the right value. A subtlety in the relation of IIB compactifications and M-Theory orientifolds to two dimensions is pointed out.Comment: 12 pages Tex file, no figure

Gravitational Couplings and Z2Z_2 Orientifolds

The interplay between gravitational couplings on branes and the occurrence of fractional flux in low dimensional orientifolds is examined. It is argued that gravitational couplings need to be assigned not only to D-branes but also to orientifold planes. The fractional charges of the orientifold $d$-planes can be understood in terms of flux quantization of the $d-3$ form potential and modified Bianchi identities. Detailed results are presented for the case of the type IIB orientifold on $T^6/Z_2$, which is dual to F-theory on a complex 4-fold with terminal singularities.Comment: 24 pages, harvmac,Numerical coefficients of R^4 couplings have been corrected, and are now in agreement with recent results of hep-th/9812071 and hep-th/9812088. No other changes. This revision supercedes the published version of this pape

Stable Non-BPS States and Their Holographic Duals

Stable non-BPS states can be constructed and studied in a variety of contexts in string theory. Here we review some interesting constructions that arise from suspended and wrapped branes. We also exhibit some stable non-BPS states that have holographic duals.Comment: 10 pages, LaTeX, 10 .eps figures (included); based on a talk given at Strings 2000, Michiga

Benefits of improved rice husk combustion, Bangladesh (NRI report no. 2764)

The report is structured as follows. Chapter 2 presents the background to this study. Based on secondary data, it first describes the rice milling sector to illustrate the characteristics of the sector and to establish the importance of small scale parboiling rice mills. No secondary data were available either on the socio-economic characteristics of the user group or on the attitudes to technological change among owners and operators of rice mills. This information was important to the design of the project methodology; for indicating the nature of technological improvements acceptable to user groups; for issues of affordability and for subsequent dissemination activities. Section 2.3, draws on the baseline survey carried out in Phase 1, to analyse these characteristics. Chapter 3 first analyses the characteristics of the traditional furnace design and then demonstrates how the new design of furnace-boiler unit has increased combustion efficiency by more than the project objective; improved the working conditions of the workers and increased profitability of the owners. It also sets out the potentials and limitations for wider replications. Chapter 4 focuses on enhancing the production of briquettes using husk from parboiled rice. It describes the current procedures used for briquette production, the difficulties of using husk of parboiled rice, and the improvements developed by this project to address these constraints. Chapter 5 discusses the wider socio-economic benefits that could be generated by the rice husk and bran saved by improved combustion efficiency. It also shows that briquettes, where available, have become the poor man's fuel. Chapter 6 initially set out the characteristics of the rice husk ash in Bangladesh. It then describes the current uses in other countries and identifies potential alternative uses in Bangladesh. Chapter 7 describes the dissemination activities already undertaken and their outcomes and then outlines further dissemination activities that could potentially enhance uptake. Chapter 8 will conclude the report with recommendations and identify further research needs in biomass fuel use

Brane Constructions, Conifolds and M-Theory

We show that a set of parallel 3-brane probes near a conifold singularity can be mapped onto a configuration of intersecting branes in type IIA string theory. The field theory on the probes can be explicitly derived from this formulation. The intersecting-brane metric for our model is obtained using various dualities and related directly to the conifold metric. The M-theory limit of this model is derived and turns out to be remarkably simple. The global symmetries and counting of moduli are interpreted in the M-theory picture.Comment: 31 pages, harvmac (b), 10 eps figures; Minor clarifications and corrections, final version, to appear in Nuclear Physics