Charged Macroscopic type II Strings and their Networks

We write down charged macroscopic string solutions in type II string theories, compactified on torii, and present an explicit solution of the spinor Killing equations to show that they preserve 1/2 of the type II supersymmetries. The S-duality symmetry of the type IIB string theory in ten-dimensions is used to write down the SL(2,Z) multiplets of such strings and the corresponding 1/2 supersymmetry conditions. Finally we present examples of planar string networks, using charged macroscopic (p,q)-strings. An interesting feature of some of these networks, which preserve 1/4 supersymmetry, is a required alignment among three parameters, namely the orientation of strings, a U(1) phase associated with the maximal compact subgroup of SL(2, Z), and an (angular) parameter associated with a solution generating transformation, which is responsible for creating charges and currents on the strings.Comment: 26 pages, Latex, typos corrected in few equations, minor change

the primacy of use over naming

In Philosophical Investigations, Wittgenstein proposed the notion of meaning that accounts for the large variety of contexts in which we apply the term “meaning”. This paper agreement with the manner in which Wittgenstein enhance his conception of meaning emphasizing his methodology of observation and description of particular cases. By applying a descriptive approach, Wittgenstein demonstrated that meaning of the term does not reside in physical or mental objects as well as in its correlations. As a result of contrasting denotative theory as well as the correspondence theory of meaning and recognizing the inadequacy of the accounts of meaning, he has proposed earlier in his Tractatus. But in later work, he has suggested that only one conception of meaning which could not be invalidated, at least for a large class of cases. This is none other than the notion of meaning which is regarded as public in nature. Consequently, the meaning of a term is not its denotation but its “use” in the language. Hence, by upholding the slogan i.e., “meaning is use” here I want to illustrate the supremacy of use over “naming” concerning to Wittgenstein’s Tractatus and Philosophical Investigations

Non-Planar String Networks on Tori

Type II strings in D=5 contain particle-like 1/8 supersymmetric BPS states. In this note we give a string-network representation of such states by considering (periodic) non-planar $(p,q,r)$-string networks of eight dimensional type II string theory on $T^3$. We obtain the BPS mass formula of such states, in terms of charges and generating-vectors of the torus, and show its invariance under an $SL(3, Z)\times SL(3, Z)$ group of transformations. Results are then generalized to string-networks associated with the $SL(5, Z)$ $U$-duality in seven dimensions. We also discuss reinterpretation of the above $(D=5)$ mass formula in terms of BPS states in world-volume theories of $U2$-branes in D=8.Comment: 11 pages, latex, one figure, very minor English correction

Multi-wavelength Intra-day Variability and Quasi-periodic Oscillation in Blazars

We reviewed multi-wavelength blazars variability and detection of quasi-periodic oscillations on intra-day timescales. The variability timescale from few minutes to up to less than a days is commonly known as intra-day variability. These fast variations are extremely useful to constrain the size of emitting region, black hole mass estimation, etc. It is noticed that in general blazars show intra-day variability in the complete electromagnetic spectrum. But some class of blazars either do not show or show very little intra-day variability in a specific band of electromagnetic spectrum. Blazars show rarely quasi-periodic oscillations in time series data in optical and X-ray bands. Other properties and emission mechanism of blazars are also briefly discussed.Comment: Invited Review; Submitted to Galaxies; a special issue on Microvariability of Blazar