Renormalization Group Analysis of Tachyon Condensation

Renormalization group analysis of boundary conformal field theory on bosonic D25-brane is used to study tachyon condensation. Placing the lump on a finite circle and triggering only the first three tachyon modes, the theory flows to nearby IR fixed point representing lumps that are extended object with definite profile. The boundary entropy corresponding to the D24-brane tension is calculated in the leading order in perturbative analysis which decreases under RG flow and agrees with the expected result to an accuracy of 8%. Multicritical behaviour of the IR theory suggests that the end point of the flow represents a configuration of two D24-branes. Analogy with Kondo physics is discussed.Comment: 37 pages, LATEX, 1 figur

On Branes and Oriented B-fields

Novel theories appear on the world-volume of branes by orienting B fields along various directions of the branes. We review some of the earlier developments and explore many new examples of these theories. In particular, among other things, we study the pinning effect of branes near conifold like singularities and brane-antibrane theories with different fluxes on their world-volumes. We show that all these theories arise from different limits of an M-theory configuration with appropriately chosen G-fluxes. This gives us a way to study them from a unified framework in M-theory.Comment: 44 pages, Harvmac, 12 .eps figures; v2: Some typos corrected and references added; More typos corrected, two footnotes added and references updated. Final version to appear in Nucl. Phys.

Power Corrections in QCD

This article provides a review of progress made in understanding inverse power law corrections 1/Q^p where Q is the hard scale for a given QCD observable. Special emphasis is given to comparisons of theory with HERA results.Comment: 10 pages, 5 figures. Contribution submitted to Ringberg workshop on HERA physics, Ringberg Castle, June 200

A Note on the Stringy Embeddings of Certain N = 2 Dualities

Seiberg-Witten theory can be embedded in F-theory using D3 branes probing an orientifold geometry. The non-perturbative corrections in the orientifold picture map directly to the instanton corrections in the corresponding gauge theory that convert the classical moduli space to the quantum one. In this short review we argue that the recently proposed class of conformal Gaiotto models may also be embedded in F-theory. The F-theory constructions help us not only to understand the Gaiotto dualities but also to extend to the non-conformal cases with and without cascading behaviors. For the conformal cases, the near horizon geometries in F-theory capture both the UV and IR behaviors succinctly.Comment: 6 pages, LaTeX, Based on the talk given by K. D at the Theory Canada Conference June 2012; v2: Typos corrected and references adde

Power Corrections in Deep Inelastic Event Shape Variables

Results are presented for the leading power-suppressed (1/Q) contributions to shape variables in deep inelastic lepton scattering. These are then combined with available leading order perturbative estimates.Comment: 6 pages,Latex2e, 2 figures. To be published in the proceedings of the 5th International workshop on Deep Inelastic Scattering, Chicago, April 199

Power corrections to the differential Drell-Yan cross section

We estimate the power corrections (infrared renormalon contributions) to the coefficient functions for the differential Drell-Yan cross-section $d^2\sigma/dQ^2dy$, where $Q^2$ is the mass squared and $y$ the rapidity of the produced lepton pair. We employ the dispersive method based on the analysis of one-loop Feynman graphs containing a massive gluon.Comment: 11 pages, 1 figure, LaTe