Exact Absorption Probability in the Extremal Six-Dimensional Dyonic String Background

We show that the minimally coupled massless scalar wave equation in the background of an six-dimensional extremal dyonic string (or D1-D5 brane intersection) is exactly solvable, in terms of Mathieu functions. Using this fact, we calculate absorption probabilities for these scalar waves, and present the explicit results for the first few low energy corrections to the leading-order expressions. For a specific tuning of the dyonic charges one can reach a domain where the low energy absorption probability goes to zero with inverse powers of the logarithm of the energy. This is a dividing domain between the regime where the low energy absorption probability approaches zero with positive powers of energy and the regime where the probability is an oscillatory function of the logarithm of the energy. By the conjectured AdS/CFT correspondence, these results shed novel light on the strongly coupled two-dimensional field theory away from its infrared conformally invariant fixed point (the strongly coupled ``non-critical'' string).Comment: Latex (3 times), 23 page

TASI Lectures: Introduction to the AdS/CFT Correspondence

This is an introductory review of the AdS/CFT correspondence and of the ideas that led to its formulation. We show how comparison of stacks of D3-branes with corresponding supergravity solutions leads to dualities between conformal large $N$ gauge theories in 4 dimensions and string backgrounds of the form $AdS_5\times X_5$ where $X_5$ is an Einstein manifold. The gauge invariant chiral operators of the field theory are in one-to-one correspondence with the supergravity modes, and their correlation functions at strong `t Hooft coupling are determined by the dependence of the supergravity action on AdS boundary conditions. The simplest case is when $X_5$ is a 5-sphere and the dual gauge theory is the ${\cal N}=4$ supersymmetric SU(N) Yang-Mills theory. We also discuss D3-branes on the conifold corresponding to $X_5$ being a coset space $T^{1,1}=(SU(2)\times SU(2))/U(1)$. This background is dual to a certain ${\cal N}=1$ superconformal field theory with gauge group $SU(N)\times SU(N)$.Comment: Lectures at TASI '99, Boulder, June 1999; 36 pages, LaTeX; v2: corrected factor of 2 in eq. (9) and related factor

Universality of conductivity in interacting graphene

The Hubbard model on the honeycomb lattice describes charge carriers in graphene with short range interactions. While the interaction modifies several physical quantities, like the value of the Fermi velocity or the wave function renormalization, the a.c. conductivity has a universal value independent of the microscopic details of the model: there are no interaction corrections, provided that the interaction is weak enough and that the system is at half filling. We give a rigorous proof of this fact, based on exact Ward Identities and on constructive Renormalization Group methods

Effective field theory approach to N=4 supersymmetric Yang-Mills at finite temperature

We study the perturbation expansion of the free energy of N=4 supersymmetric SU(N) Yang-Mills at finite temperature in powers of 't Hooft's coupling g^2 N in the large N limit. Infrared divergences are controlled by constructing a hierarchy of two 3 dimensional effective field theories. This procedure is applied to the calculation of the free energy to order (g^2 N)^(3/2), but it can be extended to higher order corrections.Comment: LaTeX, 10 pages, 1 figure, uses eps

MOTHER-TONGUE (L1) PHONOLOGICAL INTERFERENCE IN THE SPOKEN ENGLISH OF SOUVENIR SELLERS IN LOMBOK

This study aimed to examine the mother-tongue (L1) phonological interference in the spoken English of Souvenir Sellers in Lombok. Language and human are inseparable and since the languages of the world used in communication, there is bound to be a problem like mother tongue interference. The study reveals some troublesome contrasts in the two languages. The data of this study was collected through participant observation and interview. The findings proved that interference at the phonological level become one of the problems in the spoken English of souvenir sellers in Lombok. The English language teachers have to be aware and pay particular attention to the differences in the phonological systems of the first language (L1) and the foreign language (FL) which can cause interference

SUNDANESE IDENTITY REPRESENTED BY THE TALENTS OF INI TALKSHOW A STUDY OF PRAGMATICS

Media is suggested to be an effective form to maintain certain local ideology on cultural base. The action of spreading indigenous language expressions, for example, may meet its goal through media since it goes less resist and entertaining. In delivering the language expressions to rise ethnic sensitivity, choice of language and ways in delivering message are argued to be implemented. The questions rise in function, ways, and indication of adaptation. To qualify the study, descriptive-analytic method is used. The results show that four functions involved in informal conversations and songs, making it easy to be accepted and adapted

The 2D Hubbard model on the honeycomb lattice

We consider the 2D Hubbard model on the honeycomb lattice, as a model for a single layer graphene sheet in the presence of screened Coulomb interactions. At half filling and weak enough coupling, we compute the free energy, the ground state energy and we construct the correlation functions up to zero temperature in terms of convergent series; analiticity is proved by making use of constructive fermionic renormalization group methods. We show that the interaction produces a modification of the Fermi velocity and of the wave function renormalization without changing the asymptotic infrared properties of the model with respect to the unperturbed non-interacting case; this rules out the possibility of superconducting or magnetic instabilities in the ground state. We also prove that the correlations verify a Ward Identity similar to the one for massless Dirac fermions, up to asymptotically negligible corrections and a renormalization of the charge velocity.Comment: 35 pages, 2 figure