Closed String Brane-Like States, Brane Bound States and Noncommutative Branes

We study the mass and different RR charge distributions of the BPS (p,p-2)-brane bound states in the closed string brane-like $\sigma$-model. We show that such brane bound states can be realized by introducing a constant B field in the closed string theory. In addition we show that the worldvolume coordinates of these brane bound states turn out to be noncommutative.Comment: 13 pages, Latex File, v2: some misprints corrected, and a paragraph added to section 3, v3: minor changes, typos correcte

Super Yang-Mills Theory on Noncommutative Torus from Open Strings Interactions

Considering the scattering of massless open strings attached to a D2-brane living in the $B$ field background, we show that corresponding scattering upto the order of \a'^2 is exactly given by the gauge theory on noncommutative background, which is characterized by the Moyal bracket.Comment: 9 pages, Latex File, Minor changes, result

A Note on T-Duality, Open Strings in B-field Background and Canonical Transformations

In this paper we study T-duality for open strings ending on branes with non-zero B-field on them from the point of view of canonical transformations. For the particular case of type II strings on the two torus we show that the $Sl(2,Z)_N$ transformations can be understood as a sub-class of canonical transformations on the open strings in the B-field background.Comment: Tex File, 6 Pages, no figure

Noncommutative Super Yang-Mills Theories with 8 Supercharges and Brane Configurations

In this paper we consider D=4 NCSYM theories with 8 supercharges. We study these theories through a proper type IIA (and M-theory) brane configuration. We find the one loop beta function of these theories and show that there is an elliptic curve describing the moduli space of the theory, which is in principle the same as the curve for the commutative counter-part of our theory. We study some other details of the dynamics by means of this brane configuration.Comment: 14 pages, no figures, v2: typos correcte

Absence of Higher Order Corrections to Noncommutative Chern-Simons Coupling

We analyze the structure of noncommutative pure Chern-Simons theory systematically in the axial gauge. We show that there is no IR/UV mixing in this theory in this gauge. In fact, we show, using the usual BRST identities as well as the identities following from vector supersymmetry, that this is a free theory. As a result, the tree level Chern-Simons coefficient is not renormalized. It also holds that the Chern-Simons coefficient is not modified at finite temperature. As a byproduct of our analysis, we prove that the ghosts completely decouple in the axial gauge in a noncommutative gauge theory.Comment: LaTeX file, 16 pages, no figur

On the Deformation of Λ\Lambda-Symmetry in B-field Background

In this note we will show that the $\Lambda$ symmetry, namely the U(1) symmetry of the open string sigma model which relates the B-field and the U(1) gauge field of a brane to each other, is deformed to a noncommutative version in a constant B-field background.Comment: Tex file, 7 pages. v2: one reference added, typos corrected, and minor changes in discussio

Comments on Multiple M2-branes

Recently a three-dimensional field theory was derived that is consistent with all the symmetries expected of the worldvolume action for multiple M2-branes. In this note we examine several physical predictions of this model and show that they are in agreement with expected M2-brane dynamics. In particular, we discuss the quantization of the Chern-Simons coefficient, the vacuum moduli space, a massive deformation leading to fuzzy three-sphere vacua, and a possible large n limit. In this large n limit, the fuzzy funnel solution correctly reproduces the mass of an M5-brane.Comment: 18 pages. Published versio

Noncommutative SO(n) and Sp(n) Gauge Theories

We study the generalization of noncommutative gauge theories to the case of orthogonal and symplectic groups. We find out that this is possible, since we are allowed to define orthogonal and symplectic subgroups of noncommutative unitary gauge transformations even though the gauge potentials and gauge transformations are not valued in the orthogonal and symplectic subalgebras of the Lie algebra of antihermitean matrices. Our construction relies on an antiautomorphism of the basic noncommutative algebra of functions which generalizes the charge conjugation operator of ordinary field theory. We show that the corresponding noncommutative picture from low energy string theory is obtained via orientifold projection in the presence of a non-trivial NSNS B-field.Comment: 17 pages; considerations about fermions added and some minor change

Black Hole Statistics from Holography

We study the microstates of the ``small'' black hole in the \half-BPS sector of AdS$_5\times S^5$, the superstar of Myers and Tafjord, using the powerful holographic description provided by LLM. The system demonstrates the inherently statistical nature of black holes, with the geometry of Myer and Tafjord emerging only after averaging over an ensemble of geometries. The individual microstate geometries differ in the highly non-trivial topology of a quantum foam at their core, and the entropy can be understood as a partition of $N$ units of flux among 5-cycles, as required by flux quantization. While the system offers confirmation of the most controversial aspect of Mathur and Lunin's recent ``fuzzball'' proposal, we see signs of a discrepancy in interpreting its details.Comment: 21 pages, 4 figures; References adde

Inherent Holography In Fuzzy Spaces and An N-tropic Approach To The Cosmological Constant Problem

In this letter we show that the noncommutative spaces, and in particular fuzzy spheres, are natural candidates which explicitly exhibit the holography, by noting that the smallest physically accessible volume is much larger that the expected Planckian size. Moreover, we show that fuzzy spheres provide us with a new approach, ''an $N$-tropic'' approach, to the cosmological constant problem, though in a Euclidean space-time.Comment: 11 pages, no figures; v3: Presentation improved by adding a discussion on the Schwarzchild blackhole entropy, the version to appear in PL