NCOS Theory Research Articles

Instabilities of D-brane bound states and their related theories

We investigate the Gregory-Laflamme instability for bound states of branes in type II string theory and in M-theory. We examine systems with two different constituent branes: for instance, D3-F1 or D4-D0. For the cases in which the Gregory-Laflamme instability can occur, we describe the boundary of thermodynamic stability. We also present an argument for the validity of the Correlated Stability Conjecture, generalizing earlier work by Reall. We discuss the implications for OM theory and NCOS theory, finding that in both cases, there exists some critical temperature above which the system becomes unstable to clumping of the open strings/membranes.

Holography with Ramond-Ramond fluxes

Starting from the non-linear sigma model of the IIB string in the light-cone gauge, we analyze the role of RR fluxes in Holography. We find that the worldsheet theory of states with only left or right moving modes does not see the presence of RR fields threading a geometry. We use this significant simplification to compute part of the strong coupling spectrum of the two dimensional NCOS theory. We also reproduce the action of a closed string in a PP-wave background using this general formalism; and we argue for various strategies to find new systems where the closed string theory may be exactly solvable.

Supersymmetric Brane-Antibrane Systems: Matrix Model Description, Stability and Decoupling Limits

After reviewing the supertubes and super brane-antibrane systems in the context of matrix model, we look for more general higher-dimensional configurations. For D3-bar{D3}, we find a non-trivial configuration with E cdot B not equal to 0 and describe the worldvolume gauge theory. We present the string probe of D3-bar{D3} system and study the decoupling limits leading to either noncommutative Super-Yang-Mills or NCOS theories with eight supercharges.

PP-waves from Nonlocal Theories

We study the Penrose limit of ODp theory. There are two different PP-wave limits of the theory. One of them is a ten dimensional PP-wave and the other a four dimensional one. We observe the later one leads to an exactly solvable background for type II string theories where we have both NS and RR fields. The Penrose limit of different branes of string (M-theory) in a nonzero B/E field (C field) is also studied. These backgrounds are conjectured to provide dual description of NCSYM, NCOS and OM theory. We see that under S-duality the subsector of NCSYM$_4$ and NCOS$_4$ which are dual to the corresponding string theory on PP-wave coming from NCYM$_4$ and NCOS$_4$ map to each other for given null geodesic.

The Hagedorn transition in noncommutative open string theory

The Hagedorn transition in noncommutative open string theory (NCOS) is relatively simple because gravity decouples. For NCOS theories in no more than five space–time dimensions, the Hagedorn transition is second order, and the high temperature phase involves long, nearly straight fundamental strings separating from the D-brane on which the NCOS theory is defined. Above five spacetime dimensions interaction effects become important below the Hagedorn temperature. Although this complicates studies of the transition, we believe that the high temperature phase again involves long strings liberated from the bound state.

Open Branes and Little Strings

This is a short review of the newly discovered ODp-theories that are non-gravitational six-dimensional theories defined as the decoupling limit of NS5-branes in the presence of a near-critical (p + 1)-form RR fields. We discuss the motivation for these new theories, their definitions and properties, and their relation to NCOS theory, OM theory and Little String Theory, focusing on the cases p = 1, 2.

Strong coupling effects in noncommutative spaces from OM theory and supergravity

We show that a four-parameter class of (3+1)-dimensional NCOS theories can be obtained by dimensional reduction on a general 2-torus from OM theory. Compactifying two spatial directions of NCOS theory on a 2-torus, we study the transformation properties under the SO (2,2; Z ) T-duality group. We then discuss non-perturbative configurations of non-commutative super Yang–Mills theory. In particular, we calculate the tension for magnetic monopoles and ( p , q ) dyons and exhibit their six-dimensional origin, and construct a supergravity solution representing an instanton in the gauge theory. We also compute the potential for a monopole–antimonopole in the supergravity approximation.

Newtonian gravitons and D-brane collective coordinates in wound string theory

Recently it was shown that NCOS theories are part of a ten-dimensional theory known as Non-relativistic Wound string theory. We clarify the sense in which gravity is present in this theory. We show that Wound string theory contains exceptional unwound strings, including a graviton, which mediate the previously discovered instantaneous long-range interactions, but are negligible as asymptotic states. Unwound strings also provide the expected collective coordinates for the transverse D-branes in the theory. These and other results are shown to follow both from a direct analysis of the effect of the NCOS limit on the parent string theory, and from the worldsheet formalism developed by Gomis and Ooguri, about which we make some additional remarks. We also devote some attention to supergravity duals, and in particular show that the open and closed strings of the theory are respectively described by short and long strings on the supergravity side.

Open branes in space–time non-commutative little string theory

We conjecture the existence of two new non-gravitational six-dimensional string theories, defined as the decoupling limit of NS5-branes in the background of near-critical electrical two- and three-form RR fields. These theories are space-time non-commutative Little String Theories with open branes. The theory with (2,0) supersymmetry has an open membrane in the spectrum and reduces to OM theory at low energies. The theory with (1,1) supersymmetry has an open string in the spectrum and reduces to 5+1 dimensional NCOS theory for weak NCOS coupling and low energies. The theories are shown to be T-dual with the open membrane being T-dual to the open string. The theories therefore provide a connection between 5+1 dimensional NCOS theory and OM theory. We study the supergravity duals of these theories and we consider a chain of dualities that shows how the T-duality between the two theories is connected with the S-duality between 4+1 dimensional NCOS theory and OM theory.

IIA/B, wound and wrapped

We examine the T-duality relation between 1+1 NCOS and the DLCQ limit of type IIA string theory. We show that, as long as there is a compact dimension, one can meaningfully define an `NCOS' limit of IIB/A string theory even in the absence of D-branes (and even if there is no B-field). This yields a theory of closed strings with strictly positive winding, which is T-dual to DLCQ IIA/B without any D-branes. We call this the Type IIB/A Wound String Theory. The existence of decoupled sectors can be seen directly from the energy spectrum, and mirrors that of the DLCQ theory. It becomes clear then that all of the different p+1 NCOS theories are simply different states of this single Wound IIA/B theory which contain D-branes. We study some of the properties of this theory. In particular, we show that upon toroidal compactification, Wound string theory is U-dual to various Wrapped Brane theories which contain OM theory and the ODp theories as special states.

On noncommutative open string theories

We investigate new compactifications of OM theory giving rise to a (3+1)-dimensional open string theory with non-commutative x0-x1 and x2-x3 coordinates. The theory can be directly obtained by starting with a D3-brane with parallel (near critical) electric and magnetic field components, in the presence of a RR scalar field. The magnetic parameter permits to interpolate continuously between the x0-x1 non-commutative open string theory and the x2-x3 spatial non-commutative U(N) super Yang-Mills theory. We discuss SL(2,) transformations of this theory. Using the supergravity description of the large-N limit, we also compute corrections to the quark-antiquark Coulomb potential arising in the NCOS theory.