String Endpoints Research Articles

The origin of noncommutativity?

Consistent boundary Poisson structures for open string theory coupled to background $B$-field are considered using the new approach proposed in hep-th/0111005. It is found that there are infinitely many consistent Poisson structures, each leads to a consistent canonical quantization of open string in the presence of background $B$-field. Consequently, whether the $D$-branes to which the open string end points are attached is noncommutative or not depends on the choice of a particular Poisson structure.

Noncommutative D-Brane in a Nonconstant NS-NSBField Background

We show that, when the field strength H of the NS-NS B field does not vanish, the coordinates x and momenta p of open string end points satisfy a set of mixed commutation relations among themselves. Identifying x and p with the coordinates and derivatives of the D-brane world volume, we find a new type of noncommutative space which is very different from those associated with a constant B field background.

Superstring `ending' on super-D9-brane: a supersymmetric action functional for the coupled brane system

A supersymmetric action functional describing the interaction of the fundamental superstring with the D=10, type IIB Dirichlet super-9-brane is presented. A set of supersymmetric equations for the coupled system is obtained from the action principle. It is found that the interaction of the string endpoints with the super D9-brane gauge field requires some restrictions for the image of the gauge field strength. When those restrictions are not imposed, the equations imply the absence of the endpoints, and the equations coincide either with the ones of the free super-D9-brane or with the ones for the free closed type IIB superstring. Different phases of the coupled system are described. A generalization to an arbitrary system of intersecting branes is discussed.

Non-commutative open string and D-brane

In this paper we consider the quantization of open strings ending on D-branes with a background B field. We find that space-time coordinates of the open string end-points become noncommutative, and correspondingly the D-brane world-volume also becomes non-commutative. This provides a string theory derivation and generalization of the non-commutativity obtained previously in the M(atrix) model compactification. For D p-branes with p ⩾ 2 our results are new and agree with that of M(atrix) theory for the case of A = 0 (where A is the world-volume gauge field) if the T-duality radii are used.

D-branes and cosmology

D-branes, topological defects in string theory on which string endpoints can live, may give new insight into the understanding of the cosmological evolution of the Universe at early epochs. We analyze the dynamics of D-branes in curved backgrounds and discuss the parameter space of M-theory as a function of the coupling constant and of the curvature of the Universe. We show that D-branes may be efficiently produced by gravitational effects. Furthermore, in curved space-times the transverse fluctuations of the D-branes develop a tachyonic mode and when the fluctuations grow larger than the horizon the branes become tensionless and break up. This signals a transition to a new regime. We discuss the implications of our findings for the singularity problem present in string cosmology, suggesting the existence of a limiting value for the curvature which is in agreement with the value suggested by the cosmological version of the holography principle. We also comment on possible implications for the so-called brane world scenario, where the Standard Model gauge and matter fields live inside some branes while gravitons live in the bulk.

On second-quantized open superstring theory

The SO(32) theory, in the limit where it is an open superstring theory, is completely specified in the light-cone gauge as a second-quantized string theory in terms of a “matrix string” model. The theory is defined by the neighborhood of a 1 + 1-dimensional fixed point theory, characterized by an Abelian gauge theory with type IB Green-Schwarz form. Non-orientability and SO(32) gauge symmetry arise naturally, and the theory effectively constructs an orientifold projection of the (weakly coupled) matrix type IIB theory (also discussed herein). The fixed point theory is a conformal field theory with boundary, defining the free string theory. Interactions involving the interior of open and closed strings are governed by a twist operator in the bulk, while string endpoints are created and destroyed by a boundary twist operator.

STRINGS WITH INTERACTING ENDS

At the classical level we study open bosonic strings. A generic description of string self-interactions localized at string ends is given. Self-interactions are characterized by two dimensionless coupling constants. The model is rewritten using complex Liouville fields. Using these Lorentz and reparametrization invariant variables, equations of motion get greatly simplified and reduce to some boundary problem for Liouville equation. Henceforth, the Nambu-Goto string model is proved to be still rnathematically tractable if we attach finite masses and interactions at string end points. With the help of semiclassical quantization, we indicate several encouraging points for hadronic strings.

Temporal-gauge string field with open strings

A string field theory including open string fields is constructed in the temporal gauge. It consists of string interaction vertices similar to the light-cone gauge string field theory. A slight modification of the definition of the time coordinate is needed because of the existence of the open string end points.

Cosmic strings with curvature corrections

A generic model of string described by a Lagrangian density that depends on the extrinsic curvature of the string worldsheet is studied. Using a system of coordinates adapted to the string world sheet the equation of motion and the energy-momentum tensor are derived for strings evolving in curved spacetime. We find that the curvature corrections may change the relation between the string energy density and the tension. It can also introduce heat propagation along the string. We also find for the Polyakov as well as Nambu strings with a topological term that the open string end points can travel with a speed less than the velocity of light.

Dynamical string-parton model for relativistic heavy-ion collisions.

We introduce a dynamical model for the description of hadron-hadron collisions at relativistic energies. The model is based on classical Nambu-Got\ifmmode \bar{o}\else \={o}\fi{} strings. The string motion is performed in unrestricted four-dimensional space-time. The string end points are interpreted as partons which carry energy and momentum. We study ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$, e-p, and p-p collisions at various center-of-mass energies. The three basic features of our model are as follows. An ensemble of strings with different end-point dynamics is used to approximately reproduce the valence quark structure functions. We introduce an adiabatic hadronization mechanism for string breakup via qq\ifmmode\bar\else\textasciimacron\fi{} pair production. The interaction between strings is formulated in terms of a quark-quark scattering amplitude and exchange.

Relativistic string model of light mesons with massless quarks

The straightline string model of mesons with massless fermions (“quarks”) at the string endpoints is constructed. The spectrum of the model, consisting of four Regge trajectories weakly non-linear atM2∼0, is obtained. A comparison of the model predictions with the experimental spectrum of light mesons and prospects for future searches are discussed.