Worldsheet Formulation Research Articles

Worldsheet formalism for decoupling limits in string theory

We study the bosonic sector of a decoupling limit of type IIA superstring theory, where a background Ramond-Ramond one-form is fined tuned to its critical value, such that it cancels the associated background D0-brane tension. The light excitations in this critical limit are D0-branes, whose dynamics is described by the Banks-Fischler-Shenker-Susskind (BFSS) Matrix theory that corresponds to M-theory in the Discrete Light-Cone Quantization (DLCQ). We develop the worldsheet formalism for the fundamental string in the same critical limit of type IIA superstring theory. We show that the fundamental string develops singularities on its worldsheet, whose topology is described by nodal Riemann spheres as in ambitwistor string theory. We study the T-duality transformations of this string sigma model and provide a worldsheet derivation for the recently revived and expanded duality web that unifies a zoo of decoupling limits in type II superstring theories. By matching the string worldsheet actions, we demonstrate how some of these decoupling limits are related to tensionless (and ambitwistor) string theory, Carrollian string theory, the Spin Matrix limits of the AdS/CFT correspondence, and more.

Bosonic sectorized strings and the (DF)2 theory

In this work, we investigate the bosonic chiral string in the sectorized inter- pretation, computing its spectrum, kinetic action and 3-point amplitudes. As expected, the bosonic ambitwistor string is recovered in the tensionless limit. We also consider an extension of the bosonic model with current algebras. In that case, we compute the effective action and show that it is essentially the same as the action of the mass-deformed (DF )2 theory found by Johansson and Nohle. Aspects which might seem somewhat contrived in the original construction — such as the inclusion of a scalar transforming in some real representation of the gauge group — are shown to follow very naturally from the worldsheet formulation of the theory.

Heterotic type I strings at high temperature

We show that the high temperature limits of the heterotic E8xE8 and Spin(32)/Z2 strings and their Type I A/B superstring duals are finite and convergent. The Hagedorn growth of the degeneracies in the string mass level expansion is suppressed by an exponential linear in the mass level number for both heterotic strings, and suppressed by the exponential of the negative square root of the mass level number for the Type IB superstring. However, in the massless gauge field theoretic limit of the Type IB open and closed superstring, we find clear evidence for the thermal deconfinement phase transition at the self-dual temperature by examining the annulus graph alone. Above the self-dual temperature, there is a discontinuity in the first derivative with respect to temperature of both the free energy, and the heavy quark potential, leading to a deconfined thermal gluon ensemble, with universal 1/r potential, and temperature dependent corrections, as predicted by Luscher and Weisz. A number of essential aspects of the worldsheet formalism of the heterotic strings are derived in an appendix, deducing thereby the O8-D0-D8brane Type IA duals of all of the heterotic CHL island universe moduli spaces.

Non-geometric Calabi-Yau backgrounds and K3 automorphisms

We consider compactifications of type IIA superstring theory on mirror-folds obtained as K3 fibrations over two-tori with non-geometric monodromies involving mirror symmetries. At special points in the moduli space these are asymmetric Gepner models. The compactifications are constructed from non-geometric automorphisms that arise from the diagonal action of an automorphism of the K3 surface and of an automorphism of the mirror surface. We identify the corresponding gaugings of mathcal{N} = 4 supergravity in four dimensions, and show that the minima of the potential describe the same four-dimensional low-energy physics as the worldsheet formulation in terms of asymmetric Gepner models. In this way, we obtain a class of Minkowski vacua of type II string theory which preserve mathcal{N} = 2 supersymmetry. The massless sector consists of mathcal{N} = 2 supergravity coupled to 3 vector multiplets, giving the STU model. In some cases there are additional massless hypermultiplets.

Complete normal ordering 1: Foundations

We introduce a new prescription for quantising scalar field theories (in generic spacetime dimension and background) perturbatively around a true minimum of the full quantum effective action, which is to ‘complete normal order’ the bare action of interest. When the true vacuum of the theory is located at zero field value, the key property of this prescription is the automatic cancellation, to any finite order in perturbation theory, of all tadpole and, more generally, all ‘cephalopod’ Feynman diagrams. The latter are connected diagrams that can be disconnected into two pieces by cutting one internal vertex, with either one or both pieces free from external lines. In addition, this procedure of ‘complete normal ordering’ (which is an extension of the standard field theory definition of normal ordering) reduces by a substantial factor the number of Feynman diagrams to be calculated at any given loop order. We illustrate explicitly the complete normal ordering procedure and the cancellation of cephalopod diagrams in scalar field theories with non-derivative interactions, and by using a point splitting ‘trick’ we extend this result to theories with derivative interactions, such as those appearing as non-linear σ-models in the world-sheet formulation of string theory. We focus here on theories with trivial vacua, generalising the discussion to non-trivial vacua in a follow-up paper.

Macroscopic (and microscopic) massless modes

We study certain spinning strings exploring the flat directions of AdS3×S3×S3×S1, the massless sector cousins of su(2) and sl(2) sector spinning strings. We describe these, and their vibrational modes, using the D(2,1;α)2 algebraic curve. By exploiting a discrete symmetry of this structure which reverses the direction of motion on the spheres, and alters the masses of the fermionic modes s→κ−s, we find out how to treat the massless fermions which were previously missing from this formalism. We show that folded strings behave as a special case of circular strings, in a sense which includes their mode frequencies, and we are able to recover this fact in the worldsheet formalism. We use these frequencies to calculate one-loop corrections to the energy, with a version of the Beisert–Tseytlin resummation.

Euclidean time formulation for the superstring ensembles: Perturbative canonical ensemble with Neveu-SchwarzB-field backgrounds

The lengthy discussion and derivations given in this paper have been corrected, and completed with additional results and greater simplicity. We show that the high temperature limits of the heterotic E8xE8 and Spin(32)/Z2 strings and their Type I A/B superstring duals are finite and convergent. The Hagedorn growth of the degeneracies in the string mass level expansion is suppressed by an exponential linear in the mass level number for both heterotic strings, and suppressed by the exponential of the negative square root of the mass level number for the Type IB superstring. However, in the massless gauge field theoretic limit of the Type IB open and closed superstring, we find clear evidence for the thermal deconfinement phase transition at the self-dual temperature by examining the annulus graph alone. Above the self-dual temperature, there is a discontinuity in the first derivative with respect to temperature of both the free energy, and the heavy quark potential, leading to a deconfined thermal gluon ensemble, with universal 1/r potential, and temperature dependent corrections, as predicted by Luscher and Weisz. A number of essential aspects of the worldsheet formalism of the heterotic strings are derived in an appendix, deducing thereby the O8-D0-D8brane Type IA duals of all of the heterotic CHL island universe moduli spaces.

1-brane sources for the light-cone worldsheet:Q-branion–Q¯-branion scattering to one loop

This paper extends the study, initiated by Rozowsky and Thorn, of gauge fields in interaction with Dirac fields living on separated parallel 1-branes. In a light-cone description, replacing static point sources by 1-brane sources allows ${p}^{+}$ conservation to be maintained in their presence, which simplifies the light-cone quantization procedure. Here we calculate on-shell branion scattering amplitudes through one loop in light-cone gauge, and thereby resolve a puzzling ambiguity encountered in the earlier off-shell calculations. We confirm that infrared divergences cancel in properly defined scattering probabilities. This work lays the groundwork for the incorporation of 1-brane sources in the light-cone worldsheet formalism.

On the time-dependent description for the decay of unstable D-branes

We discuss how to describe time-dependent phenomena in string theory like the decay of unstable D-branes with the help of the world-sheet formulation. It is shown in a nontrivial well-controlled example that the coupling of the tachyons to propagating on-shell modes which escape to infinity can lead to time-dependent relaxation into a stationary final state. The final state corresponds to a fixed point of the RG flow generated by the relevant field from which the tachyon vertex operator is constructed. On the way we set up a fairly general formalism for the description of slow time-dependent phenomena with the help of conformal perturbation theory on the world-sheet.

Scattering of glue by glue on the light-cone worldsheet: Helicity nonconserving amplitudes

We give the light-cone gauge calculation of the one-loop on-shell scattering amplitudes for gluon-gluon scattering which violate helicity conservation. We regulate infrared divergences by discretizing the ${p}^{+}$ integrations, omitting the terms with ${p}^{+}=0$. Collinear divergences are absent diagram by diagram for the helicity nonconserving amplitudes. We also employ a novel ultraviolet regulator that is natural for the light-cone worldsheet description of planar Feynman diagrams. We show that these regulators give the known answers for the helicity nonconserving one-loop amplitudes, which do not suffer from the usual infrared vagaries of massless particle scattering. For the maximal helicity violating process we elucidate the physics of the remarkable fact that the loop momentum integrand for the on-shell Green function associated with this process, with a suitable momentum routing of the different contributing topologies, is identically zero. We enumerate the counterterms that must be included to give Lorentz covariant results to this order, and we show that they can be described locally in the light-cone worldsheet formulation of the sum of planar diagrams.

Fermions in the harmonic potential and string theory

We explicitly derive collective field theory description for the system of fermions in the harmonic potential. This field theory appears to be a coupled system of free scalar and (modified) Liouville field. This theory should be considered as an exact bosonization of the system of non-relativistic fermions in the harmonic potential. Being surprisingly similar to the world-sheet formulation of c=1 string theory, this theory has quite different physical features and it is conjectured to give space-time description of the string theory, dual to the fermions in the harmonic potential. A vertex operator in this theory is shown to be a field theoretical representation of the local fermion operator, thus describing a D0 brane in the string language. Possible generalization of this result and its derivation for the case of c=1 string theory (fermions in the inverse harmonic potential) is discussed.

Renormalization of quantum fields on the lightcone worldsheet, I: scalar fields

We show that the lightcone worldsheet formalism, constructed to represent the sum of the bare planar diagrams of scalar Φ 3 field theory, survives the renormalization procedure in space–time dimensions D ⩽ 6 . Specifically this means that all the counter-terms, necessary to produce a successful renormalized perturbation expansion to all orders, can be represented as local terms in the lightcone worldsheet action. Because the worldsheet regulator breaks Lorentz invariance, we find the need for two noncovariant counter-terms, in addition to the usual mass, coupling and wave function renormalization. One of these can be simply interpreted as a rescaling of transverse coordinates with respect to longitudinal coordinates. The second one introduces couplings between the matter and ghost worldsheet fields on the boundaries.

Meanfield approximation for field theories on the worldsheet revisited

This work is the continuation of the earlier efforts to apply the mean field approximation to the continuum worldsheet formulation of planar ϕ 3 theory. The previous attempts were either simple but without solid foundation or better founded but excessively complicated. In this article, we present an approach both simple, and also systematic and well founded. We are able to carry through the leading order mean field calculation analytically, and with a suitable tuning of the coupling constant, we find string formation.

Intersecting D-branes in a type IIB plane wave background

We study intersecting D-branes in a type IIB plane wave background using Green-Schwarz worldsheet formulation. We consider all possible $D_\pm$-branes intersecting at angles in the plane wave background and identify their residual supersymmetries. We find, in particular, that $D_\mp - D_\pm$ brane intersections preserve no supersymmetry. We also present the explicit worldsheet expressions of conserved supercharges and their supersymmetry algebras.

An improved mean field approximation on the worldsheet for planar φ3 theory

We present an improved version of our earlier work on summing the planar graphs in φ 3 field theory. The present treatment is also based on our world sheet formalism and the mean field approximation, but it makes use of no further approximations. We derive a set of equations between the expectation values of the world sheet fields, and we investigate them in certain limits. We show that the equations can give rise to (metastable) string forming solutions.

Ghost-matter mixing and feigenbaum universality in string theory

Brane-like vertex operators, defining backgrounds with the ghost-matter mixing in NSR superstring theory, play an important role in a world-sheet formulation of D-branes and M theory, being creation operators for extended objects in the second quantized formalism. In this paper we show that dilaton's beta function in ghost-matter mixing backgrounds becomes stochastic. The renormalization group (RG) equations in ghost-matter mixing backgrounds lead to non-Markovian Fokker-Planck equations which solutions describe superstrings in curved space-times with brane-like metrics.We show that Feigenbaum universality constant $\delta=4,669...$ describing transitions from order to chaos in a huge variety of dynamical systems, appears analytically in these RG equations. We find that the appearance of this constant is related to the scaling of relative space-time curvatures at fixed points of the RG flow. In this picture the fixed points correspond to the period doubling of Feigenbaum iterational schemes.

DBI ACTION FROM CLOSED STRINGS AND D-BRANE SECOND QUANTIZATION

Brane-like vertex operators play an important role in a world-sheet formulation of D-branes and M theory. In this paper we derive the DBI D-brane action from closed NSR string with brane-like states. We also show that these operators carry RR charges and define D-brane wave functions in a second quantized formalism.

Feigenbaum universality in string theory

Brane-like vertex operators, defining backgrounds with ghost-matter mixing in NSR superstring theory, play an important role in the world-sheet formulation of D-branes and M theory as creation operators for extended objects in the second quantized formalism. In this paper, we show that the dilaton beta function in ghost-matter mixing backgrounds becomes stochastic. The renormalization group (RG) equations in ghost-matter mixing backgrounds lead to non-Markovian Fokker-Planck equations whose solutions describe superstrings in curved space-times with brane-like metrics. We show that the Feigenbaum universality constant δ=4.669..., describing transitions from order to chaos in a huge variety of dynamical systems, appears analytically in these RG equations. We find that the appearance of this constant is related to the scaling of relative space-time curvatures at fixed points of the RG flow. In this picture, the fixed points correspond to the period doubling of Feigenbaum iteration schemes.

BT worldsheet for supersymmetric gauge theories

We extend the Bardakci–Thorn (BT) worldsheet formalism to supersymmetric non-Abelian gauge theory. Our method covers the cases of N=1,2,4 extended supersymmetry. This task requires the introduction of spinor valued Grassmann variables on the worldsheet analogous to those of the supersymmetric formulation of superstring theory. As in the pure Yang–Mills case, the worldsheet formalism automatically generates the correct quartic vertices from the cubic vertices. We also discuss coupling renormalization to one loop order.

A worldsheet description of planar Yang–Mills theory

We extend previous work by developing a worldsheet description of non-Abelian gauge theory (Yang–Mills). This task requires the introduction of Grassmann variables on the world sheet analogous to those of the Neveu–Schwarz–Ramond formulation of string theory. A highlight of our construction is that once the three gluon vertices of Yang–Mills Feynman diagrams are given a worldsheet description, the worldsheet formalism automatically produces all of the quartic vertices.