Related papers: On Tensionless Strings in $3+1$ Dimensions

The observable universe could be a 1+3-surface (the "brane") embedded in a 1+3+\textit{d}-dimensional spacetime (the "bulk"), with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least…

The target space theory of the N=(2,1) heterotic string may be interpreted as a theory of gravity coupled to matter in either $1+1$ or $2+1$ dimensions. Among the target space theories in $1+1$ dimensions are the bosonic, type II, and…

The string equivalent of a massless particle ($m=0$) is the tensionless string ($T=0$). The study of such strings is of interest when trying to understand the high energy limit of ordinary strings. I discuss the classical $T\to 0$ limit of…

We reexamine a family of models with a 3+1-dimensional de Sitter spacetime obtained in the standard tree-level low-energy limit of string theory with a non-trivial anisotropic axion-dilaton background. While such limiting approximations are…

We study junctions consisting of confining strings in N=1 supersymmetric large N gauge theories by means of the gauge/gravity correspondence. We realize these junctions as D-brane configurations in infrared geometries of the…

In this thesis, two aspects of string theory are discussed, tensionless strings and supersymmetric sigma models. The equivalent to a massless particle in string theory is a tensionless string. Even almost 30 years after it was first…

We consider N=2 superconformal theories defined on a 3+1 dimensional hyperplane intersection of two sets of M5 branes. These theories have (tensionless) BPS string solitons. We use a dual supergravity formulation to deduce some of their…

I suggest the possibility of a new string in ten dimensions. Evidence for this string is presented both from orientifold physics and from K-theory, along with a mystery concerning the M-theory description. Motivated by this possibility,…

Superstring theories in the critical dimension D=10 are connected to one another by a well-explored web of dualities. In this paper we use closed-string tachyon condensation to connect the supersymmetric moduli space of the critical…

It is here explained how the Green-Schwarz superstring theory arises from Matrix String Theory. This is obtained as the strong YM-coupling limit of the theory expanded around its BPS instantonic configurations, via the identification of the…

It has recently been realised that there are supersymmetry-preserving non-relativistic decoupling limits associated with each half-BPS object in String Theory and M-Theory. We argue that, given a $p$-brane and a $q$-brane for which there is…

We derive the five-dimensional effective action of strongly coupled heterotic string theory for the complete (1,1) sector of the theory by performing a reduction, on a Calabi-Yau three-fold, of M-theory on S^1/Z_2. A crucial ingredient for…

The consistency of string theory as a theory of gravity does not rely on the presence of spacetime supersymmetry; however, its absence leads to the emergence of tadpole diagrams in the on-shell worldsheet formulation, thus undermining our…

We generalize the Brane Gas Cosmological Scenario to M-theory degrees of freedom, namely $M5$ and $M2$ branes. Without brane intersections, the Brandenberger Vafa(BV) arguments applied to M-theory degrees of freedom generically predict a…

We construct two new SL(2,Z) invariant vacua of type IIB string theory which are bound states of $(p,q)$ strings with $(m,n)$ 5-branes, written as ((F, D1), (NS5, D5)) and preserve 1/4 of the full space-time supersymmetries. For the first…

M5 branes on a D-type ALE singularity display various phenomena that introduce additional massless degrees of freedom. The M5 branes are known to fractionate on a D-type singularity. Whenever two fractional M5 branes coincide, tensionless…

We consider a brane world scenario which arises as the near-horizon region of a non-extremal D5-brane. There is a quasi-localized massive graviton mode, as well as harmonic modes of higher mass which are bound to the brane to a lesser…

We study a system of intersecting NS and D-branes in type IIA string theory in R^{9,1}. We show that the 3+1 dimensional non-supersymmetric theory at the intersection has unstable vacua which are long-lived in some regions of the parameter…

We review the recent developments in superstrings. We start with a brief summary of various consistent superstring theories and discuss T-duality which necessarily leads to the presence of D-branes. The properties of D-branes are summarized…

We demonstrate that the spectrum of any consistent string theory in $D$ dimensions must satisfy a number of supertrace constraints: $ Str~M^{2n}=0 $ for $0 \leq n < D/2-1$, integer $n$. These results hold for a large class of string…