Effective string theory describes the physics of long confining strings in theories, like Yang-Mills theory, where the mass gap M_gap^2 is of the same order as the string tension T. In 2+1 dimensions, there is a class of confining theories, including massive QED_3 as first analyzed by Polyakov, for which M_gap^2≪ T. These theories are weakly coupled at low energies of order M_gap, and may be analyzed perturbatively. In this paper, we analyze the physics of strings in such theories, focusing on QED_3, at energies of order M_gap (but still well below √(T)). We argue that the width of the string in these theories should be of order 1/M_gap independently of its length, as long as the string is not exponentially long. We also compute at leading order in perturbation theory the ground state energy of a confining string on a circle, and the scattering of Nambu-Goldstone bosons on the string worldsheet.

Two dimensional gauge theories with charged matter fields are useful toy models for studying gauge theory dynamics, and in particular for studying the duality of large N gauge theories to perturbative string theories. A useful starting point for such studies is the pure Yang-Mills theory, which is exactly solvable. Its 1/N expansion was interpreted as a string theory by Gross and Taylor 30 years ago, but they did not provide a worldsheet action for this string theory, and such an action is useful for coupling it to matter fields. The chiral sector of the Yang-Mills theory can be written as a sum over holomorphic maps and has useful worldsheet descriptions, but the full theory includes more general extremal-area maps; a formal worldsheet action including all these maps in a “topological rigid string theory” was written by Hořava many years ago, but various subtleties arise when trying to use it for computations. In this paper we suggest a Polyakov-like generalization of Hořava’s worldsheet action which is well-defined, and we show how it reproduces the free limit of the Yang-Mills theory, both by formal arguments and by explicitly computing its partition function in several cases. In the future we plan to generalize this string theory to the finite-coupling gauge theory, and to analyze it with boundaries, corresponding either to Wilson loops or to dynamical matter fields in the fundamental representation.

Abstract In previous work we constructed an explicit mapping between large N vector models (free or critical) in d dimensions and a non-local high-spin gravity theory on AdS d+1, such that the gravitational theory reproduces the field theory correlation functions order by order in 1/N. In this paper we discuss three aspects of this mapping. First, our original mapping was not valid non-perturbatively in 1/N, since it did not include non- local correlations between the gravity fields which appear at finite N. We show that by using a bi-local G − Σ type formalism similar to the one used in the SYK model, we can construct an exact mapping to the bulk that is valid also at finite N. The theory in the bulk contains additional auxiliary fields which implement the finite N constraints. Second, we discuss the generalization of our mapping to the field theory on S d , and in particular how the sphere free energy matches exactly between the two sides, and how the mapping can be consistently regularized. Finally, we discuss the field theory at finite temperature, and show that the low-temperature phase of the vector models can be mapped to a high-spin gravity theory on thermal AdS space.

We study the large N phase diagram of an asymptotically free UV completion of 𝒩 = 1 SU( N ) super-Yang-Mills-Chern-Simons theory coupled to a single massive fundamental scalar multiplet with a quartic superpotential coupling. We compute the effective superpotential at small gauge coupling λ ≡ N/k , and combine this with previous results in the literature to obtain the full phase diagram in this regime. We find that tuning the UV parameters allows us to reach various phases and fixed points of Chern-Simons theory that were recently discovered using large N techniques, as well as new phases that characterize the Yang-Mills theory. We also conjecture the form of the phase diagram for general values of λ and for finite N .