arXiv subjects

Michael Bershadsky

Publications and source records attributed to Michael Bershadsky.

9 recordsLinked to original sources

arXiv1999

$PSL(n|n)$ Sigma Model as a Conformal Field Theory

We discuss the sigma model on the $PSL(n|n)$ supergroup manifold. We demonstrate that this theory is exactly conformal. The chiral algebra of this model is given by some extension of the Virasoro algebra, similar to the $W$ algebra of Zamolodchikov. We also show that all group invariant correlation functions are coupling constant independent and can be computed in the free theory. The non invariant correlation functions are highly nontrivial and coupling dependent. At the end we compare two and three-point correlation functions of the $PSL(1,1|2)$ sigma model with the correlation functions in the boundary theory of $AdS_3 \times S^3$ and find a qualitative agreement.

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arXiv1998

F-Theory with Quantized Fluxes

We present evidence that the CHL string in eight dimensions is dual to F-theory compactified on an elliptic K3 with a $Γ_{0}(2)$ monodromy group. The monodromy group $Γ_{0}(2)$ allows one to turn on the flux of an antisymmetric two form along the base. The $B_{μν}$ flux is quantized and therefore the moduli space of the CHL string is disconnected from the moduli space of F-theory/Heterotic strings (as expected). The non-zero $B_{μν}$ flux obstructs certain deformations restricting the moduli of elliptic K3 to a 10 dimensional moduli space. We also discuss how one can reconstruct the gauge groups from the elliptic fibration structure.

hep-th↗

arXiv1998

Large N limit of orbifold field theories

We consider certain orbifoldization of the ${\cal N}=4$ field theories that leads to ${\cal N}=2,1,0$ field theories in 4 dimensions. These theories were recently analyzed using the string theory perturbation technique. It was found that in the large $N$ limit all correlation functions of the orbifold theories coincide with those of ${\cal N}=4$, modulo the rescaling of the gauge coupling constant. In this paper we repeat the same analysis using the field theoretical language.

hep-th↗

arXiv1998

String Expansion as Large N Expansion of Gauge Theories

We consider string perturbative expansion in the presence of D-branes imbedded in orbifolded space-time. In the regime where the string coupling is weak and $α'\to 0$, the string perturbative expansion coincides with `t Hooft's large N expansion. We specifically concentrate on theories with d=4 and ${\cal N}=0,1,2,4$, and use world-sheet orbifold techniques to prove vanishing theorems for the field theory beta functions to all orders in perturbation theory in the large N limit. This is in accord with recent predictions.

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arXiv1997

F Theory on K3xK3 and Instantons on 7-branes

We discuss N=2 supersymmetric compactifications to four dimensions from the point of view of F-theory and heterotic theory. In a relatively simple setup, we illustrate the spectral theory for vector bundles on K3xT^2 and discuss the heterotic -- F-theory map. The moduli space of instantons on the 7-brane wrapped around K3 is discussed from the point of view of Higgs mechanism in the effective four-dimensional N=2 theory. This allows us to elaborate on the transitions between various branches of the moduli space of the heterotic/F-theory. We also describe the F-theory compactification on smooth K3xK3 without the 3-branes in which the anomaly is cancelled by the gauge fields.

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arXiv1997

Global Anomalies and Geometric Engineering of Critical Theories in Six Dimensions

We show the existence of global gauge anomalies in six dimensions for gauge groups SU(2),SU(3) and G_2 coupled to matter, characterized by an element of Z_{12},Z_6 and Z_3 respectively. Consideration of this anomaly rules out some of the recently proposed 6 dimensional N=1 QFT's which were conjectured to possess IR fixed point at infinite coupling. We geometrically engineer essentially all the other models with one tensor multiplet using F-theory. In addition we construct 3 infinite series using F-theory geometry which do not have field theory analogs. All these models in the maximally Higgsed phase correspond to the strong coupling behaviour of E_8 x E_8 heterotic string compactification on K3 with instanton numbers (12+n,12-n).

hep-th↗

arXiv1997

On Four-Dimensional Compactifications of F-Theory

Branches of moduli space of F-theory in four dimensions are investigated. The transition between two branches is described as a 3-brane-instanton transition on a 7-brane. A dual heterotic picture of the transition is presented and the F-theory - heterotic theory map is given. The F-theory data - complex structure of the Calabi-Yau fourfold and the instanton bundle on the 7-brane is mapped to the heterotic bundle on the elliptic Calabi-Yau threefold CY_3. The full moduli space has a web structure which is also found in the moduli space of semi-stable bundles on $CY_3$. Matter content of the four-dimensional theory is discussed in both F-theory and heterotic theory descriptions.

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arXiv1996

Colliding Singularities in F-theory and Phase Transitions

We study F-theory on elliptic threefold Calabi-Yau near colliding singularities. We demonstrate that resolutions of those singularities generically correspond to transitions to phases characterized by new tensor multiplets and enhanced gauge symmetry. These are governed by the dynamics of tensionless strings. We also find new transition points which are associated with several small instantons simultaneously shrinking to zero size.

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arXiv1994

Theory of Kähler Gravity

In this paper we discuss the connection on a space of $N=2$ TCFT's that appears in the context of background (in)dependence. We formulate a family of {\it target space field theories} with a similar connection on it. Each theory is a gauge theory (with the gauge group being ${\cal SD}iff $ in the case of $3$-fold). It describes deformations of Kähler structures much like Kodaira Spencer theory describes deformations of the complex structures. It is manifestly background independent. It appears to be a target space field theory for supersymmetric quantum mechanics.

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