802 publications from this institution
A bstract We discuss aspects of the possible transition between small black holes and highly excited fundamental strings. We focus on the connection between black holes and the self gravitating string solution of Horowitz and Polchinski. This solution is interesting because it has non-zero entropy at the classical level and it is natural to suspect that it might be continuously connected to the black hole. Surprisingly, we find a different behavior for heterotic and type II cases. For the type II case we find an obstruction to the idea that the two are connected as classical solutions of string theory, while no such obstruction exists for the heterotic case. We further provide a linear sigma model analysis that suggests a continuous connection for the heterotic case. We also describe a solution generating transformation that produces a charged version of the self gravitating string. This provides a fuzzball-like construction of near extremal configurations carrying fundamental string momentum and winding charges. We provide formulas which are exact in α ′ relating the thermodynamic properties of the charged and the uncharged solutions.
Perturbative superstring theory is revisited, with the goal of giving a simpler and more direct demonstration that multi-loop amplitudes are gauge-invariant (apart from known anomalies), satisfy space-time supersymmetry when expected, and have the expected infrared behavior. The main technical tool is to make the whole analysis, including especially those arguments that involve integration by parts, on supermoduli space, rather than after descending to ordinary moduli space.
We re-examine the question of heterotic/heterotic string duality in six dimensions and argue that the E 8 × E 8 heterotic string, compactified on K3 with equal instanton numbers in the two E 8's, has a self-duality that inverts the coupling, dualizes the antisymmetric tensor, acts non-trivially on the hypermultiplets, and exchanges gauge fields that can be seen in perturbation theory with gauge fields of a non-perturbatioe origin. The special role of the symmetric embedding of the anomaly in the two E 8's can be seen from field theory considerations or from an eleven-dimensional point of view. The duality can be deduced by looking in two different ways at eleven-dimensional M-theory compactified on K3 × S1/Z 2 .
It is known that certain spontaneously broken gauge theories give rise to stable strings or vortex lines. In this paper it is shown that under certain conditions such strings behave like superconducting wires whose passage through astrophysical magnetic fields would generate a variety of striking and perhaps observable effects. The superconducting charge carriers may be either bosons (if a charged Higgs field has an expectation value in the core of the string) or fermions (if charged fermions are trapped in zero modes along the string, as is known to occur in certain circumstances). They might be observable as synchrotron sources or as sources of high-energy cosmic rays. If the charge carriers are ordinary quarks and leptons, the strings have important baryon number violating interactions with magnetic fields; such a string, traversing a galactic magnetic field of 10−6 G, creates baryons (or antibaryons) at a rate of order 1012 particles/cm of string per second.
These are notes on the theory of super Riemann surfaces and their moduli spaces, aiming to collect results that are useful for a better understanding of superstring perturbation theory in the RNS formalism.
In this talk, I survey the merits and demerits of Supersymmetry, as well as other approaches to the gauge hierarchy problem.
No abstract is provided for this article.
We describe a mechanism for using discrete symmetries to solve the doublet-triplet splitting problem of four-dimensional supersymmetric GUT's. We present two versions of the mechanism, one via ``deconstruction,'' and one in terms of M-theory compactification to four dimensions on a manifold of G_2 holonomy.
Knowing that a four-dimensional theory with gauge group G0 is unified in theory with gauge group G puts restrictions on what global symmetries are possible in the low-energy world. Here we analyze those restrictions assuming that unification in G occurs inn four dimensions and assuming that unification occurs only in a higher-dimensional theory. There are possibilities for global symmetries which are not possible in the former case, so in principle indirect evidence for higher dimensions might be found by finding peculiar global symmetries in the low-energy world.
It is argued that the ground state of the Kaluza-Klein unified theory is unstable against a process of semiclassical barrier penetration. This is related to the fact that the positive energy conjecture does not hold for the Kaluza-Klein theory; an explicit counter-example is given. The reasoning presented here assumes that in general relativity one should include manifolds of non-vacuum topology. It is argued that the existence of elementary fermions (not present in the original Kaluza-Klein theory) would stabilize the Kaluza-Klein vacuum.
No abstract is provided for this article.
Several years ago, it was proposed that the usual solutions of the Yang-Baxter equation associated to Lie groups can be deduced in a systematic way from fourdimensional gauge theory.In the present paper, we extend this picture, fill in many details, and present the arguments in a concrete and down-to-earth way.Many interesting effects, including the leading nontrivial contributions to the Rmatrix, the operator product expansion of line operators, the framing anomaly, and the quantum deformation that leads from g[[z]] to the Yangian, are computed explicitly via Feynman diagrams.We explain how rational, trigonometric, and elliptic solutions of the Yang-Baxter equation arise in this framework, along with a generalization that is known as the dynamical Yang-Baxter equation.
No abstract is provided for this article.
These are notes on the theory of super Riemann surfaces and their moduli spaces, aiming to collect results that are useful for a better understanding of superstring perturbation theory in the RNS formalism.
The supersymmetric Yang-Mills multiplet in ten dimensions is parity violating; the massless fermions are spinors of SO(1,9) of one chirality or the other, but not both. In the context of string theory, this means that the massless fermion states of the open superstring have parity-violating gauge couplings. In fact, parity violation appears because there are two possible choices for the GSO projection in the Ramond sector, and one or the other must be chosen. Because of the role of the open superstring in constructing closed-string theories, most of the closed-string theories are likewise parity violating. For the type I and type IIB theories, the use of one GSO projection or the other introduces parity violation for closed strings just as it does for open strings. Parity violation is avoided in the type IIA theory, because one GSO projection is made for right-moving modes on the world sheet while the opposite GSO projection is made for left movers, and the overall system is invariant under simultaneous reflections or parity transformations of the world sheet and space-time. It is not invariant under separate world-sheet or space-time reflections. The heterotic theories are parity violating in the space-time sense (and on the world sheet), because a parity-violating right-moving multiplet is coupled to a parity-conserving left-moving multiplet.
The article is devoted to a quantum field theory explanation of the relationship (noticed some years ago by Gepner) between the Verlinde algebra of the group $U(k)$ at level $N-k$ and the cohomology of the Grassmannian. The argument proceeds by starting with the two dimensional sigma model whose target space is the Grassmannian and integrating out some fields in a standard way. It has long been known that the resulting low energy effective action describes a theory with a mass gap; the novelty here is that this theory in fact is equivalent at long distances to a gauged WZW model of $U(k)/U(k)$, and hence is related to the Verlinde algebra.
The Coulomb branch of N = 2 supersymmetric gauge theories in four dimensions is described in general by an integrable Hamiltonian system in the holomorphic sense. A natural construction of such systems comes from two-dimensional gauge theory and spectral curves. Starting from this point of view, we propose an integrable system relevant to the N = 2 SU(n) gauge theory with a hypermultiplet in the adjoint representation, and offer much evidence that it is correct. The model has an SL(2,Z) S-duality group (with the central element −1 of SL(2,Z) acting as charge conjugation); SL(2,Z) permutes the Higgs, confining, and oblique confining phases in the expected fashion. We also study more exotic phases.
Recent developments involving JT gravity in two dimensions indicate that under some conditions, a gravitational path integral is dual to an average over an ensemble of boundary theories, rather than to a specific boundary theory. For an example in one dimension more, one would like to compare a random ensemble of two-dimensional CFT's to Einstein gravity in three dimensions. But this is difficult. For a simpler problem, here we average over Narain's family of two-dimensional CFT's obtained by toroidal compactification. These theories are believed to be the most general ones with their central charges and abelian current algebra symmetries, so averaging over them means picking a random CFT with those properties. The average can be computed using the Siegel-Weil formula of number theory and has some properties suggestive of a bulk dual theory that would be an exotic theory of gravity in three dimensions. The bulk dual theory would be more like $U(1)^{2D}$ Chern-Simons theory than like Einstein gravity.
