String and M-theory: answering the critics

Using as a springboard a three-way debate between theoretical physicist Lee Smolin, philosopher of science Nancy Cartwright and myself, I address in layman's terms the issues of why we need a unified theory of the fundamental interactions and why, in my opinion, string and M-theory currently offer the best hope. The focus will be on responding more generally to the various criticisms. I also describe the diverse application of string/M-theory techniques to other branches of physics and mathematics which render the whole enterprise worthwhile whether or not "a theory of everything" is forthcoming.Comment: Update on EPSRC. (Contribution to the Special Issue of Foundations of Physics: "Forty Years Of String Theory: Reflecting On the Foundations", edited by Gerard 't Hooft, Erik Verlinde, Dennis Dieks and Sebastian de Haro. 22 pages latex

Putting String/Fivebrane Duality to the Test

According to string/fivebrane duality, the Green-Schwarz factorization of the $D=10$ spacetime anomaly polynomial $I_{12}$ into $X_4\, X_8$ means that just as $X_4$ is the anomaly polynomial of the $d=2$ string worldsheet so $X_8$ should be the anomaly polynomial of the $d=6$ fivebrane worldvolume. To test this idea we perform a fivebrane calculation of $X_8$ and find perfect agreement with the string one--loop result.Comment: 14 pages, CERN TH-6614/92, CTP-TAMU 60/9

Reducing SS- duality to TT- duality

The infrared limit of $D=4,~~N=4$ Yang-Mills theory with compact gauge group $G$ compactified on a two-torus is governed by an effective superconformal field theory. We conjecture that this is a certain orbifold involving the maximal torus of $G$. Yang-Mills $S$-duality makes predictions for all correlators of this effective conformal field theory. These predictions are shown to be implied by the standard $T$-duality of the conformal field theory. Consequently, Montonen-Olive duality between electric and magnetic states reduces to the standard two-dimensional duality between momentum and winding states.Comment: 13 pages, harvmac, no figures. (Some Comments added. Some references added.

D=6, N=1 String Vacua and Duality

We review the structure $D=6, N=1$ string vacua with emphasis on the different connections due to T-dualities and S-dualities. The topics discussed include: Anomaly cancellation; K3 and orbifold $D=6, N=1$ heterotic compactifications; T-dualities between $E_8\times E_8$ and $Spin(32)/Z_2$ heterotic vacua; non-perturbative heterotic vacua and small instantons; N=2 Type-II/Heterotic duality in D=4 ; F-theory/heterotic duality in D=6; and heterotic/heterotic duality in six and four dimensions.Comment: 52 pages, plain Latex. To appear in the proceedings of the APCTP Winter School on Duality, Mt. Sorak (Korea), February 199

Freudenthal Dual Lagrangians

The global U-dualities of extended supergravity have played a central role in differentiating the distinct classes of extremal black hole solutions. When the U-duality group satisfies certain algebraic conditions, as is the case for a broad class of supergravities, the extremal black holes enjoy a further symmetry known as Freudenthal duality (F-duality), which although distinct from U-duality preserves the Bekenstein-Hawking entropy. Here it is shown that, by adopting the doubled Lagrangian formalism, F-duality, defined on the doubled field strengths, is not only a symmetry of the black hole solutions, but also of the equations of motion themselves. A further role for F-duality is introduced in the context of world-sheet actions. The Nambu-Goto world-sheet action in any (t, s) signature spacetime can be written in terms of the F-dual. The corresponding field equations and Bianchi identities are then related by F-duality allowing for an F-dual formulation of Gaillard-Zumino duality on the world-sheet. An equivalent polynomial "Polyakov- type" action is introduced using the so-called black hole potential. Such a construction allows for actions invariant under all groups of type E7, including E7 itself, although in this case the stringy interpretation is less clear.Comment: 1+16 pages, 1 Table, updated to match published versio

A Comment on String Solitons

We derive an exact string-like soliton solution of D=10 heterotic string theory. The solution possesses $SU(2)\times SU(2)$ instanton structure in the eight-dimensional space transverse to the worldsheet of the soliton.Comment: 4 page

Real Special Geometry

We give a coordinate-free description of real manifolds occurring in certain four dimensional supergravity theories with antisymmetric tensor fields. The relevance of the linear multiplets in the compactification of string and five-brane theories is also discussed.Comment: 10 pgs (TeX with Harvmac), CERN-TH.7211/94, UCLA/94/TEP/14, POLFIS-TH.01/9

On the Dirac-Born-Infeld Action for D-branes

In this note, we consider the reformulation of the Dirac-Born-Infeld action for a Dirichlet p-brane in Brink-Di Vecchia-Howe-Tucker form, i.e., including an independent non-propagating world-volume metric. When p>2, the action becomes non-polynomial. A closed expression is derived for p=3. For selfdual field-strengths, the DBI action is reproduced by an action with a simple F^2 term. We speculate on supersymmetrization of the D_3-brane action. We also give the governing equations for arbitrary p, and derive an implicit expression for the D_4-brane lagrangian.Comment: Plain TeX, 7 pages, TeX file and one postscript figure in compressed tar archiv

Vacuum interpolation in supergravity via super p-branes

We show that many of the recently proposed supersymmetric p-brane solutions of d=10 and d=11 supergravity have the property that they interpolate between Minkowski spacetime and a compactified spacetime, both being supersymmetric supergravity vacua. Our results imply that the effective worldvolume action for small fluctuations of the super p-brane is a supersingleton field theory for $(adS)_{p+2}$, as has been often conjectured in the past.Comment: 8p