Gauge Symmetries and Amplitudes in N=2 Strings

Picture changed operators are discussed in $N=2$ strings with space-time signature $(2,2)$. A gauge symmetry algebra is derived in a background of torus space-time $T^{2,2}$ and its simple representation on the picture changed operators is given. Simple Ward identities associated with the gauge algebra and their consequences for three and four point amplitudes of arbitrary loops are also discussed.Comment: 16 page

Quantum version of the N=8 superconformal algebra

The quantized form of the soft N=8 superconformal algebra is investigated. Its operator product expansions are shown to exhibit a one-parameter-class of (soft) anomalies, which may be arbitrarily shifted by certain suitable quantum corrections of the generators. In particular, the BRST operator can be constructed and made nilpotent in the quantum version of all known realizations of the algebra. This generalizes the results of Cederwall and Preitschopf, who studied the $\widehat{S^7}$-algebra, that is contained as a soft Kac-Moody part in the superconformal algebra. A Fock-space representation is given, that has to be somewhat unusual in certain modes.Comment: 19 pages, LATE

Unravelling the On-shell Constraints of Self-dual Supergravity Theories

We review a construction, using the harmonic space method, of solutions to the superfield equations of motion for N-extended self-dual supergravity theories. A superspace gauge condition suitable for the performance of a component analysis is discussed.Comment: 5 pages, latex using espcrc2.sty, talk at the 29th International Ahreshoop Symposium, Buckow, August 199

Toward the Universal Theory of Strings

We show that the $N=2$ superstrings may be viewed as a special class of the $N=4$ superstrings and demonstrate their equivalence. This allows us to realize all known string theories based on linear algebras and with $N<4$ supersymmetries as special choices of the vacua in the $N=4$ superstring.Comment: Latex file, 8 pages, NBI-HET-94-08. The preprint number is changed and one reference is adde

Comments on N=4 Superconformal Algebras

We present a new and asymmetric N=4 superconformal algebra for arbitrary central charge, thus completing our recent work on its classical analogue with vanishing central charge. Besides the Virasoro generator and 4 supercurrents, the algebra consists of an internal SL(2) \otimes U(1) Kac-Moody algebra in addition to two spin 1/2 fermions and a bosonic scalar. The algebra is shown to be invariant under a linear twist of the generators, except for a unique value of the continuous twist parameter. At this value, the invariance is broken and the algebra collapses to the small N=4 superconformal algebra. In the context of string theory, the asymmetric N=4 superconformal algebra is provided with an explicit construction on the boundary of AdS_3, and is induced by an affine SL(2|2) current superalgebra residing on the world sheet. Substituting the world sheet SL(2|2) by the coset SL(2|2)/U(1) results in the small N=4 superconformal algebra on the boundary of AdS_3.Comment: 18 pages, LaTe

Worldsheets with Extended Supersymmetry

We determine the equations which govern the gauge symmetries of worldsheets with local supersymmetry of arbitrary rank $(N,N')$, and their possible anomalies. Both classical and ghost conformally invariant multiplets of the left or right sector are assembled into the components of a single $O(N)$-superfield. The component with ghost number zero of this superfield is the $N$-supersymmetric generalization of the Beltrami differential. In a Lagrangian approach, and after gauge-fixing, it becomes the super-moduli of Riemann surfaces coupled to local supersymmetry of rank $N$. It is also the source of all linear superconformal currents derived from ordinary operator product techniques. The interconnection between BRST invariant actions with different values of $N\geq 3$, and their possible link to topological 2D-gravity coupled to topological sigma models, are shown by straightforward algebraic considerations.Comment: 15 pages, Latex. A section on the connection to topological action is adde

A Comment on the Holographic Renormalization Group and the Soft Dilaton Theorem

The equivalence between the holographic renormalization group and the soft dilaton theorem is shown for a class of wrapped metrics solutions of the string beta function equations for the bosonic string.Comment: LaTeX,7 pages. Typos corrected. Minor change

The Even and the Odd Spectral Flows on the N=2 Superconformal Algebras

There are two different spectral flows on the N=2 superconformal algebras (four in the case of the Topological algebra). The usual spectral flow, first considered by Schwimmer and Seiberg, is an even transformation, whereas the spectral flow previously considered by the author and Rosado is an odd transformation. We show that the even spectral flow is generated by the odd spectral flow, and therefore only the latter is fundamental. We also analyze thoroughly the four ``topological'' spectral flows, writing two of them here for the first time. Whereas the even and the odd spectral flows have quasi-mirrored properties acting on the Antiperiodic or the Periodic algebras, the topological even and odd spectral flows have drastically different properties acting on the Topological algebra. The other two topological spectral flows have mixed even and odd properties. We show that the even and the even-odd topological spectral flows are generated by the odd and the odd-even topological spectral flows, and therefore only the latter are fundamental.Comment: 15 pages, Latex. Minor improvements in the last paragraph of the conclusions. Numbering of references has change

SYM, Chern-Simons, Wess-Zumino Couplings and their higher derivative corrections in IIA Superstring theory

We find the entire form of the amplitude of two fermion strings (with different chirality), a massless scalar field and one closed string Ramond-Ramond (RR) in IIA superstring theory which is different from its IIB one. We make use of a very particular gauge fixing and explore several new couplings in IIA. All infinite $u$- channel scalar poles and $t,s$- channel fermion poles are also constructed. We find new form of higher derivative corrections to two fermion two scalar couplings and show that the first simple $(s+t+u)-$ channel scalar pole for $p+2=n$ case can be obtained by having new higher derivative corrections to SYM couplings at third order of $\alpha'$. We find that the general structure and the coefficients of higher derivative corrections to two fermion two scalar couplings are completely different from the derived $\alpha'$ higher derivative corrections of type IIB.Comment: 29 pages, no figure,Latex file,published version in EPJ