The N=4 string is the same as the N=2 string

We redo the quantization of the N=4 string, taking into account the reducibility of the constraints. The result is equivalent to the N=2 string, with critical dimension D=4 and signature (++--). The N=4 formulation has several advantages: the sigma-model field equations are implied classically, rather than by quantum/beta-function calculations; self-duality/chirality is one of the super-Virasoro constraints; SO(2,2) covariance is manifest. This reveals that the theory includes fermions, and is apparently spacetime supersymmetric.Comment: 7 pg (uuencoded dvi file; otherwise same as original

Green-Schwarz Formulation of Self-Dual Superstring

The self-dual superstring has been described previously in a Neveu-Schwarz-Ramond formulation with local N=2 or 4 world-sheet supersymmetry. We present a Green-Schwarz-type formulation, with manifest spacetime supersymmetry.Comment: 11 pg., (uuencoded dvi file) ITP-SB-92-5

The N=2(4) string is self-dual N=4 Yang-Mills

N=2 string amplitudes, when required to have the Lorentz covariance of the equivalent N=4 string, describe a self-dual form of N=4 super Yang-Mills in 2+2 dimensions. Spin-independent couplings and the ghost nature of SO(2,2) spacetime make it a topological-like theory with vanishing loop corrections.Comment: 7 pg., ITP-SB-92-24 (uuencoded dvi file; otherwise same as original

The BRST Operator for the Large N=4N=4 Superconformal Algebra

We review the detailed structure of the large $N=4$ superconformal algebra, and construct its BRST operator which constitutes the main object for analyzing $N=4$ strings. We then derive the general condition for the nilpotency of the BRST operator and show that there exists a line of critical $N=4$ string theories.Comment: Latex file, 16 pages, NBI-HE-94-1

A Hierarchy of Superstrings

We construct a hierarchy of supersymmetric string theories by showing that the general N-extended superstrings may be viewed as a special class of the (N+1)-extended superstrings. As a side result, we find a twisted (N+2) superconformal algebra realized in the N-extended string.Comment: 9 pages, LaTex, NBI-HE-94-2

Self-Dual N=8 Supergravity as Closed N=2(4) Strings

As open N=2 or 4 strings describe self-dual N=4 super Yang-Mills in 2+2 dimensions, the corresponding closed (heterotic) strings describe self-dual ungauged (gauged) N=8 supergravity. These theories are conveniently formulated in a chiral superspace with general supercoordinate and local OSp(8|2) gauge invariances. The super-light-cone and covariant-component actions are analyzed. Because only half the Lorentz group is gauged, the gravity field equation is just the vanishing of the torsion.Comment: 17 pg., (uuencoded dvi file; revision: forgot 1 stupid term in the last equation) ITP-SB-92-3

Families of N=2 Strings

In a given 4d spacetime bakcground, one can often construct not one but a family of distinct N=2 string theories. This is due to the multiple ways N=2 superconformal algebra can be embedded in a given worldsheet theory. We formulate the principle of obtaining different physical theories by gauging different embeddings of the same symmetry algebra in the same ``pre-theory.'' We then apply it to N=2 strings and formulate the recipe for finding the associated parameter spaces of gauging. Flat and curved target spaces of both (4,0) and (2,2) signatures are considered. We broadly divide the gauging choices into two classes, denoted by alpha and beta, and show them to be related by T-duality. The distinction between them is formulated topologically and hinges on some unique properties of 4d manifolds. We determine what their parameter spaces of gauging are under certain simplicity ansatz for generic flat spaces (R^4 and its toroidal compactifications) as well as some curved spaces. We briefly discuss the spectra of D-branes for both alpha and beta families.Comment: 66+1 pages, 2 tables, latex 2e, hyperref. ver2: typos corrected, reference adde

Higher Order 1/m1/m Corrections at Zero Recoil

The general structure of the $1/m$ corrections at zero recoil is studied. The relevant matrix elements are forward matrix elements of local higher dimensional operators and their time ordered products with higher order terms from the Lagrangian. These matrix elements may be classified in a simple way and the analysis at the non recoil point for the form factor of heavy quark currents simplifies drastically. The second order recoil corrections to the form factor $h_{A1}$ of the axial vector current, relevant for the $|V_{cb}|$ determination from $B \to D^*$ decays, are estimated to be $-5\% < h_{A1} - 1 < 0$.Comment: LaTeX, 25 pages, one figure, appended after \end{document} as uu-encoded and compressed eps file, uses epsf, CERN-TH.7162/9

D-branes in N=2 Strings

We study various aspects of D-branes in the two families of closed N=2 strings denoted by \alpha and \beta in hep-th/0211147. We consider two types of N=2 boundary conditions, A-type and B-type. We analyse the D-branes geometry. We compute open and closed string scattering amplitudes in the presence of the D-branes and discuss the results. We find that, except the space filling D-branes, the B-type D-branes decouple from the bulk. The A-type D-branes exhibit inconsistency. We construct the D-branes effective worldvolume theories. They are given by a dimensional reduction of self-dual Yang-Mills theory in four dimensions. We construct the D-branes gravity backgrounds. Finally, we discuss possible N=2 open/closed string dualities.Comment: 25 pages, Latex2

On (non-Hermitian) Lagrangeans in (particle) physics and their dynamical generation

On the basis of a new method to derive the effective action the nonperturbative concept of "dynamical generation" is explained. A non-trivial, non-Hermitian and PT-symmetric solution for Wightman's scalar field theory in four dimensions is dynamically generated, rehabilitating Symanzik's precarious phi**4-theory with a negative quartic coupling constant as a candidate for an asymptotically free theory of strong interactions. Finally it is shown making use of dynamically generation that a Symanzik-like field theory with scalar confinement for the theory of strong interactions can be even suggested by experiment.Comment: 12 pages, no figures, accepted for publication in Czech.J.Phys., revised with respect to obvious typo