String Theory and Quark Confinement

This article is based on a talk given at the ``Strings'97'' conference. It discusses the search for the universality class of confining strings. The key ingredients include the loop equations, the zigzag symmetry, the non-linear renormalization group. Some new tests for the equivalence between gauge fields and strings are proposed.Comment: 13 pages, latex; talk at STRINGS'9

Hard exclusive production of two pions: Dipion mass distributions in gamma* N -->pi pi N and gamma* gamma --> pi pi

The leading twist parametrization of dipion mass distribution in hard exclusive reactions is proposed. Its parameters are related to quark distributions (usual and skewed) in the pion and to distributions amplitudes of mesons ($\pi$, $\rho$, etc.). We show that measurements of the shape of dipion mass distribution in hard exclusie reactions can give important information about partonic structure of the pion. The expression for the amplitude of the reaction $\gamma^*\gamma\to \pi\pi$ near the threshold in terms of singlet quark distribution in the pion is presented.Comment: Talk given at 7th International Workshop on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen, Germany, 19-23 Apr 1999. Minor typos are correcte

Various Properties of Compact QED and Confining Strings

The effects bringing about by the finiteness of the photon mass due to the Debye screening in the monopole gas in three-dimensional compact QED are studied. In this respect, a representation of the partition function of this theory as an integral over monopole densities is derived. Dual formulation of the Wilson loop yields a new theory of confining strings, which in the low-energy limit almost coincides with the one corresponding to the case when the photon is considered to be massless, whereas in the high-energy limit these two theories are quite different from each other. The confining string mass operator in the low-energy limit is also found, and its dependence on the volume of observation is studied.Comment: 7 pages, LaTeX, no figures, 1 reference is added, final version to appear in Phys. Lett.

Ghost Cohomologies and Hidden Space-Time Symmetries

We observe and study new non-linear global space-time symmetries of the full ghost+matter action of RNS superstring theory. We show that these surprising new symmetries are generated by the special worldsheet currents (vertex operators) of RNS superstring theory, violating the equivalence of superconformal ghost pictures. We review the questions of BRST invariance and non-triviality of picture-dependent vertex operators and show their relation to hidden space-time symmetries and hidden space-time dimensions. In particular, we relate the space-time transformations, induced by the picture-dependent currents, to the symmetries observed in the 2T physics approach.Comment: 21 page

New Superstring Isometries and Hidden Dimensions

We explore the hierarchy of hidden space-time symmetries of noncritical strings in RNS formalism, realized nonlinearly. Under these symmetry transformations the variation of the matter part of the RNS action is cancelled by that of the ghost part. These symmetries, referred to as the $\alpha$-symmetries, are induced by special space-time generators, violating the equivalence of ghost pictures. We classify the $\alpha$-symmetry generators in terms of superconformal ghost cohomologies $H_{n}\sim{H_{-n-2}}(n\geq{0})$ and associate these generators with a chain of hidden space-time dimensions, with each ghost cohomology $H_{n}\sim{H_{-n-2}}$ ``contributing'' an extra dimension. Namely, we show that each ghost cohomology $H_{n}\sim{H_{-n-2}}$ of non-critical superstring theory in $d$-dimensions contains $d+n+1$ $\alpha$-symmetry generators and the generators from $H_{k}\sim{H_{-k-2}},1\leq{k}\leq{n}$, combined together, extend the space-time isometry group from the naive $SO(d,2)$ to $SO(d+n,2)$. In the simplest case of $n=1$ the $\alpha$-generators are identified with the extra symmetries of the $2T$-physics formalism, also known to originate from a hidden space-time dimension.Comment: 26 pages typos correcte