2-d Gravity as a Limit of the SL(2,R) Black Hole

The transformation of the $SL(2,R)/U(1)$ black hole under a boost of the subgroup U(1) is studied. It is found that the tachyon vertex operators of the black hole go into those of the $c=1$ conformal field theory coupled to gravity. The discrete states of the black hole also tend to the discrete states of the 2-d gravity theory. The fate of the extra discrete states of the black hole under boost are discussed.Comment: LaTeX file, 14 page

Vector-Chiral Equivalence in Null Gauged WZNW Theory

We consider the standard vector and chiral gauged WZNW models by their gauged maximal null subgroups and show that they can be mapped to each other by a special transformation. We give an explicit expression for the map in the case of the classical Lie groups $A_N$, $B_N$, $C_N$, $D_N$, and note its connection with the duality map for the Riemmanian globally symmetric spaces.Comment: 13 pages, LaTe

A Unified Scheme for Modular Invariant Partition Functions of WZW Models

We introuduce a unified method which can be applied to any WZW model at arbitrary level to search systematically for modular invariant physical partition functions. Our method is based essentially on modding out a known theory on group manifold $G$ by a discrete group $\Gamma$. We apply our method to $\widehat {su(n)}$ with $n=2,3,4,5,6$, and to $\widehat {g_2}$ models, and obtain all the known partition functions and some new ones, and give explicit expressions for all of them.Comment: 30 page ,SUTDP/11/93/72 Department of Physics, Sharif University of Technolog

Nilpotent Gauging of SL(2,R)WZNWWZNW models, and Liouville Field

We consider the gauging of $SL(2,R)$ WZNW model by its nilpotent subgroup E(1). The resulting space-time of the corresponding sigma model is seen to collapse to a one dimensional field theory of Liouville. Gauging the diagonal subgroup $E(1) \times U(1)$ of $SL(2,R) \times U(1)$ theory yields an extremal three dimensional black string. We show that these solutions are obtained from the two dimensional black hole of Witten and the three dimensional black string of Horne and Horowitz by boosting the gauge group.Comment: 17 pages, late

Noncommutative SO(n) and Sp(n) Gauge Theories

We study the generalization of noncommutative gauge theories to the case of orthogonal and symplectic groups. We find out that this is possible, since we are allowed to define orthogonal and symplectic subgroups of noncommutative unitary gauge transformations even though the gauge potentials and gauge transformations are not valued in the orthogonal and symplectic subalgebras of the Lie algebra of antihermitean matrices. Our construction relies on an antiautomorphism of the basic noncommutative algebra of functions which generalizes the charge conjugation operator of ordinary field theory. We show that the corresponding noncommutative picture from low energy string theory is obtained via orientifold projection in the presence of a non-trivial NSNS B-field.Comment: 17 pages; considerations about fermions added and some minor change

Short communication: Occurrence of Ophidonais serpentina in Potamon persicum from Jajrood River, Iran

Crustaceans are ecologically important, because of their effective role in food web and community structure of ecosystems. Taxonomic identity of fresh water crabs has been studied in Iran representing Potamidae family as dominant fluvial crabs. In 2001 Khatami recorded an unknown oligochaete in the mantle cavity of fresh water crab Potamon persicum. The present study further separated and identified an oligochaete from Potamon persicum in Jajrood River, east of Tehran, Iran. Two hundred and fifteen specimens of Potamon persicum were collected using a trap during four seasons from Jajrood River (51° 41´ to 51° 48´N and 35° 37´ to 35° 47´E) during March to August 2004. The specimens were taken to the research laboratory, dissected after biometry and the mantle and branchial cavities were examined for the existence of oligochaetes

Gauge Invariant Cutoff QED

A hidden generalized gauge symmetry of a cutoff QED is used to show the renormalizability of QED. In particular, it is shown that corresponding Ward identities are valid all along the renormalization group flow. The exact Renormalization Group flow equation corresponding to the effective action of a cutoff lambda phi^4 theory is also derived. Generalization to any gauge group is indicated.Comment: V1: 18 pages, 2 figures; V2: Discussions improved. Version accepted for publication in Physica Script

BRST Quantization of Noncommutative Gauge Theories

In this paper, the BRST symmetry transformation is presented for the noncommutative U(N) gauge theory. The nilpotency of the charge associated to this symmetry is then proved. As a consequence for the space-like non-commutativity parameter, the Hilbert space of physical states is determined by the cohomology space of the BRST operator as in the commutative case. Further, the unitarity of the S-matrix elements projected onto the subspace of physical states is deduced.Comment: 20 pages, LaTeX, no figures, one reference added, to appear in Phys. Rev.