Non-Abelian Structures in BSFT and RR couplings

In this talk we show that the tachyon annihilation combined with an approximation, in which string theory non-commutativity structure is captured by the algebra of differential operators on space-time, gives a unified point of view on: non-Abelian structures on $D$-branes; all lowest energy excitations on $D$-branes; all RR couplings in type II string theory.Comment: Latex, 13pp., Minor correction (references added); This is the extended version of the talk presented at 10th Tohwa International Symposium on String theory which was held in Fukuoka, July 200

Non-commutative Gross-Neveu model at large N

The non-commutative O(N) Gross-Neveu model is solved in the large N limit in two and three space-time dimensions. The commutative version of the two dimensional model is a renormalizable quantum field theory, both in a coupling constant expansion and an expansion in 1/N. The non-commutative version has a renormalizable coupling constant expansion where ultraviolet divergences can be removed by adjusting counterterms to each order. On the other hand, in a previous work, we showed that the non-commutative theory is not renormalizable in the large N expansion. This is argued to be due to a combined effect of asymptotic freedom and the ultraviolet/infrared mixing that occurs in a non-commutative field theory. In the present paper we will elaborate on this result and extend it to study the large N limit of the three dimensional Gross-Neveu model. We shall see that the large N limit of the three dimensional theory is also trivial when the ultraviolet cutoff is removed.Comment: 23 page

Subtleties in the quasi-classical calculation of Hawking radiation

he quasi-classical method of deriving Hawking radiation is investigated. In order to recover the original Hawking temperature one must take into account a previously ignored contribution coming from the temporal part of the action. This contribution plus a contribution coming from the spatial part of the action gives the correct temperature.Comment: 6 pages revtex. Honorable Mention in 2008 GRF essay contest, typos fixed, sign errors corrected. To be published in Special Issue of IJMP

On Unification of RR Couplings

We consider the couplings of RR fields with open string sector for $Dp$-${\overline{Dp}}$ backgrounds of various $p$. Proposed approach, based on the approximation of the open string algebra by the algebra of differential operators, provides the unified description of these couplings and their interrelations.Comment: References added, Latex, 18 page