Patching DFT, T-duality and Gerbes

We clarify the role of the dual coordinates as described from the perspectives of the Buscher T-duality rules and Double Field Theory. We show that the T-duality angular dual coordinates cannot be identified with Double Field Theory dual coordinates in any of the proposals that have been made in the literature for patching the doubled spaces. In particular, we show with explicit examples that the T-duality angular dual coordinates can have non-trivial transition functions over a spacetime and that their identification with the Double Field Theory dual coordinates is in conflict with proposals in which the latter remain inert under the patching of the B-field. We then demonstrate that the Double Field Theory coordinates can be identified with some C-space coordinates and that the T-dual spaces of a spacetime are subspaces of the gerbe in C-space. The construction provides a description of both the local $O(d,d)$ symmetry and the T-dual spaces of spacetime.Comment: minor changes, references adde

Null Strings in Kerr Spacetime

The null string's equations of motion and constraints in the Kerr spacetime are given. We assume a generic ansatz for the null strings in the Kerr spacetime and we present the resulting solutions in quadratures. Some specific string configurations, that follow from the generic one, are considered separately. In each case we also extract the corresponding solutions in the Schwarzschild spacetime.Comment: 11 pages, LaTex, no figures, final version to be published in Phys.Lett.B, references adde

Purchasing Power Parity among developing countries and their trade-partners. Evidence from selected CEECs and Implications for their membership of EU.

The purpose of the paper is twofold. Firstly, we test the validity of the PPP hypothesis for selected CEEC (Czech Republic; Hungary; Poland and Slovak Republic). Secondly, we attempt to define those countries’ trade linkages between Euro Area; US and the rest of the world. By applying both univariate unit root and a multivariate cointegration test, we find stronger evidence of PPP from the latter test. Moreover, any failure to accept PPP cannot be attributed to structural breaks, apart from one case (between Czech Republic and EU). In overall, there is evidence of strong-form PPP in 6 out of the 8 cases, while for the rest two, weak-form PPP is accepted. Thus, we confirm PPP as a long run equilibrium baseline for these exchange rates per EURO. Furthermore, the fact that PPP holds between these countries and Euro Area indicates absence of trade frictions and other barriers. The implied well-developed trade relations are consistent with those countries’ entry into EMU.PPP, Unit Root, Structural Breaks, Cointegration, Developing Countries