The Loop Group of E8 and Targets for Spacetime

The dimensional reduction of the E8 gauge theory in eleven dimensions leads to a loop bundle in ten dimensional type IA string theory. We show that the restriction to the Neveu-Schwarz sector leads naturally to a sigma model with target space E8 with the ten-dimensional spacetime as the source. The corresponding bundle has a structure group the group of based loops, whose classifying space we study. We explore some consequences of this proposal such as possible Lagrangians and existence of flat connections.Comment: 17 pages, main section improved, change in title, reference and acknowledgement adde

Instanton operators in five-dimensional gauge theories

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are creditedN.L. is supported in part by STFC grant ST/J002798/1. C.P. is a Royal Society Research Fellow.N.L. is supported in part by STFC grant ST/J002798/1. C.P. is a Royal Society Research Fellow.N.L. is supported in part by STFC grant ST/J002798/1. OPen Aceess funded by SCOAP

Magnetic effects in a holographic Fermi-like liquid

We explore the magnetic properties of the Fermi-like liquid represented by the D3-D7' system. The system exhibits interesting magnetic properties such as ferromagnetism and an anomalous Hall effect, which are due to the Chern-Simons term in the effective gravitational action. We investigate the spectrum of quasi-normal modes in the presence of a magnetic field and show that the magnetic field mitigates the instability towards a striped phase. In addition, we find a critical magnetic field above which the zero sound mode becomes massive.Comment: 18 pages, 15 figure

Exactly stable non-BPS spinors in heterotic string theory on tori

Considering SO(32) heterotic string theory compactified on a torus of dimension 4 and less, stability of non-supersymmetric states is studied. A non-supersymmetric state with robust stability is constructed, and its exact stability is proven in a large region of moduli space against all the possible decay mechanisms allowed by charge conservation. Using various T-duality transform matrices, we translate various selection rules about conserved charges into simpler problems resembling partition and parity of integers. For heterotic string on T^4, we give a complete list of BPS atoms with elementary excitations, and we study BPS and non-BPS molecules with various binding energies. Using string-string duality, the results are interpreted in terms of Dirichlet-branes in type IIA string theory compactified on an orbifold limit of a K3 surface.Comment: 47 pages, 14 figures, LaTe

DDF Construction and D-Brane Boundary States in Pure Spinor Formalism

Open string boundary conditions for non-BPS D-branes in type II string theories discussed in hep-th/0505157 give rise to two sectors with integer (R sector) and half-integer (NS sector) modes for the combined fermionic matter and bosonic ghost variables in pure spinor formalism. Exploiting the manifest supersymmetry of the formalism we explicitly construct the DDF (Del Giudice, Di Vecchia, Fubini) states in both the sectors which are in one-to-one correspondence with the states in light-cone Green-Schwarz formalism. We also give a proof of validity of this construction. A similar construction in the closed string sector enables us to define a physical Hilbert space in pure spinor formalism which is used to project the covariant boundary states of both the BPS and non-BPS instantonic D-branes. These projected boundary states take exactly the same form as those found in light-cone Green-Schwarz formalism and are suitable for computing the cylinder diagram with manifest open-closed duality.Comment: 37 pages, typos corrected, some organisational changes mad

Moduli Space Dimensions of Multi-Pronged Strings

The numbers of bosonic and fermionic zero modes of multi-pronged strings are counted in ${\cal N}=4$ super-Yang-Mills theory and compared with those of the IIB string theory. We obtain a nice agreement for the fermionic zero modes, while our result for the bosonic zero modes differs from that obtained in the IIB string theory. The possible origin of the discrepancy is discussedComment: 15 pages, 2 figure

Lectures on Non-BPS Dirichlet branes

A comprehensive introduction to the boundary state approach to Dirichlet branes is given. Various examples of BPS and non-BPS Dirichlet branes are discussed. In particular, the non-BPS states in the duality of Type IIA on K3 and the heterotic string on T4 are analysed in detail.Comment: 46 pages, 5 figures, LaTeX; lectures given at the TMR network school on `Quantum aspects of gauge theories, supersymmetry and quantum gravity', Torino, 26 January - 2 February 2000, and at the `Spring workshop on Superstrings and related matters', Trieste, 27 March - 4 April 2000; references adde