2,300 research outputs found
The Character of Pure Spinors
The character of holomorphic functions on the space of pure spinors in ten,
eleven and twelve dimensions is calculated. From this character formula, we
derive in a manifestly covariant way various central charges which appear in
the pure spinor formalism for the superstring. We also derive in a simple way
the zero momentum cohomology of the pure spinor BRST operator for the D=10 and
D=11 superparticle.Comment: 42 pages, 2 picture
On noncommutative Nahm transform
Motivated by the recently observed relation between the physics of -branes
in the background of -field and the noncommutative geometry we study the
analogue of Nahm transform for the instantons on the noncommutative torus.Comment: Latex, 22 p
Electronic Structure of New AFFeAs Prototype of Iron Arsenide Superconductors
This work is provoked by recent discovery of new class prototype systems
AFFeAs (A=Sr,Ca) of novel layered ironpnictide High-Tc superconductors
(Tc=36K). Here we report ab initio LDA results for electronic structure of the
AFFeAs systems. We provide detailed comparison between electronic properties of
both new systems and reference LaOFeAs (La111) compound. In the vicinity of the
Fermi level all three systems have essentially the same band dispersions.
However for iron fluoride systems F(2p) states were found to be separated in
energy from As(4p) ones in contrast to La111, where O(2p) states strongly
overlaps with As(4p). Thus it should be more plausible to include only Fe(3d)
and As(4p) orbitals into a realistic noninteracting model than for La111.
Moreover Sr substitution with smaller ionic radius Ca in AFFeAs materials leads
to a lattice contruction and stronger Fe(3d)-As(4p) hybridization resulting in
smaller value of the density of states at the Fermi level in the case of Ca
compound. So to some extend Ca system reminds RE111 with later Rare Earths.
However Fermi surface of new fluorides is found to be nearly perfect
two-dimensional. Also we do not expect strong dependence of superconducting
properties with respect to different types of A substitutes.Comment: 5 pages, 4 figure
Milne Universe, Tachyons, and Quantum Group
We analyze the spectrum of the bosonic and superstring on the orbifold of the
space-time by a boost, leading to the cosmological singularity. We show that
the modular invariance leads to the spectrum where the twisted sector tachyon,
together with all other twisted sector fields, present in the Euclidean version
of the orbifold, is absent. This makes impossible to resolve the singularity by
a marginal deformation of the worldsheet CFT. We also establish a relation
between the resolution of rotational orbifolds in Euclidean and Lorentzian
setups, and quantum groups. The analysis confirms the impossibility of
resolving the cosmological orbifold singularity.Comment: harvmac, 14p
Noncommutative Field Theory
We review the generalization of field theory to space-time with noncommuting
coordinates, starting with the basics and covering most of the active
directions of research. Such theories are now known to emerge from limits of M
theory and string theory, and to describe quantum Hall states. In the last few
years they have been studied intensively, and many qualitatively new phenomena
have been discovered, both on the classical and quantum level.
To appear in Reviews of Modern Physics.Comment: Revtex, 56 pp, 6 figures. Final versio
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