202 research outputs found
Some comments on Anti-de Sitter D-branes
We present some preliminary investigations about the AdS2*S2 D3-branes in
AdS3*S3. We analyse the quadratic fluctuations of Dirac-Born-Infeld action
around a given semi-classical D-brane configuration and compare them with
results obtained by using conformal field theory techniques. We finally study
classical motions of open strings attached to those D-branes and analyse the
role of the spectral flow in this context.Comment: 12 pages, no figure
H(3)+ correlators from Liouville theory
We prove that arbitrary correlation functions of the H(3)+ model on a sphere
have a simple expression in terms of Liouville theory correlation functions.
This is based on the correspondence between the KZ and BPZ equations, and on
relations between the structure constants of Liouville theory and the H(3)+
model. In the critical level limit, these results imply a direct link between
eigenvectors of the Gaudin Hamiltonians and the problem of uniformization of
Riemann surfaces. We also present an expression for correlation functions of
the SL(2)/U(1) coset model in terms of correlation functions in Liouville
theory.Comment: 24 pages, v3: minor changes, references adde
On AGT description of N=2 SCFT with N_f=4
We consider Alday-Gaiotto-Tachikawa (AGT) realization of the Nekrasov
partition function of N=2 SCFT. We focus our attention on the SU(2) theory with
N_f=4 flavor symmetry, whose partition function, according to AGT, is given by
the Liouville four-point function on the sphere. The gauge theory with N_f=4 is
known to exhibit SO(8) symmetry. We explain how the Weyl symmetry
transformations of SO(8) flavor symmetry are realized in the Liouville theory
picture. This is associated to functional properties of the Liouville
four-point function that are a priori unexpected. In turn, this can be thought
of as a non-trivial consistency check of AGT conjecture. We also make some
comments on elementary surface operators and WZW theory.Comment: 18 pages. v2, a misinterpretation in the gauge theory side has been
corrected; title and introduction were changed accordingl
Quantum Hall effect anomaly and collective modes in the magnetic-field-induced spin-density-wave phases of quasi-one-dimensional conductors
We study the collective modes in the magnetic-field-induced spin-density-wave
(FISDW) phases experimentally observed in organic conductors of the Bechgaard
salts family. In phases that exhibit a sign reversal of the quantum Hall effect
(Ribault anomaly), the coexistence of two spin-density waves gives rise to
additional collective modes besides the Goldstone modes due to spontaneous
translation and rotation symmetry breaking. These modes strongly affect the
charge and spin response functions. We discuss some experimental consequences
for the Bechgaard salts.Comment: Final version (LaTex, 8 pages, no figure), to be published in
Europhys. Let
Quantum Hall Transitions in (TMTSF)PF
We have studied the temperature dependence of the integer quantum Hall
transitions in the molecular crystal (TMTSF)PF. We find that the
transition width between the quantum Hall plateaus does not exhibit the
universal power-law scaling behavior of the integer quantum Hall effect
observed in semiconducting devices. Instead, the slope of the
risers, , and the (inverse) width of the peaks,
, show a BCS-like energy gap temperature dependence. We
discuss these results in terms of the field-induced spin-density wave gap and
order parameter of the system.Comment: 10 pages, RevTeX, 4 PostScript figure
Notes On The S-Matrix Of Bosonic And Topological Non-Critical Strings
We show that the equivalence between the c=1 non-critical bosonic string and
the N=2 topologically twisted coset SL(2)/U(1) at level one can be checked very
naturally on the level of tree-level scattering amplitudes with the use of the
Stoyanovsky-Ribault-Teschner map, which recasts correlation functions
in terms of Liouville field theory amplitudes. This observation can be applied
equally well to the topologically twisted SL(2)/U(1) coset at level n>1, which
has been argued recently to be equivalent with a c<1 non-critical bosonic
string whose matter part is defined by a time-like linear dilaton CFT.Comment: harvmac, 22 pages; v2 typos corrected, version appearing in JHE
Affine sl(N) conformal blocks from N=2 SU(N) gauge theories
Recently Alday and Tachikawa proposed a relation between conformal blocks in
a two-dimensional theory with affine sl(2) symmetry and instanton partition
functions in four-dimensional conformal N=2 SU(2) quiver gauge theories in the
presence of a certain surface operator. In this paper we extend this proposal
to a relation between conformal blocks in theories with affine sl(N) symmetry
and instanton partition functions in conformal N=2 SU(N) quiver gauge theories
in the presence of a surface operator. We also discuss the extension to
non-conformal N=2 SU(N) theories.Comment: 40 pages. v2: minor changes and clarification
The abelian cosets of the Heisenberg group
In this paper we study the abelian cosets of the H(4) WZW model. They
coincide or are related to several interesting three-dimensional backgrounds
such as the Melvin model, the conical point-particle space-times and the null
orbifold. We perform a detailed CFT analysis of all the models and compute the
coset characters as well as some typical three-point couplings of coset
primaries.Comment: 26 pages; v2: minor typos corrected, also added section 3.3 and 4.3
with a few comments on a third class of geometries that have not been
discussed in v
Generalized susceptibility of quasi-one dimensional system with periodic potential: model for the organic superconductor (TMTSF)ClO
The nesting vector and the magnetic susceptibility of the
quasi-one-dimensional system having imperfectly nested Fermi surface are
studied analytically and numerically. The magnetic susceptibility has the
plateau-like maximum in ``\textit{sweptback}'' region in the momentum space,
which is surrounded by ( is the
Fermi wave number, , and , and
are given in this paper). The best nesting vector, at which
the susceptibility has the absolute maximum at T=0, is
obtained near but not at the inflection point, . The effect of the periodic potential on the
susceptibility is studied, which is important for the successive transitions of
the field-induced spin density wave in (TMTSF)ClO. We obtain that the
sweptback region (surrounded by , and
when ) becomes small as increases and it shrinks to
for , where gives the degree of imperfect
nesting of the Fermi surface, i.e. the second harmonics of the warping in the
Fermi surface. The occurrence of the sign reversal of the Hall coefficient in
the field-induced spin density wave states is discussed to be possible only
when , where is the amplitude of the fourth harmonics of
the warping in the Fermi surface. This gives the novel limitation for the
magnitude of
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