2,284 research outputs found
On the energy-shell contributions of the three-particle~-~ three-hole excitations
The response functions for the extended second and third random phase
approximation are compared. A second order perturbation calculation shows that
the first-order amplitude for the direct excitation from the ground
state cancels with those that are engendered by the - coupling. As
a consequence nonvanishing effects to the response involve off
energy shell renormalization only. On shell processes are absent.Comment: 12 pages text (LaTex) and 1 figure included, to be published in Phys.
Rev.
Momentum Distribution in Nuclear matter within a Perturbation Approximation
It is shown that the norm corrections, introduced to avoid the violation of
the constraints on the depletion of the hole states in the standard
perturbative 2p2h approach, leads in nuclear matter to a dependence of the
momentum distribution with the total nucleon number. This unphysical behavior,
which in turn makes the depletion to be non-extensive, arises from
contributions of disconnected diagrams contained in the norm. It is found that
the extensivity is again recovered when the 4p4h excitations in the ground
state are included, and a reasonable value for the total number of nucleons
promoted above the Fermi level is obtained.Comment: 11 pages, LaTeX, 5 figures, figures 1 to 3 included in the latex
file, postscript files of figures 4 and 5 available from the Authors.
Accepted for publication in Phys. Rev.
Topological Insulators and Superconductors from String Theory
Topological insulators and superconductors in different spatial dimensions
and with different discrete symmetries have been fully classified recently,
revealing a periodic structure for the pattern of possible types of topological
insulators and supercondutors, both in terms of spatial dimensions and in terms
of symmetry classes. It was proposed that K-theory is behind the periodicity.
On the other hand, D-branes, a solitonic object in string theory, are also
known to be classified by K-theory. In this paper, by inspecting low-energy
effective field theories realized by two parallel D-branes, we establish a
one-to-one correspondence between the K-theory classification of topological
insulators/superconductors and D-brane charges. In addition, the string theory
realization of topological insulators and superconductors comes naturally with
gauge interactions, and the Wess-Zumino term of the D-branes gives rise to a
gauge field theory of topological nature, such as ones with the Chern-Simons
term or the -term in various dimensions. This sheds light on
topological insulators and superconductors beyond non-interacting systems, and
the underlying topological field theory description thereof. In particular, our
string theory realization includes the honeycomb lattice Kitaev model in two
spatial dimensions, and its higher-dimensional extensions. Increasing the
number of D-branes naturally leads to a realization of topological insulators
and superconductors in terms of holography (AdS/CFT).Comment: 13 pages, 3 figures;references update
Topological String on OSP(1|2)/U(1)
We propose an equivalence between topological string on OSP(1|2)/U(1) and
\hat{c} \leq 1 superstring with N=1 world-sheet supersymmetry. We examine this
by employing a free field representation of OSP(1|2) WZNW model and find an
agreement on the spectrum. We also analyze this proposal at the level of
scattering amplitudes by applying a map between correlation functions of
OSP(1|2) WZNW model and those of N=1 Liouville theory.Comment: 25 pages, refereces adde
Notes on S-Matrix of Non-critical N=2 String
In this paper we discuss the scattering S-matrix of non-critical N=2 string
at tree level. First we consider the \hat{c}<1 string defined by combining the
N=2 time-like linear dilaton SCFT with the N=2 Liouville theory. We compute
three particle scattering amplitudes explicitly and find that they are actually
vanishing. We also find an evidence that this is true for higher amplitudes.
Next we analyze another \hat{c}<1 string obtained from the N=2 time-like
Liouville theory, which is closely related to the N=2 minimal string. In this
case, we find a non-trivial expression for the three point functions. When we
consider only chiral primaries, the amplitudes are very similar to those in the
(1,n) non-critical bosonic string.Comment: 27 pages, harvmac, section 5 modified: a relation to (1,n)
non-critical bosonic string adde
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
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