653 research outputs found
On the perturbative corrections around D-string instantons
We study -threshold corrections in an eight dimensional S-dual
pair of string theories, as a prototype of dual string vacua with sixteen
supercharges. We show that the orbifold CFT description of D-string instantons
gives rise to a perturbative expansion similar to the one appearing on the
fundamental string side. By an explicit calculation, using the Nambu-Goto
action in the static gauge, we show that the first subleading term agrees
precisely on the two sides. We then give a general argument to show that the
agreement extends to all orders.Comment: 12 page
AdS/CFT correspondence and D1/D5 systems in theories with 16 supercharges
We discuss spectra of supergravities, arising in the near horizon
geometry of D1/D5 systems in orbifolds/orientifolds of type IIB theory with 16
supercharges. These include models studied in a recent paper (hep-th/0012118),
where the group action involves also a shift along a transversal circle, as
well as IIB/, which is dual to IIB on . After appropriate
assignements of the orbifold group eigenvalues and degrees to the supergravity
single particle spectrum, we compute the supergravity elliptic genus and find
agreement, in the expected regime of validity, with the elliptic genus obtained
using U-duality map from (4,4) CFTs of U-dual backgrounds. Since this U-duality
involves the exchange of KK momentum and D1 charge , it allows us to
test the (4,4) CFTs in the and regimes by two different
supergravity duals.Comment: 28 pages, no figure
Structure constants of planar N =4 Yang Mills at one loop
We study structure constants of gauge invariant operators in planar N=4
Yang-Mills at one loop with the motivation of determining features of the
string dual of weak coupling Yang-Mills. We derive a simple renormalization
group invariant formula characterizing the corrections to structure constants
of any primary operator in the planar limit. Applying this to the scalar SO(6)
sector we find that the one loop corrections to structure constants of gauge
invariant operators is determined by the one loop anomalous dimension
Hamiltonian in this sector. We then evaluate the one loop corrections to
structure constants for scalars with arbitrary number of derivatives in a given
holomorphic direction. We find that the corrections can be characterized by
suitable derivatives on the four point tree function of a massless scalar with
quartic coupling. We show that individual diagrams violating conformal
invariance can be combined together to restore it using a linear inhomogeneous
partial differential equation satisfied by this function.Comment: 52 pages, 12 figures, Typos fixed, reference adde
Towards a string bit formulation of N=4 super Yang-Mills
We show that planar cal N=4 Yang-Mills theory at zero 't Hooft coupling can
be efficiently described in terms of 8 bosonic and 8 fermionic oscillators. We
show that these oscillators can serve as world-sheet variables, the string
bits, of a discretized string. There is a one to one correspondence between the
on shell gauge invariant words of the free Y-M theory and the states in the
oscillators' Hilbert space, obeying a local gauge and cyclicity constraints.
The planar two-point functions and the three-point functions of all gauge
invariant words are obtained by the simple delta-function overlap of the
corresponding discrete string world sheet. At first order in the 't Hooft
coupling, i.e. at one-loop in the Y-M theory, the logarithmic corrections of
the planar two-point and the three-point functions can be incorporated by
nearest neighbour interactions among the discretized string bits. In the SU(2)
sub-sector we show that the one-loop corrections to the structure constants can
be uniquely determined by the symmetries of the bit picture. For the SU(2)
sub-sector we construct a gauged, linear, discrete world-sheet model for the
oscillators, with only nearest neighbour couplings, which reproduces the
anomalous dimension Hamiltonian up to two loops. This model also obeys BMN
scaling to all loops.Comment: 64 pages, 6 figures, typos fixed, references adde
Fivebrane instantons and higher derivative couplings in type I theory
We express the infinite sum of D-fivebrane instanton corrections to couplings in type I string vacua, in terms of an elliptic
index counting 1/2-BPS excitations in the effective brane theory. We
compute the index explicitly in the infrared, where the effective theory is
argued to flow to an orbifold CFT. The form of the instanton sum agrees
completely with the predicted formula from a dual one-loop computation in type
IIA theory on . The proposed CFT provides a proper description of
the whole spectrum of masses, charges and multiplicities for 1/2- and 1/4- BPS
states, associated to bound states of D5-branes and KK momenta. These results
are applied to show how fivebrane instanton sums, entering higher derivative
couplings which are sensitive to 1/4-BPS contributions, also match the
perturbative results in the dual type IIA theory.Comment: 14 pages, corrected some typos. Version to appear in Nucl. Phys.
Heavy Quark Interactions in Finite Temperature QCD
We study the free energy of a heavy quark-antiquark pair in a thermal medium.
We constuct a simple ansatz for the free energy for two quark flavors motivated
by the Debye-H\"uckel theory of screening.Comment: 4 pages, 4 figures, contribution to the proceedings of the
International Conference on Hard and Electromagnetic Probes of High Energy
Nuclear Collisions, Ericeira, Portugal, Nov. 4-10, 200
- …