273 research outputs found
Generalized QCD via the Bilocal Method
We use the bilocal method to derive the large solution of the most
general .Comment: 10 pag., NORDITA-94-35
The Master Field of QCD and the 'T Hooft Equation
We rewrite the action for in the light cone gauge only in terms of a
bilocal mesonic field. In this formalism the expansion can be done in a
straightforward way by a saddle point technique that determines the master
field to be identified with the vacuum expectation value of the bilocal field.
Finally we show that the equation of motion for the fluctuations around the
master field is identical with the 't Hooft meson equation.Comment: 7 pages, Latex, NORDITA-93-4
Partial N=2 --> N=1 Local Supersymmetry Breaking and Solvable Lie Algebras
Generic partial supersymmetry breaking of N=2 supergravity with zero vacuum
energy and with surviving unbroken arbitrary gauge groups is exhibited.
Specific examples are given.Comment: 5 pages, 1 LaTeX-style file, 1 TeX, 2 Postscript figures. Seminar
given at the Work-Shop on "Gauge Theories, Applied Supersymmetry and Quantum
Gravity", Imperial College, London, 5-10 July 199
Wrapped Magnetized Branes: Two Alternative Descriptions?
We discuss two inequivalent ways for describing magnetized D-branes wrapped N
times on a torus T^2. The first one is based on a non-abelian gauge bundle
U(N), while the second one is obtained by means of a Narain T-duality
transformation acting on a theory with non-magnetized branes. We construct in
both descriptions the boundary state and the open string vertices and show that
they give rise to different string amplitudes. In particular, the description
based on the gauge bundle has open string vertex operators with momentum
dependent Chan-Paton factors.Comment: 60 pages, LaTe
Spacetime Superalgebra in AdS_4 \times S^7 via Supermembrane Probe
The spacetime superalgebra via the supermembrane probe in the background of
AdS_4 \times S^7 is discussed to the lowest order in the spinor coordinate
\t. To obtain the correct spacetime superalgebras, all \t^2 order
corrections for supervielbein and super 3-form gauge potential have to be
included. The central extension of the superalgebra OSp(8|4) of the super
isometries for AdS_4 \times S^7 is found.Comment: 8 pages, Latex, minor corrections, final version to appear in Phys.
Rev.
The twisted open string partition function and Yukawa couplings
We use the operator formalism to derive the bosonic contribution to the
twisted open string partition function in toroidal compactifications. This
amplitude describes, for instance, the planar interaction between g+1
magnetized or intersecting D-branes. We write the result both in the closed and
in the open string channel in terms of Prym differentials on the appropriate
Riemann surface. Then we focus on the g=2 case for a 2-torus. By factorizing
the twisted partition function in the open string channel we obtain an explicit
expression for the 3-twist field correlator, which is the main ingredient in
the computation of Yukawa couplings in D-brane phenomenological models. This
provides an alternative method for computing these couplings that does not rely
on the stress-energy tensor technique.Comment: 32 pages, 5 figures, Latex; v2: typos correcte
Superparticle and superstring in AdS_3 x S^3 Ramond-Ramond background in light-cone gauge
We discuss superparticle and superstring dynamics in AdS_3 x S^3 supported by
R-R 3-form background using light-cone gauge approach. Starting with the
superalgebra psu(1,1|2) + psu(1,1|2) representing the basic symmetry of this
background we find the light-cone superparticle Hamiltonian. We determine the
harmonic decomposition of light-cone superfield describing fluctuations of type
IIB supergravity fields expanded near AdS_3 x S^3 background and compute the
corresponding Kaluza-Klein spectrum. We fix the fermionic and bosonic
light-cone gauges in the covariant Green-Schwarz AdS_3 x S^3 superstring action
and find the light-cone string Hamiltonian. We also obtain a realization of the
generators of psu(1,1|2) + psu(1,1|2) in terms of the superstring 2-d fields in
the light-cone gauge.Comment: 32 pages, late
New twist field couplings from the partition function for multiply wrapped D-branes
We consider toroidal compactifications of bosonic string theory with
particular regard to the phases (cocycles) necessary for a consistent
definition of the vertex operators, the boundary states and the T-duality
rules. We use these ingredients to compute the planar multi-loop partition
function describing the interaction among magnetized or intersecting D-branes,
also in presence of open string moduli. It turns out that unitarity in the open
string channel crucially depends on the presence of the cocycles. We then focus
on the 2-loop case and study the degeneration limit where this partition
function is directly related to the tree-level 3-point correlators between
twist fields. These correlators represent the main ingredient in the
computation of Yukawa couplings and other terms in the effective action for
D-brane phenomenological models. By factorizing the 2-loop partition function
we are able to compute the 3-point couplings for abelian twist fields on
generic non-factorized tori, thus generalizing previous expressions valid for
the 2-torus.Comment: 36 pages, 1 figure; v2: typos corrected, proof in the Appendix
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