4,512 research outputs found

### Exceptional sheaves on the Hirzebruch surface Fâ

We investigate exceptional sheaves on the Hirzebruch surface $\mathbb{F}_2$,
as the first attempt toward the classification of exceptional objects on weak
del Pezzo surfaces.Comment: 25 page

### Field Redefinitions, T-duality and Solutions in Closed String Field Theories

We investigate classical solutions in closed bosonic string field theory and
heterotic string field theory that are obtained order by order starting from
solutions of the linearized equations of motion, and we discuss the ``field
redefinitions'' which relate massless fields in the string field theory side
and the low energy effective theory side. Massless components of the string
field theory solutions are not corrected and from them we can infer
corresponding solutions in the effective theory: the chiral null model and the
pp-wave solution with B-field, which have been known to be alpha'-exact. These
two sets of solutions in the two sides look slightly different because of the
field redefinitions. It turns out that T-duality is a useful tool to determine
them: We show that some part of the field redefinitions can be determined by
using the correspondence between T-duality rules in the two sides, irrespective
of the detail of the interaction terms and the integrating-out procedure.
Applying the field redefinitions, we see that the solutions in the effective
theory side are reproduced from the string field theory solutions.Comment: LaTeX, 40 pages, no figure v2: minor corrections v3: minor correctio

### An Exploratory Study of Nucleon-Nucleon Scattering Lengths in Lattice QCD

An exploratory study is made of the nucleon-nucleon $s$-wave scattering
lengths in quenched lattice QCD with the Wilson quark action. The $\pi$-$N$ and
$\pi$-$\pi$ scattering lengths are also calculated for comparison. The
calculations are made with heavy quarks corresponding to $m_\pi/m_\rho\approx
0.73-0.95$. The results show that the $N$-$N$ system has an attractive force in
both spin-singlet and triplet channels, with their scattering lengths
significantly larger than those for the $\pi$-$N$ and $\pi$-$\pi$ cases, a
trend which is qualitatively consistent with the experiment. Problems toward a
more realistic calculation for light quarks are discussed.Comment: 9 pages. Latex file. Figures are also included as ps file

### Renormalization of four-fermion operators for higher twist calculations

The evaluation of the higher twist contributions to Deep Inelastic Scattering
amplitudes involves a non trivial choice of operator bases for the higher
orders of the OPE expansion of the two hadronic currents. In this talk we
discuss the perturbative renormalization of the four-fermion operators that
appear in the above bases.Comment: LATTICE98(matrixelement), 3 page

### Tachyon Condensation with B-field

We discuss classical solutions of a graviton-dilaton-B_{\mu\nu}-tachyon
system. Both constant tachyon solutions, including AdS_3 solutions, and
space-dependent tachyon solutions are investigated, and their possible
implications to closed string tachyon condensation are argued. The stability
issue of the AdS_3 solutions is also discussed.Comment: 10 pages, references adde

### Tachyon Vacuum Solution in Open String Field Theory with Constant B Field

We show that Schnabl's tachyon vacuum solution is an exact solution of the
equation of motion of Witten's open bosonic string field theory in the
background of constant antisymmetric two-form field. The action computed at the
vacuum solution is given by the Dirac-Born-Infeld factor multiplied to that
without the antisymmetric tensor field.Comment: 8 page

### The off-shell Veneziano amplitude in Schnabl gauge

We give a careful definition of the open string propagator in Schnabl gauge
and present its worldsheet interpretation. The propagator requires two
Schwinger parameters and contains the BRST operator. It builds surfaces by
gluing strips of variable width to the left and to the right of off-shell
states with contracted or expanded local frames. We evaluate explicitly the
four-point amplitude of off-shell tachyons. The computation involves a subtle
boundary term, crucial to enforce the correct exchange symmetries.
Interestingly, the familiar on-shell physics emerges even though string
diagrams produce Riemann surfaces more than once. Off-shell, the amplitudes do
not factorize over intermediate on-shell states.Comment: 48 pages, 10 figures. v2:acknowledgments adde

### Conformal Symmetry and A New Gauge in the Matrix Model

We generalize the background gauge in the Matrix model to propose a new gauge
which is useful for discussing the conformal symmetry. In this gauge, the
special conformal transformation (SCT) as the isometry of the near-horizon
geometry of the D-particle solution is directly reproduced with the correct
coefficient as the quantum correction to the SCT in the Matrix model. We also
present a general argument for the relation between the gauge choice and the
field redefinition in the Matrix model.Comment: 17 pages, LaTeX, no figures; v2: Introduction modified, references
added and typos corrected; v3: Introduction changed; v4: Eq.(12) corrected;
v5: final version to appear in Phys. Rev.

### Exact marginality in open string field theory: a general framework

We construct analytic solutions of open bosonic string field theory for any
exactly marginal deformation in any boundary conformal field theory when
properly renormalized operator products of the marginal operator are given. We
explicitly provide such renormalized operator products for a class of marginal
deformations which include the deformations of flat D-branes in flat
backgrounds by constant massless modes of the gauge field and of the scalar
fields on the D-branes, the cosine potential for a space-like coordinate, and
the hyperbolic cosine potential for the time-like coordinate. In our
construction we use integrated vertex operators, which are closely related to
finite deformations in boundary conformal field theory, while previous analytic
solutions were based on unintegrated vertex operators. We also introduce a
modified star product to formulate string field theory around the deformed
background.Comment: 63 pages, 10 figures, LaTeX2

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