61,580 research outputs found
Dibaryon Spectroscopy
The AdS/CFT correspondence relates dibaryons in superconformal gauge theories
to holomorphic curves in Kaehler-Einstein surfaces. The degree of the
holomorphic curves is proportional to the gauge theory conformal dimension of
the dibaryons. Moreover, the number of holomorphic curves should match, in an
appropriately defined sense, the number of dibaryons. Using AdS/CFT backgrounds
built from the generalized conifolds of Gubser, Shatashvili, and Nekrasov
(1999), we show that the gauge theory prediction for the dimension of
dibaryonic operators does indeed match the degree of the corresponding
holomorphic curves. For AdS/CFT backgrounds built from cones over del Pezzo
surfaces, we are able to match the degree of the curves to the conformal
dimension of dibaryons for the n'th del Pezzo surface, n=1,2,...,6. Also, for
the del Pezzos and the A_k type generalized conifolds, for the dibaryons of
smallest conformal dimension, we are able to match the number of holomorphic
curves with the number of possible dibaryon operators from gauge theory.Comment: 30 pages, 6 figures, corrected refs; v3 typos correcte
New Curves from Branes
We consider configurations of Neveu-Schwarz fivebranes, Dirichlet fourbranes
and an orientifold sixplane in type IIA string theory. Upon lifting the
configuration to M-theory and proposing a description of how to include the
effects of the orientifold sixplane we derive the curves describing the Coulomb
branch of N=2 gauge theories with orthogonal and symplectic gauge groups,
product gauge groups of the form SU(k_1)...SU(k_i) x SO(N) and
SU(k_1)...SU(k_i) x Sp(N). We also propose new curves describing theories with
unitary gauge groups and matter in the symmetric or antisymmetric
representation.Comment: 29 pages (harvmac b-mode), 2 figure
GUTs in Type IIB Orientifold Compactifications
We systematically analyse globally consistent SU(5) GUT models on
intersecting D7-branes in genuine Calabi-Yau orientifolds with O3- and
O7-planes. Beyond the well-known tadpole and K-theory cancellation conditions
there exist a number of additional subtle but quite restrictive constraints.
For the realisation of SU(5) GUTs with gauge symmetry breaking via U(1)_Y flux
we present two classes of suitable Calabi-Yau manifolds defined via del Pezzo
transitions of the elliptically fibred hypersurface P_{1,1,1,6,9}[18] and of
the Quintic P_{1,1,1,1,1}[5], respectively. To define an orientifold projection
we classify all involutions on del Pezzo surfaces. We work out the model
building prospects of these geometries and present five globally consistent
string GUT models in detail, including a 3-generation SU(5) model with no
exotics whatsoever. We also realise other phenomenological features such as the
10 10 5 Yukawa coupling and comment on the possibility of moduli stabilisation,
where we find an entire new set of so-called swiss-cheese type Calabi-Yau
manifolds. It is expected that both the general constrained structure and the
concrete models lift to F-theory vacua on compact Calabi-Yau fourfolds.Comment: 138 pages, 9 figures; v2, v3: typos corrected, one reference adde
The Particle Spectrum of Heterotic Compactifications
Techniques are presented for computing the cohomology of stable, holomorphic
vector bundles over elliptically fibered Calabi-Yau threefolds. These
cohomology groups explicitly determine the spectrum of the low energy,
four-dimensional theory. Generic points in vector bundle moduli space manifest
an identical spectrum. However, it is shown that on subsets of moduli space of
co-dimension one or higher, the spectrum can abruptly jump to many different
values. Both analytic and numerical data illustrating this phenomenon are
presented. This result opens the possibility of tunneling or phase transitions
between different particle spectra in the same heterotic compactification. In
the course of this discussion, a classification of SU(5) GUT theories within a
specific context is presented.Comment: 77 pages, 3 figure
Are ghost surfaces quadratic-flux-minimizing?
Two candidates for "almost-invariant" toroidal surfaces passing through
magnetic islands, namely quadratic-flux-minimizing (QFMin) surfaces and ghost
surfaces, use families of periodic pseudo-orbits (i.e. paths for which the
action is not exactly extremal). QFMin pseudo-orbits, which are
coordinate-dependent, are field lines obtained from a modified magnetic field,
and ghost-surface pseudo-orbits are obtained by displacing closed field lines
in the direction of steepest descent of magnetic action, . A generalized Hamiltonian definition of ghost
surfaces is given and specialized to the usual Lagrangian definition. A
modified Hamilton's Principle is introduced that allows the use of Lagrangian
integration for calculation of the QFMin pseudo-orbits. Numerical calculations
show QFMin and Lagrangian ghost surfaces give very similar results for a
chaotic magnetic field perturbed from an integrable case, and this is explained
using a perturbative construction of an auxiliary poloidal angle for which
QFMin and Lagrangian ghost surfaces are the same up to second order. While
presented in the context of 3-dimensional magnetic field line systems, the
concepts are applicable to defining almost-invariant tori in other
degree-of-freedom nonintegrable Lagrangian/Hamiltonian systems.Comment: 8 pages, 3 figures. Revised version includes post-publication
corrections in text, as described in Appendix C Erratu
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