4,289 research outputs found
Puzzles for Matrix Models of Chiral Field Theories
We summarize the field-theory/matrix model correspondence for a chiral N=1
model with matter in the adjoint, antisymmetric and conjugate symmetric
representations as well as eight fundamentals to cancel the chiral anomaly. The
associated holomorphic matrix model is consistent only for two fundamental
fields, which requires a modification of the original Dijkgraaf-Vafa
conjecture. The modified correspondence holds in spite of this mismatch.Comment: Contribution to the proceedings of the 36th International Symposium
Ahrenshoop, Berlin, August 26-30, 2003; 6 Page
GUT theories from Calabi-Yau 4-folds with SO(10) Singularities
We consider an SO(10) GUT model from F-theory compactified on an elliptically
fibered Calabi-Yau with a D5 singularity. To obtain the matter curves and the
Yukawa couplings, we use a global description to resolve the singularity. We
identify the vector and spinor matter representations and their Yukawa
couplings and we explicitly build the G-fluxes in the global model and check
the agreement with the semi-local results. As our bundle is of type SU(2k),
some extra conditions need to be applied to match the fluxes.Comment: 27 page
Compact F-theory GUTs with U(1)_PQ
We construct semi-local and global realizations of SU(5) GUTs in F-theory
that utilize a U(1)_PQ symmetry to protect against dimension four proton decay.
Symmetries of this type, which assign charges to H_u and H_d that forbid a tree
level \mu term, play an important role in scenarios for neutrino physics and
gauge mediation that have been proposed in local F-theory model building. As
demonstrated in arXiv:0906.4672, the presence of such a symmetry implies the
existence of non-GUT exotics in the spectrum, when hypercharge flux is used to
break the GUT group and to give rise to doublet-triplet splitting. These
exotics are of precisely the right type to solve the unification problem in
such F-theory models and might also comprise a non-standard messenger sector
for gauge mediation. We present a detailed description of models with U(1)_PQ
in the semi-local regime, which does not depend on details of any specific
Calabi-Yau four-fold, and then specialize to the geometry of arXiv:0904.3932 to
construct three-generation examples with the minimal allowed number of non-GUT
exotics. Among these, we find a handful of models in which the D3-tadpole
constraint can be satisfied without requiring the introduction of
anti-D3-branes. Finally, because SU(5) singlets that carry U(1)_PQ charge may
serve as candidate right-handed neutrinos or can be used to lift the exotics,
we study their origin in compact models and motivate a conjecture for how to
count their zero modes in a semi-local setting.Comment: 73 pages, 5 figures, v2: minor corrections to 4.3 and 6.3.1,
reference adde
Flavor Structure in F-theory Compactifications
F-theory is one of frameworks in string theory where supersymmetric grand
unification is accommodated, and all the Yukawa couplings and Majorana masses
of right-handed neutrinos are generated. Yukawa couplings of charged fermions
are generated at codimension-3 singularities, and a contribution from a given
singularity point is known to be approximately rank 1. Thus, the approximate
rank of Yukawa matrices in low-energy effective theory of generic F-theory
compactifications are minimum of either the number of generations N_gen = 3 or
the number of singularity points of certain types. If there is a geometry with
only one E_6 type point and one D_6 type point over the entire 7-brane for
SU(5) gauge fields, F-theory compactified on such a geometry would reproduce
approximately rank-1 Yukawa matrices in the real world. We found, however, that
there is no such geometry. Thus, it is a problem how to generate hierarchical
Yukawa eigenvalues in F-theory compactifications. A solution in the literature
so far is to take an appropriate factorization limit. In this article, we
propose an alternative solution to the hierarchical structure problem (which
requires to tune some parameters) by studying how zero mode wavefunctions
depend on complex structure moduli. In this solution, the N_gen x N_gen CKM
matrix is predicted to have only N_gen entries of order unity without an extra
tuning of parameters, and the lepton flavor anarchy is predicted for the lepton
mixing matrix. We also obtained a precise description of zero mode
wavefunctions near the E_6 type singularity points, where the up-type Yukawa
couplings are generated.Comment: 148 page
Geometrically Induced Phase Transitions at Large N
Utilizing the large N dual description of a metastable system of branes and
anti-branes wrapping rigid homologous S^2's in a non-compact Calabi-Yau
threefold, we study phase transitions induced by changing the positions of the
S^2's. At leading order in 1/N the effective potential for this system is
computed by the planar limit of an auxiliary matrix model. Beginning at the two
loop correction, the degenerate vacuum energy density of the discrete confining
vacua split, and a potential is generated for the axion. Changing the relative
positions of the S^2's causes discrete jumps in the energetically preferred
confining vacuum and can also obstruct direct brane/anti-brane annihilation
processes. The branes must hop to nearby S^2's before annihilating, thus
significantly increasing the lifetime of the corresponding non-supersymmetric
vacua. We also speculate that misaligned metastable glueball phases may
generate a repulsive inter-brane force which stabilizes the radial mode present
in compact Calabi-Yau threefolds.Comment: 47 pages, 7 figure
Meta-Stable Brane Configurations by Adding an Orientifold-Plane to Giveon-Kutasov
In hep-th/0703135, they have found the type IIA intersecting brane
configuration where there exist three NS5-branes, D4-branes and anti-D4-branes.
By analyzing the gravitational interaction for the D4-branes in the background
of the NS5-branes, the phase structures in different regions of the parameter
space were studied in the context of classical string theory. In this paper, by
adding the orientifold 4-plane and 6-plane to the above brane configuration, we
describe the intersecting brane configurations of type IIA string theory
corresponding to the meta-stable nonsupersymmetric vacua of these gauge
theories.Comment: 21 pp, 6 figures; reduced bytes of figures, DBI action analysis added
and to appear in JHE
Supersymmetry Breaking Vacua from M Theory Fivebranes
We consider intersecting brane configurations realizing N=2 supersymmetric
gauge theories broken to N=1 by multitrace superpotentials, and softly to N=0.
We analyze, in the framework of M5-brane wrapping a curve, the supersymmetric
vacua and the analogs of spontaneous supersymmetry breaking and soft
supersymmetry breaking in gauge theories. We show that the M5-brane does not
exhibit the analog of metastable spontaneous supersymmetry breaking, and does
not have non-holomorphic minimal volume curves with holomorphic boundary
conditions. However, we find that any point in the N=2 moduli space can be
rotated to a non-holomorphic minimal volume curve, whose boundary conditions
break supersymmetry. We interpret these as the analogs of soft supersymmetry
breaking vacua in the gauge theory.Comment: 32 pages, 8 figures, harvmac; v2: corrections in eq. 3.6 and in
section 6, reference adde
A shortcut to identifying small molecule signals that regulate behavior and development in Caenorhabditis elegans
Small molecule metabolites play important roles in Caenorhabditis elegans biology, but effective approaches for identifying their chemical structures are lacking. Recent studies revealed that a family of glycosides, the ascarosides, differentially regulate C. elegans development and behavior. Low concentrations of ascarosides attract males and thus appear to be part of the C. elegans sex pheromone, whereas higher concentrations induce developmental arrest at the dauer stage, an alternative, nonaging larval stage. The ascarosides act synergistically, which presented challenges for their identification via traditional activity-guided fractionation. As a result the chemical characterization of the dauer and male attracting pheromones remained incomplete. Here, we describe the identification of several additional pheromone components by using a recently developed NMR-spectroscopic approach, differential analysis by 2D NMR spectroscopy (DANS), which simplifies linking small molecule metabolites with their biological function. DANS-based comparison of wild-type C. elegans and a signaling-deficient mutant, daf-22, enabled identification of 3 known and 4 previously undescribed ascarosides, including a compound that features a p-aminobenzoic acid subunit. Biological testing of synthetic samples of these compounds revealed additional evidence for synergy and provided insights into structure–activity relationships. Using a combination of the three most active ascarosides allowed full reconstitution of the male-attracting activity of wild-type pheromone extract. Our results highlight the efficacy of DANS as a method for identifying small-molecule metabolites and placing them within a specific genetic context. This study further supports the hypothesis that ascarosides represent a structurally diverse set of nematode signaling molecules regulating major life history traits
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