507 research outputs found
Froggatt-Nielsen models from E8 in F-theory GUTs
This paper studies F-theory SU(5) GUT models where the three generations of
the standard model come from three different curves. All the matter is taken to
come from curves intersecting at a point of enhanced E8 gauge symmetry. Giving
a vev to some of the GUT singlets naturally implements a Froggatt-Nielsen
approach to flavour structure. A scan is performed over all possible models and
the results are filtered using phenomenological constraints. We find a unique
model that fits observations of quark and lepton masses and mixing well. This
model suffers from two drawbacks: R-parity must be imposed by hand and there is
a doublet-triplet splitting problem.Comment: 42 pages; v2:journal version; v3:corrected typo in neutrino masse
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
On hypercharge flux and exotics in F-theory GUTs
We study SU(5) Grand Unified Theories within a local framework in F-theory
with multiple extra U(1) symmetries arising from a small monodromy group. The
use of hypercharge flux for doublet-triplet splitting implies massless exotics
in the spectrum that are protected from obtaining a mass by the U(1)
symmetries. We find that lifting the exotics by giving vacuum expectation
values to some GUT singlets spontaneously breaks all the U(1) symmetries which
implies that proton decay operators are induced. If we impose an additional
R-parity symmetry by hand we find all the exotics can be lifted while proton
decay operators are still forbidden. These models can retain the gauge coupling
unification accuracy of the MSSM at 1-loop. For models where the generations
are distributed across multiple curves we also present a motivation for the
quark-lepton mass splittings at the GUT scale based on a Froggatt-Nielsen
approach to flavour.Comment: 38 pages; v2: emphasised possibility of avoiding exotics in models
without a global E8 structure, added ref, journal versio
D-branes at Toric Singularities: Model Building, Yukawa Couplings and Flavour Physics
We discuss general properties of D-brane model building at toric
singularities. Using dimer techniques to obtain the gauge theory from the
structure of the singularity, we extract results on the matter sector and
superpotential of the corresponding gauge theory. We show that the number of
families in toric phases is always less than or equal to three, with a unique
exception being the zeroth Hirzebruch surface. With the physical input of three
generations we find that the lightest family of quarks is massless and the
masses of the other two can be hierarchically separated. We compute the CKM
matrix for explicit models in this setting and find the singularities possess
sufficient structure to allow for realistic mixing between generations and CP
violation.Comment: 55 pages, v2: typos corrected, minor comments adde
Emerging Non-Anomalous Baryonic Symmetries in the AdS_5/CFT_4 Correspondence
We study the breaking of baryonic symmetries in the AdS_5/CFT_4
correspondence for D3 branes at Calabi-Yau three-fold singularities. This
leads, for particular VEVs, to the emergence of non-anomalous baryonic
symmetries during the renormalization group flow. We claim that these VEVs
correspond to critical values of the B-field moduli in the dual supergravity
backgrounds. We study in detail the C^3/Z_3 orbifold, the cone over F_0 and the
C^3/Z_5 orbifold. For the first two examples, we study the dual supergravity
backgrounds that correspond to the breaking of the emerging baryonic symmetries
and identify the expected Goldstone bosons and global strings in the infra-red.
In doing so we confirm the claim that the emerging symmetries are indeed
non-anomalous baryonic symmetries.Comment: 65 pages, 15 figures;v2: minor changes, published versio
Wavefunctions and the Point of E8 in F-theory
In F-theory GUTs interactions between fields are typically localised at
points of enhanced symmetry in the internal dimensions implying that the
coefficient of the associated operator can be studied using a local
wavefunctions overlap calculation. Some F-theory SU(5) GUT theories may exhibit
a maximum symmetry enhancement at a point to E8, and in this case all the
operators of the theory can be associated to the same point. We take initial
steps towards the study of operators in such theories. We calculate
wavefunctions and their overlaps around a general point of enhancement and
establish constraints on the local form of the fluxes. We then apply the
general results to a simple model at a point of E8 enhancement and calculate
some example operators such as Yukawa couplings and dimension-five couplings
that can lead to proton decay.Comment: 46 page
Flux and Instanton Effects in Local F-theory Models and Hierarchical Fermion Masses
We study the deformation induced by fluxes and instanton effects on Yukawa
couplings involving 7-brane intersections in local F-theory constructions. In
the absence of non-perturbative effects, holomorphic Yukawa couplings do not
depend on open string fluxes. On the other hand instanton effects (or gaugino
condensation on distant 7-branes) do induce corrections to the Yukawas. The
leading order effect may also be captured by the presence of closed string
(1,2) IASD fluxes, which give rise to a non-commutative structure. We check
that even in the presence of these non-perturbative effects the holomorphic
Yukawas remain independent of magnetic fluxes. Although fermion mass
hierarchies may be obtained from these non-perturbative effects, they would
give identical Yukawa couplings for D-quark and Lepton masses in SU(5) F-theory
GUT's, in contradiction with experiment. We point out that this problem may be
solved by appropriately normalizing the wavefunctions. We show in a simple toy
model how the presence of hypercharge flux may then be responsible for the
difference between D-quarks and Lepton masses in local SU(5) GUT's.Comment: 84 pages, 1 figure. v2: minor corrections and references adde
F-Theory GUT Vacua on Compact Calabi-Yau Fourfolds
We present compact three-generation F-theory GUT models meeting in particular
the constraints of D3-tadpole cancellation and D-term supersymmetry. To this
end we explicitly construct elliptically fibered Calabi-Yau fourfolds as
complete intersections in a toric ambient space. Toric methods enable us to
control the singular geometry of the SU(5) GUT model. The GUT brane wraps a
non-generic del Pezzo surface admitting GUT symmetry breaking via hypercharge
flux. It is contractible to a curve and we demonstrate the existence of a
consistent decoupling limit. We compute the Euler characteristic of the
singular Calabi-Yau fourfold to show that our three-generation flux solutions
obtained via the spectral cover construction are consistent with D3-tadpole
cancellation.Comment: 22+12 pages; v2: minor clarifications on decoupling limi
Abelian Gauge Fluxes and Local Models in F-Theory
We analyze the Abelian gauge fluxes in local F-theory models with G_S=SU(6)
and SO(10). For the case of G_S=SO(10), there is a no-go theorem which states
that for an exotic-free spectrum, there are no solutions for U(1)^2 gauge
fluxes. We explicitly construct the U(1)^2 gauge fluxes with an exotic-free
bulk spectrum for the case of G_S=SU(6). We also analyze the conditions for the
curves supporting the given field content and discuss non-minimal spectra of
the MSSM with doublet-triplet splitting.Comment: 43 pages, 15 tables; typos corrected, 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
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