5,617 research outputs found
Breaking democracy with non renormalizable mass terms
The exact democratic structure for the quark mass matrix, resulting from the
action of the family symmetry group , is broken by the
vaccum expectation values of heavy singlet fields appearing in non
renormalizable dimension 6 operators. Within this specific context of breaking
of the family symmetry we formulate a very simple ansatz which leads to correct
quark masses and mixings.Comment: 6 pages, RevTe
Spin and abelian electromagnetic duality on four-manifolds
We investigate the electromagnetic duality properties of an abelian gauge
theory on a compact oriented four-manifold by analysing the behaviour of a
generalised partition function under modular transformations of the
dimensionless coupling constants. The true partition function is invariant
under the full modular group but the generalised partition function exhibits
more complicated behaviour depending on topological properties of the
four-manifold concerned. It is already known that there may be "modular
weights" which are linear combinations of the Euler number and Hirzebruch
signature of the four-manifold. But sometimes the partition function transforms
only under a subgroup of the modular group (the Hecke subgroup). In this case
it is impossible to define real spinor wave functions on the four-manifold. But
complex spinors are possible provided the background magnetic fluxes are
appropriately fractional rather that integral. This gives rise to a second
partition function which enables the full modular group to be realised by
permuting the two partition functions, together with a third. Thus the full
modular group is realised in all cases. The demonstration makes use of various
constructions concerning integral lattices and theta functions that seem to be
of intrinsic interest.Comment: 29 pages, Plain Te
CP Violation and Flavour Mixings in Orbifold GUTs
We address the flavour problem by incorporating the hypothesis of universal
strength of Yukawa couplings in the framework of a 5D GUT model compactified on
an orbifold. We show that a quantitatively
successful picture of fermion masses and mixings emerges from the interplay
between the bulk suppression factors of geometric origin and the phases of the
Yukawa matrices. We give an explicit example, where we obtain a good fit for
both the CKM and PMNS matrices.Comment: 8 pages, no figures; v2: minor changes, published in Phys Rev D
(Rapid Communication
Non-Factorizable Phases, Yukawa Textures and the Size of sin (2 beta)
We emphasize the crucial r\^ ole played by non-factorizable phases in the
analysis of the Yukawa flavour structure performed in weak bases with Hermitian
mass matrices and with vanishing entries. We show that non-factorizable
phases are important in order to generate a sufficiently large .
A method is suggested to reconstruct the flavour structure of Yukawa couplings
from input experimental data both in this Hermitian basis and in a
non-Hermitian basis with a maximal number of texture zeros. The corresponding
Froggatt--Nielsen patterns are presented in both cases.Comment: 15 pages, 3 figure
Symmetries, Large Leptonic Mixing and a Fourth Generation
We show that large leptonic mixing occurs most naturally in the framework of
the Sandard Model just by adding a fourth generation. One can then construct a
small discrete symmetry, instead of the large ,
which requires that the neutrino as well as the charged lepton mass matrices be
proportional to a democratic mass matrix, where all entries are
equal to unity. Without considering the see-saw mechanism, or other more
elaborate extensions of the SM, and contrary to the case with only 3
generations, large leptonic mixing is obtained when the symmetry is broken.Comment: 6 pages, ReVTeX, no figure
Quasidegeneracy of Majorana Neutrinos and the Origin of Large Leptonic Mixing
We propose that the observed large leptonic mixing may just reflect a
quasidegeneracy of three Majorana neutrinos. The limit of exact degeneracy of
Majorana neutrinos is not trivial, as leptonic mixing and even CP violation may
occur. We conjecture that the smallness of , when compared to the
other elements of , may just reflect the fact that, in the limit of
exact mass degeneracy, the leptonic mixing matrix necessarily has a vanishing
element. We show that the lifting of the mass degeneracy can lead to the
measured value of while at the same time accommodating the observed
solar and atmospheric mixing angles. In the scenario we consider for the
breaking of the mass degeneracy there is only one CP violating phase, already
present in the limit of exact degeneracy, which upon the lifting of the
degeneracy generates both Majorana and Dirac-type CP violation in the leptonic
sector. We analyse some of the correlations among physical observables and
point out that in most of the cases considered, the implied strength of
leptonic Dirac-type CP violation is large enough to be detected in the next
round of experiments.Comment: 16 pages, 4 figures. Matches published version, references added,
improved discussion, results unchange
- …