12 research outputs found
Breaking classical Lie groups to finite subgroups - an automated approach
The decomposition of representations of compact classical Lie groups into
representations of finite subgroups is discussed. A Mathematica package is
presented that can be used to compute these branching rules using the Weyl
character formula. For some low order finite groups including and
general analytical formulas are presented for the branching rules
of arbitrary representations of their smallest Lie super-groups.Comment: 21 pages, minor changes, matches published versio
Symmetries of symmetries and geometrical CP violation
We investigate transformations which are not symmetries of a theory but
nevertheless leave invariant the set of all symmetry elements and
representations. Generalizing from the example of a three Higgs doublet model
with symmetry, we show that the possibility of such
transformations signals physical degeneracies in the parameter space of a
theory. We show that stationary points only appear in multiplets which are
representations of the group of these so-called equivalence transformations. As
a consequence, the stationary points are amongst the solutions of a set of
homogeneous linear equations. This is relevant to the minimization of
potentials in general and sheds new light on the origin of calculable phases
and geometrical CP violation.Comment: 20+9 pages, 1 figure; v1: minor changes, added clarification, matches
the published versio
On predictions from spontaneously broken flavor symmetries
We discuss the predictive power of supersymmetric models with flavor
symmetries, focusing on the lepton sector of the standard model. In particular,
we comment on schemes in which, after certain `flavons' acquire their vacuum
expectation values (VEVs), the charged lepton Yukawa couplings and the neutrino
mass matrix appear to have certain residual symmetries. In most analyses, only
corrections to the holomorphic superpotential from higher-dimensional operators
are considered (for instance, in order to generate a realistic
mixing angle). In general, however, the flavon VEVs also modify the K\"ahler
potential and, therefore, the model predictions. We show that these corrections
to the naive results can be sizable. Furthermore, we present simple analytic
formulae that allow us to understand the impact of these corrections on the
predictions for the masses and mixing parameters.Comment: 12 pages, 4 figures; improved version matching PLB articl
Predictivity of models with spontaneously broken non-Abelian discrete flavor symmetries
In a class of supersymmetric flavor models predictions are based on residual
symmetries of some subsectors of the theory such as those of the charged
leptons and neutrinos. However, the vacuum expectation values of the so-called
flavon fields generally modify the K\"ahler potential of the setting, thus
changing the predictions. We derive simple analytic formulae that allow us to
understand the impact of these corrections on the predictions for the masses
and mixing parameters. Furthermore, we discuss the effects on the vacuum
alignment and on flavor changing neutral currents. Our results can also be
applied to non--supersymmetric flavor models.Comment: 34 pages, 4 figures, related Mathematica package can be found at
http://einrichtungen.ph.tum.de/T30e/codes/KaehlerCorrections/, updated
version with added reference, matching NPB articl
CP Violation from Finite Groups
We discuss the origin of CP violation in settings with a discrete (flavor)
symmetry . We show that physical CP transformations always have to be
class-inverting automorphisms of . This allows us to categorize finite
groups into three types: (i) Groups that do not exhibit such an automorphism
and, therefore, in generic settings, explicitly violate CP. In settings based
on such groups, CP violation can have pure group-theoretic origin and can be
related to the complexity of some Clebsch-Gordan coefficients. (ii) Groups for
which one can find a CP basis in which all the Clebsch-Gordan coefficients are
real. For such groups, imposing CP invariance restricts the phases of coupling
coefficients. (iii) Groups that do not admit real Clebsch-Gordan coefficients
but possess a class-inverting automorphism that can be used to define a proper
(generalized) CP transformation. For such groups, imposing CP invariance can
lead to an additional symmetry that forbids certain couplings. We make use of
the so-called twisted Frobenius-Schur indicator to distinguish between the
three types of discrete groups. With , , and
we present one explicit example for each type of group, thereby
illustrating the CP properties of models based on them. We also show that
certain operations that have been dubbed generalized CP transformations in the
recent literature do not lead to physical CP conservation.Comment: 45 pages, 3 figure
Anomaly-safe discrete groups
We show that there is a class of finite groups, the so-called perfect groups,
which cannot exhibit anomalies. This implies that all non-Abelian finite simple
groups are anomaly-free. On the other hand, non-perfect groups generically
suffer from anomalies. We present two different ways that allow one to
understand these statements.Comment: 11 page
No-go theorems for R symmetries in four-dimensional GUTs
We prove that it is impossible to construct a grand unified model, based on a
simple gauge group, in four dimensions that leads to the exact MSSM, nor to a
singlet extension, and possesses an unbroken R symmetry. This implies that no
MSSM model with either a Z_{M>=3}^R or U(1)_R symmetry can be completed by a
four-dimensional GUT in the ultraviolet. However, our no-go theorem does not
apply to GUT models with extra dimensions. We also show that it is impossible
to construct a 4D GUT that leads to the MSSM plus an additional anomaly-free
symmetry that forbids the mu term.Comment: 11+1 page
SUPERSYMMETRIC UNIFICATION AND R SYMMETRIES
We review the role of R symmetries in models of supersymmetric unification in
four and more dimensions, and in string theory. We show that, if one demands
anomaly freedom and fermion masses, only R symmetries can forbid the
supersymmetric Higgs mass term mu. We then review the proof that R symmetries
are not available in conventional grand unified theories (GUTs) and argue that
this prevents natural solutions to the doublet-triplet splitting problem in
four dimensions. On the other hand, higher-dimensional GUTs do not suffer from
this problem. We briefly comment on an explicit string-derived model in which
the mu and dimension five proton decay problems are solved simultaneously by an
order four discrete R symmetry. We also comment on the higher-dimensional
origin of this symmetry.Comment: 17 pages, based on invited talks given at String Phenomenology 2012,
CETUP 2012, PACIFIC 2012, the 4th Bethe Center Workshop and the Universe
Cluster Science Week 201