110 research outputs found
Properties of the general NHDM. I. The orbit space
We study the scalar sector of the general N-Higgs-doublet model via geometric
constructions in the space of gauge orbits. We give a detailed description of
the shape of the orbit space both for general N and, in more detail, for N=3.
We also comment on remarkable analogies between NHDM and quantum information
theory.Comment: 27 pages, 2 figure
Beyond basis invariants
Physical observables cannot depend on the basis one chooses to describe
fields. Therefore, all physically relevant properties of a model are, in
principle, expressible in terms of basis-invariant combinations of the
parameters. However, in many cases it becomes prohibitively difficult to
establish key physical features exclusively in terms of basis invariants. Here,
we advocate an alternative route in such cases: the formulation of
basis-invariant statements in terms of basis-covariant objects. We give several
examples where the basis-covariant path is superior to the traditional approach
in terms of basis invariants. In particular, this includes the formulation of
necessary and sufficient basis-invariant conditions for various physically
distinct forms of CP conservation in two- and three-Higgs-doublet models.Comment: 20 pages, no figure
Custodial SO(4) symmetry and CP violation in N-Higgs-doublet potentials
We study the implementation of global
symmetry in general potentials with N-Higgs-doublets in order to obtain models
with custodial symmetry. We conclude that any implementation of the
custodial SO(4) symmetry is equivalent, by a basis transformation, to a
canonical one if is the gauge factor, is embedded in
and we require copies of the doublet representation of .
The invariance by SO(4) automatically leads to a CP invariant potential and the
basis of the canonical implementation of SO(4) is aligned to a basis where
CP-symmetry acts in the standard fashion. We show different but equivalent
implementations for the 2HDM, including an implementation not previously
considered.Comment: 22pp, REVTeX4. Published versio
On the Classification of Accidental Symmetries of the Two Higgs Doublet Model Potential
Recently, it has been shown [arXiv:1106.3482] that the
two-Higgs-doublet-model potential may exhibit a maximum of 13 distinct
accidental symmetries. Such a classification is based on a six-dimensional
bilinear scalar field formalism realizing the SO(1,5) symmetry group. This note
presents the transformation relations for each of the 13 symmetries in the
original scalar field space and their one-to-one correspondence to the space of
scalar bilinears, thereby providing firm support for the completeness of the
classification.Comment: 11 pages, comments on custodial symmetry added; final version to
appear in Physics Letters
Frustrated symmetries in multi-Higgs-doublet models
Within multi-Higgs-doublet models, one can impose symmetries on the Higgs
potential, either discrete or continuous, that mix several doublets. In
two-Higgs-doublet model any such symmetry can be conserved or spontaneously
violated after the electroweak symmetry breaking (EWSB), depending on the
coefficients of the potential. With more than two doublets, there exist
symmetries which are always spontaneously violated after EWSB. We discuss the
origin of this phenomenon and show its similarity to geometric frustration in
condensed-matter physics.Comment: 7 pages, no figure
Symmetry breaking patterns in 3HDM
An attractive feature of New Physics models with multiple Higgs fields is
that they are equipped with discrete symmetry groups in the Higgs and flavour
sectors. These symmetry groups are often broken at the global minimum of the
Higgs potential, either completely or to a proper subgroup, with certain
phenomenological consequences. Here, we systematically explore these symmetry
breaking patterns in the scalar sector of the three-Higgs-doublet model (3HDM).
We use the full list of discrete symmetry groups allowed in 3HDM, and for each
group we find all possible ways it can break by the Higgs vacuum expectation
value alignment. We also discuss the interplay between these symmetry groups
and various forms of CP-violation in the scalar sector of 3HDM. Not only do our
results solve the problem for 3HDM, but they also hint at several general
features in multi-scalar sectors.Comment: 24 pages, 5 figures, 2 tables; v2: expanded introduction, matches
published versio
CP properties of symmetry-constrained two-Higgs-doublet models
The two-Higgs-doublet model can be constrained by imposing Higgs-family
symmetries and/or generalized CP symmetries. It is known that there are only
six independent classes of such symmetry-constrained models. We study the CP
properties of all cases in the bilinear formalism. An exact symmetry implies CP
conservation. We show that soft breaking of the symmetry can lead to
spontaneous CP violation (CPV) in three of the classes.Comment: 14 pages, 2 tables, revised version adapted to the journal
publicatio
Autophagy activation and enhanced mitophagy characterize the Purkinje cells of pcd mice prior to neuronal death
Purkinje cells are a class of specialized neurons in the cerebellum, and are among the most metabolically active of all neurons, as they receive immense synaptic stimulation, and provide the only efferent output from the cerebellum. Degeneration of Purkinje cells is a common feature of inherited ataxias in humans and mice. To understand Purkinje neuron degeneration, investigators have turned to naturally occurring Purkinje cell degeneration phenotypes in mice to identify key regulatory proteins and cellular pathways. The Purkinje cell degeneration (pcd) mouse is a recessive mutant characterized by complete and dramatic post-natal, cell autonomous Purkinje neuron degeneration and death. As the basis of Purkinje cell death in pcd is unresolved, and contradictory data has emerged for the role of autophagy in Purkinje cell degeneration, we studied the mechanism of Purkinje cell death in pcd mice. BAX null status did not suppress Purkinje neuron death in pcd mice, indicating that classic apoptosis is not responsible for Purkinje cell loss. Interestingly, LC3 Western blot analysis and GFP-LC3 immunostaining of degenerating pcd cerebellum revealed activation of the autophagy pathway. Ultrastructural studies confirmed increased autophagy pathway activity in Purkinje cells, and yielded evidence for mitophagy, in agreement with LC3 immunoblotting of cerebellar fractions. As p62 levels were decreased in pcd cerebellum, our findings suggest that pcd Purkinje cell neurons can execute effective autophagy. However, our results support a role for dysregulated autophagy activation in pcd, and suggest that increased or aberrant mitophagy contributes to the Purkinje cell degeneration in pcd mice
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