7,965 research outputs found
with leptoquarks and the origin of Yukawa couplings
We construct a model where the Yukawa couplings of the Standard Model (SM)
fermions arise from the breaking of a symmetry and through mixing with a
fourth family of vector-like fermions. By adding a scalar leptoquark, which is
an electroweak triplet and odd under the symmetry, we obtain an
explanation for that is linked to the origin of the Yukawa
couplings. The coupling of SM fermions to the leptoquark is mediated by the
fourth family fermions, and is predicted to be related to CKM entries and mass
ratios of SM fermions.Comment: 17 pages, 2 figures. Version accepted for publication in JHE
Invariant approach to CP in family symmetry models
We propose the use of basis invariants, valid for any choice of CP
transformation, as a powerful approach to studying specific models of CP
violation in the presence of discrete family symmetries. We illustrate the
virtues of this approach for examples based on and family
symmetries. For , we show how to elegantly obtain several known results in
the literature. In we use the invariant approach to identify how
explicit (rather than spontaneous) CP violation arises, which is geometrical in
nature, i.e. persisting for arbitrary couplings in the Lagrangian.Comment: 4 pages plus references. v2: to be published in PR
Invariant approach to CP in unbroken
The invariant approach is a powerful method for studying CP violation for
specific Lagrangians. The method is particularly useful for dealing with
discrete family symmetries. We focus on the CP properties of unbroken
invariant Lagrangians with Yukawa-like terms, which proves to be a
rich framework, with distinct aspects of CP, making it an ideal group to
investigate with the invariant approach. We classify Lagrangians depending on
the number of fields transforming as irreducible triplet representations of
. For each case, we construct CP-odd weak basis invariants and use
them to discuss the respective CP properties. We find that CP violation is
sensitive to the number and type of representations.Comment: 24 pages, 1 figure. v2: to be published in NP
Minima of multi-Higgs potentials with triplets of and
We analyse the minima of scalar potentials for multi-Higgs models where the
scalars are arranged as either one triplet or two triplets of the discrete
symmetries , , , , as well as
and with . The results should be useful for both
multi-Higgs models involving electroweak doublets and multi-flavon models
involving electroweak singlets, where in both cases the fields transform as
triplets under some non-Abelian discrete symmetry.Comment: 15 page
CP-odd invariants for multi-Higgs models: applications with discrete symmetry
CP-odd invariants provide a basis independent way of studying the CP
properties of Lagrangians. We propose powerful methods for constructing basis
invariants and determining whether they are CP-odd or CP-even, then
systematically construct all of the simplest CP-odd invariants up to a given
order, finding many new ones. The CP-odd invariants are valid for general
potentials when expressed in a standard form. We then apply our results to
scalar potentials involving three (or six) Higgs fields which form irreducible
triplets under a discrete symmetry, including invariants for both explicit as
well as spontaneous CP violation. The considered cases include one triplet of
Standard Model (SM) gauge singlet scalars, one triplet of SM Higgs doublets,
two triplets of SM singlets, and two triplets of SM Higgs doublets. For each
case we study the potential symmetric under one of the simplest discrete
symmetries with irreducible triplet representations, namely , ,
or , as well as the infinite classes of discrete
symmetries or .Comment: 54 pages, 39 diagrams, minor changes, version accepted in PR
Measuring stellar differential rotation with high-precision space-borne photometry
We introduce a method of measuring a lower limit to the amplitude of surface
differential rotation from high-precision, evenly sampled photometric time
series. It is applied to main-sequence late-type stars whose optical flux
modulation is dominated by starspots. An autocorrelation of the time series was
used to select stars that allow an accurate determination of starspot rotation
periods. A simple two-spot model was applied together with a Bayesian
information criterion to preliminarily select intervals of the time series
showing evidence of differential rotation with starspots of almost constant
area. Finally, the significance of the differential rotation detection and a
measurement of its amplitude and uncertainty were obtained by an a posteriori
Bayesian analysis based on a Monte Carlo Markov Chain approach. We applied our
method to the Sun and eight other stars for which previous spot modelling had
been performed to compare our results with previous ones. We find that
autocorrelation is a simple method for selecting stars with a coherent
rotational signal that is a prerequisite for successfully measuring
differential rotation through spot modelling. For a proper Monte Carlo Markov
Chain analysis, it is necessary to take the strong correlations among different
parameters that exist in spot modelling into account. For the planet-hosting
star Kepler-30, we derive a lower limit to the relative amplitude of the
differential rotation of \Delta P / P = 0.0523 \pm 0.0016. We confirm that the
Sun as a star in the optical passband is not suitable for measuring
differential rotation owing to the rapid evolution of its photospheric active
regions. In general, our method performs well in comparison to more
sophisticated and time-consuming approaches.Comment: Accepted to Astronomy and Astrophysics, 15 pages, 13 figures, 4
tables and an Appendi
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