3,385 research outputs found
Flavour Physics and CP Violation in the Standard Model and Beyond
We present the invited lectures given at the Third IDPASC School which took
place in Santiago de Compostela in January 2013. The students attending the
school had very different backgrounds, some of them were doing their Ph.D. in
experimental particle physics, others in theory. As a result, and in order to
make the lectures useful for most of the students, we focused on basic topics
of broad interest, avoiding the more technical aspects of Flavour Physics and
CP Violation. We make a brief review of the Standard Model, paying special
attention to the generation of fermion masses and mixing, as well as to CP
violation. We describe some of the simplest extensions of the SM, emphasising
novel flavour aspects which arise in their framework.Comment: Invited talk at the Third IDPASC School 2013, January 21st - February
2nd 2013, Santiago de Compostela, Galiza, Spain; 36 pages, 8 figures, 2
tables; version with few misprints correcte
Spontaneous CP Violation in the Next-to-Minimal Supersymmetric Standard Model Revisited
We re-examine spontaneous CP violation at the tree level in the context of
the next-to-minimal supersymmetric standard model (NMSSM) with two Higgs
doublets and a gauge singlet field. We analyse the most general Higgs potential
without a discrete Z_3 symmetry, and derive an upper bound on the mass of the
lightest neutral Higgs boson consistent with present experimental data. We
investigate, in particular, its dependence on the admixture and CP-violating
phase of the gauge singlet field, as well as on tan(beta). To assess the
viability of the spontaneous CP violation scenario, we estimate epsilon_K by
applying the mass insertion approximation. We find that a non-trivial flavour
structure in the soft-breaking A terms is required to account for the observed
CP violation in the neutral kaon sector. Furthermore, combining the
minimisation conditions for spontaneous CP violation with the constraints
coming from K0-K0bar mixing, we find that the upper bound on the lightest
Higgs-boson mass becomes stronger. We also point out that the electric dipole
moments of electron and neutron are a serious challenge for SUSY models with
spontaneous CP violation.Comment: 19 pages, LaTeX2e, 5 figures; matches the published versio
Jarlskog-like invariants for theories with scalars and fermions
Within the framework of theories where both scalars and fermions are present,
we develop a systematic prescription for the construction of CP-violating
quantities that are invariant under basis transformations of those matter
fields. In theories with Spontaneous Symmetry Breaking, the analysis involves
the vevs' transformation properties under a scalar basis change, with a
considerable simplification of the study of CP violation in the scalar sector.
These techniques are then applied in detail to the two Higgs-doublet model with
quarks. It is shown that there are new invariants involving scalar-fermion
interactions, besides those already derived in previous analyses for the
fermion-gauge and scalar-gauge sectors.Comment: 12 pages, Latex, no figure
Higgs masses of the general 2HDM in the Minkowski-space formalism
We study the masses of the Higgs bosons in the most general two-Higgs-doublet
model in a basis-independent approach. We adapt the recently developed
Minkowski-space formalism to this problem and calculate traces of any power of
the mass-matrix in a compact and reparametrization-invariant form. Our results
can be used to gain insight into the dynamics of the scalar sector of the
general 2HDM.Comment: 14 pages, no figures; v2: reference added, misprints correcte
Small violations of unitarity, the phase in Bs mixing and visible t->cZ decays at the LHC
We show that it is possible to accommodate the observed size of the phase in
--, mixing in the framework of a model with violation of
unitarity. This violation is associated to the presence of a new
isosinglet quark , which mixes both with and and has a mass
not exceeding 500 GeV. The crucial point is the fact that this framework allows
for of order , to be
contrasted with the situation in the Standard Model, where is
constrained to be of order . We point out that this scenario implies
rare top decays at a rate observable at the LHC and
significantly different from unity. In this framework, one may also account for
the observed size of -- mixing without having to invoke long
distance contributions. It is also shown that in the present scenario, the
observed size of -- mixing constrains
to be of order
, which is significantly smaller than what is allowed in generic
models with violations of unitarity.Comment: 20 pages. References added. Additional observables considered,
updated numerical examples, conclusions unchange
Primary Antiphospholipid Syndrome: Pregnancy Outcome in a Portuguese Population
Introduction:Women with antiphospholipid syndrome(APS) may suffer from recurrent miscarriage, fetal death, fetal growth restriction (FGR), pre-eclampsia, placental abruption, premature delivery and thrombosis. Treatment with aspirin and
low molecular weight heparin (LMWH) combined
with close maternal-fetal surveillance can change these outcomes.
Objective: To assess maternal and perinatal outcome in a cohort of Portuguese women with primary APS.
Patients and Methods: A retrospective analysis of 51 women with primary APS followed in our institution (January 1994 to December 2007). Forty one(80.4%) had past pregnancy morbidity and 35.3%(n=18) suffered previous thrombotic events. In their past they had a total of 116 pregnancies of which
only 13.79 % resulted in live births. Forty four patients had positive anticardiolipin antibodies and 33 lupus anticoagulant. All women received treatment with low dose aspirin and LMWH.
Results: There were a total of 67 gestations (66 single and one multiple). The live birth rate was 85.1%(57/67) with 10 pregnancy failures: seven in the first and second trimesters, one late fetal death and two
medical terminations of pregnancy (one APS related).
Mean (± SD) birth weight was 2837 ± 812 g
and mean gestational age 37 ± 3.3 weeks. There were nine cases of FGR and 13 hypertensive complications(4 HELLP syndromes). 54.4% of the patients
delivered by caesarean section.
Conclusions: In our cohort, early treatment with aspirin and LMWH combined with close maternal-fetal surveillance was associated with a very high chance of a live newborn
Quark mixings and flavor changing interactions with singlet quarks
Aspects of the quark mixings and flavor changing interactions are
investigated in electroweak models with singlet quarks. The effects on the
ordinary quark mixing are determined in terms of the quark masses and the
parameters describing the mixing between the ordinary quarks q and the singlet
quarks Q (q-Q mixing). Some salient features arise in the flavor changing
interactions through the q-Q mixing. The unitarity of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix within the ordinary quark sector is
violated, and the flavor changing neutral currents (FCNC's) appear both in the
gauge and scalar couplings. The flavor changing interactions are calculated
appropriately in terms of the q-Q mixing parameters and the quark masses, which
really exhibit specific flavor structures. It is found that there are
reasonable ranges of the model parameters to reproduce the ordinary quark mass
hierarchy and the actual CKM structure even in the presence of q-Q mixing. Some
phenomenological effects of the singlet quarks are also discussed. In
particular, the scalar FCNC's may be more important in some cases, if the
singlet quarks as well as the extra scalar particles from the singlet Higgs
fields have masses 100 GeV -- 1 TeV.Comment: 32 pages, 7 figures, added reference
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