Flavour Changing Higgs Couplings in a Class of Two Higgs Doublet Models

We analyse various flavour changing processes like $t\to hu,hc$, $h\to \tau e,\tau\mu$ as well as hadronic decays $h\to bs,bd$, in the framework of a class of two Higgs doublet models where there are flavour changing neutral scalar currents at tree level. These models have the remarkable feature of having these flavour-violating couplings entirely determined by the CKM and PMNS matrices as well as $\tan\beta$. The flavour structure of these scalar currents results from a symmetry of the Lagrangian and therefore it is natural and stable under the renormalization group. We show that in some of the models the rates of the above flavour changing processes can reach the discovery level at the LHC at 13 TeV even taking into account the stringent bounds on low energy processes, in particular $\mu\to e\gamma$.Comment: 33 pages, 8 figures; matches version accepted for publicatio

Leptonic Invariants, Neutrino Mass-Ordering and the Octant of θ23\theta_{23}

We point out that leptonic weak-basis invariants are an important tool for the study of the properties of lepton flavour models. In particular, we show that appropriately chosen invariants can give a clear indication of whether a particular lepton flavour model favours normal or inverted hierarchy for neutrino masses and what is the octant of $\theta_{23}$. These invariants can be evaluated in any conveniently chosen weak-basis and can also be expressed in terms of neutrino masses, charged lepton masses, mixing angles and CP violation phases.Comment: 10 pages, no figure

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 $(1,1)$ entries. We show that non-factorizable phases are important in order to generate a sufficiently large $\sin 2 \beta$. 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

Yukawa Textures, New Physics and Nondecoupling

We point out that New Physics can play an important r\^ ole in rescuing some of the Yukawa texture zero ans\" atze which would otherwise be eliminated by the recent, more precise measurements of $V_{CKM}$. As an example, a detailed analysis of a four texture zero ansatz is presented, showing how the presence of an isosinglet vector-like quark which mixes with standard quarks, can render viable this Yukawa texture. The crucial point is the nondecoupling of the effects of the isosinglet quark, even for arbitrary large values of its mass.Comment: 13 pages, no figure

What if the Masses of the First Two Quark Families are not Generated by the Standard Higgs?

We point out that, in the context of the SM, $|V^2_{13}| + | V^2_{23}|$ is expected to be large, of order one. The fact that $|V^2_{13}| + |V^2_{23}| \approx 1.6 \times 10^{-3}$ motivates the introduction of a symmetry S which leads to $V_{CKM} ={1\>\!\!\!\mathrm{I}}$, with only the third generation of quarks acquiring mass. We consider two scenarios for generating the mass of the first two quark generations and full quark mixing. One consists of the introduction of a second Higgs doublet which is neutral under S. The second scenario consists of assuming New Physics at a high energy scale , contributing to the masses of light quark generations, in an effective field theory approach. This last scenario leads to couplings of the Higgs particle to $s\overline s$ and $c \overline c$ which are significantly enhanced with respect to those of the SM. In both schemes, one has scalar-mediated flavour- changing neutral currents which are naturally suppressed. Flavour violating top decays are predicted in the second scenario at the level \mbox{Br} (t \rightarrow h c ) \geq 5\times 10^{-5}.Comment: 11 pages, 1 figur

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 $|U_{13}|$, when compared to the other elements of $U_{PMNS}$, 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 $|U_{13}|$ 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

Vector-like Quarks at the Origin of Light Quark Masses and Mixing

We show how a novel fine-tuning problem present in the Standard Model can be solved through the introduction of a single flavour symmetry G, together with three $Q = - 1/3$ quarks, three $Q = 2/3$ quarks, as well as a complex singlet scalar. The symmetry G is extended to the additional fields and it is an exact symmetry of the Lagrangian, only spontaneously broken by the vacuum. Specific examples are given and a phenomenological analysis of the main features of the model is presented. It is shown that even for vector-like quarks with masses accessible at the LHC, one can have realistic quark masses and mixing, while respecting the strict constraints on process arising from flavour changing neutral currents (FCNC). The vector-like quark decay channels are also described.Comment: 25 pages, no figure

On the backreaction of frame dragging

The backreaction on black holes due to dragging heavy, rather than test, objects is discussed. As a case study, a regular black Saturn system where the central black hole has vanishing intrinsic angular momentum, J^{BH}=0, is considered. It is shown that there is a correlation between the sign of two response functions. One is interpreted as a moment of inertia of the black ring in the black Saturn system. The other measures the variation of the black ring horizon angular velocity with the central black hole mass, for fixed ring mass and angular momentum. The two different phases defined by these response functions collapse, for small central black hole mass, to the thin and fat ring phases. In the fat phase, the zero area limit of the black Saturn ring has reduced spin j^2>1, which is related to the behaviour of the ring angular velocity. Using the `gravitomagnetic clock effect', for which a universality property is exhibited, it is shown that frame dragging measured by an asymptotic observer decreases, in both phases, when the central black hole mass increases, for fixed ring mass and angular momentum. A close parallelism between the results for the fat phase and those obtained recently for the double Kerr solution is drawn, considering also a regular black Saturn system with J^{BH}\neq 0.Comment: 18 pages, 8 figure

An unusual presentation of osteogenesis imperfecta type I

Marta Rebelo, Jandira Lima, José Diniz Vieira, José Nascimento CostaDepartment of Internal Medicine, University Hospital of Coimbra, Coimbra, PortugalAbstract: Osteogenesis imperfecta (OI) is a rare inherited disorder with a broad spectrum of clinical and genetic variability. The genetic diversity involves, in the majority of the cases, mutations in one of the genes that encodes the type 1 collagen protein (COL1 A1 and COL1 A2), but it is not a requirement for the diagnosis. The most benign form is OI type I. The authors present a case report of a 25-year-old woman who had severe low back pain associated with incapacity to walk and breast-feed post-partum. Symptoms developed 2 weeks after delivery. The radiological examination revealed severe osteoporosis with no abnormalities in the laboratory findings. The clinical signs and a positive personal and family history of multiple fractures in childhood suggested OI type I, although other diagnosis, such as pregnancy-associated osteoporosis, was also considered. The atypical presentation of this rare disorder in adulthood calls attention to the need for early diagnosis for prompt treatment. Treatment of OI is never curative, but it improves the quality of the patient’s life.Keywords: osteogenesis imperfecta, collagen, pregnancy, osteoporosi