We discuss theoretical and phenomenological aspects of two-Higgs-doublet extensions of the Standard Model. In general, these extensions have scalar mediated flavour changing neutral currents which ...are strongly constrained by experiment. Various strategies are discussed to control these flavour changing scalar currents and their phenomenological consequences are analysed. In particular, scenarios with natural flavour conservation are investigated, including the so-called type I and type II models as well as lepton-specific and inert models. Type III models are then discussed, where scalar flavour changing neutral currents are present at tree level, but are suppressed by either a specific ansatz for the Yukawa couplings or by the introduction of family symmetries leading to a natural suppression mechanism. We also consider the phenomenology of charged scalars in these models. Next we turn to the role of symmetries in the scalar sector. We discuss the six symmetry-constrained scalar potentials and their extension into the fermion sector. The vacuum structure of the scalar potential is analysed, including a study of the vacuum stability conditions on the potential and the renormalization-group improvement of these conditions is also presented. The stability of the tree level minimum of the scalar potential in connection with electric charge conservation and its behaviour under CP is analysed. The question of CP violation is addressed in detail, including the cases of explicit CP violation and spontaneous CP violation. We present a detailed study of weak basis invariants which are odd under CP. These invariants allow for the possibility of studying the CP properties of any two-Higgs-doublet model in an arbitrary Higgs basis. A careful study of spontaneous CP violation is presented, including an analysis of the conditions which have to be satisfied in order for a vacuum to violate CP. We present minimal models of CP violation where the vacuum phase is sufficient to generate a complex CKM matrix, which is at present a requirement for any realistic model of spontaneous CP violation.
We analyse various flavour-changing processes like
t
→
h
u
,
h
c
,
h
→
τ
e
,
τ
μ
as well as hadronic decays
h
→
b
s
,
b
d
, 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
β
. The flavour structure of these scalar currents results from a symmetry of the Lagrangian and therefore it is natural and stable under the renormalisation 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
μ
→
e
γ
.
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•Zirconia dental pieces were produced by robocasting (AM) and subtractive manufacturing (SM).•AM samples revealed to be biologically safe and present adequate properties.•AM samples ...are more porous, less hard and tough and more hydrophilic than SM samples.•Although both samples do not suffer wear on chewing simulation, cusps wear less against AM.•Glazing of both samples led to a dramatic increase of the antagonist cusps wear.
The main goal of this work is to evaluate the suitability of nanostructured zirconia pieces obtained by robocasting additive manufacturing (AM), for dental applications.
The density, crystalline structure, morphology/porosity, surface roughness, hardness, toughness, wettability and biocompatibility of the produced samples were compared with those of samples obtained by conventional subtractive manufacturing (SM) of a similar commercial zirconia material. Chewing simulation studies were carried out against dental human cusps in artificial saliva. The wear of the material was quantified and the wear mechanisms investigated, as well as the influence of glaze coating.
AM samples, that revealed to be biocompatible, are slightly less dense and more porous than SM samples, showing lower hardness, toughness and wettability than SM samples. After chewing tests, no wear was found both on AM and SM samples. However, the dental wear was significantly lower when AM samples were used as counterbody. Concerning the glazed samples, both coated surfaces and dental cusps suffered wear, being the cusps’ wear higher than that found for unglazed samples. More, cusps tested against AM coated samples suffered less wear comparatively to those opposed to SM coated samples.
Overall, the results presented in this paper show that AM processed nanostructured zirconia can be used in dental restorations, with important advantages from the point of view of processing and tribological performance. Moreover, the option for glaze finishing should be carefully considered both in SM and AM processed specimens.
Leptonic CP violation Branco, G C; Felipe, R G; Joaquim, FR
Reviews of modern physics,
04/2012, Letnik:
84, Številka:
2
Journal Article
Recenzirano
This article surveys the theoretical origins and experimental implications of possible CP violation in the lepton sector. The formalism for CP violation and its possible relation to neutrino masses ...are described. Experimental and observational constraints and possibilities involving neutrino oscillations, neutrinoless double beta decay, rare decays of charged leptons, nonunitary effects induced by heavy decoupled particles, and the possible collider signatures of the doubly charged scalars found in some theories are discussed. Finally, the possible explanation of the cosmological baryon asymmetry by the leptogenesis mechanism is reviewed. This article surveys the theoretical origins and experimental implications of possible CP violation in the lepton sector. The formalism for CP violation and its possible relation to neutrino masses are described. Experimental and observational constraints and possibilities involving neutrino oscillations, neutrinoless double beta decay, rare decays of charged leptons, nonunitary effects induced by heavy decoupled particles, and the possible collider signatures of the doubly charged scalars found in some theories are discussed. Finally, the possible explanation of the cosmological baryon asymmetry by the leptogenesis mechanism is reviewed.
A
bstract
We point out that hints of deviations from unitarity in the first row of the CKM matrix may be explained by the presence of a single vector-like top. We study how the stringent experimental ...constraints arising from CP Violation in the kaon sector and from meson mixing such as
D
0
‐
D
¯
0
,
K
0
‐
K
¯
0
and
B
d
,
s
0
‐
B
¯
d
,
s
0
can be satisfied in the proposed framework. In order for the deviations from unitarity to be of the required size while keeping the theory perturbative, the new top quark should have a mass
m
T
≲ 7 TeV which could be probed in upcoming experiments at the energy frontier.
Type-I seesaw with eV-scale neutrinos Branco, G. C.; Penedo, J. T.; Pereira, Pedro M. F. ...
The journal of high energy physics,
07/2020, Letnik:
2020, Številka:
7
Journal Article
Recenzirano
Odprti dostop
A
bstract
We consider seesaw type-I models including at least one (mostly-)sterile neutrino with mass at the eV scale. Three distinct situations are found, where the presence of light extra neutrinos ...is naturally justified by an approximately conserved lepton number symmetry. To analyse these scenarios consistently, it is crucial to employ an exact parametrisation of the full mixing matrix. We provide additional exact results, including generalised versions of the seesaw relation and of the Casas-Ibarra parametrisation, valid for every scale of seesaw. We find that the existence of a light sterile neutrino imposes an upper bound on the lightest neutrino mass. We further assess the impact of light sterile states on short- and long-baseline neutrino oscillation experiments, emphasise future detection prospects, and address CP Violation in this framework via the analysis of CP asymmetries and construction of weak basis invariants. The proposed models can accommodate enough active-sterile mixing to play a role in the explanation of short-baseline anomalies.
Does quark mixing play a role in the lepton sector? Albergaria, Francisco; Branco, G. C.; Bastos, José Filipe ...
European physical journal. C, Particles and fields,
06/2024, Letnik:
84, Številka:
6
Journal Article
Recenzirano
Odprti dostop
We suggest a simple relation between the quark and the lepton mixing within the framework of type-I seesaw mechanism. We show that within our ansatz the empirical King–Mohapatra–Smirnov relation, ...which suggests a connection between the CKM and PMNS mixing where
|
V
13
PMNS
|
≈
sin
θ
C
/
2
, can be derived. This is possible within a restricted region of the Dirac and Majorana mass parameters.
We point out that in the standard model there is meaningful quark mixing even in the extreme chiral (EC) limit, where only the third generation of quarks acquires mass. This mixing is in general ...expected to be of order 1 and the fact that |V13|2+|V23|2≈1.6×10−3 implies a novel fine-tuning problem in the SM which we point out for the first time. We propose a possible way of avoiding this fine-tuning by introducing a symmetry S which leads to VCKM=1, 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 based on the assumption that the masses of the first two quark families are not generated by the standard Higgs. 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 ss¯ and cc¯ which are significantly enhanced with respect to those of the SM. In both schemes, one has scalar-mediated flavor-changing neutral currents which are naturally suppressed. Flavor-violating top decays are predicted in the second scenario at the level Br(t→hc)≥5×10−5.
We show how a novel fine-tuning problem present in the Standard Model can be solved through the introduction of a
Z
6
flavour symmetry, together with three
Q
=
-
1
/
3
quarks, three
Q
=
2
/
3
quarks, ...as well as a complex singlet scalar. The
Z
6
symmetry is extended to the additional fields and it is an exact symmetry of the Lagrangian, only softly broken in the scalar potential, in order to avoid the domain-wall problem. 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 processes arising from flavour changing neutral currents. The vector-like quark decay channels are also described.
We put forward the conjecture that the small numbers in the
V
CKM
matrix, are generated by physics beyond the Standard Model. We identify as small numbers
V
ub
and the strength of CP violation, ...measured by
|
Im
Q
|
, where
Q
stands for a rephasing invariant quartet of
V
CKM
. We illustrate how the conjecture can be realised in the context of an extension of the Standard Model where an up-type vector-like quark is introduced leading to a realistic spectrum of quark masses and an effective
V
CKM
in agreement with experiment.
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