1,597 research outputs found
Flavour Changing Higgs Couplings in a Class of Two Higgs Doublet Models
We analyse various flavour changing processes like , as well as hadronic decays , 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 . 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 .Comment: 33 pages, 8 figures; matches version accepted for publicatio
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
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, is
expected to be large, of order one. The fact that motivates the introduction of a symmetry S which
leads to , 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
and 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
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 quarks, three 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
Reparametrization invariance of B decay amplitudes and implications for new physics searches in B decays
When studying B decays within the Standard Model, it is customary to use the
unitarity of the CKM matrix in order to write the decay amplitudes in terms of
only two of the three weak phases which appear in the various diagrams.
Occasionally, it is mentioned that those two weak phases can be used in order
to describe any decay amplitude, even beyond the Standard Model. Here we point
out that, when describing a generic decay amplitude, the two weak phases can be
chosen completely at will, and we study the behavior of the decay amplitudes
under changes in the two weak phases chosen as a basis. Of course, physical
observables cannot depend on such reparametrizations. This has an impact in
discussions of the SM and in attempts to parametrize new physics effects in the
decay amplitudes. We illustrate these issues by looking at B --> psi K_S and
the isospin analysis in B --> pi pi.Comment: 16 pages, RevTe
Bounds on gamma from CP violation measurements in B -> pi+ pi- and B -> psi K_S
We study the determination of gamma from CP-violating observables in B -> pi+
pi- and B -> psi K_S. This determination requires theoretical input to one
combination of hadronic parameters. We show that a mild assumption about this
quantity may allow bounds to be placed on gamma, but we stress the pernicious
effects that an eightfold discrete ambiguity has on such an analysis. The
bounds are discussed as a function of the direct (C) and interference (S)
CP-violating observables obtained from time-dependent B -> pi+ pi- decays, and
their behavior in the presence of new physics effects in B-Bbar mixing is
studied. (V2: Misprints corrected. Slightly improved discussion.)Comment: 11 pages, RevTex 4, 5 eps figures include
Squamation and ecology of thelodonts
Thelodonts are an enigmatic group of Paleozoic jawless vertebrates that have been well studied from taxonomical, biostratigraphic and paleogeographic points of view, although our knowledge of their ecology and mode of life is still scant. Their bodies were covered by micrometric scales whose morphology, histology and the developmental process are extremely similar to those of extant sharks. Based on these similarities and on the well-recognized relationship between squamation and ecology in sharks, here we explore the ecological diversity and lifestyles of thelodonts. For this we use classic morphometrics and discriminant analysis to characterize the squamation patterns of a significant number of extant shark species whose ecology is well known. Multivariate analyses have defined a characteristic squamation pattern for each ecological group, thus establishing a comparative framework for inferring lifestyles in thelodonts. We then use this information to study the squamation of the currently described 147 species of thelodonts, known from both articulated and disarticulated remains. Discriminant analysis has allowed recognizing squamation patterns comparable to those of sharks and links them to specific ecological groups. Our results suggest a remarkable ecological diversity in thelodonts. A large number of them were probably demersal species inhabiting hard substrates, within caves and crevices in rocky environments or reefs, taking advantage of the flexibility provided by their micromeric squamations. Contrary to classical interpretations, only few thelodonts were placed among demersal species inhabiting sandy and muddy substrates. Schooling species with defensive scales against ectoparasites could be also abundant suggesting that social interactions and pressure of ectoparasites were present in vertebrates as early the Silurian. The presence of species showing scales suggestive of low to moderate speed and a lifestyle presumably associated with open water environments indicates adaptation of thelodonts to deep water habitats. Scale morphology suggests that some other thelodonts were strong-swimming pelagic species, most of them radiating during the Early Devonian in association with the Nekton Revolution
Tree-level flavor-changing neutral currents in the B system: From CP asymmetries to rare decays
Tree-level flavor-changing neutral currents (FCNC) are characteristic of models with extra vectorlike quarks. These new couplings can strongly modify the B/sup 0/ CP asymmetries without conflicting with low-energy constraints. In the light of low CP asymmetry in B to J/ psi K/sub S/, we discuss the implications of these contributions. We find that even these low values can be easily accommodated in these models. Furthermore, we show that the new data from B factories tend to favor an O(20) enhancement of the b to dll transition over the SM expectation. (25 refs)
Supernova Neutrino Oscillations
Observing a high-statistics neutrino signal from a galactic supernova (SN)
would allow one to test the standard delayed explosion scenario and may allow
one to distinguish between the normal and inverted neutrino mass ordering due
to the effects of flavor oscillations in the SN envelope. One may even observe
a signature of SN shock-wave propagation in the detailed time-evolution of the
neutrino spectra. A clear identification of flavor oscillation effects in a
water Cherenkov detector probably requires a megatonne-class experiment.Comment: Proc. 129 Nobel Symposium "Neutrino Physics", 19-24 Aug 2004, Swede
How sensitive to FCNC can CP asymmetries be?
We show that the study of CP asymmetries in neutral B-meson decays provides a
very sensitive probe of flavour-changing neutral currents (FCNC). We introduce
two new angles, and , whose main feature is that they
can be readily obtained from the measurement of the CP asymmetries , and the ratio , providing a quantitative test of the
presence of new physics in a model-independent way.
Assuming that new physics is due to the presence of an isosinglet down-type
quark, we indicate how to reconstruct the unitarity quadrangles and point out
that the measurements of the above asymmetries, within the expected
experimental errors, may detect FCNC effects, even for values of at the level of a few times .Comment: 19 pages including 9 figure
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