933 research outputs found
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
Hierarchical Quark Mass Matrices
I define a set of conditions that the most general hierarchical Yukawa mass
matrices have to satisfy so that the leading rotations in the diagonalization
matrix are a pair of (2,3) and (1,2) rotations. In addition to Fritzsch
structures, examples of such hierarchical structures include also matrices with
(1,3) elements of the same order or even much larger than the (1,2) elements.
Such matrices can be obtained in the framework of a flavor theory. To leading
order, the values of the angle in the (2,3) plane (s_{23}) and the angle in the
(1,2) plane (s_{12}) do not depend on the order in which they are taken when
diagonalizing. We find that any of the Cabbibo-Kobayashi-Maskawa matrix
parametrizations that consists of at least one (1,2) and one (2,3) rotation may
be suitable. In the particular case when the s_{13} diagonalization angles are
sufficiently small compared to the product s_{12}s_{23}, two special CKM
parametrizations emerge: the R_{12}R_{23}R_{12} parametrization follows with
s_{23} taken before the s_{12} rotation, and vice versa for the
R_{23}R_{12}R_{23} parametrization.Comment: LaTeX, 19 pages. References added, minor changes in text. Version
published in Phys. Rev.
Hierarchy and Up-Down Parallelism of Quark Mass Matrices
In view of the quark mass hierarchy and in the assumption of the up-down
parallelism, we derive two phenomenologically-favored patterns of Hermitian
quark mass matrices from the quark flavor mixing matrix. We compare one of them
with two existing {\it Anstze} proposed by Rosner and Worah and by
Roberts {\it et al}, and find that only the latter is consistent with the
present experimental data.Comment: RevTex 9 pages. Accepted for publication in Phys. Rev.
The see-saw mechanism: neutrino mixing, leptogenesis and lepton flavor violation
The see-saw mechanism to generate small neutrino masses is reviewed. After
summarizing our current knowledge about the low energy neutrino mass matrix we
consider reconstructing the see-saw mechanism. Low energy neutrino physics is
not sufficient to reconstruct see-saw, a feature which we refer to as ``see-saw
degeneracy''. Indirect tests of see-saw are leptogenesis and lepton flavor
violation in supersymmetric scenarios, which together with neutrino mass and
mixing define the framework of see-saw phenomenology. Several examples are
given, both phenomenological and GUT-related. Variants of the see-saw mechanism
like the type II or triplet see-saw are also discussed. In particular, we
compare many general aspects regarding the dependence of LFV on low energy
neutrino parameters in the extreme cases of a dominating conventional see-saw
term or a dominating triplet term. For instance, the absence of mu -> e gamma
or tau -> e gamma in the pure triplet case means that CP is conserved in
neutrino oscillations. Scanning models, we also find that among the decays mu
-> e gamma, tau -> e gamma and tau -> mu gamma the latter one has the largest
branching ratio in (i) SO(10) type I see-saw models and in (ii) scenarios in
which the triplet term dominates in the neutrino mass matrix.Comment: 26 pages, 7 figures. Expanded version of talk given at 10th Workshop
In High Energy Physics Phenomenology (WHEPP 10), January 2008, Chennai,
India. Typos corrected, comments and references adde
SO(10) GUT and Quark-Lepton Mass Matrices
The phenomenological model that all quark and lepton mass matrices have the
same zero texture, namely their (1,1), (1,3) and (3,1) components are zeros, is
discussed in the context of SO(10) Grand Unified Theories (GUTs). The mass
matrices of type I for quarks are consistent with the experimental data in the
quark sector. For the lepton sector, consistent fitting to the data of neutrino
oscillation experiments force us to use the mass matrix for the charged leptons
which is slightly deviated from type I. Given quark masses and charged lepton
masses, the model includes 19 free parameters, whereas the SO(10) GUTs gives 16
constrained equations. Changing the remaining three parameters freely, we can
fit all the entries of the CKM quark mixing matrix and the MNS lepton mixing
matrix, and three neutrino masses consistently with the present experimental
data.Comment: 32pp, REV TeX, 12 EPS Figure
D^0-\bar{D}^0 Mixing and CP Violation in Neutral D-meson Decays
D^0-\bar{D}^0 mixing at the detectable level or significant CP violation in
the charm system may strongly signify the existence of new physics. In view of
the large discovery potential associated with the fixed target experiments, the
B-meson factories and the \tau-charm factories, we make a further study of the
phenomenology of D^0-\bar{D}^0 mixing and CP violation in neutral -meson
decays. The generic formulas for the time-dependent and time-integrated decay
rates of both coherent and incoherent D^0\bar{D}^0 events are derived, and
their approximate expressions up to the second order of the mixing parameters
x_D and y_D are presented. Explicitly we discuss D^0-\bar{D}^0 mixing and
various CP-violating signals in neutral D decays to the semileptonic final
states, the hadronic CP eigenstates, the hadronic non-CP eigenstates and the
CP-forbidden states. A few non-trivial approaches to the separate determination
of x_D and y_D and to the demonstration of direct and indirect CP asymmetries
in the charm sector are suggested.Comment: Latex 42 pages (including 6 PS figures). Minor changes: a) the more
popular notation for D^0-\bar{D}^0 mixing is adopted; b) the possibility to
test CPT symmetry in D^0-\bar{D}^0 system is not overrated. The present
version is going to appear in Phys. Rev. D 1 (January 1997
Texture zeros for the standard model Quark mass matrices
ABSTRACT: A way of counting free parameters in the quark mass matrices of the standard model, including the constraints coming from weak basis transformations, is presented; this allow to understand the exact physical meaning of the parallel and non-parallel texture zeros which appear in some “ans¨atz” of the 3 × 3 quark mass matrices, including the CP violation phenomena in the analysis, it is shown why the six texture zeros are ruled out. Finally, a five texture zeros “ans¨atze”which properly copes with all experimental constrains, including the angles of the unitary triangle, is presented
Yet Another Extension of the Standard Model: Oases in the Desert?
We have searched for conceptually simple extensions of the standard model,
and describe here a candidate model which we find attractive. Our starting
point is the assumption that off-diagonal CKM mixing matrix elements are
directly related by lowest order perturbation theory to the quark mass
matrices. This appears to be most easily and naturally implemented by assuming
that all off-diagonal elements reside in the down-quark mass matrix. This
assumption is in turn naturally realized by introducing three generations of
heavy, electroweak-singlet down quarks which couple to the Higgs sector
diagonally in flavor, while mass-mixing off-diagonally with the light
down-quarks. Anomaly cancellation then naturally leads to inclusion of
electroweak vector-doublet leptons. It is then only a short step to completing
the extension to three generations of fundamental representations of E(6).
Assuming only that the third generation B couples to the Higgs sector at least
as strongly as does the top quark, the mass of the B is roughly estimated to
lie between 1.7 TeV and 10 TeV, with lower-generation quarks no heavier. The
corresponding guess for the new leptons is a factor two lower. Within the
validity of the model, flavor and CP violation are ``infrared'' in nature,
induced by semi-soft mass mixing terms, not Yukawa couplings. If the Higgs
couplings of the new quarks are flavor symmetric, then there necessarily must
be at least one ``oasis'' in the desert, induced by new radiative corrections
to the top quark and Higgs coupling constants, and roughly at 1000 TeV.Comment: LaTex, 40 page
Model for fermion mass matrices and the origin of quark-lepton symmetry
Several phenomenological features of fermion masses and mixings can be
accounted for by a simple model for fermion mass matrices, which suggests an
underlying U(2) horizontal symmetry. In this context, it is also proposed how
an approximate quark-lepton symmetry can be achieved without unified gauge
theories.Comment: 12 pages, RevTex. Minor changes, some references adde
Leptogenesis in Neutrino Textures with Two Zeros
The leptogenesis is studied in the neutrino textures with two zeros, which
reduce the number of independent phases of the CP violation. The
phenomenological favored neutrino textures with two zeros are decomposed into
the Dirac neutrino mass matrix and the right-handed Majorana one in the see-saw
mechanism. Putting the condition to suppress the decay
enough, the texture zeros of the Dirac neutrino mass matrix are fixed in the
framework of the MSSM with right-handed neutrinos. These textures have only one
CP violatig phase. The magnitude of each entry of the Dirac mass matrix is
determined in order to explain the baryon asymmetry of the universe by solving
the Boltzman equations. The relation between the leptogenesis and the low
energy CP violation is presented in these textures.Comment: Latex file with 20 pages, 6 eps figure
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