796 research outputs found
Relating the scalar flavour-changing neutral couplings to the CKM matrix
We build a class of two-Higgs-doublet models in which the flavour-changing
couplings of the neutral scalars are related in an exact way to elements of the
quark mixing matrix. In this framework, we explore the different possibilities
for CP violation and find some interesting scenarios, like a realization of the
superweak idea without CP violation in the -meson system. In another
scenario the neutral scalars can be relatively light, and their contributions
to the -- transitions can alter the standard-model predictions
for CP violation in that system.Comment: 12 pages LATEX, no figure
Mixing in the Presence of Isosinglet Quarks
We analyse transitions in the framework of a minimal extension
of the Standard Model where either a or a isosinglet quark is
added to the standard quark spectrum. In the case of a isosinglet
quark, it is shown that there is a significant region of parameter space where
mixing is sufficiently enhanced to be observed at the next
round of experiments. On the contrary, in the case of a isosinglet
quark, it is pointed out that obtaining a substancial enhancement of mixing, while complying with the experimental constraints on rare
kaon decays, requires a contrived choice of parameters.Comment: 10 pages plus four figures. The figures are not included but are
available upon reques
Embedding Phenomenological Quark-Lepton Mass Matrices into SU(5) Gauge Models
We construct phenomenological quark-lepton mass matrices based on S
permutation symmetry in a manner fully compatible with SU(5) grand unification.
The Higgs particles we need are {\bf 5}, {\bf 45} and their conjugates. The
model gives a charge 1/3 quark vs charged lepton mass relation, and also a
good fit to mass-mixing relations for the quark sector, as well as an
attractive mixing pattern for the lepton sector, explaining a large mixing
angle between and , and either large or small
mixing angle, depending on the choice of couplings, consistent
with the currently accepted solutions to the solar neutrino problem.Comment: 12 pages, LaTex file, no figure
CP Violation from Dimensional Reduction: Examples in 4+1 Dimensions
We provide simple examples of the generation of complex mass terms and hence
CP violation through dimensional reduction.Comment: 6 pages, typos corrected, 1 reference adde
CP--Violating Invariants in Supersymmetry
I study the weak basis CP-violating invariants in supersymmetric models, in
particular those which cannot be expressed in terms of the Jarlskog--type
invariants, and find basis--independent conditions for CP conservation. With an
example of the K-anti-K mixing, I clarify what are the combinations of
supersymmetric parameters which are constrained by experiment.Comment: matches the PRD versio
Vacuum Stability Higgs Mass Bound Revisited with Implications for Extra Dimension Theories
We take the standard model to be an effective theory including higher
dimensional operators suppressed by scale and re-examine the higgs
mass bounds from the requirements of vacuum stability. Our results show that
the effects of the higher dimensional operators on the higgs mass limits are
significant. As an implication of our results, we study the vacuum stability
higgs mass bounds in theories with extra dimensions.Comment: Latex, 14 pages, 1 figure. Added references. To appear in Phys. Rev.
CP-Violating Observables in Tagged -- Decays
We perform a systematic study of CP-violating observables in \ddbar\ decays.
We show that given a final state, which may be a CP eigenstate or not, all the
observables can in principle be measured if decay-time information is available
and if, for CP non-eigenstates, both decay rates into and are
considered. As an illustration of our analysis we discuss an effective
superweak scenario.Comment: 9 pages LATEX, no figure
Minimal Flavour Violation and Multi-Higgs Models
We propose an extension of the hypothesis of Minimal Flavour Violation (MFV)
to general multi-Higgs Models without the assumption of Natural Flavour
Conservation in the Higgs sector. We study in detail under what conditions the
neutral Higgs couplings are only functions of and propose a MFV
expansion for the neutral Higgs couplings to fermions.Comment: 16 pages, no figures. References adde
Modeling transport through single-molecule junctions
Non-equilibrium Green's functions (NEGF) formalism combined with extended
Huckel (EHT) and charging model are used to study electrical conduction through
single-molecule junctions. Analyzed molecular complex is composed of asymmetric
1,4-Bis((2'-para-mercaptophenyl)-ethinyl)-2-acetyl-amino-5-nitro-benzene
molecule symmetrically coupled to two gold electrodes [Reichert et al., Phys.
Rev. Lett. Vol.88 (2002), pp. 176804]. Owing to this model, the accurate values
of the current flowing through such junction can be obtained by utilizing basic
fundamentals and coherently deriving model parameters. Furthermore, the
influence of the charging effect on the transport characteristics is
emphasized. In particular, charging-induced reduction of conductance gap,
charging-induced rectification effect and charging-generated negative value of
the second derivative of the current with respect to voltage are observed and
examined for molecular complex.Comment: 8 pages, 3 figure
Bi-large Neutrino Mixing and Mass of the Lightest Neutrino from Third Generation Dominance in a Democratic Approach
We show that both small mixing in the quark sector and large mixing in the
lepton sector can be obtained from a simple assumption of universality of
Yukawa couplings and the right-handed neutrino Majorana mass matrix in leading
order. We discuss conditions under which bi-large mixing in the lepton sector
is achieved with a minimal amount of fine-tuning requirements for possible
models. From knowledge of the solar and atmospheric mixing angles we determine
the allowed values of sin \theta_{13}. If embedded into grand unified theories,
the third generation Yukawa coupling unification is a generic feature while
masses of the first two generations of charged fermions depend on small
perturbations. In the neutrino sector, the heavier two neutrinos are model
dependent, while the mass of the lightest neutrino in this approach does not
depend on perturbations in the leading order. The right-handed neutrino mass
scale can be identified with the GUT scale in which case the mass of the
lightest neutrino is given as (m_{top}^2/M_{GUT}) sin^2 \theta_{23} sin^2
\theta_{12} in the limit sin \theta_{13} = 0. Discussing symmetries we make a
connection with hierarchical models and show that the basis independent
characteristic of this scenario is a strong dominance of the third generation
right-handed neutrino, M_1, M_2 < 10^{-4} M_3, M_3 = M_{GUT}.Comment: typos correcte
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