1,341 research outputs found
B Physics: CP Violation Beyond the SM
We analyse the present experimental evidence for a complex CKM matrix, even
allowing for New Physics contributions to , %,
, , and the piece of and . We emphasize the crucial r\^{o}le played by
the angle in both providing irrefutable evidence for a 33
complex CKM matrix and placing constraints on the size of NP contributions. It
is shown that even if one allows for New Physics a real CKM matrix is excluded
at a 99.92% C.L., and the probability for the phase to be in the
interval is
99.7%. Large value of the phase , e.g. of order , is only
possible in models where the unitarity of the
Cabibbo-Kobayashi-Maskawa matrix is violated through the introduction of extra
quarks. We study the allowed range for and the effect of a
large on various low-energy observables, such as CP asymmetries in
meson decays. We also discuss the correlated effects which would be observable
at high energy colliders, like decays , etc..Comment: 14 pages, 7 figures. Presented at the Symposium in Honour of Gustavo
C. Branco "CP Violation and the Flavour Puzzle", Lisbon, Portugal, 19-20 July
2005. To appear in Acta Physica Polonica
Dynamical zeros in neutrino-electron elastic scattering at leading order
We show the existence of dynamical zeros in the helicity amplitudes for
neutrino-electron elastic scattering at lowest order in the standard theory. In
particular, the non-flip electron helicity amplitude in the
electron antineutrino process vanishes for an incident neutrino energy
and forward electrons (maximum recoil
energy). The rest of helicity amplitudes show kinematical zeros in this
configuration and therefore the cross section vanishes. Prospects to search for
neutrino magnetic moment are discussed.Comment: 9 pg.+ 2 figures (not included available upon request
Invariant approach to flavour-dependent CP-violating phases in the MSSM
We use a new weak basis invariant approach to classify all the observable
phases in any extension of the Standard Model (SM). We apply this formalism to
determine the invariant CP phases in a simplified version of the Minimal
Supersymmetric SM with only three non-trivial flavour structures. We propose
four experimental measures to fix completely all the observable phases in the
model. After these phases have been determined from experiment, we are able to
make predictions on any other CP-violating observable in the theory, much in
the same way as in the Standard Model all CP-violation observables are
proportional to the Jarlskog invariant.Comment: 25 pages, 12 figure
A Novel Kind of Neutrino Oscillation Experiment
A novel method to look for neutrino oscillations is proposed based on the
elastic scattering process , taking advantage of the dynamical zero present in the differential
cross section for . An
effective tunable experiment between the "appearance" and "disappearance"
limits is made possible. Prospects to exclude the allowed region for
atmospheric neutrino oscillations are given.Comment: 11 pages (+3 figures, available upon request),Standard Latex,
FTUV/94-3
Can one detect new physics in I=0 and/or I=2 contributions to the decays B --> pi pi?
We study the effects of new-physics contributions to B --> pi pi decays,
which can be parametrized as four new complex quantities. A simple analysis is
provided by utilizing the reparametrization invariance of the decay amplitudes.
We find that six quantities can be reabsorbed into the definitions of Standard
Model-like parameters. As a result, the usual isospin analysis provides only
two constraints on new physics which are independent of estimates for the
Standard Model contributions. In particular, we show that one is not sensitive
to new physics affecting the I=0 amplitudes. On the other hand, I=2 new physics
can be detected, and its parameters can be measured by using independent
determinations of the weak phases. We obtain constraints on these new-physics
parameters through a fit to the current experimental data.Comment: 8 pages, RevTe
Measurements of New Physics in B -> pi pi Decays
If new physics (NP) is present in B -> pi pi decays, it can affect the
isospin I=2 or I=0 channels. In this paper, we discuss various methods for
detecting and measuring this NP. The techniques have increasing amounts of
theoretical hadronic input. If NP is eventually detected in B -> pi pi -- there
is no evidence for it at present -- one will be able to distinguish I=2 and
I=0, and measure its parameters, using these methods.Comment: 24 pages, no figures, revte
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
Measure of the size of CP violation in extended models
In this letter we introduce a possible measure of the size of CP violation in
the Standard Model and its extensions, based on quantities invariant under the
change of weak quark basis. We also introduce a measure of the ``average size''
of CP violation in a model, which can be used to compare the size of CP
violation in models involving extra sequential or vector-like quarks, or
left-right symmetry.Comment: LaTeX, 7 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, 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
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