2,089 research outputs found
The B -> pi K Puzzle and its Relation to Rare B and K Decays
The Standard-Model interpretation of the ratios of charged and neutral B-> pi
K rates, R_c and R_n, respectively, points towards a puzzling picture. Since
these observables are affected significantly by colour-allowed electroweak (EW)
penguins, this ``B -> pi K puzzle'' could be a manifestation of new physics in
the EW penguin sector. Performing the analysis in the R_n-R_c plane, which is
very suitable for monitoring various effects, we demonstrate that we may, in
fact, move straightforwardly to the experimental region in this plane through
an enhancement of the relevant EW penguin parameter q. We derive analytical
bounds for q in terms of a quantity L, that measures the violation of the
Lipkin sum rule, and point out that strong phases around 90 deg are favoured by
the data, in contrast to QCD factorisation. The B -> pi K modes imply a
correlation between q and the angle gamma that in the limit of negligible
rescattering effects and colour suppressed EW penguins depends only on the
value of L. Concentrating on a minimal flavour-violating new-physics scenario
with enhanced Z^0 penguins, we find that the current experimental values on
B -> X_s mu^+ mu^- require roughly L pi K data give L =
5.7 +- 2.4, L has either to move to smaller values once the B -> pi K data
improve or new sources of flavour and CP violation are needed. In turn, the
enhanced values of L seen in the B -> pi K data could be accompanied by
enhanced branching ratios for rare decays. Most interesting turns out to be the
correlation between the B -> pi K modes and BR(K^+ -> pi^+ nu nu), with the
latter depending approximately on a single ``scaling'' variable \bar L= L
(|V_{ub}/V_{cb}|/0.086)^2.3.Comment: 19 pages, 7 figures, a few typos corrected and two references adde
The B -> pi pi, pi K Puzzles: Implications for Hadron Physics, New Physics and Rare Decays
The B-meson system is an interesting probe for the exploration of strong
interactions, the quark-flavour sector of the Standard Model, and the search
for new physics. In this programme, non-leptonic B decays, which are
particularly challenging from the point of view of QCD, play a key role. After
discussing strategies to deal with the corresponding hadronic matrix elements
of four-quark operators and popular avenues for new physics to manifest itself
in B decays, we focus on puzzling patterns in the B-factory data for B -> pi
pi, pi K decays; we explore their implications for hadron physics, new physics
and rare K and B decays.Comment: 10 pages, 2 figures, plenary talk at the International Conference on
QCD and Hadronic Physics, Peking University, Beijing, China, 16-20 June 2005,
to appear in the Proceeding
New Aspects of B -> pi pi, pi K and their Implications for Rare Decays
We analyse the B -> pi pi, pi K modes in the light of the most recent
B-factory data, and obtain the following new results: (i) the B0 -> pi+ pi-,
pi- K+ modes prefer gamma=(74+-6)deg, which - together with |V_ub/V_cb| -
allows us to determine the ``true'' unitarity triangle and to search for
CP-violating new-physics contributions to B0_d-\bar B0_d mixing; (ii) the B ->
pi K puzzle reflected in particular by the low experimental value of the ratio
R_n of the neutral B -> pi K rates persists and still favours new physics in
the electroweak penguin sector with a new CP-violating phase phi ~ -90deg,
although now also phi ~ +90deg can bring us rather close to the data; (iii) the
mixing-induced B0 -> pi0 K_S CP asymmetry is a sensitive probe of the sign of
this phase, and would currently favour phi ~ +90deg, as well as the direct CP
asymmetry of B+- -> pi0 K+-, which suffers, however, from large hadronic
uncertainties; (iv) we investigate the sensitivity of our B -> pi K analysis to
large non-factorizable SU(3)-breaking effects and find that their impact is
surprisingly small so that it is indeed exciting to speculate on new physics;
(v) assuming that new physics enters through Z0 penguins, we study the
interplay between B -> pi K and rare B, K decays and point out that the most
recent B-factory constraints for the latter have interesting implications,
bringing us to a few scenarios for the future evolution of the data, where also
the mixing-induced CP violation in B0 -> pi0 K_S plays a prominent role.Comment: Two references added, to appear in the European Physical Journal
Waiting for Clear Signals of New Physics in B and K Decays
We classify the extensions of the Standard Model (SM) according to the
structure of local operators in the weak effective Hamiltonian and the presence
or absence of new flavour and CP-violating interactions beyond those
represented by the CKM matrix. In particular we review characteristic
properties of models with minimal flavour violation (MFV), models with
significant contributions from Higgs penguins and models with enhanced Z^0
penguins carrying a large new CP-violating phase. Within the latter models, the
anomalous behaviour of certain B\to\pi K observables implies large departures
from the SM predictions for rare and CP-violating K and B decays. Most
spectacular is the enhancement of Br(K_L->pi^0 nu nubar) by one order of
magnitude and a strong violation of the MFV relation
(\sin2\beta)_{\pi\nu\bar\nu}=(\sin2\beta)_{\psi K_S}. On the other hand our
prediction for (\sin2\beta)_{\phi K_S}\approx 0.9 differs from the Belle result
by the sign but is consistent with the BaBar value. We give a personal shopping
list for the coming years.Comment: Main latex-file, 4 figures, 22 page
Limitations in Measuring the Angle by Using Relations for -Meson Decay-Amplitudes
Flavour symmetry of strong interactions and certain dynamical
assumptions have been used in a series of recent publications to extract weak
CKM phases from -decays into final states. We
point out that irrespectively of -breaking effects the presence of
QCD-penguin contributions with internal - and -quarks precludes a clean
determination of the angle in the unitarity triangle by using the
branching ratios only. This difficulty can be overcome by measuring in addition
the ratio of to mixings. The
measurement of the angle is unaffected by these new contributions.
Some specific uncertainties related to -breaking effects and electroweak
penguin contributions are briefly discussed.Comment: 15 pages (LaTeX) + 5 figures included, Munich Technical University
preprint TUM-T31-69/9
Flavour constraints on multi-Higgs-doublet models: Yukawa alignment
In multi-Higgs-doublet models, the alignment in flavour space of all Yukawa
matrices coupling to a given right-handed fermion guarantees the absence of
tree-level flavour-changing neutral couplings, while introducing new sources of
CP violation. With N Higgs doublets (and no right-handed neutrinos) the Yukawa
Lagrangian is characterized by the fermion masses, the CKM quark mixing matrix
and 3(N-1) complex couplings. Quantum corrections break the alignment,
generating a minimal-flavour-violation structure with flavour-blind phases. The
aligned multi-Higgs-doublet models lead to a rich and viable phenomenology with
an interesting hierarchy of flavour-changing neutral current effects,
suppressing them in light-quark systems while allowing potentially relevant
signals in heavy-quark transitions.Comment: 6 pages, 5 figures. Talk given in the "Third Workshop on Theory,
Phenomenology and Experiments in Heavy Flavour Physics" (Capri, 5-7 July
2010
CP Violation in B -> pi+ pi- and the Unitarity Triangle
We analyze the extraction of weak phases from CP violation in
decays. We propose to determine the unitarity triangle
by combining the information on mixing induced CP
violation in , , with the precision observable
obtained from the CP asymmetry in . It is then possible to write
down exact analytical expressions for and as simple
functions of the observables and , and of the penguin
parameters and . As an application clean lower bounds on
and can be derived as functions of and ,
essentially without hadronic uncertainty. Computing and within QCD
factorization yields precise determinations of and since
the dependence on and is rather weak. It is emphasized that the
sensitivity to the phase enters only at second order and is extremely
small for moderate values of this phase, predicted in the heavy-quark limit.
Transparent analytical formulas are further given and discussed for the
parameter of direct CP violation in . We also discuss
alternative ways to analyze and that can be useful if new physics
affects -- mixing. Predictions and uncertainties for and
in QCD factorization are examined in detail. It is pointed out that a
simultaneous expansion in and 1/N leads to interesting simplifications.
At first order infrared divergences are absent, while the most important
effects are retained. Independent experimental tests of the factorization
framework are briefly discussed.Comment: 26 pages, 7 figure
On fermion masses and mixing in a model with symmetry
In a recently proposed multi-Higgs extension of the standard model in which
discrete symmetries, and are imposed we show that, after
accommodating the fermion masses and the mixing matrices in the charged
currents, the mixing matrices in the neutral currents induced by neutral
scalars are numerically obtained. However, the flavor changing neutral currents
are under control mainly by mixing and/or mass suppressions in the neutral
scalar sector.Comment: Version accepted for publication in International Journal of Modern
Physics A. In this version we added a discussion on the charged lepton and
neutrino masses. The title has been changed. Other minor changes do not
modify the conclusion
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