1,053 research outputs found
CP asymmetry and branching ratio of B -> pi pi
We investigate the branching ratios and CP asymmetries of the B -> pi pi
processes measured in B factory experiments. Fits to the experimental data of
this process indicate a large ratio of color-suppressed (C) to color-allowed
(T) tree contributions. We investigate whether the large C/T can be explained
within the QCD based model computation with i) a large effect from the
end-point singularity or with ii) large final-state-interaction phase between
two different isospin amplitudes. We show that the current experimental data do
not exclude either possibility but we may be able to distinguish these two
effects in future measurements of direct CP asymmetry of B -> pi^0 pi^0.Comment: 8 pages, 10 figure
Effects of R-parity violation on direct CP violation in B decays and extraction of
In the standard model, direct CP-violating asymmetries for are roughly 2% based on perturbative calculation. Rescattering effects might
enhance it to at most (20-25)%. We show that lepton-number-violating couplings
in supersymmetric models without R-parity are capable of inducing as large as
100% CP asymmetry in this channel. Such effects drastically modify the allowed
range of the CKM parameter arising from the combinations of the
observed charged and neutral B decays in the modes. With a multichannel
analysis in B decays, one can either discover this exciting new physics, or
significantly improve the existing constraints on it.Comment: Latex, 5 pages; minor changes, to appear in Phys Rev Let
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
On the Correlations between Flavour Observables in Minimal U(2)^3 Models
The stringent correlations between flavour observables in models with CMFV
are consistent with the present data except for the correlation Delta
M_{s,d}-epsilon_K. Motivated by the recent work of Barbieri et al, we compare
the CMFV correlations with the ones present in a special class of models with
an approximate global U(2)^3 flavour symmetry, constrained by a minimal set of
spurions governing the breakdown of this symmetry and the assumption that only
SM operators are relevant in flavour physics. This analog of CMFV to be called
MU(2)^3 allows to avoid the Delta M_{s,d}-epsilon_K tension in question because
of reduced flavour symmetry and implied non-MFV contributions to Delta M_{s,d}.
While the patterns of flavour violation in K meson system is the same as in
CMFV models, the CP-violation in B_{s,d} meson systems can deviate from the one
in the SM and CMFV models. We point out a stringent triple S_{psi K_S}-S_{psi
phi}-|V_ub| correlation in this class of models that could in the future
provide a transparent distinction between different MU(2)^3 models and in the
context of these models determine |V_ub| by means of precise measurements of
S_{psi K_S} and S_{psi phi} with only small hadronic uncertainties. For fixed
S_{psi K_S} the correlation between B(B^+ -> tau^+nu_tau) and S_{psi phi}
follows. We also find that MU(2)^3 models could in principle accommodate a
negative value of S_{psi phi}, provided |V_ub| is found to be in the ballpark
of exclusive determinations and the particular MU(2)^3 model provides a 25%
enhancement of epsilon_K. A supersymmetric U(2)^3 model worked out in the
Barbieri-School appears to satisfy these requirements. However if B(B^+ ->
tau^+nu_tau)>1.0 10^{-4} will be confirmed by future experiments only positive
S_{psi phi} is allowed in this framework. We summarize briefly the pattern of
flavour violation in rare K and B_{s,d} decays in MU(2)^3 models.Comment: 28 pages, 6 figures; v2: Few references and discussion on CP
violation in B_s-> mu^+ mu^- added; v3: Several clarifying comments added,
conclusions unchanged, version accepted for publication in JHE
Rare K and B Decays in the Littlest Higgs Model without T-Parity
We analyze rare K and B decays in the Littlest Higgs (LH) model without
T-parity. We find that the final result for the Z^0-penguin contribution
contains a divergence that is generated by the one-loop radiative corrections
to the currents corresponding to the dynamically broken generators. Including
an estimate of these logarithmically enhanced terms, we calculate the branching
ratios for the decays K^+ -> pi^+ nu bar nu, K_L -> pi^0 nu bar nu, B_{s,d} ->
mu^+ mu^- and B -> X_{s,d} nu bar nu. We find that for the high energy scale
f=O(2-3) TeV, as required by the electroweak precision studies, the enhancement
of all branching ratios amounts to at most 15% over the SM values. On the
technical side we identify a number of errors in the existing Feynman rules in
the LH model without T-parity that could have some impact on other analyses
present in the literature. Calculating penguin and box diagrams in the unitary
gauge, we find divergences in both contributions that are cancelled in the sum
except for the divergence mentioned above.Comment: 39 pages, 8 figures, typos corrected, comment on (2.17) and (2.18)
added, references added, results unchange
A Critical Study of B Decays to Light Pseudoscalar
Motivated by the large branching ratios observed for the process
, we examine critically all the ingredients that go into
estimates of B decays into two light pseudoscalars. Within factorization
approximation, we examine several assumptions on the input parameters that
could have a strong bearing on the predictions. Among these are (i) the QCD
scale (ii) value of the form factors (iii) value of the light quark
masses, and in particular (iv) the value , (v) charm content
of . It is possible to account for all the data without invoking
new physics, though future experiments will provide tighter constraints on the
parameter space. We fin that CP violating asymmetries are in the observable
range for some modes.Comment: 29 pages(Latex), 17 figures, a few changes have been made, version to
appear in Phys.Rev.
Flavor Changing Neutral Current Effects and CP Violation in the Minimal 3-3-1 Model
We investigate in detail the flavor structure of the minimal 331 model and
its implications for several flavor changing neutral current (FCNC) processes.
In this model, where the weak SU(2)_L gauge group of the Standard Model is
extended to a SU(3)_L, the by far dominant new contributions come from an
additional neutral Z' gauge boson, that can transmit FCNCs at tree-level. At
the same time, electroweak precision observables receive new contributions only
at the loop level and do not constrain the model very strongly. In our
analysis, we take into account new CP violating effects that have been
neglected in earlier analyses, and account for a general flavor structure
without reference to a certain parameterization of the new mixing matrix. We
begin by studying the bounds obtained from quantities such as Delta M_K,
epsilon_K, Delta M_{d/s} as well as sin 2 beta|_{J/psi K_S}, and go on to
explore the implications for several clean rare decay channels, namely the
decays K+->pi+ nu nu, K_L -> pi0 nu nu, B_{d/s} -> mu+ mu- and K_L -> pi0 l+l-.
We find sizeable effects in all these decays, but the most interesting quantity
turns out to be the B_s - bar B_s mixing phase beta_s, as measured in the
mixing induced CP asymmetry of B_s -> J/psi phi, which can be large. In
general, we find effects in purely hadronic channels to be larger than in
(semi-)leptonic ones, due to a suppression of the Z'-lepton couplings.Comment: 29 pages, 11 figures, Some Comments and References added, version to
appear in Phys Rev
Low Scale Non-universal, Non-anomalous U(1)'_F in a Minimal Supersymmetric Standard Model
We propose a non-universal U(1)'_F symmetry combined with the Minimal
Supersymmetric Standard Model. All anomaly cancellation conditions are
satisfied without exotic fields other than three right-handed neutrinos.
Because our model allows all three generations of chiral superfields to have
different U(1)'_F charges, upon the breaking of the U(1)'_F symmetry at a low
scale, realistic masses and mixing angles in both the quark and lepton sectors
are obtained. In our model, neutrinos are predicted to be Dirac fermions and
their mass ordering is of the inverted hierarchy type. The U(1)'_F charges of
the chiral super-fields also naturally suppress the mu term and automatically
forbid baryon number and lepton number violating operators. While all
flavor-changing neutral current constraints in the down quark and charged
lepton sectors can be satisfied, we find that constraint from D0-D0bar turns
out to be much more stringent than the constraints from the precision
electroweak data.Comment: 21 pages, 2 figures; v2: discussion on sparticle mass spectrum
included, 27 pages, 2 figure
Implications of the CP asymmetry in semileptonic B decay
Recent experimental searches for , the CP asymmetry in semileptonic B
decay, have reached an accuracy of order one percent. Consequently, they give
meaningful constraints on new physics. We find that cancellations between the
Standard Model (SM) and new physics contributions to mixing
cannot be as strong as was allowed prior to these measurements. The predictions
for this asymmetry within the SM and within models of minimal flavor violation
(MFV) are below the reach of present and near future measurements. Including
order and corrections we obtain the SM
prediction: . Future
measurements can exclude not only the SM, but MFV as well, if the sign of the
asymmetry is opposite to the SM or if it is same-sign but much enhanced. We
also comment on the CP asymmetry in semileptonic decay, and update the
range of the angle in the SM: .Comment: 16 pages, a sign typo in eq.(11) fixed, to appear in Phys. Rev.
An upper bound on the Kaon B-parameter and Re(epsilon_K)
New precise data in B physics and theoretical developments in K physics lead
us to reconsider the weak K^0-\bar{K}^0 transition from a large-N_c viewpoint,
N_c being the number of colors. In this framework, we infer an upper limit on
\hat{B}_K and the Kaon indirect CP violation.Comment: 11 pages, 4 figures. V2 : Minor corrections, final version accepted
for publication in JHE
- …