854 research outputs found
Non-perturbative Effects in
The rare decay provides excellent prospects for precision
tests of Standard Model flavour dynamics. The process can be computed in
perturbation theory with small uncertainty. However, in order to ensure a
reliable theoretical prediction, also potentially important effects from
non-perturbative QCD have to be controlled with sufficient accuracy. The
present article summarizes recent developments related to this topic.Comment: Invited Talk presented at the QCD Euroconference 98, Montpellier, 2-8
July 1998, 7 pages, 1 figur
Connections between epsilon'/epsilon and Rare Kaon Decays in Supersymmetry
We analyze the rare kaon decays , , and in conjunction
with the CP violating ratio in a general class of
supersymmetric models in which - and magnetic-penguin contributions can be
substantially larger than in the Standard Model. We point out that radiative
effects relate the double left-right mass insertion to the single left-left
one, and that the phenomenological constraints on the latter reflect into a
stringent bound on the supersymmetric contribution to the penguin. Using
this bound, and those coming from recent data on we find
{\rm BR}(K_L \to \pi^0 \nu \bar \nu)\lsim 1.2\cdot 10^{-10}, {\rm BR}(K^+
\to \pi^+ \nu \bar \nu)\lsim 1.7\cdot 10^{-10}, {\rm BR}(K_L \to \pi^0 e^+
e^-)_{\rm dir}\lsim 2.0\cdot 10^{-11}, assuming the usual determination of the
CKM parameters and neglecting the possibility of cancellations among different
supersymmetric effects in . Larger values are possible, in
principle, but rather unlikely. We stress the importance of a measurement of
these three branching ratios, together with improved data and improved theory
of , in order to shed light on the realization of various
supersymmetric scenarios. We reemphasize that the most natural enhancement of
, within supersymmetric models, comes from chromomagnetic
penguins and show that in this case sizable enhancements of can also be expected.Comment: 40 pages, 5 figure
Two-Loop Large- Electroweak Corrections to for Arbitrary Higgs Boson Mass
We consider for the first time the leading large top mass corrections,
arising at higher order in electroweak interactions, to the rare decays
and the related modes and . Higher order effects of similar type have previously been calculated
in the large- limit for key observables of precision electroweak physics
at Z-factories. Here we obtain the corresponding corrections of order at the amplitude level for short-distance dominated rare meson
decays. This allows us to quantify the importance of higher order electroweak
effects for these processes, which can be reliably computed and have very small
uncertainties from strong interactions. Simultaneously it becomes possible to
remove, to some extent, ambiguities in the definition of electroweak parameters
describing the strength of FCNC interactions. The corrections we discuss are at
the level of a few percent.Comment: 11 pages, LaTeX, 1 eps-figur
CP Violation in Neutral Kaon Decays
A brief review of the theoretical status of CP violation in decays of neutral
kaons is presented. We focus on three important topics: ,
and .Comment: 5 pages, Latex; Invited Talk presented at the Symposium on
Flavor-Changing Neutral Currents, Santa Monica, California, February 19-21,
1997; to appear in the proceeding
Cosmo-Particle Searches for Supersymmetry at the Collider Detector at Fermilab
Some theories of particle physics are so compelling that it is worth doing a
comprehensive and systematic set of experimental searches to see if they are
realized in nature. Supersymmetry is one such theory. This review focuses on
the motivation for a broad set of cosmology-inspired search strategies at the
Tevatron and on their implementation and results at the Collider Detector at
Fermilab (CDF) with the first few fb of integrated luminosity of data.Comment: 15 Pages, 23 figure
Note on Anomalous Higgs-Boson Couplings in Effective Field Theory
We propose a parametrization of anomalous Higgs-boson couplings that is both
systematic and practical. It is based on the electroweak chiral Lagrangian,
including a light Higgs boson, as the effective field theory (EFT) at the
electroweak scale . This is the appropriate framework for the case of
sizeable deviations in the Higgs couplings of order from the Standard
Model, considered to be parametrically larger than new-physics effects in the
sector of electroweak gauge interactions. The role of power counting in
identifying the relevant parameters is emphasized. The three relevant scales,
, the scale of new Higgs dynamics , and the cut-off ,
admit expansions in and . The former corresponds
to an organization of operators by their canonical dimension, the latter by
their loop order or chiral dimension. In full generality the EFT is thus
organized as a double expansion. However, as long as the EFT
systematics is closer to the chiral counting. The leading effects in the
consistent approximation provided by the EFT, relevant for the presently most
important processes of Higgs production and decay, are given by a few
(typically six) couplings. These parameters allow us to describe the properties
of the Higgs boson in a general and systematic way, and with a precision
adequate for the measurements to be performed at the LHC. The framework can be
systematically extended to include loop corrections and higher-order terms in
the EFT.Comment: 7 pages, no figures; typos corrected; references adde
Rare K decays in a model of quark and lepton masses
An extension of a model of neutrino masses to the quark sector provides an
interesting link between these two sectors. A parameter which is important to
describe neutrino oscillations and masses is found to be a crucial one
appearing in various ``penguin'' operators, in particular the so-called Z
penguin. This parameter is severely constrained by the rare decay process
. This in turn has interesting implications on the
decay rates of other rare processes such as , etc..., as well
as on the masses of the neutrinos and the masses of the vector-like quarks and
leptons which appear in our model.Comment: 34 pages, 10 figures, corrected some typos in the introductio
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