580 research outputs found
Rare Charm Decays
Rare FCNC decay modes of charmed mesons are reviewed. The standard model
predictions, including both short and long distance contributions, are
summarized. Several new physics options that can give detectable signals are
described.Comment: 4 pages. Presented at the 6th International Conference on Hyperons,
Charm and Beauty Hadrons, IIT, Chicago, june 27-july 3, 2004. To be published
in the Proceeding
Scalars from Top-condensation Models at Hadron Colliders
We study the production and decay of neutral scalars and pseudo-scalars at
hadron colliders, in theories where the top-quark mass is the result of a
condensate. We show that the dominant decay channel for masses below
the threshold is the flavor changing mode . This is a consequence
of the non-universal nature of the underlying interactions in all
top-condensation models and provides a model-independent signature of these
scenarios. We show that an upgraded Tevatron is sensitive to a sizeable region
of the interesting parameter space and that the LHC will highly constrain these
models through this flavor violating channel.Comment: 4 pages, 4 figures. Minor changes in figures for readibility. final
version to appear in PR
First study of semileptonic decay form factors using NRQCD
We present a quenched calculation of the form factors of the semileptonic
weak decay with NRQCD heavy quark and Wilson
light quark on a lattice at . The form factors are
evaluated at six heavy quark masses, in the range of GeV.
dependence of matrix elements are investigated and compared with HQET
predictions. We observe clear signal for the form factors near ,
even at the -quark mass range. is compared with
based on the soft pion theorem and significant difference is
observed.Comment: 3 pages, 5 ps figures, uses espcrc2.sty and epsf.sty, Talk presented
at Lattice'9
Top quark associated production of the neutral top-pion at high energy colliders
In the context of topcolor-assisted technicolor (TC2) models, we calculate
the associated production of the neutral top-pion with a pair of
top quarks via the process . We
find that the production cross section is larger than that of the process both in the standard model (SM) and in the
minimal supersymmetric SM. With reasonable values of the parameters in TC2
models, the cross section can reach . The neutral top-pion
may be direct observed via this process.Comment: Latex files, 10 pages and 3 figure
A Possible Arena for Searching New Physics - the Ratio
We propose to investigate flavour changing neutral currents in the transition through the measurement of the difference between and . This is based on
the observation that is due to long distance
physics while arises from the
transition. The effect of mixing is included. A difference in
the decay widths of more than about 30% would be indicative of new physics.Comment: 7 pages, 1 figure include
Anomalous couplings of the third generation in rare B Decays
We study the potential effect of anomalous couplings of the third generation quarks to gauge bosons in rare B decays. We focus on the constraints from flavor changing neutral current processes such as and . We consider both dimension-four and dimension-five operators and show that the latter can give large deviations from the standard model in the still unobserved dilepton modes, even after the bounds from and precision electroweak observables are taken into account
Dispersive Approach to Semileptonic Form-Factors in Heavy-to-Light Meson Decays
We study the semileptonic decays of heavy mesons into light pseudoscalars by
making use of dispersion relations. Constraints from heavy quark symmetry,
chiral symmetry and perturbative QCD are implemented into a dispersive model
for the form-factors. Large deviations from -pole dominance are observed
in . We discuss the model prediction for this mode and its
possible impact on the extraction of .Comment: 30 pages, including 5 Postcript figure
Dominance of the light-quark condensate in the heavy-to-light exclusive decays
Using the QCD {\it hybrid} (moments-Laplace) sum rule, we show
- that, in the limit M_b \rar \infty, the and
behaviours of the heavy-to-light exclusive (\bar B\rar \rho~(\pi)
semileptonic as well as the B\rar \rho\gamma rare) decay--form factors are
dominated by the contribution of the soft light-quark condensate
rather than that of the hard perturbative diagram. The QCD-analytic
behaviour of the form factors is a polynomial in , which mimics
quite well the usual pole parametrization, except in the case of the
form factor, where there is a significant deviation from this polar form. The
-dependence of the form factors expected from HQET and lattice results is
recovered. We extract with a good accuracy the ratios: , and ; combined with the ``world average" value of or/and
, these ratios lead to the decay rates: $\Gamma_{\bar B\rar \pi e\bar
\nu} \simeq (4.3 \pm 0.7)Comment: 10 pages, CERN-TH 7237/94 (the previous version contains numerical
errors). Latex file (run twice) 3 ps.figures available by mai
Constraints on the Bulk Standard Model in the Randall-Sundrum Scenario
We derive constraints on the Randall-Sundrum scenario with the standard model
fields in the bulk. These result from tree level effects associated with the
deformation of the zero mode wave-functions of the W and the Z once electroweak
symmetry is broken. Recently Cs\'{a}ki, Erlich and Terning pointed out that
this implies large contributions to electroweak oblique parameters. Here we
find that when fermions are allowed in the bulk the couplings of the and
the to zero-mode fermions are also affected. We perform a fit to
electroweak observables assuming universal bulk fermion masses and including
all effects and find constraints that are considerably stronger than for the
case with fermions localized in the low energy boundary. These put the lowest
Kaluza-Klein excitation out of reach of the Large Hadron Collider. We then
relax the universality assumption and study the effects of flavor violation in
the bulk and its possible signatures.Comment: 18 pages, 2 ps figure
Is the LHC Observing the Pseudo-scalar State of a Two-Higgs Doublet Model ?
The ATLAS and CMS collaborations have recently shown data suggesting the
presence of a Higgs boson in the vicinity of 125 GeV. We show that a two-Higgs
doublet model spectrum, with the pseudo-scalar state being the lightest, could
be responsible for the diphoton signal events. In this model, the other scalars
are considerably heavier and are not excluded by the current LHC data. If this
assumption is correct, future LHC data should show a strengthening of the
signal, while the signals in the and
channels should diminish and eventually disappear, due
to the absence of diboson tree-level couplings of the CP-odd state. The heavier
CP-even neutral scalars can now decay into channels involving the CP-odd light
scalar which, together with their larger masses, allow them to avoid the
existing bounds on Higgs searches. We suggest additional signals to confirm
this scenario at the LHC, in the decay channels of the heavier scalars into
and . Finally, this inverted two-Higgs doublet spectrum is
characteristic in models where fermion condensation leads to electroweak
symmetry breaking. We show that in these theories it is possible to obtain the
observed diphoton signal at or somewhat above of the prediction for the
standard model Higgs for the typical values of the parameters predicted.Comment: 6 pages, 5 figures, final version in Physical Review
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