365 research outputs found

### Effects of Littlest Higgs model in rare D meson decays

A tree-level flavor changing neutral current in the up-like quark sector
appears in one of the variations of the Littlest Higgs model. We investigate
the effects of this coupling in the D+ -> pi+ l+ l- and D0 -> rho0 l+ l-
decays, which are the most appropriate candidates for the experimental studies.
However, the effects are found to be too small to be observed in the current
and the foreseen experimental facilities. These decays are still dominated by
the standard model long-distance contributions, which are reevaluated based on
the new experimental input.Comment: 13 pages, 3 figures; new constraint on scale f taken into account and
effects on charm meson decays recalculate

### 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

### Long distance contribution to $B^- \to K^- K^- \pi^+$, - a searching ground mode for new physics

The decay $B^- \to K^- K^- \pi^+$ has been sugested as a test for minimal
supersymmetric standard model and for supersymmetric models with R-parity
violating couplings, in view of its extreme smallnesss in the standard model.
We calculate two long distance contributions to this decay, that associated
with $DD$ and $D\pi$ intermediate states and that induced by virtual $D$, $\pi$
mesons. The branching ratio due to these contributions is $6 \times 10^{-12}$,
which is somewhat smaller than the standard model short distance result,
leaving this decay free for the search of new physics.Comment: 13 pages, 2 figures, revised versio

### A Possible Arena for Searching New Physics - the $\Gamma(D^0 \to \rho^0 \gamma)/\Gamma (D^0 \to \omega \gamma)$ Ratio

We propose to investigate flavour changing neutral currents in the $c \to u
\gamma$ transition through the measurement of the difference between $\Gamma
(D^0 \to \rho^0 \gamma)$ and $\Gamma (D^0 \to \omega \gamma)$. This is based on
the observation that $D^0 \to (d \bar d) \gamma$ is due to long distance
physics while $D^0 \to (u \bar u) \gamma$ arises from the $c \to u \gamma$
transition. The effect of $\rho - \omega$ 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

### Updated constraints on new physics in rare charm decays

Motivated by recent experimental results on charm physics we investigate
implications of the updated constraints of new physics in rare charm meson
decays. We first reconsider effects of the MSSM in $c\to u \gamma$ constrained
by the recent experimental evidence on $\Delta m_D$ and find, that due to the
dominance of long distance physics, $D \to V \gamma$ decay rates cannot be
modified by MSSM contributions. Then we consider effects of the extra heavy up
vector-like quark models on the decay spectrum of $D^+ \to \pi^+ l^+ l^-$ and
$D_s^+ \to K^+ l^+ l^-$ decays. We find a possibility for the tiny increase of
the differential decay rate in the region of large dilepton mass. The R-parity
violating supersymmetric model can also modify short distance dynamics in $c
\to u l^+ l^-$ decays. We constrain relevant parameters using current upper
bound on the $D^+ \to \pi^+ l^+ l^-$ decay rate and investigate impact of that
constraint on the $D_s^+ \to K^+ l^+ l^-$ differential decay dilepton
distribution. Present bounds still allow small modification of the standard
model differential decay rate distribution.Comment: 15 pages, 4 figure

### Long distance contributions in $D \to V \gamma$ decays

Using the factorization scheme for the nonleptonic $D \to V V_0$ weak
amplitudes, we classify all diagrams which arise in $D \to V \gamma$ decays and
calculate them with the help of the hybrid model which combines the heavy quark
effective theory and the chiral Lagrangian approach. Thus we determine the long
distance contribution to the amplitudes of Cabibbo allowed and Cabibbo
suppressed $D \to V\gamma$ decays. The calculation of the expected range of the
branching ratios of nine different $D \to V \gamma$ channels is compared with
results of other approaches. The present work establishes an increase of the
parity violating contribution in these decays in comparison with previous
analyses.Comment: 15 pages, latex, 2 figures; we have changed Table 2 and the caption
of Table 1. To be published in Eur. Phys.

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