644 research outputs found
Decay and Supersymmetry
The inclusive radiative -decay is a sensitive probe of new physics,
especially if related to the virtual exchange of a charged Higgs boson.
Supersymmetric models provide a particularly interesting example. In the limit
of exact supersymmetry, BR()~=~0, due to the vanishing of any
magnetic-moment transition operator. We illustrate the impact of this
constraint for realistic values of the supersymmetry-breaking parameters.Comment: 7 pages, CERN-TH.6830/93 (Minor changes; a comment on the case >1 has been added
Tree-level contributions to B -> Xs gamma
Weak radiative decay B -> X_s gamma is known to be a loop-generated process.
However, it does receive tree-level contributions from CKM-suppressed b -> u
ubar s gamma transitions. In the present paper, we evaluate such contributions
together with similar ones from the QCD penguin operators. For a low value of
the photon energy cutoff E_0 ~ m_b/20 that has often been used in the
literature, they can enhance the inclusive branching ratio by more than 10%.
For E_0 = 1.6 GeV or higher, the effect does not exceed 0.4%, which is due to
phase-space suppression. Our perturbative results contain collinear logarithms
that depend on the light quark masses m_q (q=u,d,s). We have allowed m_b/m_q to
vary from 10 to 50, which corresponds to values of m_q that are typical for the
constituent quark masses. Such a rough method of estimation may be improved in
the future with the help of fragmentation functions once the considered effects
begin to matter in the overall error budget for BR(B -> X_s gamma).Comment: v3: Corrected factors of 2 in the subdominant T_3 contributions.
Minor changes in the numerical results (Table II
Decay in Extensions of the Standard Model
The rare radiative decay is studied in extensions of the Standard Model. Matching conditions for
coefficients of operators appearing in the low energy effective Hamiltonian for
this process are derived, and QCD corrections to these coefficients are
analyzed. The decay rate is then calculated and compared with
the corresponding Standard Model result. We find that observable deviations
from Standard Model predictions can occur in theories for a reasonable range of parameter values.Comment: 17 pages with 5 figures not included but available upon request,
CALT-68-1893, TUM-T31-52/9
Exact Calculation of , \
We present an exact calculation of the Wilson coefficients
associated with the dipole moment operators. We also give an estimate of the
branching ratio for . We find that higher dimensional
effects are under control within for .Comment: 12 pages (plain TeX), 2 postscript figures available upon request.
UM-TH-93-20 , IP-ASTP-29-9
Using to Probe Top Quark Couplings
Possible anomalous couplings of the top-quark to on-shell photons and gluons
are constrained by the recent results of the CLEO Collaboration on both
inclusive and exclusive radiative decays. We find that the process \bsg\
can lead to reasonable bounds on both the anomalous electric and magnetic
dipole moments of the top-quark, while essentially no limits are obtained on
the corresponding chromoelectric and chromomagnetic moments, which enter the
expression for the decay rate only through operator mixing.Comment: 10 pages plus 6 figures (available by request), LaTex,
ANL-HEP-PR-93-3
Recalculation of QCD Corrections to Decay
We give a more complete calculation of decay, including
leading log QCD corrections from to in addition to corrections
from to . We have included the full set of dimension-6 operators
and corrected numerical mistakes of anomalous dimensions in a previous
paper\cite{Cho}. Comparing with the calculations without QCD running from
to \cite{Mis}, the inclusive decay rate is found to be enhanced.
At GeV, it results in 12\% enhancement, and for GeV, 15\% is
found. The total QCD effect makes an enhanced factor of 4.2 at GeV,
and 3.2 for GeV.Comment: 16 pages, 7 figures (uuencoded ps files), Changes of description. To
appear in Phys. Rev.
Constraints on the minimal supergravity model from the b->s+\gamma decay
The constraints on the minimal supergravity model from the b->s+\gamma decay
are studied. A large domain in the parameter space for the model satisfies the
CLEO bound, BR(b->s+\gamma)<5.4X10^{-4}. However, the allowed domain is
expected to diminish significantly with an improved bound on this decay. The
dependence of the b->s+\gamma branching ratio on various parameters is studied
in detail. It is found that, for A_t<0 and the top quark mass within the
vicinity of the center of the CDF value, m_t^{pole}=174\pm17 GeV, there exists
only a small allowed domain because the light stop is tachyonic for most of the
parameter space. A similar phenomenon exists for a lighter top and A_t negative
when the GUT coupling constant is slightly reduced. For A_t>0, however, the
branching ratio is much less sensitive to small changes in m_t, and \alpha_G.Comment: 12 pages, plain tex file, three figures avaliable upon request,
CTP-TAMU-03/94, NUB-TH.7316/94, and CERN-TH.3092/9
Rare radiative B decays to orbitally excited K mesons
The exclusive rare radiative B meson decays to orbitally excited axial-vector
mesons K_1^*(1270), K_1(1400) and to the tensor meson K_2^*(1430) are
investigated in the framework of the relativistic quark model based on the
quasipotential approach in quantum field theory. These decays are considered
without employing the heavy quark expansion for the s quark. Instead the s
quark is treated to be light and the expansion in inverse powers of the large
recoil momentum of the final K^{**} meson is used to simplify calculations. It
is found that the ratio of the branching fractions of rare radiative B decays
to axial vector K^*_1(1270) and K_1(1400) mesons is significantly influenced by
relativistic effects. The obtained results for B decays to the tensor meson
K_2^*(1430) agree with recent experimental data from CLEO.Comment: 17 pages, revte
The transition in softly broken supersymmetry
We study the effect of supersymmetric contributions to the effective quark
transition , including leading order QCD effects. We apply
the discussion to the decay . Even though one-particle
irreducible contributions could play a role, numerical cancelations make the
amplitude for the two-photon emission strongly correlated to the
amplitude which is sharply constrained by experiment. A quite general statement
follows: as long as non-standard physics effects appear only in the matching of
the Wilson coefficients of the standard effective operator basis, the
deviations from the standard model expectations of the decay rates induced by
are bound to follow closely the corresponding deviations
on . Effects of new physics are therefore bound to be small.Comment: Latex2e, RevTex, 22 pages, 8 eps figures, comments and references
adde
Determining the Sign of the Z-Penguin Amplitude
We point out that the precision measurements of the pseudo observables R_b^0,
A_b, and A_FB^0,b performed at LEP and SLC suggest that in models with
minimal-flavor-violation the sign of the Z-penguin amplitude is identical to
the one present in the standard model. We determine the allowed range for the
non-standard contribution to the Inami-Lim function C and show by analyzing
possible scenarios with positive and negative interference of standard model
and new physics contributions, that the derived bound holds in each given case.
Finally, we derive lower and upper limits for the branching ratios of K^+ ->
pi^+ nu nubar, K_L -> pi^0 nu nubar, K_L -> mu^+ mu^-, B -> X_d,s nu nubar, and
B_d,s -> mu^+ mu^- within constrained minimal-flavor-violation making use of
the wealth of available data collected at the Z-pole.Comment: 20 pages, 5 pdf figures, 5 tables, uses pdflatex; further typos
corrected, matches PRD versio
- …