341 research outputs found
One-loop flavor changing electromagnetic transitions
We discuss the effect of the external fermion masses in the flavor-changing
radiative transitions of a heavy fermion (quark or lepton) to a lighter fermion
at the one-loop level, and point out an often overlooked crucial difference in
the sign of a charge factor between transitions of the down type
and the up type . We give formulas for the
effective vertex in various approximations and the exact formula for and .Comment: LaTeX 16 pages + 4 postscript figures. Misprints corrected, some
Comments adde
Lepton polarization asymmetry in radiative dileptonic B-meson decays in MSSM
In this paper we study the polarization asymmetries of the final state lepton
in the radiative dileptonic decay of B meson (\bsllg) in the framework of
Minimal Supersymmetric Standard Model (MSSM) and various other unified models
within the framework of MSSM e.g. mSUGRA, SUGRA (where condition of
universality of scalar masses is relaxed) etc. Lepton polarization, in addition
of having a longitudinal component (\pl), can have two other components, \pt
and \pn, lying in and perpendicular to the decay plane, which are proportional
to \ml and hence are significant for final state being or
. We analyse the dependence of these polarization asymmetries
on the parameters of the various models.Comment: typos corrected to match with published versio
Two-body Cabibbo-suppressed Decays of Charmed Baryons into Vector Mesons and into Photons
The heavy quark effective theory and the factorization approximation are used
to treat the Cabibbo-suppressed decays of charmed baryons to vector mesons,
,
and . The input from two recent experimental results on
decays allows the estimation of the branching ratios for these modes, which
turn out to be between and . The long distance contribution
of these transitions via vector meson dominance to the radiative weak processes
, and
leads to quite small branching ratios,
; the larger value holds if a sum rule between the coupling
constants of the vector mesons is broken.Comment: 11 pages, latex, no figure
CP violating asymmetries in single top quark production at the Tevatron p pbar collider
Analytic expressions for the angular distributions of the -quarks
associated with single -quark production in and of the leptons from the subsequent decay are
obtained in the laboratory system. CP violation in the -production vertex is
assumed. Different angular and total cross section CP violating asymmetries are
considered. Relations testing CP violation solely in the -decay vertex are
also obtained. A numerical analysis is performed in the MSSM with a CP
violating phase of the trilinear coupling . The asymmetries are
typically of the order - .Comment: The numerical results are corrected and some changes that meet the
requirements of Phys. Rev. D are mad
B->rho pi decays, resonant and nonresonant contributions
We point out that a new contribution to B decays to three pions is relevant
in explaining recent data from the CLEO and BABAR collaborations, in particular
the results on quasi-two-body decays via a rho meson. We also discuss the
relevance of these contribution to the measurement of CP violations.Comment: 5 pages, 2 figures, few references and minor comments adde
Collision-Induced Decay of Metastable Baby Skyrmions
Many extensions of the standard model predict heavy metastable particles
which may be modeled as solitons (skyrmions of the Higgs field), relating their
particle number to a winding number. Previous work has shown that the
electroweak interactions admit processes in which these solitons decay,
violating standard model baryon number. We motivate the hypothesis that
baryon-number-violating decay is a generic outcome of collisions between these
heavy particles. We do so by exploring a 2+1 dimensional theory which also
possesses metastable skyrmions. We use relaxation techniques to determine the
size, shape and energy of static solitons in their ground state. These solitons
could decay by quantum mechanical tunneling. Classically, they are metastable:
only a finite excitation energy is required to induce their decay. We attempt
to induce soliton decay in a classical simulation by colliding pairs of
solitons. We analyze the collision of solitons with varying inherent
stabilities and varying incident velocities and orientations. Our results
suggest that winding-number violating decay is a generic outcome of collisions.
All that is required is sufficient (not necessarily very large) incident
velocity; no fine-tuning of initial conditions is required.Comment: 24 pages, 7 figures, latex. Very small changes onl
Gluon interference effects in t-tbar production at the Next Linear Collider
We study the effects of gluon interference in the production and
semi-leptonic decay of a t-tbar pair above threshold at the Next Linear
Collider (NLC). We calculate all matrix elements to next-to-leading order and
use the resulting expressions for the development of a Monte Carlo event
generator. Our results show effects at the level of 10% in differential
cross-sections. We thus extend previous results obtained by analytical means in
the soft-gluon limit.Comment: 20 pages, incl. 9 figures, LaTeX (revtex, eepic, axodraw
Rare Decay of the Top t->c l lbar and Single Top Production at International Linear Collider
We perform a complete and detailed analysis of the flavor changing neutral
current rare top quark decays t-> cl+l- and t->c nu_i bar nu_i at one-loop
level in the Standard Model, Two Higgs Doublet Models (I and II) and in MSSM.
The branching ratios are very small in all models, O(10^-14), except for the
case of the unconstrained MSSM, where they can reach O(10^-6) for e+e- and nu_i
bar nu_i, and O(10^-5) for tau+ tau-. This branching ratio is comparable to the
ones for t-> c V, cH. We also study the production rates of single top and the
forward-backward asymmetry in e+e- -> t cbar and comment on the observability
of such a signal at the International Linear Collider.Comment: 32 pages and 18 figures, minor clarification in the text, references
added. To be published in Phys. Rev.
New scalar resonances from sneutrino-Higgs mixing in supersymmetry with small lepton number (R-parity) violation
We consider new s-channel scalar exchanges in top quark and massive
gauge-bosons pair production in e+e- collisions, in supersymmetry with a small
lepton number violation. We show that a soft bilinear lepton number violating
term in the scalar potential which mixes the Higgs and the slepton fields can
give rise to a significant scalar resonance enhancement in e+e- -> ZZ, W+W- and
in e+e- -> t t(bar). The sneutrino-Higgs mixed state couples to the incoming
light leptons through its sneutrino component and to either the top quark or
the massive gauge bosons through its Higgs component. Such a scalar resonance
in these specific production channels cannot result from trilinear Yukawa-like
R-parity violation alone, and may, therefore, stand as strong evidence for the
existence of R-parity violating bilinears in the supersymmetric scalar
potential. We use the LEP2 measurements of the WW and ZZ cross-sections to
place useful constrains on this scenario, and investigate the expectations for
the sensitivity of a future linear collider to these signals. We find that
signals of these scalar resonances, in particular in top-pair production, are
well within the reach of linear colliders in the small lepton number violation
scenario.Comment: 22 pages in revtex, 10 figures embadded in the text using epsfi
Direct CP violation in radiative b decays in and beyond the Standard Model
We consider the partial rate asymmetry in the inclusive decay modes b to s
gamma and b to d gamma, concentrating on non-standard models with new charged
Higgs interactions. We find that the charged Higgs contribution to the
asymmetry for b to s gamma is small in such models due to a universal
cancellation mechanism. The asymmetry is therefore difficult to distinguish
experimentally from the Standard Model (SM) value, which is also small. The
cancellation mechanism is found to be rendered inoperative in supersymmetry due
to the presence of chargino loops. Unlike b to s gamma, the rate asymmetry for
b to d gamma in Higgs models can be quite different from its SM value,
generally ranging from -20% to +20%. Specific model calculations are performed
for the Three-Higgs Doublet Model and the ``Top'' Two-Higgs Doublet Model to
serve as illustrations. We also offer some suggestions that may be helpful to
experimentalists in the detection of the inclusive mode b to d gamma.Comment: RevTex, 24 pages, 6 figures, minor changes, version to appear in PR
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