144 research outputs found
Lepton flavor violation in type I + III seesaw
In the presence of a low scale seesaw of type I + III, flavor violating
effects in the leptonic sector are expected. Their presence in the charged
sector is due to the mixing of the fermionic vector-like weak triplets with the
chiral doublets, which cause non-universality of the tree-level Z coupling. We
investigate the bounds on the Yukawa couplings which are responsible for the
mixing and present the results for two minimal cases, a fermionic triplet with
a singlet or two fermionic triplets. Different channels for these processes are
considered and their current and future potential to probe these couplings is
discussed.Comment: 20 pages, 2 figures; corrected misprints, conclusions unchange
FCNC portals to the dark sector
The most general basis of operators parametrizing a low-scale departure from
the SM particle content is constructed. The SM gauge invariance is enforced,
and operators of lowest dimensions are retained separately for a new light
neutral particle of spin 0, 1/2, 1, and 3/2. The basis is further decomposed
into couplings to the SM Higgs/gauge fields, to pairs of quark/lepton fields,
and to baryon/lepton number violating combinations of fermion fields. This
basis is then used to systematically investigate the discovery potential of the
rare FCNC decays of the K and B mesons with missing energy in the final state.
The most sensitive decay modes in the s to d, b to d, and b to s sectors are
identified and compared for each type of couplings to the new invisible state.Comment: 55 pages. Minor corrections & references added. To appear in JHE
Back to 1974: The -onium
We show that the 750 GeV di-photon excess could be explained by the
onium system of a new QCD-like theory with fermions vectorial
under the SM. Beside the spin-0 di-photon singlet this scenario predicts almost
degenerate colored scalars and spin-1 resonances analogous to the in
QCD. All these states are within the reach of the LHC. An apparent large width
can be explained as due to production of excited states with splitting .Comment: 6 pages. v2: QCD effects and splitting of SU(2) multiplets added. v3:
final version to appear in PL
Shedding light on CP violation in the charm system via D to V gamma decays
Recent evidence for direct CP violation in non-leptonic charm decays cannot
be easily accommodated within the Standard Model (SM). On the other hand, it
fits well in new physics models generating CP violating Delta C=1
chromomagnetic dipole operators. We show that in these frameworks sizable
direct CP asymmetries in radiative D to P+ P- gamma decays (P=pi,K), with M_PP
close to the rho or the phi peak, can be expected. Enhanced matrix elements of
the electromagnetic dipole operators can partly compensate the long distance
dominance in these decays, leading to CP asymmetries of the order of several
percent. If observed at this level, these would provide a clean signal of
physics beyond the SM and of new dynamics associated to dipole operators. We
briefly comment on related CP violating observables accessible via time
dependent D(Dbar) to P+ P- gamma studies and angular decay product
distributions in rare semileptonic D decays.Comment: 5 page
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