18 research outputs found
Minimal Zee model for lepton and -mass shifts
We present a unique Yukawa structure of the Zee model that can accommodate
neutrino oscillation data, solves the muon problem, and explains the
recent boson mass measurement. Our Yukawa structure is minimal in the sense
that it contains the least possible number of parameters. In this minimal
scenario, neutrino masses are quasidegenerate and are compatible with both
normal and inverted orderings. The mixing angle is predicted to
lie in the second (first) octant for normal (inverted) ordering. In both cases,
the CP violating phase is close to 3. The minimal texture also predicts
a large branching fraction of the heavy neutral Higgs boson into a pair of
electron and muon.Comment: 6 pages, 1 figure. v2 expanded introduction on LFV in the Zee model,
references added, to be appeared on PRD. v3 corrected typos, matched PRD
versio
Collider Constraints on a Dark Matter Interpretation of the XENON1T Excess
In light of the excess in the low-energy electron recoil events reported by
XENON1T, many new physics scenarios have been proposed as a possible origin of
the excess. One possible explanation is that the excess is a result of a fast
moving dark matter (DM), with velocity and mass between 1 MeV
and 10 GeV, scattering off an electron. Assuming the fast moving DM-electron
interaction is mediated by a vector particle, we derive collider constraints on
the said DM-electron interaction. The bounds on DM-electron coupling is then
used to constrain possible production mechanisms of the fast moving DM. We find
that the preferred mass of the vector mediator is relatively light (
1 GeV) and the coupling of the vector to the electron is much smaller than the
coupling to the fast moving DM.Comment: 6 pages, 5 figures, references added, CMB constraints included,
low-energy bounds updated, conclusion unchange
A New Higgs Boson with Electron-Muon Flavor-Violating Couplings
Recently, the CMS Collaboration performed a search on a new resonance
decaying to in the mass range of 110 GeV to 160 GeV. The search
also hints a possible excess at 146 GeV with a of local
(global) significance. Motivated by that, we try to interpret the results in
the context of the type-III two-Higgs-doublet-model. We find that the excess is
only moderately constrained by low-energy lepton-flavor-violation processes, in
particular the decay. We also compare the CMS bounds across
the entire search region against constraints of and
conversion in nuclei. Our finding indicates that the collider bounds can be
superior to those of low-energy processes for the scalar mass between and , suggesting the importance of this mass
range for future searches.Comment: v1: 7 pages, 2 figures; v2 add compatibility analysis between CMS
signal and ATLAS data, matched PLB versio
New Physics Models of Direct CP Violation in Charm Decays
In view of the recent LHCb measurement of Delta A_CP, the difference between
the time-integrated CP asymmetries in D --> K+K- and D --> pi+pi- decays, we
perform a comparative study of the possible impact of New Physics degrees of
freedom on the direct CP asymmetries in singly Cabibbo suppressed D meson
decays. We systematically discuss scenarios with a minimal set of new degrees
of freedom that have renormalizable couplings to the SM particles and that are
heavy enough such that their effects on the D meson decays can be described by
local operators. We take into account both constraints from low energy flavor
observables, in particular D0-D0bar mixing, and from direct searches. While
models that explain the large measured value for Delta A_CP with chirally
enhanced chromomagnetic penguins are least constrained, we identify a few
viable models that contribute to the D meson decays at tree level or through
loop induced QCD penguins. We emphasize that such models motivate direct
searches at the LHC.Comment: 24 pages, 13 figures. v2: typos corrected, reference added, published
versio
Zee model with quasidegenerate neutrino masses and where to find it
We present a Zee model with a family dependent symmetry for radiative neutrino masses. Our motivation is to get a model that correctly describes neutrino oscillation phenomena, while at the same time offers definite predictions. The imposed symmetry greatly reduces the number of free parameters in the model. These parameters are then determined from the neutrino data, from which one can study its outcomes. Our setup only admits quasidegenerate neutrino masses with the sum of neutrino masses between 100 and 130 meV, the effective Majorana mass between 20 and 40 meV, and the effective electron neutrino mass between 48 and 53 meV. The ratio of the vacuum expectation values of the Higgs doublets, , is found to be and . The former is ruled out by lepton flavor violation (LFV) processes, such as and conversion, which are determined up to two loops. For the latter, these LFV processes are within reach of the next generation of experiments. Moreover, for , the couplings of heavy neutral scalars to dimuon are significant. If they are sufficiently light, i.e., GeV, collider search for their decays into muon pair provides a stronger constraint on most parts of the model parameter space than the LFV ones
The dark penguin shines light at colliders
Abstract: Collider experiments are one of the most promising ways to constrain Dark Matter (DM) interactions. For several types of DM-Standard Model couplings, a meaningful interpretation of the results requires to go beyond effective field theory, considering simplified models with light mediators. This is especially important in the case of loop-mediated interactions. In this paper we perform the first simplified model study of the magnetic dipole interacting DM, by including the one-loop momentum-dependent form factors that mediate the coupling — given by the Dark Penguin — in collider processes. We compute bounds from the monojet, monophoton, and diphoton searches at the 8 and 14 TeV LHC, and compare the results to those of direct and indirect detection experiments. Future searches at the 100 TeV hadron collider and at the ILC are also addressed. We find that the optimal search strategy requires loose cuts on the missing transverse energy, to capture the enhancement of the form factors near the threshold for on-shell production of the mediators. We consider both minimal models and models where an additional state beyond the DM is accessible. In the latter case, under the assumption of anarchic flavor structure in the dark sector, the LHC monophoton and diphoton searches will be able to set much stronger bounds than in the minimal scenario. A determination of the mass of the heavier dark fermion might be feasible using the MT2 variable. In addition, if the Dark Penguin flavor structure is almost aligned with that of the DM mass, a displaced signal from the decay of the heavier dark fermion into the DM and photon can be observed. This allows us to set constraints on the mixings and couplings of the model from an existing search for non-pointing photons