Testing new physics with the electron g − 2

We study the lepton sector of composite Higgs models with partial compositeness. The standard anarchic scenario is in conflict with the absence of observable charged lepton flavor violation. This tension can be completely solved in MFV scenarios that require either left-handed or right-handed SM leptons to be equally composite. Constraints on this scenario are weak and the composite lepton partners could be as light as few hundreds GeVs with interesting LHC signatures. The contribution to the muon (g − 2) in theories where the Higgs is a pseudo Nambu-Goldstone boson is also discussed.

“…This correlation is of potential interest as it could be tested in future experiments [24]. At face value, to reproduce the muon anomaly, ∆a µ ≈ 2.8 · 10 −9 , one finds…”

Section: Muon G −mentioning

confidence: 87%

Leptons in composite MFV

Redi

2013

“…The explicit expression for the derivative can be found in (3.3). However, given the uncertainty of the current experimental results and the precision of the SM predictions [66] …”

Section: Anomalous Magnetic Momentsmentioning

confidence: 99%

“…The analysis in this section has to be contrasted with the results from studies of models of new vector-like leptons, which have the exact same quantum numbers as their SM cousins. In these models, highly non-generic CP and flavor structures are necessary in order to satisfy the constraints discussed in this section, see for example [66] and references therein.…”

Section: Lepton Flavor Violationmentioning

confidence: 99%

Exotic leptons: Higgs, flavor and collider phenomenology

Altmannshofer

Bauer

Carena

2014

We study extensions of the standard model by one generation of vector-like leptons with non-standard hypercharges, which allow for a sizable modification of the h → γγ decay rate for new lepton masses in the 300 GeV-1 TeV range. We analyze vacuum stability implications for different hypercharges. Effects in h → Zγ are typically much smaller than in h → γγ, but distinct among the considered hypercharge assignments. Nonstandard hypercharges constrain or entirely forbid possible mixing operators with standard model leptons. As a consequence, the leading contributions to the experimentally strongly constrained electric dipole moments of standard model fermions are only generated at the two loop level by the new CP violating sources of the considered setups. We derive the bounds from dipole moments, electro-weak precision observables and lepton flavor violating processes, and discuss their implications. Finally, we examine the production and decay channels of the vector-like leptons at the LHC, and find that signatures with multiple light leptons or taus are already probing interesting regions of parameter space.

“…New physics contributions to ∆(a e ) are generally assumed to be very small (although in [51] it was suggested that this observable could be used to probe and constrain new physics scenarios, an idea also recently explored in [52]); in fact, the precision in the determination of a e has rendered it the preferred means to determine the value of the fine-structure constant α (see, for example, [53]). On the other hand, the anomalous magnetic moment of the muon has revealed a (yet unresolved) discrepancy between the SM expected value and the experimental determination.…”

Section: Sterile Neutrinos and Lepton Magnetic Momentsmentioning

confidence: 99%

Effect of steriles states on lepton magnetic moments and neutrinoless double beta decay

Abada

Romeri

Teixeira

2014

Abstract:We address the impact of sterile fermion states on the anomalous magnetic moment of charged leptons, as well as their contribution to neutrinoless double beta decays. We illustrate our results in a minimal, effective extension of the Standard Model by one sterile fermion state, and in a well-motivated framework of neutrino mass generation, embedding the Inverse Seesaw into the Standard Model. The simple "3+1" effective case succeeds in alleviating the tension related to the muon anomalous magnetic moment, albeit only at the 3σ level, and for light sterile states (corresponding to a cosmologically disfavoured regime). Interestingly, our analysis shows that a future 0ν2β observation does not necessarily imply an inverted hierarchy for the active neutrinos in this simple extension. Although the Inverse Seesaw realisation here addressed could indeed ease the tension in (g − 2) µ , bounds from lepton universality in kaon decays mostly preclude this from happening. However, these scenarios can also have a strong impact on the interpretation of a future 0ν2β signal regarding the hierarchy of the active neutrino mass spectrum.