Vectorlike fermions and Higgs couplings

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.

Section: Jhep01(2014)060mentioning

confidence: 63%

Section: S and T Parametermentioning

confidence: 99%

See 1 more Smart Citation

Exotic leptons: Higgs, flavor and collider phenomenology

Altmannshofer

Bauer

Carena

2014

“…Refs. [27][28][29][30] also deal with various aspects of vector-like fermions. There is also interest in vector-like states from a purely agnostic phenomenological inquiry to potentially better fit Higgs boson data [31,32].…”

Section: Jhep09(2014)130mentioning

confidence: 99%

Survey of vector-like fermion extensions of the Standard Model and their phenomenological implications

Ellis

Godbole

Gopalakrishna

et al. 2014

111

With the renewed interest in vector-like fermion extensions of the Standard Model, we present here a study of multiple vector-like theories and their phenomenological implications. Our focus is mostly on minimal flavor conserving theories that couple the vector-like fermions to the SM gauge fields and mix only weakly with SM fermions so as to avoid flavor problems. We present calculations for precision electroweak and vector-like state decays, which are needed to investigate compatibility with currently known data. We investigate the impact of vector-like fermions on Higgs boson production and decay, including loop contributions, in a wide variety of vector-like extensions and their parameter spaces.

“…Recently, their effects on Higgs boson decays were also studied. For example, they allow for a sizable modification of h → γγ [7][8][9][10][11][12][13][14] or they can significantly contribute to h → 4 or 2 2ν, through flavor violating Higgs decays, thus possibly affecting measurements of h → ZZ * and h → W W * [15,16]. Even without couplings to SM fermions they were studied in connection with the unification of gauge couplings in the minimal supersymmetric model extended by a complete vectorlike family [17] and the SM extended by several vectorlike families [18,19].…”

Section: Introductionmentioning

confidence: 99%

Limits on vectorlike leptons from searches for anomalous production of multi-lepton events

Dermíšek

Hall

Lunghi

et al. 2014

We consider extensions of the Standard Model by vectorlike leptons and set limits on a new charged lepton, e ± 4 , using the ATLAS search for anomalous production of multi-lepton events. It is assumed that only one Standard Model lepton, namely the muon, dominantly mixes with vectorlike leptons resulting in possible decays e ± 4 → W ± ν µ , e ± 4 → Zµ ± , and e ± 4 → hµ ± . We derive generally applicable limits on the new lepton treating the branching ratios for these processes as free variables. We further interpret the general limits in two scenarios with e ± 4 originating predominantly from either the SU(2) doublet or the SU(2) singlet. The doublet case is more constrained as a result of larger production cross-section and extra production processes e ± 4 ν 4 and ν 4 ν 4 in addition to e + 4 e − 4 , where ν 4 is a new neutral state accompanying e 4 . We find that some combinations of branching ratios are poorly constrained, whereas some are constrained up to masses of more than 500 GeV. In the doublet case, assuming BR(ν 4 → W µ) = 1, all masses below about 300 GeV are ruled out. Even if this condition is relaxed and additional decay modes, ν 4 → Zν µ and ν 4 → hν µ , are allowed, below the Higgs threshold still almost all of the parameter space (of independent branching ratios) is ruled out. Nevertheless, even assuming the maximal production cross-section, which coincides with the doublet case, the new charged lepton can still be as light as the LEP-II limit allows. We discuss several possible improvements of current experimental analyses that would dramatically reduce the allowed parameter space, even with current data.