The two lower panels of figure 1 are mildly modified while all other numerical results are unaffected. In tables 3–5 we adopt a more useful parameterization for the branching ratios in the case of a vectorlike quark doublet with couplings to H  u  and H  d .

United States

Radovan Dermíšek

Enrico Lunghi

South Korea

Seodong Shin

Erratum to: Hunting for vectorlike quarks

We report on an intriguing observation that the values of all the couplings in the standard model, except those related to first two generations, can be understood from the IR fixed point structure of renormalization group equations in the minimal supersymmetric model extended by one complete vectorlike family with the scale of new physics in a multi-TeV range.

Navin McGinnis

Seven Largest Couplings of the Standard Model as IR Fixed Points

We analyze decays of vectorlike quarks in extensions of the standard model and a two Higgs doublet model. We identify several typical patterns of branching ratios of the lightest new up-type quark, t 4, and down-type quark, b 4, depending on the structure of Yukawa couplings that mix the vectorlike and standard model quarks (we assume only mixing with the third generation) and also on their doublet or singlet nature. We find that decays into heavy neutral or charged Higgs bosons, when kinematically open, can easily dominate and even be close to 100%: b 4 → Hb at medium to large tan β, t 4 → Ht at small tan β and b 4 → H ± t, t 4 → H ± b at both large and small tan β. The pair production of vectorlike quarks leads to 6t, 4t2b, 2t4b and 6b final states. The decay modes into W, Z and h follow the pattern expected from the Goldstone boson equivalence limit that we generalize to scenarios with all possible couplings. We also discuss in detail the structure of Yukawa couplings required to significantly deviate from the pattern characteristic of the Goldstone boson equivalence limit that can result in essentially arbitrary branching ratios.

Hunting for vectorlike quarks

In the MSSM extended by a complete vectorlike family, precise top, bottom and tau Yukawa coupling unification can be achieved assuming SUSY threshold corrections which are typical for comparable superpartner masses. Furthermore, the unification is possible with a large unified coupling, implying that all three fermion masses can be simultaneously close to their IR fixed points. Assuming unified Yukawa couplings of order one or larger, the preferred common scale of new physics (superpartners and vectorlike matter) is in the 3 TeV to 30 TeV range, with larger couplings favoring smaller scales. Splitting superpartner masses from masses of vectorlike fields, the preferred scales extend in both directions. The multi-TeV scale for superpartners is compatible with and independently suggested by the Higgs boson mass.

Top-bottom-tau Yukawa coupling unification in the MSSM plus one vectorlike family and fermion masses as IR fixed points

We use the IR fixed point predictions for gauge couplings and the top Yukawa coupling in the minimal supersymmetric model (MSSM) extended with vectorlike families to infer the scale of vectorlike matter and superpartners. We quote results for several extensions of the MSSM and present results in detail for the MSSM extended with one complete vectorlike family. We find that for a unified gauge coupling <math><msub><mi>α</mi><mi>G</mi></msub><mo>&gt;</mo><mn>0.3</mn></math> vectorlike matter or superpartners are expected within 1.7 TeV (2.5 TeV) based on all three gauge couplings being simultaneously within 1.5% (5%) from observed values. This range extends to about 4 TeV for <math><msub><mi>α</mi><mi>G</mi></msub><mo>&gt;</mo><mn>0.2</mn></math>. We also find that in the scenario with two additional large Yukawa couplings of vectorlike quarks the IR fixed point value of the top Yukawa coupling independently points to a multi-TeV range for vectorlike matter and superpartners. Assuming a universal value for all large Yukawa couplings at the grand unified theory scale, the measured top quark mass can be obtained from the IR fixed point for <math><mi>tan</mi><mi>β</mi><mo>≃</mo><mn>4</mn></math>. The range expands to any <math><mi>tan</mi><mi>β</mi><mo>&gt;</mo><mn>3</mn></math> for significant departures from the universality assumption. Considering that the Higgs boson mass also points to a multi-TeV range for superpartners in the MSSM, adding a complete vectorlike family at the same scale provides a compelling scenario where the values of gauge couplings and the top quark mass are understood as a consequence of the particle content of the model.

Mass scale of vectorlike matter and superpartners from IR fixed point predictions of gauge and top Yukawa couplings

One of the cleanest signatures of a heavy Higgs boson in models with vectorlike leptons is H → e 4 ± ℓ ∓ → h ℓ + ℓ − $$ H\to {e}_{{}^4}^{\pm }{\ell}^{\mp}\to h{\ell}^{+}{\ell}^{-} $$ which, in two Higgs doublet model type-II, can even be the dominant decay mode of heavy Higgses. Among the decay modes of the standard model like Higgs boson, h , we consider b b ¯ $$ b\overline{b} $$ and γγ as representative channels with sizable and negligible background, respectively. We obtained new model independent limits on production cross section for this process from recasting existing experimental searches and interpret them within the two Higgs doublet model. In addition, we show that these limits can be improved by about two orders of magnitude with appropriate selection cuts immediately with existing data sets. We also discuss expected sensitivities with integrated luminosity up to 3 ab −1 and present a brief overview of other channels.

New constraints and discovery potential for Higgs to Higgs cascade decays through vectorlike leptons

In models with extended Higgs sector and additional matter fields, the decay modes of heavy Higgs bosons can be dominated by cascade decays through the new fermions rendering present search strategies ineffective. We investigate new decay topologies of heavy neutral Higgses in two Higgs doublet model with vectorlike leptons. We also discus constraints from existing searches and discovery prospects. Among the most interesting signatures are monojet, mono Z, mono Higgs, and Z and Higgs bosons produced with a pair of charged leptons.

New decay modes of heavy Higgs bosons in a two Higgs doublet model with vectorlike leptons

We study a two Higgs doublet model extended by vectorlike leptons mixing with one family of standard model leptons. Generated flavor violating couplings between heavy and light leptons can dramatically alter the decay patterns of heavier Higgs bosons. We focus on pp → H → ν 4 ν μ → W μν μ , where ν 4 is a new neutral lepton, and study possible effects of this process on the measurements of pp → W W and H → W W since it leads to the same final states. We discuss predictions for contributions to pp → W W and H → WW and their correlations from the region of the parameter space that satisfies all available constraints including precision electroweak observables and from pair production of vectorlike leptons. Large contributions, close to current limits, favor small tan β region of the parameter space. We find that, as a result of adopted cuts in experimental analyses, the contribution to pp → W W can be an order of magnitude larger than the contribution to H → W W . Thus, future precise measurements of pp → W W will further constrain the parameters of the model. In addition, we also consider possible contributions to pp → W W from the heavy Higgs decays into a new charged lepton e 4 ( H → e 4 μ → W μν μ ), exotic SM Higgs decays, and pair production of vectorlike leptons.

Two Higgs doublet model with vectorlike leptons and contributions to pp → W W and H → W W

We study contributions to  <math><mi>pp</mi><mo>→</mo><msup><mi>W</mi><mo>+</mo></msup><msup><mi>W</mi><mo>−</mo></msup><mo>→</mo><mi>ℓ</mi><msub><mi>ν</mi><mi>ℓ</mi></msub><msup><mi>ℓ</mi><mo>′</mo></msup><msub><mi>ν</mi><msup><mi>ℓ</mi><mo>′</mo></msup></msub></math> $$ pp\to {W}^{+}{W}^{-}\to \ell {\nu}_{\ell }{\ell}^{\prime }{\nu}_{\ell^{\prime }} $$ in models with a new Higgs boson, H, and a neutral lepton, ν 4, with couplings H − ν 4 − ν  μ  and W − ν 4 −  <math><mi>μ</mi></math> $$ \mu $$ through the process pp → H → ν 4 ν  μ  → Wμν  μ  → ℓν  ℓ  μν  μ . Contrary to naive expectations, we find that contributions to pp → W W can be very large while satisfying constraints from standard H → W W and H → γγ searches. Even the excess observed by ATLAS in pp → W W , if taken at face value, can be easily accommodated. The various kinematic distributions fit nicely the experimentally determined ones. This scenario can arise for example in a two Higgs doublet model with vectorlike leptons.

Contributions of flavor violating couplings of a Higgs boson to pp → W W

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 → Wμ ) = 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.