Simultaneous extraction of the Fermi constant and PMNS matrix elements in the presence of a fourth generation

Lacker, H.; Menzel, Andreas M.

doi:10.1007/jhep07(2010)006

Cited by 44 publications

(47 citation statements)

References 62 publications

(68 reference statements)

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“…The phenomenological consequences of a fourth generation on the flavour sector of neutrinos, charged leptons and quarks have been extensively explored (cf., e.g., Refs. [74][75][76][77][78][79][80][81][82][83][84][85] and the review [86]). The impact on electroweak precision data at the Z-pole and on Higgs physics has been studied in Refs.…”

Section: Models With a Sequential Fourth Fermion Generationmentioning

confidence: 99%

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Updated status of the global electroweak fit and constraints on new physics

Goêbel²,

et al. 2012

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-We present an update of the Standard Model fit to electroweak precision data. We include newest experimental results on the top quark mass, the W mass and width, and the Higgs boson mass bounds from LEP, Tevatron and the LHC. We also include a new determination of the electromagnetic coupling strength at the Z pole. We find for the Higgs boson mass 91 +30 −23 GeV and 120 +12−5 GeV when not including and including the direct Higgs searches, respectively. From the latter fit we indirectly determine the W mass to be (80.360 +0.014 −0.013 ) GeV. We exploit the data to determine experimental constraints on the oblique vacuum polarisation parameters, and confront these with predictions from the Standard Model (SM) and selected SM extensions. By fitting the oblique parameters to the electroweak data we derive allowed regions in the BSM parameter spaces. We revisit and consistently update these constraints for a fourth fermion generation, two Higgs doublet, inert Higgs and littlest Higgs models, models with large, universal or warped extra dimensions and technicolour. In most of the models studied a heavy Higgs boson can be made compatible with the electroweak precision data.

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Section: Models With a Sequential Fourth Fermion Generationmentioning

confidence: 99%

“…The value of |V tb | is found in this analysis to exceed 0.93. The no-mixing assumption allows us to use the measured value of GF , extracted from the muon lifetime under the SM3 hypothesis, to its full precision [84].…”

Section: Models With a Sequential Fourth Fermion Generationmentioning

confidence: 99%

Updated status of the global electroweak fit and constraints on new physics

Goêbel²,

et al. 2012

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show abstract

“…We treat the masses of the extra fermions as free parameters and allow for arbitrary flavor mixings among the quarks of the four generations in our fits. Large mixings of the fourth-generation lepton doublet with those of the first three generations are ruled out [1] from data on lepton-flavor violating decays and lepton-flavor universality [2]. Recent NA62 data constrain these mixing angles even further [3].…”

Section: Methods and Inputsmentioning

confidence: 99%

Status of the fourth fermion generation before ICHEP2012: Higgs data and electroweak precision observables

et al. 2012

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We perform a global fit of the parameters of the Standard Model with a sequential fourth generation (SM4) to LHC and Tevatron Higgs data and electroweak precision data. Using several likelihood ratio tests, we compare the performance of the SM4 and the Standard Model (SM3) at describing the measured data. Since the SM3 and SM4 are not nested (i.e., the SM3 cannot be considered as a special case of the SM4 with some parameters fixed), the usual analytical formulae for p-values in likelihood ratio tests do not hold. We thus apply a new method to compute these p-values. For a Higgs mass of 126.5 GeV and fourth-generation quark masses above 600 GeV, we find that the SM4 is excluded at 3:1. I. METHOD AND INPUTSIn this paper, we study the Standard Model with a sequential fourth generation (SM4), which differs from the established Standard Model (denoted by SM3) by an additional fermion generation. We treat the masses of the extra fermions as free parameters and allow for arbitrary flavor mixings among the quarks of the four generations in our fits. Large mixings of the fourth-generation lepton doublet with those of the first three generations are ruled out [1] from data on lepton-flavor violating decays and lepton-flavor universality [2]. Recent NA62 data constrain these mixing angles even further [3]. Including lepton mixing within the allowed range has a negligible impact on the electroweak precision observables (EWPOs). In the absence of lepton mixing, the decay of the Higgs boson into neutrinos is invisible as long as the fourth-generation charged lepton is heavier than the corresponding neutrino. This invisible Higgs decay mode increases the total Higgs width and potentially counterbalances the effect of the enhanced gg ! H production mechanism [4,5], because the branching fractions into the observed final states are reduced [6,7]. Allowing for (even small) mixing of the fourth with the other lepton doublets can render the neutrino decay mode visible. Since we want to quantify the level at which the SM4 is ruled out, we may confine ourselves to the most conservative scenario with an unmixed fourth-generation lepton doublet. Like the SM3, the SM4 can be studied with Dirac or Majorana neutrinos. In the fits presented in this paper, we use Dirac neutrinos. In our conclusions, we briefly discuss the (marginal) changes in the results expected for Majorana neutrinos.From a model-building point of view, the hierarchy between three almost massless neutrinos and a fourth neutrino with mass of order of the electroweak scale can be motivated by a symmetry enforcing massless neutrinos in the exact symmetry limit: e.g., three right-handed neutrino fields might carry some U(1) charge while the fourth neutrino field and the left-handed lepton doublets are uncharged under this new symmetry. The Yukawa couplings are small spurions breaking this symmetry, leading to three tiny neutrino masses and tiny mixings between the fourth and the other generations.A sequential fourth generation of fermions decouples neither from the product...

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“…In a model, where charged Higgs exchange is the dominant SUSY contribution, an increase of R K by O(1%) could be possible [11]. R K is also sensitive to neutrino mixing parameters with SM extensions involving a fourth generation of quarks and leptons [12] or sterile neutrinos [13]. Indeed, new physics that differentiates between lepton species has been discussed, e.g.…”

Section: Search For Lepton-universality Violation In a Measurement Ofmentioning

confidence: 99%

Searches for New Physics with the TREK Detector

Strauch¹

2013

Proceedings of 2013 Kaon Physics International Conference — PoS(KAON13)

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The KEK Experiment E246 has provided the best upper limit of the transverse muon polarization in K µ3 decays to date. The TREK collaboration is now upgrading the E246 detector and upcoming experiments with this detector at the J-PARC facility will allow new high-precision measurements in search for physics beyond the Standard Model. These measurements include the search for T violation in kaon decays, the search for lepton universality violation in the ratio of the K e2 and K µ2 decay widths, as well as the search for a heavy sterile neutrino and a massive gauge boson A .

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Simultaneous extraction of the Fermi constant and PMNS matrix elements in the presence of a fourth generation

Cited by 44 publications

References 62 publications

Updated status of the global electroweak fit and constraints on new physics

Updated status of the global electroweak fit and constraints on new physics

Status of the fourth fermion generation before ICHEP2012: Higgs data and electroweak precision observables

Searches for New Physics with the TREK Detector

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