Electroweak limits on general new vector bosons

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Abstract:We classify all possible new scalar particles that can have renormalizable linear couplings to Standard Model fields and therefore be singly produced at colliders. We show that this classification exhausts the list of heavy scalar particles that contribute at the tree level to the Standard Model effective Lagrangian to dimension six. We compute this effective Lagrangian for a general scenario with an arbitrary number of new scalar particles and obtain flavor-preserving constraints on their couplings and masses. This completes the tree-level matching of the coefficients of dimension five and six operators in the effective Lagrangian to arbitrary extensions of the Standard Model.

Section: Jhep04(2015)078supporting

confidence: 61%

Section: Jhep04(2015)078mentioning

confidence: 99%

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Observable effects of general new scalar particles

Blas

Chala

Pérez-Victoria

et al. 2015

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“…To this end, we use the list of models presented in ref. [28], considering the addition of each new particle individually. (These models were examined in the context of the forward-backward asymmetry in e.g.…”

Section: Jhep12(2012)053mentioning

confidence: 99%

Predictions from heavy new physics interpretation of the top forward-backward asymmetry

Delaunay

Gedalia

Hochberg

et al. 2012

We derive generic predictions at hadron colliders from the large forwardbackward asymmetry observed at the Tevatron, assuming the latter arises from heavy new physics beyond the Standard Model. We use an effective field theory approach to characterize the associated unknown dynamics. By fitting the Tevatron tt data we derive constraints on the form of the new physics. Furthermore, we show that heavy new physics explaining the Tevatron data generically enhances at high invariant masses both the top pair production cross section and the charge asymmetry at the LHC. This enhancement can be within the sensitivity of the 8 TeV run, such that the 2012 LHC data should be able to exclude a large class of models of heavy new physics or provide hints for its presence. The same new physics implies a contribution to the forward-backward asymmetry in bottom pair production at low invariant masses of order a permil at most.

“…This discrepancy and its interplay with the indirect determination of the Higgs mass has stimulated a number of theoretical works that attempt to resolve this mystery, see e.g. [12], [13], [11], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23].…”

mentioning

confidence: 99%

Higgs couplings and precision electroweak data

Batell

Gori

Wang

2013

In light of the discovery of a Higgs-like particle at the LHC, we revisit the status of the precision electroweak data, focusing on two discrepant observables: 1) the long-standing 2.4σ deviation in the forward-backward asymmetry of the bottom quark A b F B , and 2) the 2.3σ deviation in R b , the ratio of the Z → bb partial width to the inclusive hadronic width, which is now in tension after a recent calculation including new two-loop electroweak corrections. We consider possible resolutions of these discrepancies. Taking the data at face value, the most compelling scenario is that new physics directly affects A b F B and R b , bringing the prediction into accord with the measured values. We propose a modified 'Beautiful Mirrors' scenario which contains new vector-like quarks that mix with the b quark, modifying the Zbb vertex and thus correcting A b F B and R b . We show that this scenario can lead to modifications to the production rates of the Higgs boson in certain channels, and in particular a sizable enhancement in the diphoton channel. We also describe additional collider tests of this scenario.The ATLAS and CMS experiments have recently discovered a new boson with properties closely resembling those of the Standard Model (SM) Higgs boson [1,2]. The focus of the experimental collaborations now turns to determining the properties of this state, such as its quantum numbers and its couplings to other SM particles. This is an extremely important task since any deviation from the SM Higgs boson predictions will unambiguously point to new physics (NP) at the TeV scale. In this respect it is intriguing that both experiments observe a slight enhancement in the h → γγ channel, though with the current dataset this enhancement is not statistically significant [3, 4].If, as the current data suggest, this new state is indeed the Higgs boson, its mass m h ∼ 125 GeV will be in accord with the expectation indirectly suggested by the precision electroweak data, which favors a light SMlike Higgs boson. Of the many precision measurements used to test the electroweak sector, most of them are in good agreement with the SM predictions, see for example [5],[6], [7]. However, there are a couple of notable discrepancies. The forward-backward asymmetry of the bottom quark A b F B measured at the Z-pole at LEP1 constitutes a long-standing exception. The measured value and SM prediction are [5], [7],and thus exhibit a 2.4σ discrepancy. Furthermore, a recent calculation of R b , the ratio of the Z → bb partial width to the inclusive hadronic width, which includes new two-loop electroweak corrections, now puts the prediction in tension with the measured value [8]. The measurement and prediction read [5], [7],displaying a 2.3σ discrepancy.It is a matter of debate whether these deviations call for NP. Among a large ensemble of measurements, such as that used in the electroweak fit, one may expect an occasional discrepancy of this size, which could be the result of a statistical fluctuation or unknown systematic error. However, a possib...