scholarly journals Global analysis of leptophilic Z′ bosons

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Andrzej J. Buras ◽  
Andreas Crivellin ◽  
Fiona Kirk ◽  
Claudio Andrea Manzari ◽  
Marc Montull
Keyword(s):  
Global Analysis ◽  
Magnetic Moments ◽  
Z Bosons ◽  
Left Handed ◽  
The Standard Model ◽  
Global Fit ◽  
Charged Leptons ◽  
Precision Observables ◽  
Electroweak Precision ◽  
Additional Constraints

Abstract New neutral heavy gauge bosons (Z′) are predicted within many extensions of the Standard Model. While in case they couple to quarks the LHC bounds are very stringent, leptophilic Z′ bosons (even with sizable couplings) can be much lighter and therefore lead to interesting quantum effects in precision observables (like (g − 2)μ) and generate flavour violating decays of charged leptons. In particular, $$ \mathrm{\ell}\to \mathrm{\ell}^{\prime }v\overline{v} $$ ℓ → ℓ ′ v v ¯ decays, anomalous magnetic moments of charged leptons, ℓ → ℓ′γ and ℓ → 3ℓ′ decays place stringent limits on leptophilic Z′ bosons. Furthermore, in case of mixing Z′ with the SM Z, Z pole observables are affected. In light of these many observables we perform a global fit to leptophilic Z′ models with the main goal of finding the bounds for the Z′ couplings to leptons. To this end we consider a number of scenarios for these couplings. While in generic scenarios correlations are weak, this changes once additional constraints on the couplings are imposed. In particular, if one considers an Lμ− Lτ symmetry broken only by left-handed rotations, or considers the case of τ − μ couplings only. In the latter setup, on can explain the (g − 2)μ anomaly and the hint for lepton flavour universality violation in $$ \tau \to \mu v\overline{v}/\tau \to ev\overline{v} $$ τ → μv v ¯ / τ → ev v ¯ without violating bounds from electroweak precision observables.

scholarly journals Constraining the gauge and scalar sectors of the doublet left-right symmetric model

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Véronique Bernard ◽  
Sébastien Descotes-Genon ◽  
Luiz Vale Silva
Keyword(s):  
Symmetry Breaking ◽  
Electroweak Symmetry Breaking ◽  
Symmetric Model ◽  
Electroweak Symmetry ◽  
Gauge Bosons ◽  
Spontaneous Breakdown ◽  
The Standard Model ◽  
Low Energies ◽  
Precision Observables ◽  
Electroweak Precision

Abstract We consider a left-right symmetric extension of the Standard Model where the spontaneous breakdown of the left-right symmetry is triggered by doublets. The electroweak ρ parameter is protected from large corrections in this Doublet Left-Right Model (DLRM), contrary to the triplet case. This allows in principle for more diverse patterns of symmetry breaking. We consider several constraints on the gauge and scalar sectors of DLRM: the unitarity of scattering processes involving gauge bosons with longitudinal polarisations, the radiative corrections to the muon ∆r parameter and the electroweak precision observables measured at the Z pole and at low energies. Combining these constraints within the frequentist CKMfitter approach, we see that the fit pushes the scale of left-right symmetry breaking up to a few TeV, while favouring an electroweak symmetry breaking triggered not only by the SU(2)L×SU(2)R bi-doublet, which is the case most commonly considered in the literature, but also by the SU(2)L doublet.

scholarly journals Theory requirements for SM Higgs and EW precision physics at the FCC-ee

2021 ◽  
Vol 136 (9) ◽  
Author(s):  
S. Heinemeyer ◽  
S. Jadach ◽  
J. Reuter
Keyword(s):  
Higgs Boson ◽  
Standard Model ◽  
High Precision ◽  
Boson Mass ◽  
Experimental Measurements ◽  
Mixing Angle ◽  
The Standard Model ◽  
The Status ◽  
Precision Observables ◽  
Electroweak Precision

AbstractHigh-precision experimental measurements of the properties of the Higgs boson at $$\sim 125$$ ∼ 125  GeV as well as electroweak precision observables such as the W-boson mass or the effective weak leptonic mixing angle are expected at future $$e^+e^-$$ e + e - colliders such as the FCC-ee. This high anticipated precision has to be matched with theory predictions for the measured quantities at the same level of accuracy. We briefly summarize the status of these predictions within the standard model and of the tools that are used for their determination. We outline how the theory predictions will have to be improved in order to reach the required accuracy, and also comment on the simulation frameworks for the Higgs and EW precision program.

scholarly journals Global fits of third family hypercharge models to neutral current B-anomalies and electroweak precision observables

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
B. C. Allanach ◽  
J. Eliel Camargo-Molina ◽  
Joe Davighi
Keyword(s):  
Standard Model ◽  
Neutral Current ◽  
Data Set ◽  
The Standard Model ◽  
Precision Observables ◽  
Electroweak Precision ◽  
Combined Data

AbstractWhile it is known that third family hypercharge models can explain the neutral current B-anomalies, it was hitherto unclear whether the $$Z-Z^\prime $$ Z - Z ′ mixing predicted by such models could simultaneously fit electroweak precision observables. Here, we perform global fits of several third family hypercharge models to a combination of electroweak data and those data pertinent to the neutral current B-anomalies. While the Standard Model is in tension with this combined data set with a p-value of .0007, simple versions of the models (fitting two additional parameters each) provide much improved fits. The original Third Family Hypercharge Model, for example, has a p-value of $${.065}$$ . 065 , with $$\sqrt{\Delta \chi ^2}=6.5\sigma $$ Δ χ 2 = 6.5 σ .

scholarly journals On a standard model extension with vector-like fermions and Abelian symmetry

2020 ◽  
Vol 30 (3) ◽  
Author(s):  
Hieu Minh Tran ◽  
Sang Quang Dinh ◽  
Trang Quynh Trieu
Keyword(s):  
Mass Spectrum ◽  
Gauge Symmetry ◽  
Standard Model ◽  
Z Bosons ◽  
Lepton Sector ◽  
Standard Model Extension ◽  
Abelian Gauge ◽  
Model Extension ◽  
The Standard Model ◽  
Electroweak Precision

We investigate an extension of the standard model with vector-like fermions and an extra Abelian gauge symmetry. The particle mass spectrum is calculated explicitly. The Lagrangian terms for all the gauge interactions of leptons and quarks in the model are derived. We observe that while there is no new mixing in the lepton sector, the quark mixing plays an important role in the magnitudes of gauge interactions for quarks, particularly the interactions with massive \(W\), \(Z\) and \(Z'\) bosons. We calculate the contributions of the new vector-like leptons and quarks to the Peskin-Takeuchi parameters as well as the \(\rho\) parameter of the electroweak precision tests, and show that the model is realistic.

scholarly journals EFFECTIVE THEORIES AND ELECTROWEAK PRECISION CONSTRAINTS

2008 ◽  
Vol 23 (18) ◽  
pp. 2653-2685 ◽  
Author(s):  
ZHENYU HAN
Keyword(s):  
Standard Model ◽  
New Physics ◽  
Effective Theory ◽  
Theory Method ◽  
The Standard Model ◽  
Precision Observables ◽  
Electroweak Precision ◽  
Effective Theories ◽  
Effective Operators

This is a pedagogical and self-contained review on obtaining electroweak precision constraints on TeV scale new physics using the effective theory method. We identify a set of relevant effective operators in the Standard Model and calculate from them corrections to all major electroweak precision observables. The corrections are compared with data to put constraints on the effective operators. Various approaches and applications in the literature are reviewed.

scholarly journals STATUS OF STANDARD MODEL CALCULATION OF LEPTON g - 2

2014 ◽  
Vol 35 ◽  
pp. 1460405 ◽  
Author(s):  
MARC KNECHT
Keyword(s):  
Standard Model ◽  
Magnetic Moments ◽  
Structure Constant ◽  
Fine Structure Constant ◽  
Precision Determination ◽  
The Standard Model ◽  
Charged Leptons ◽  
Experimental Values ◽  
High Precision Determination

The contributions from the standard model interactions to the anomalous magnetic moments of the two lightest charged leptons, the electron and the muon, are reviewed. Comparison with the very accurately measured experimental values is made, using the most recent high-precision determination of the fine structure constant.

scholarly journals Mixed EW-QCD leading fermionic three-loop corrections at $$ \mathcal{O} $$(αsα2) to electroweak precision observables

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Lisong Chen ◽  
Ayres Freitas
Keyword(s):  
Top Quark ◽  
Z Boson ◽  
W Boson ◽  
Boson Mass ◽  
Top Quark Mass ◽  
Weak Mixing Angle ◽  
Mixing Angle ◽  
The Standard Model ◽  
Precision Observables ◽  
Electroweak Precision

Abstract Measurements of electroweak precision observables at future electron-position colliders, such as the CEPC, FCC-ee, and ILC, will be sensitive to physics at multi-TeV scales. To achieve this sensitivity, precise predictions for the Standard Model expectations of these observables are needed, including corrections at the three- and four-loop level. In this article, results are presented for the calculation of a subset of three-loop mixed electroweak-QCD corrections, stemming from diagrams with a gluon exchange and two closed fermion loops. The numerical impact of these corrections is illustrated for a number of applications: the prediction of the W-boson mass from the Fermi constant, the effective weak mixing angle, and the partial and total widths of the Z boson. Two alternative renormalization schemes for the top-quark mass are considered, on-shell and $$ \overline{\mathrm{MS}} $$ MS ¯ .

scholarly journals The Gauge-Higgs legacy of the LHC run II

2019 ◽  
Vol 6 (6) ◽  
Author(s):  
Anke Biekoetter ◽  
Tyler Corbett ◽  
Tilman Plehn
Keyword(s):  
Global Analysis ◽  
Physics Program ◽  
Combine Rate ◽  
Electroweak Sector ◽  
Precision Observables ◽  
Electroweak Precision ◽  
Effective Operators

We present a global analysis of the Higgs and electroweak sector based on LHC Run II and electroweak precision observables. We show which measurements provide the leading constraints on Higgs-related operators, and how the achieved LHC precision makes it necessary to combine rate measurements with electroweak precision observables. The SFitter framework allows us to include kinematic distributions beyond pre-defined ATLAS and CMS observables, independently study correlations, and avoid Gaussian assumptions for theory uncertainties. These Run II results are a step towards a precision physics program at the LHC, interpreted in terms of effective operators.

scholarly journals Flavour violating effects of Yukawa running in SMEFT

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Jason Aebischer ◽  
Jacky Kumar
Keyword(s):  
Renormalization Group ◽  
Standard Model ◽  
Low Energy ◽  
Effective Theory ◽  
Rotation Effect ◽  
High Scale ◽  
The Standard Model ◽  
Flavour Violation ◽  
Precision Observables ◽  
Electroweak Precision

Abstract We study Yukawa Renormalization Group (RG) running effects in the context of the Standard Model Effective Theory (SMEFT). The Yukawa running being flavour dependent leads to RG-induced off-diagonal entries, so that initially diagonal Yukawa matrices at the high scale have to be rediagonalized at the electroweak (EW) scale. Performing such flavour rotations can lead to flavour violating operators which differ from the ones obtained through SMEFT RG evolution. We show, that these flavour rotations can have a large impact on low-energy phenomenology. In order to demonstrate this effect, we com- pare the two sources of flavour violation numerically as well as analytically and study their influence on several examples of down-type flavour transitions. For this purpose we con- sider $$ {B}_s-{\overline{B}}_s $$ B s − B ¯ s mixing, b → sγ, b → sℓℓ as well as electroweak precision observables. We show that the rotation effect can be comparable or even larger than the contribution from pure RGE evolution of the Wilson coefficients.

Sign in / Sign up

Export Citation Format

Share Document