scholarly journals Global electroweak fit and vector-like leptons in light of the Cabibbo angle anomaly

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Andreas Crivellin ◽  
Fiona Kirk ◽  
Claudio Andrea Manzari ◽  
Marc Montull
Keyword(s):  
New Physics ◽  
Tree Level ◽  
Cabibbo Angle ◽  
Kaon Decays ◽  
Context Vector ◽  
Global Fit ◽  
Best Fit ◽  
Invariant Dimension ◽  
Better Than ◽  
Lepton Flavour

Abstract The “Cabibbo Angle Anomaly” (CAA) originates from the disagreement between the CKM elements Vud and Vus extracted from superallowed beta and kaon decays, respectively, once compared via CKM unitarity. It points towards new physics with a significance of up to 4 σ, depending on the theoretical input used, and can be explained through modified W couplings to leptons. In this context, vector-like leptons (VLLs) are prime candidates for a corresponding UV completion since they can affect Wℓν couplings at tree-level, such that this modification can have the dominant phenomenological impact. In order to consistently assess agreement data, a global fit is necessary which we perform for gauge-invariant dimension-6 operators and all patterns obtained for the six possible representations (under the SM gauge group) of VLLs. We find that even in the lepton flavour universal case, including the measurements of the CKM elements Vus and Vud into the electroweak fit has a relevant impact, shifting the best fit point significantly. Concerning the VLLs we discuss the bounds from charged lepton flavour violating processes and observe that a single representation cannot describe experimental data significantly better than the SM hypothesis. However, allowing for several representations of VLLs at the same time, we find that the simple scenario in which N couples to electrons via the Higgs and Σ1 couples to muons not only explains the CAA but also improves the rest of the electroweak fit in such a way that its best fit point is preferred by more than 4 σ with respect to the begin.

scholarly journals QUARK MIXING AND CP VIOLATION — THE CKM MATRIX

2006 ◽  
Vol 21 (08n09) ◽  
pp. 1724-1737 ◽  
Author(s):  
ULRICH NIERSTE
Keyword(s):  
Neutral Current ◽  
New Physics ◽  
Tree Level ◽  
B Decays ◽  
Ckm Matrix ◽  
Penguin Decays ◽  
The Status ◽  
First Results ◽  
Global Fit

I summarize the theoretical progress in the determination of the CKM elements since Lepton-Photon 2003 and present the status of the elements and parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. One finds |Vus| = 0.2227 ± 0.0017 from K and τ decays and |Vcb| = (41.6 ± 0.5) · 10-3 from inclusive semileptonic B decays. The unitarity triangle can now be determined from tree-level quantities alone and the result agrees well with the global fit including flavour-changing neutral current (FCNC) processes, which are sensitive to new physics. From the global fit one finds the three CKM angles θ12 = 12.9° ± 0.1°, θ23 = 2.38° ± 0.03° and θ13 = 0.223° ± 0.007° in the standard PDG convention. The CP phase equals [Formula: see text] at 1σ CL and [Formula: see text] at 2σ CL. A major progress are first results from fully unquenched lattice QCD computations for the hadronic quantities entering the UT fit. I further present the calculation of three-loop QCD corrections to the charm contribution in [Formula: see text] decays, which removes the last relevant theoretical uncertainty from the [Formula: see text] system. Finally I discuss mixing-induced CP asymmetries in [Formula: see text] penguin decays, whose naive average is below its Standard Model value by 3σ.

scholarly journals First-generation new physics in simplified models: from low-energy parity violation to the LHC

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
Andreas Crivellin ◽  
Martin Hoferichter ◽  
Matthew Kirk ◽  
Claudio Andrea Manzari ◽  
Luc Schnell
Keyword(s):  
Parity Violation ◽  
First Generation ◽  
New Physics ◽  
Effective Field ◽  
Low Energy ◽  
Tree Level ◽  
Cabibbo Angle ◽  
Simplified Models ◽  
Precision Observables ◽  
Electroweak Precision

Abstract New-physics (NP) constraints on first-generation quark-lepton interactions are particularly interesting given the large number of complementary processes and observables that have been measured. Recently, first hints for such NP effects have been observed as an apparent deficit in first-row CKM unitarity, known as the Cabibbo angle anomaly, and the CMS excess in $$ q\overline{q} $$ q q ¯ → e+e−. Since the same NP would inevitably enter in searches for low-energy parity violation, such as atomic parity violation, parity-violating electron scattering, and coherent neutrino-nucleus scattering, as well as electroweak precision observables, a combined analysis is required to assess the viability of potential NP interpretations. In this article we investigate the interplay between LHC searches, the Cabibbo angle anomaly, electroweak precision observables, and low-energy parity violation by studying all simplified models that give rise to tree-level effects related to interactions between first-generation quarks and leptons. Matching these models onto Standard Model effective field theory, we derive master formulae in terms of the respective Wilson coefficients, perform a complete phenomenological analysis of all available constraints, point out how parity violation can in the future be used to disentangle different NP scenarios, and project the constraints achievable with forthcoming experiments.

scholarly journals The impact of flavour data on global fits of the MFV SMEFT

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Rafael Aoude ◽  
Tobias Hurth ◽  
Sophie Renner ◽  
William Shepherd
Keyword(s):  
Initial Conditions ◽  
New Physics ◽  
Effective Field ◽  
Tree Level ◽  
Minimal Flavour Violation ◽  
The Standard Model ◽  
Flavour Violation ◽  
Stringent Test ◽  
Global Fit ◽  
The Impact

Abstract We investigate the information that can be gained by including flavour data in fits of the Standard Model Effective Field Theory (SMEFT) with the assumption of Minimal Flavour Violation (MFV), allowing — as initial conditions at the high scale — leading terms in spurionic Yukawas only. Starting therefore from a theory with no tree level flavour changing neutral currents at the scale of new physics, we calculate effects in flavour changing processes at one loop, and the resulting constraints on linear combinations of SMEFT coefficients, consistently parameterising the electroweak parameters and the CKM within the SMEFT. By doing a global fit including electroweak, Higgs and low energy precision measurements among others, we show that flavour observables put strong constraints on previously unconstrained operator directions. The addition of flavour data produces four independent constraints at order TeV or above on otherwise flat directions; reducing to three when complete U(3)5 flavour symmetry is assumed. Our findings demonstrate that flavour remains a stringent test for models of new physics, even in the most flavourless scenario.

scholarly journals Predictions for $$B_s \rightarrow {\bar{K}}^* \ell \,\ell $$ in non-universal $$Z'$$ models

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
Ashutosh Kumar Alok ◽  
Amol Dighe ◽  
Shireen Gangal ◽  
Dinesh Kumar
Keyword(s):  
Branching Ratio ◽  
New Physics ◽  
Significant Enhancement ◽  
Wilson Coefficient ◽  
Zero Crossing ◽  
Meson Decays ◽  
Lepton Flavor ◽  
Simultaneous Measurements ◽  
Global Fit ◽  
Best Fit

Abstract The lepton flavor universality violating (LFUV) measurements $$R_K$$RK and $$R_{K^*}$$RK∗ in B meson decays can be accounted for in non-universal $$Z'$$Z′ models. We constrain the couplings of these $$Z'$$Z′ models by performing a global fit to correlated $$b \rightarrow s \ell \ell $$b→sℓℓ and $$b \rightarrow d \ell \ell $$b→dℓℓ processes, and calculate their possible implications for $$B_s \rightarrow {\bar{K}}^*\ell \ell $$Bs→K¯∗ℓℓ observables. For real new physics (NP) couplings, the 1$$\sigma $$σ favored parameters allow the corresponding LFUV ratio $$R_{K^*}^{(s)}$$RK∗(s) in $$B_s \rightarrow {\bar{K}}^*\ell \ell $$Bs→K¯∗ℓℓ to range between 0.8 and 1.2 at low $$q^2$$q2. Complex NP couplings improve the best fit only marginally, however they allow a significant enhancement of the branching ratio, while increasing the range of $$R_{K^*}^{(s)}\ $$RK∗(s)at low $$q^2$$q2 to 0.8–1.8. We find that NP could cause zero-crossing in the forward–backward asymmetry $$A_{FB}$$AFB to shift towards lower $$q^2$$q2 values, and enhancement in the magnitude of integrated $$A_{FB}$$AFB. The CP asymmetry $$A_{CP}$$ACP may be suppressed and even change sign. The simultaneous measurements of integrated $$R_{K^*}^{(s)}\ $$RK∗(s)and $$A_{CP}$$ACP values to 0.1 and 1% respectively, would help in constraining the effective NP Wilson coefficient $$C_9$$C9 in $$ b \rightarrow d \mu \mu $$b→dμμ interactions.

scholarly journals Interplay of New Physics effects in (g − 2)ℓ and h → ℓ+ℓ− — lessons from SMEFT

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Svjetlana Fajfer ◽  
Jernej F. Kamenik ◽  
M. Tammaro
Keyword(s):  
Closed Operator ◽  
Higgs Doublet ◽  
New Physics ◽  
Effective Field ◽  
Tree Level ◽  
Electroweak Symmetry ◽  
Scalar Leptoquark ◽  
Doublet Model ◽  
The One ◽  
Two Higgs Doublet Model

Abstract We explore the interplay of New Physics (NP) effects in (g− 2)ℓ and h→ℓ+ℓ− within the Standard Model Effective Field Theory (SMEFT) framework, including one-loop Renormalization Group (RG) evolution of the Wilson coefficients as well as matching to the observables below the electroweak symmetry breaking scale. We include both the leading dimension six chirality flipping operators including a Higgs and SU(2)L gauge bosons as well as four-fermion scalar and tensor operators, forming a closed operator set under the SMEFT RG equations. We compare present and future experimental sensitivity to different representative benchmark scenarios. We also consider two simple UV completions, a Two Higgs Doublet Model and a single scalar LeptoQuark extension of the SM, and show how tree level matching to SMEFT followed by the one-loop RG evolution down to the electroweak scale can reproduce with high accuracy the (g−2)ℓ and h→ℓ+ℓ− contributions obtained by the complete one- and even two-loop calculations in the full models.

scholarly journals Flavour Anomalies in a U(1) SUSY Extension of the SM

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 191
Author(s):  
Alexander Bednyakov ◽  
Alfiia Mukhaeva
Keyword(s):  
Standard Model ◽  
Parameter Space ◽  
Gauge Boson ◽  
New Physics ◽  
Low Energy ◽  
Effective Theory ◽  
The Standard Model ◽  
Meson Mixing ◽  
Additional Anomaly ◽  
Lepton Flavour

Flavour anomalies have attracted a lot of attention over recent years as they provide unique hints for possible New Physics. Here, we consider a supersymmetric (SUSY) extension of the Standard Model (SM) with an additional anomaly-free gauge U(1) group. The key feature of our model is the particular choice of non-universal charges to the gauge boson Z′, which not only allows a relaxation of the flavour discrepancies but, contrary to previous studies, can reproduce the SM mixing matrices both in the quark and lepton sectors. We pay special attention to the latter and explicitly enumerate all parameters relevant for our calculation in the low-energy effective theory. We find regions in the parameter space that satisfy experimental constraints on meson mixing and LHC Z′ searches and can alleviate the flavour anomalies. In addition, we also discuss the predictions for lepton-flavour violating decays B+→K+μτ and B+→K+eτ.

scholarly journals Exploding operators for Majorana neutrino masses and beyond

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
John Gargalionis ◽  
Raymond R. Volkas
Keyword(s):  
Neutrino Mass ◽  
Model Building ◽  
Dominant Role ◽  
New Physics ◽  
Majorana Neutrino ◽  
Effective Field ◽  
Tree Level ◽  
Mass Generation ◽  
Neutrino Mass Models ◽  
Almost All

Abstract Building UV completions of lepton-number-violating effective operators has proved to be a useful way of studying and classifying models of Majorana neutrino mass. In this paper we describe and implement an algorithm that systematises this model-building procedure. We use the algorithm to generate computational representations of all of the tree-level completions of the operators up to and including mass-dimension 11. Almost all of these correspond to models of radiative neutrino mass. Our work includes operators involving derivatives, updated estimates for the bounds on the new-physics scale associated with each operator, an analysis of various features of the models, and a look at some examples. We find that a number of operators do not admit any completions not also generating lower-dimensional operators or larger contributions to the neutrino mass, ruling them out as playing a dominant role in the neutrino-mass generation. Additionally, we show that there are at most five models containing three or fewer exotic multiplets that predict new physics that must lie below 100 TeV. Accompanying this work we also make available a searchable database containing all of our results and the code used to find the completions. We emphasise that our methods extend beyond the study of neutrino-mass models, and may be useful for generating completions of high-dimensional operators in other effective field theories. Example code: ref. [37].

scholarly journals Cosmological phase transitions: is effective field theory just a toy?

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Marieke Postma ◽  
Graham White
Keyword(s):  
Field Theory ◽  
Phase Transition ◽  
Phase Transitions ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Tree Level ◽  
Dark Sector ◽  
First Order ◽  
First Order Phase

Abstract To obtain a first order phase transition requires large new physics corrections to the Standard Model (SM) Higgs potential. This implies that the scale of new physics is relatively low, raising the question whether an effective field theory (EFT) description can be used to analyse the phase transition in a (nearly) model-independent way. We show analytically and numerically that first order phase transitions in perturbative extensions of the SM cannot be described by the SM-EFT. The exception are Higgs-singlet extension with tree-level matching; but even in this case the SM-EFT can only capture part of the full parameter space, and if truncated at dim-6 operators, the description is at most qualitative. We also comment on the applicability of EFT techniques to dark sector phase transitions.

scholarly journals Constructing Semantic Models From Words, Images, and Emojis

2020 ◽  
Author(s):  
Armand Stefan Rotaru ◽  
Gabriella Vigliocco
Keyword(s):  
Visual Information ◽  
Semantic Processing ◽  
Empirical Work ◽  
Abstract Concepts ◽  
Visual Model ◽  
Semantic Data ◽  
Text Corpora ◽  
Abstract Words ◽  
Best Fit ◽  
Better Than

A number of recent models of semantics combine linguistic information, derived from text corpora, and visual information, derived from image collections, demonstrating that the resulting multimodal models are better than either of their unimodal counterparts, in accounting for behavioural data. Empirical work on semantic processing has shown that emotion also plays an important role especially for abstract concepts, however, models integrating emotion along with linguistic and visual information are lacking. Here, we first improve on visual and affective representations, derived from state-of-the-art existing models, by choosing models that best fit available human semantic data and extending the number of concepts they cover. Crucially then, we assess whether adding affective representations (obtained from a neural network model designed to predict emojis from co-occurring text) improves the model’s ability to fit semantic similarity/relatedness judgements from a purely linguistic and linguistic-visual model. We find that, given specific weights assigned to the models, adding both visual and affective representations improve performance, with visual representations providing an improvement especially for more concrete words, and affective representations improving especially the fit for more abstract words.

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