scholarly journals What is Leading Order for LFV in SMEFT?

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Marco Ardu ◽  
Sacha Davidson
Keyword(s):  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Power Counting ◽  
Leading Order ◽  
Small Power ◽  
Anomalous Dimensions ◽  
Simplifying Assumptions ◽  
The One ◽  
Lepton Flavour

Abstract Upcoming searches for lepton flavour change (LFV) aim to probe New Physics (NP) scales up to ΛNP ∼ 104 TeV, implying that they will be sensitive to NP at lower scales that is suppressed by loops or small couplings. We suppose that the NP responsable for LFV is beyond the reach of the LHC and can be parametrised in Effective Field Theory, introduce a small power-counting parameter λ (à la Cabibbo-Wolfenstein), and assess whether the existing dimension six operator basis and one-loop RGEs provide a good approximation for LFV. We find that μ ↔ e observables can be sensitive to a few dozen dimension eight operators, and to some effects of two-loop anomalous dimensions, for ΛNP ≲ 20 − 100 TeV. We also explore the effect of some simplifying assumptions in the one-loop RGEs, such as neglecting flavour-changing effects.

scholarly journals The one-loop tadpole in the geoSMEFT

2021 ◽  
Vol 11 (5) ◽  
Author(s):  
Tyler Corbett
Keyword(s):  
Field Theory ◽  
Standard Model ◽  
Effective Field Theory ◽  
Effective Field ◽  
Power Counting ◽  
Leading Order ◽  
The Standard Model ◽  
The One ◽  
Near Future ◽  
Geometric Formulation

Making use of the geometric formulation of the Standard Model Effective Field Theory we calculate the one-loop tadpole diagrams to all orders in the Standard Model Effective Field Theory power counting. This work represents the first calculation of a one-loop amplitude beyond leading order in the Standard Model Effective Field Theory, and discusses the potential to extend this methodology to perform similar calculations of observables in the near future.

scholarly journals Erratum to: Effective field theory after a new-physics discovery

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Stefan Alte ◽  
Matthias König ◽  
Matthias Neubert
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Momentum Fraction ◽  
Linear Relations ◽  
Right Hand ◽  
Anomalous Dimensions ◽  
The One ◽  
The Right

The two linear relations between operators shown in eq. (3.29) were missing an integral over the momentum fraction u on the right-hand side. In the one-particle anomalous dimensions in eq. (5.7) two fractions were mistyped.

scholarly journals Towards the renormalisation of the Standard Model effective field theory to dimension eight: Bosonic interactions I

2021 ◽  
Vol 11 (3) ◽  
Author(s):  
Mikael Chala ◽  
Guilherme Guedes ◽  
Maria Ramos ◽  
Jose Santiago
Keyword(s):  
Standard Model ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Tree Level ◽  
Electroweak Phase Transition ◽  
Anomalous Dimensions ◽  
Weakly Coupled ◽  
The Standard Model ◽  
The One

We compute the one-loop renormalisation group running of the bosonic Standard Model effective operators to order v^4/\Lambda^4v4/Λ4, with v\sim 246v∼246 GeV being the electroweak scale and \LambdaΛ the unknown new physics threshold. We concentrate on the effects triggered by pairs of the leading dimension-six interactions, namely those that can arise at tree level in weakly-coupled ultraviolet completions of the Standard Model. We highlight some interesting consequences, including the interplay between positivity bounds and the form of the anomalous dimensions; the non-renormalisation of the SS and UU parameters; or the importance of radiative corrections to the Higgs potential for the electroweak phase transition. As a byproduct of this work, we provide a complete Green basis of operators involving only the Higgs and derivatives at dimension-eight, comprising 13 redundant interactions.

scholarly journals Completeness and complementarity for μ → eγ, μ → $$ e\overline{e}e $$ and μA → eA

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
S. Davidson
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Complementary Information ◽  
Weak Scale ◽  
Lepton Flavour Violation ◽  
Flavour Violation ◽  
Lepton Flavour

Abstract Lepton Flavour Violation (LFV) is New Physics that must occur, but is stringently constrained by experiments searching for μ ↔ e flavour change, such as μ → eγ, μ →$$ e\overline{e}e $$ e e ¯ e or μ → e conversion. However, in an Effective Field Theory(EFT) parametrisation, there are many more μ ↔ e operators than restrictive constraints, so determining operator coefficients from data is a remote dream. It is nonetheless interesting to learn about New Physics from data, so this manuscript introduces “observable-vectors” in the space of operator coefficients, which identify at any scale the combination of coefficients probed by the observable. These vectors have an overlap ≳ 10−3 with most of the coefficients, and are used to study whether μ → eγ, μ →$$ e\overline{e}e $$ e e ¯ e and μ → e conversion give complementary information about New Physics. The appendix gives updated sensitivities of these processes, (and a subset of τ → ℓ decays), to operator coefficients at the weak scale in the SMEFT and in the EFT below mW.

scholarly journals General non-leptonic ∆F = 1 WET at the NLO in QCD

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
Jason Aebischer ◽  
Christoph Bobeth ◽  
Andrzej J. Buras ◽  
Jacky Kumar ◽  
Mikołaj Misiak
Keyword(s):  
Field Theory ◽  
Standard Model ◽  
Effective Field Theory ◽  
High Energy ◽  
Effective Field ◽  
Effective Theory ◽  
Leading Order ◽  
The Standard Model ◽  
Complete Set ◽  
The One

Abstract We reconsider the complete set of four-quark operators in the Weak Effective Theory (WET) for non-leptonic ∆F = 1 decays that govern s → d and b → d, s transitions in the Standard Model (SM) and beyond, at the Next-to-Leading Order (NLO) in QCD. We discuss cases with different numbers Nf of active flavours, intermediate threshold corrections, as well as the issue of transformations between operator bases beyond leading order to facilitate the matching to high-energy completions or the Standard Model Effective Field Theory (SMEFT) at the electroweak scale. As a first step towards a SMEFT NLO analysis of K → ππ and non-leptonic B-meson decays, we calculate the relevant WET Wilson coefficients including two-loop contributions to their renormalization group running, and express them in terms of the Wilson coefficients in a particular operator basis for which the one-loop matching to SMEFT is already known.

scholarly journals Z lepton flavour violation as a probe for new physics at future $$e^+e^-$$ colliders

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Lorenzo Calibbi ◽  
Xabier Marcano ◽  
Joydeep Roy
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Low Energy ◽  
The Standard Model ◽  
Discovery Potential ◽  
Flavour Violation ◽  
Model Independent ◽  
Lepton Flavour

AbstractIn this work we assess the potential of discovering new physics by searching for lepton-flavour-violating (LFV) decays of the Z boson, $$Z\rightarrow \ell _i \ell _j$$ Z → ℓ i ℓ j , at the proposed circular $$e^+e^-$$ e + e - colliders CEPC and FCC-ee. Both projects plan to run at the Z-pole as a “Tera Z factory”, i.e., collecting $${\mathcal {O}}\left( 10^{12} \right) $$ O 10 12 Z decays. In order to discuss the discovery potential in a model-independent way, we revisit the LFV Z decays in the context of the Standard Model effective field theory and study the indirect constraints from LFV $$\mu $$ μ and $$\tau $$ τ decays on the operators that can induce $$Z\rightarrow \ell _i \ell _j$$ Z → ℓ i ℓ j . We find that, while the $$Z\rightarrow \mu e$$ Z → μ e rates are beyond the expected sensitivities, a Tera Z factory is promising for $$Z\rightarrow \tau \ell $$ Z → τ ℓ decays, probing New Physics at the same level of future low-energy LFV observables.

scholarly journals Anomalous dimensions from gauge couplings in SMEFT with right-handed neutrinos

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Alakabha Datta ◽  
Jacky Kumar ◽  
Hongkai Liu ◽  
Danny Marfatia
Keyword(s):  
Standard Model ◽  
Anomalous Dimension ◽  
Gauge Coupling ◽  
New Physics ◽  
Effective Field ◽  
Effective Theory ◽  
Anomalous Dimensions ◽  
Group Evolution ◽  
Majorana Neutrinos ◽  
The One

Abstract Standard Model Neutrino Effective Field Theory (SMNEFT) is an effective theory with Standard Model (SM) gauge-invariant operators constructed only from SM and right-handed neutrino fields. For the full set of dimension-six SMNEFT operators, we present the gauge coupling terms of the one-loop anomalous dimension matrix for renormalization group evolution (RGE) of the Wilson coefficients between a new physics scale and the electroweak scale. We find that the SMNEFT operators can be divided into five subsets which are closed under RGE. Our results apply for both Dirac and Majorana neutrinos. We also discuss the operator mixing pattern numerically and comment on some interesting phenomenological implications.

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 Renormalization Group evolution from on-shell SMEFT

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Minyuan Jiang ◽  
Teng Ma ◽  
Jing Shu
Keyword(s):  
Field Theory ◽  
Renormalization Group ◽  
Standard Model ◽  
Effective Field Theory ◽  
Effective Field ◽  
High Dimensional ◽  
Anomalous Dimensions ◽  
The Standard Model ◽  
Group Evolution

Abstract We describe the on-shell method to derive the Renormalization Group (RG) evolution of Wilson coefficients of high dimensional operators at one loop, which is a necessary part in the on-shell construction of the Standard Model Effective Field Theory (SMEFT), and exceptionally efficient based on the amplitude basis in hand. The UV divergence is obtained by firstly calculating the coefficients of scalar bubble integrals by unitary cuts, then subtracting the IR divergence in the massless bubbles, which can be easily read from the collinear factors we obtained for the Standard Model fields. Examples of deriving the anomalous dimensions at dimension six are presented in a pedagogical manner. We also give the results of contributions from the dimension-8 H4D4 operators to the running of V+V−H2 operators, as well as the running of B+B−H2D2n from H4D2n+4 for general n.

scholarly journals On the three-particle analog of the Lellouch-Lüscher formula

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Fabian Müller ◽  
Akaki Rusetsky
Keyword(s):  
Field Theory ◽  
Finite Volume ◽  
Effective Field Theory ◽  
Effective Field ◽  
Infinite Volume ◽  
Leading Order ◽  
Particle Decay ◽  
Particle Decays

Abstract Using non-relativistic effective field theory, we derive a three-particle analog of the Lellouch-Lüscher formula at the leading order. This formula relates the three-particle decay amplitudes in a finite volume with their infinite-volume counterparts and, hence, can be used to study the three-particle decays on the lattice. The generalization of the approach to higher orders is briefly discussed.

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