Sacha Davidson
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View article: Left-handed physics is not right for leptonic EDMs
Left-handed physics is not right for leptonic EDMs Open
Heavy New Physics models with lepton flavour-changing interactions are motivated by neutrino masses, and generically induce dipole interactions for charged leptons – which can be flavour-changing ( $$l_j\rightarrow l_i \gamma $$ …
View article: Left-Handed Physics is not right for EDMs
Left-Handed Physics is not right for EDMs Open
Heavy New Physics models with lepton flavour-changing interactions are motivated by neutrino masses, and generically induce dipole interactions for leptons, which can be flavour-changing ($l_j\to l_i γ$) or flavour-diagonal (magnetic and e…
View article: Constraining new physics models from $$\mu \rightarrow e $$ observables in bottom-up EFT
Constraining new physics models from $$\mu \rightarrow e $$ observables in bottom-up EFT Open
Upcoming experiments will improve the sensitivity to $$\mu \rightarrow e$$ processes by several orders of magnitude, and could observe lepton flavour-changing contact interactions for the first time. In this paper, we investigate what…
View article: Constraining New Physics models from $μ\to e$ observables in bottom-up EFT
Constraining New Physics models from $μ\to e$ observables in bottom-up EFT Open
Upcoming experiments will improve the sensitivity to $μ\to e$ processes by several orders of magnitude, and could observe lepton flavour-changing contact interactions for the first time. In this paper, we investigate what could be learned …
View article: Workshop on a future muon program at FNAL
Workshop on a future muon program at FNAL Open
The Snowmass report on rare processes and precision measurements recommended Mu2e-II and a next generation muon facility at Fermilab (Advanced Muon Facility) as priorities for the frontier. The Workshop on a future muon program at FNAL was…
View article: Distinguishing models with $μ\to e $ observables
Distinguishing models with $μ\to e $ observables Open
Upcoming experiments will improve the reach for the lepton flavour violating (LFV) processes $μ\to e γ$, $μ\to e \bar{e} e$ and $μA \to e A$ by orders of magnitude. We investigate whether this upcoming data could rule out some popular TeV-…
View article: Reach and complementarity of $$\mu \rightarrow e$$ searches
Reach and complementarity of $$\mu \rightarrow e$$ searches Open
View article: Charged Lepton Flavor Violation
Charged Lepton Flavor Violation Open
This reports summarizes the activities of the Charged Lepton Flavor Violation group of the 2022 Community Summer Study. Charged lepton flavor violating reactions provide unique information on the scale and dynamics of flavor generation, an…
View article: Sensitivity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>μ</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>e</mml:mi></mml:math> processes to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>τ</mml:mi></mml:math> flavor change
Sensitivity of processes to flavor change Open
International audience
View article: Reach and complementarity of $\\mu\\to e$ searches
Reach and complementarity of $\\mu\\to e$ searches Open
In Effective Field Theory, we describe $\\mu\\leftrightarrow e$ flavour\nchanging transitions using an operator basis motivated by experimental\nobservables. In a six-dimensional subspace probed by $\\mu \\to e \\gamma$, $\\mu\n\\to 3e$ an…
View article: Science Case for the new High-Intensity Muon Beams HIMB at PSI
Science Case for the new High-Intensity Muon Beams HIMB at PSI Open
In April 2021, scientists active in muon physics met to discuss and work out the physics case for the new High-Intensity Muon Beams (HIMB) project at PSI that could deliver of order $10^{10}$\,s$^{-1}$ surface muons to experiments. Ideas a…
View article: What is Leading Order for LFV in SMEFT?
What is Leading Order for LFV in SMEFT? Open
View article: Completeness and complementarity for μ → eγ, μ → $$ e\overline{e}e $$ and μA → eA
Completeness and complementarity for μ → eγ, μ → $$ e\overline{e}e $$ and μA → eA Open
A bstract 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 → $$ e\overline{e}e $$ or μ → e conversion. However, in an …
View article: Probing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>μ</mml:mi><mml:mi>e</mml:mi><mml:mi>γ</mml:mi><mml:mi>γ</mml:mi></mml:math> contact interactions with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>μ</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>e</mml:mi></mml:math> conversion
Probing contact interactions with conversion Open
Contact interactions of a muon, an electron and two photons can contribute to\nthe decay $\\mu \\to e \\gamma \\gamma$, but also to the conversion of a muon into\nan electron in the electric field of a nucleus. We calculate the $\\mu \\to …
View article: Charged lepton flavor change and nonstandard neutrino interactions
Charged lepton flavor change and nonstandard neutrino interactions Open
Non-Standard neutrino Interactions (NSI) are vector contact interactions involving two neutrinos and two first generation fermions, which can affect neutrino propagation in matter. SU(2) gauge invariance suggests that NSI should be accompa…
View article: Selecting μ → e conversion targets to distinguish lepton flavour-changing operators
Selecting μ → e conversion targets to distinguish lepton flavour-changing operators Open
The experimental sensitivity to $\\mu \\to e$ conversion on nuclei is set to\nimprove by four orders of magnitude in coming years. However, various operator\ncoefficients add coherently in the amplitude for $\\mu \\to e$ conversion,\nweigh…
View article: Axion absorption and the spin temperature of primordial hydrogen
Axion absorption and the spin temperature of primordial hydrogen Open
An absorption dip in the spectrum of the cosmic microwave background observed by the EDGES experiment suggests an unexplained reduction of the hydrogen spin temperature at cosmic redshift z ~ 17. The mass of dark-matter axions could corres…
View article: Constraints on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>ℓ</mml:mo><mml:mn>2</mml:mn></mml:mrow><mml:mi>q</mml:mi></mml:mrow></mml:math> operators from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>μ</mml:mi><mml:mo stretchy="false">↔</mml:mo><mml:mi>e</mml:mi></mml:math> flavor-changing meson decays
Constraints on operators from flavor-changing meson decays Open
We study lepton flavour violating two- and three-body decays of pseudoscalar\nmesons in Effective Field Theory (EFT). We give analytic formulae for the decay\nrates in the presence of a complete basis of QED and QCD-invariant operators.\nT…
View article: Majorana neutrino masses in the renormalization group equations for lepton flavor violation
Majorana neutrino masses in the renormalization group equations for lepton flavor violation Open
We suppose that the observed neutrino masses can be parametrised by a lepton number violating dimension-five operator, and calculate the mixing of double insertions of this operator into lepton flavour changing dimension-six operators of t…
View article: Neutrino Physics
Neutrino Physics Open
This is summary of three lectures on neutrino physics at the CERN school in Evora, Portugal, for experimental PhD students. There is a brief review of neutrino interactions in the Standard Model, Majorana and Dirac mass terms, oscillations…
View article: Spin-dependent μ→e conversion
Spin-dependent μ→e conversion Open
View article: Renormalisation-group improved analysis of μ → e processes in a systematic effective-field-theory approach
Renormalisation-group improved analysis of μ → e processes in a systematic effective-field-theory approach Open
In this article, a complete analysis of the three muonic lepton-flavour violating processes $\mu\to e \gamma$, $\mu\to 3e$ and coherent nuclear $\mu\to e$ conversion is performed in the framework of an effective theory with dimension six o…
View article: Complementarity in lepton-flavour violating muon decay experiments
Complementarity in lepton-flavour violating muon decay experiments Open
This note presents an analysis of lepton-flavour-violating muon decays within the framework of a low-energy effective field theory that contains higher-dimensional operators allowed by QED and QCD symmetries. The decay modes $μ\to e γ$ and…
View article: A facility to search for hidden particles at the CERN SPS: the SHiP physics case
A facility to search for hidden particles at the CERN SPS: the SHiP physics case Open
This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles …
View article: Rotating drops of axion dark matter
Rotating drops of axion dark matter Open
We consider how QCD axions produced by the misalignment mechanism could form galactic dark matter halos. We recall that stationary, gravitationally stable axion field configurations have the size of an asteroid with masses of order $10^{-1…
View article: $$\mu \rightarrow e \gamma $$ μ → e γ in the 2HDM: an exercise in EFT
$$\mu \rightarrow e \gamma $$ μ → e γ in the 2HDM: an exercise in EFT Open
\n The 2 Higgs Doublet Model of type III has renormalisable Lepton Flavour-Violating couplings, and its one- and two-loop (“Barr–Zee”) contributions to $$\\mu \\rightarrow e \\gamma $$ are known. In the decoupling limit, where the mass sca…
View article: Two Higgs doublets to explain the excesses $pp\rightarrow \gamma\gamma(750\ {\rm GeV})$ and $h \to \tau^\pm \mu^\mp$
Two Higgs doublets to explain the excesses $pp\rightarrow \gamma\gamma(750\ {\rm GeV})$ and $h \to \tau^\pm \mu^\mp$ Open
View article: Two Higgs doublets to explain the excesses pp → γγ(750 GeV) and h → τ ± μ ∓
Two Higgs doublets to explain the excesses pp → γγ(750 GeV) and h → τ ± μ ∓ Open
The two Higgs doublet model emerges as a minimal scenario in which to\naddress, at the same time, the $\\gamma\\gamma$ excess at 750 GeV and the lepton\nflavour violating decay into $\\tau^\\pm \\mu^\\mp $ of the 125 GeV Higgs boson.\nThe …
View article: Mu to e gamma in the 2 Higgs Doublet Model: an exercise in EFT
Mu to e gamma in the 2 Higgs Doublet Model: an exercise in EFT Open
The 2 Higgs Doublet Model (2HDM) of type III has renormalisable Lepton Flavour-Violating couplings, and its one and two-loop ("Barr-Zee") contributions to $μ\to e γ$ are known. In the decoupling limit, where the mass scale M of the second …
View article: Of contact interactions and colliders
Of contact interactions and colliders Open
The hierarchy of scales which would allow dimension-six contact interactions to parametrise New Physics may not be verified at colliders. Instead, we explore the feasability and usefulness of parametrising the high-energy tail of distribut…