Electron Electric Dipole Moment Research Articles

Global constraints on Yukawa operators in the standard model effective theory

CP-violating contributions to Higgs-fermion couplings are absent in the standard model of particle physics (SM), but are motivated by models of electroweak baryogenesis. Here, we employ the framework of the SM effective theory (SMEFT) to parameterise deviations from SM Yukawa couplings. We present the leading contributions of the relevant operators to the fermionic electric dipole moments (EDMs). We obtain constraints on the SMEFT Wilson coefficients from the combination of LHC data and experimental bounds on the electron, neutron, and mercury EDMs. We perform, for the first time, a combined fit to LHC and EDM data allowing the presence of CP-violating contributions from several fermion species simultaneously. Among other results, we find non-trivial correlations between EDM and LHC constraints even in the multi-parameter scans, for instance, when floating the CP-even and CP-odd couplings to all third-generation fermions.

Measurement of the H3Δ1 radiative lifetime in ThO

The best limit on the electron electric dipole moment (eEDM) comes from the ACME II experiment [Nature \textbf{562} (2018), 355-360] which probes physics beyond the Standard Model at energy scales well above 1 TeV. ACME II measured the eEDM by monitoring electron spin precession in a cold beam of the metastable H$^3\Delta_1$ state of thorium monoxide (ThO) molecules, with an observation time $\tau \approx 1$ ms for each molecule. We report here a new measurement of the lifetime of the ThO (H$^3\Delta_1$) state, $\tau_H = 4.2\pm 0.5$ ms. Using an apparatus within which $\tau \approx \tau_H$ will enable a substantial reduction in uncertainty of an eEDM measurement.

Lepton flavor violation, lepton (g − 2)μ, e and electron EDM in the modular symmetry

We study the lepton flavor violation (LFV), the leptonic magnetic moments (g − 2)μ, e and the electric dipole moment (EDM) of the electron in the Standard-Model Effective Field Theory with the ΓN modular flavor symmetry. We employ the stringy Ansatz on coupling structure that 4-point couplings of matter fields are written by a product of 3-point couplings of matter fields. We take the level 3 finite modular group, Γ3 for the flavor symmetry, and discuss the dipole operators at nearby fixed point τ = i, where observed lepton masses and mixing angles are well reproduced. Suppose the anomaly of the anomalous magnetic moment of the muon to be evidence of the new physics (NP), we have related it with (g − 2)e, LFV decays, and the electron EDM. It is found that the NP contribution to (g − 2)e is proportional to the lepton masses squared likewise the naive scaling. We also discuss the correlations among the LFV processes μ → eγ, τ → μγ and τ → eγ, which are testable in the future. The electron EDM requires the tiny imaginary part of the relevant Wilson coefficient in the basis of real positive charged lepton masses, which is related to the μ → eγ transition in our framework.

Constraining the {mathcal {C}}{mathcal {P}} structure of Higgs-fermion couplings with a global LHC fit, the electron EDM and baryogenesis

{mathcal {C}}{mathcal {P}} violation in the Higgs couplings to fermions is an intriguing, but not yet extensively explored possibility. We use inclusive and differential LHC Higgs boson measurements to fit the {mathcal {C}}{mathcal {P}} structure of the Higgs Yukawa couplings. Starting with simple effective models featuring {mathcal {C}}{mathcal {P}} violation in a single Higgs–fermion coupling, we probe well-motivated models with up to nine free parameters. We also investigate the complementarity of LHC constraints with the electron electric dipole moment bound, taking into account the possibility of a modified electron Yukawa coupling, and assess to which extent {mathcal {C}}{mathcal {P}} violation in the Higgs–fermion couplings can contribute to the observed baryon asymmetry of the universe. Even after including the recent analysis of angular correlations in Hrightarrow tau ^+tau ^- decays, we find that a complex tau Yukawa coupling alone may be able to account for the observed baryon asymmetry, but with large uncertainties in the baryogenesis calculation. A combination of complex top and bottom quark Yukawa couplings yields a result four times larger than the sum of their separate contributions, but remains insufficient to account for the observed baryon asymmetry.

Electrostatic focusing of cold and heavy molecules for the ACME electron EDM search

The current best upper limit for electron electric dipole moment (EDM), |d e| < 1.1 × 10−29 e cm (90% confidence), was set by the ACME Collaboration in 2018. The ACME experiment uses a spin-precession measurement in a cold beam of thorium monoxide (ThO) molecules to detect d e. An improvement in statistical uncertainty would be possible with more efficient use of molecules from the cryogenic buffer gas beam source. Here, we demonstrate electrostatic focusing of the ThO beam with a hexapole lens. This results in a factor of 16 enhancement in the molecular flux detectable downstream, in a beamline similar to that built for the next generation of ACME. We also demonstrate an upgraded rotational cooling scheme that increases the ground state population by 3.5 times compared to no cooling, consistent with expectations and a factor of 1.4 larger than previously in ACME. When combined with other demonstrated improvements, we project over an order of magnitude improvement in statistical sensitivity for the next generation ACME electron EDM search.

Sensitivity of the YbOH molecule to PT -odd effects in an external electric field

An electron electric dipole moment (eEDM) search using laser-coolable triatomics such as YbOH is one of the most sensitive probes for physics beyond the standard model. The eEDM-induced energy shift is proportional to the polarization ($P$) of the molecule. Similarly to diatomics with an $\mathrm{\ensuremath{\Omega}}$-doubling structure, it was assumed that for triatomics with an $l$-doubling structure, related to the vibrational angular momentum, $P$ can be easily saturated to almost 100% with a moderate external electric field. We developed a method for the calculation of the properties of triatomic molecules and applied it to a calculation of $P$ of $^{174}\mathrm{YbOH}$ in the first excited $v=1$ bending mode. Calculations showed that most of the levels reach less than 50% efficiency. We showed that this fact is related to the Hund's case $b$ coupling scheme of YbOH. As the coupling scheme (for $\mathrm{\ensuremath{\Omega}}=1/2$ molecules) approaches the $a$ (or $c$) case, polarization increases up to 100%. The results of our calculations should be used for the correct extracting of the eEDM value from YbOH experiments and similar calculations are required for other molecules.

Muon electric dipole moment as a probe of flavor-diagonal CP violation

Electric dipole moments (EDMs) of elementary particles are powerful probes of new physics with flavor-diagonal CP violation. The reported discrepancy in the muon anomalous magnetic moment motivates us to explore to what extent new physics with flavor-diagonal CP violation to address the discrepancy is probed by searches for the muon EDM. As a benchmark, we focus on a CP-violating two-Higgs-doublet model to explain the muon g−2 anomaly where the muon exclusively couples to one Higgs doublet. Since contributions to flavor violating processes as well as the electron EDM are suppressed, the muon EDM becomes an essential probe of the model. Our result shows that some viable parameter space leads to the muon EDM of around dμ≃6×10−23e cm probed by the PSI experiment and most of the parameter space is covered by the proposed J-PARC experiment.

CP -violating dark photon kinetic mixing and type-III seesaw model

The hypothetical dark photon portal connecting the visible and dark sectors of the Universe has received considerable attention in recent years, with a focus on CP-conserving kinetic mixing between the Standard Model (SM) hypercharge gauge boson and a new U(1)$_X$ gauge boson. In the effective field theory context, one may write down non-renormalizable CP-violating kinetic mixing interactions involving the $X$ and SU(2)$_L$ gauge bosons. We construct for the first time a renormalizable model for CP-violating kinetic mixing that induces CP-violating non-Abelian kinetic mixing at mass dimension five. The model grows out of the type-III seesaw model, with the lepton triplets containing right-handed neutrinos playing a crucial role in making the model renormalizable and providing a bridge to the origin of neutrino mass. This scenario also accommodates electron electric dipole moments (EDM) as large as current experimental bound, making future EDM searches an important probe of this scenario.

Transverse positron polarization in the polarized μ+ decay related with the muonium-to-antimuonium transition

The constructions of the new high-intensity muon beamlines are progressing in facilities around the world, and new physics searches related to the muons are expected. The facilities can observe the transverse positron polarization of the polarized ${\ensuremath{\mu}}^{+}$ decay to test the standard model. The transition of muonium into antimuonium (Mu-to-$\overline{\mathrm{Mu}}$ transition), which is one of the interesting possibilities in the models beyond the standard model, can be also tested. An observation of the transition in the near future would have a great impact since it would indicate that there is an approximate discrete symmetry in the lepton sector. If the Mu-to-$\overline{\mathrm{Mu}}$ transition operator is generated, a new muon decay operator can exist, and it may interfere with the standard model muon decay operator to induce the corrections to the transverse positron polarization in the ${\ensuremath{\mu}}^{+}$ decay. We examine the possibility that the Mu-to-$\overline{\mathrm{Mu}}$ transition and the correction to the transverse positron polarization are related, and we show that the two are related in the model of a neutral flavor gauge boson. We also investigate the models to generate the Mu-to-$\overline{\mathrm{Mu}}$ transition, such as an inert $SU(2{)}_{L}$ doublet, an $SU(2{)}_{L}$ triplet for the type-II seesaw model, a dilepton gauge boson, and a left-right model. The nonzero value of the transverse polarization for one of the two directions, ${P}_{{\mathrm{T}}_{2}}$, violates the time-reversal invariance, and the experimental constraint of the electron electric dipole moment can provide a severe constraint on ${P}_{{\mathrm{T}}_{2}}$, depending on the model.

Gravitational wave and electroweak baryogenesis with two Higgs doublet models

We study stochastic gravitational wave production and baryon number generation at electroweak phase transition with the two Higgs doublet models. The produced stochastic gravitational wave during the strongly first-order phase transition can be probed by future space-based interferometers. The nonlocal electroweak baryogenesis cannot address the observed Baryon asymmetry of the Universe successfully in the strongly first-order phase transition parameter spaces due to the CP violation phase is severely bounded by the electron electric dipole moment measurement ACMEII.

CP Violation for the Heavens and the Earth

Electroweak baryogenesis can be driven by the top quark in a general two Higgs doublet model with extra Yukawa couplings. Higgs quartics provide the first order phase transition, while extra top Yukawa coupling ρtt can fuel the cosmic baryon asymmetry through the λtImρtt product, with flavor-changing ρtc coupling as backup. The impressive ACME 2018 bound on the electron electric dipole moment calls for an extra electron coupling ρee for exquisite cancellation among dangerous diagrams, broadening the baryogenesis solution space. The mechanism suggests that extra Yukawa couplings echo the hierarchical structure of standard Yukawa couplings. Phenomenological consequences in the Higgs search and flavor physics are discussed, with μ and τ EDM touched upon.

Spectroscopic study of B2Σ+–X1 2Π1/2 transition of electron electric dipole moment candidate PbF

PbF, a valuable candidate for measuring the electron electric dipole moment (eEDM), is of great significance in measuring its spectrum and deriving its molecular constants in experiment. In the present work, the rovibronic spectrum of the B2Σ+–X1 2Π1/2 transition of PbF in a wavelength range of 260 nm–285 nm is studied by the laser ablation/laser induced fluorescence method. The molecular parameters of the X1 2Π1/2 (v″ = 0) and B2Σ+ (v′ = 0, 1) states are derived from the recorded spectra of the (0, 0) and (1, 0) bands of the B2Σ+–X1 2Π1/2 transition. Also, the Franck–Condon factors (FCFs) of the transitions between the B2Σ+ and X1 2Π1/2 states are calculated by the RKR/LEVEL method and the Morse potential method, respectively.

Static electric dipole moment of the francium atom induced by axionlike particle exchange

The francium atom is considered as a prospective candidate system to search for the T,P-violating electron electric dipole moment [T. Aoki et al Quantum Sci. Technol. 6, 044008 (2021)]. We demonstrate that the same experiment can be used for axionlike particles (ALP) search. For this, we calculate electronic structure constants of ALP-mediated interaction for a wide range of ALP masses. Using the recently updated constraints on the ALP-electron and ALP-nucleon coupling constants, we show that the contribution of considered interactions corresponding to these constraints can give significant contribution to atomic electric dipole moment. Therefore, obtainment of stronger restrictions for ALP characteristics in the francium atom electric dipole moment experiment is possible.

Rotating and vibrating symmetric-top molecule RaOCH3 in fundamental P, T -violation searches

We study the influence of the rotations and vibrations of the symmetric-top ${\mathrm{RaOCH}}_{3}$ molecule on its effectiveness as a probe for the $\mathcal{P}, \mathcal{T}$-violating effects, such as the electron electric dipole moment and the scalar-pseudoscalar electron-nucleon interaction. The corresponding enhancement parameters ${E}_{\mathrm{eff}}$ and ${E}_{\mathrm{s}}$ are computed for the ground and first excited rovibrational states with different values of the angular momentum component $K$. For the lowest $K$ doublet with ${v}_{\ensuremath{\perp}}=0$ and $K=1$ the values are ${E}_{\mathrm{eff}}=47.647\phantom{\rule{0.28em}{0ex}}\mathrm{GV}/\mathrm{cm}$ and ${E}_{\mathrm{s}}=62.109\phantom{\rule{0.16em}{0ex}}\mathrm{kHz}$. The results show larger deviation from the equilibrium values than in triatomic molecules.

Laser-coolable AcOH+ ion for CP -violation searches

The ${\mathrm{AcOH}}^{+}$ molecular ion is identified as a prospective system to search for $\mathcal{CP}$-violation effects. According to our study ${\mathrm{AcOH}}^{+}$ belongs to the class of laser-coolable polyatomic molecular cations implying a large coherence time in the experiments to study symmetry-violating effects of fundamental interactions. We perform both nuclear and high-level relativistic coupled cluster electronic structure calculations to express the experimentally measurable $\mathcal{T},\mathcal{P}$-violating energy shift in terms of fundamental quantities such as the nuclear magnetic quadrupole moment (MQM), electron electric dipole moment ($e\mathrm{EDM}$) and dimensionless scalar-pseudoscalar nuclear-electron interaction constant. We further express nuclear MQM in terms of the strength constants of $\mathcal{CP}$-violating nuclear forces: quantum chromodynamics vacuum angle $\overline{\ensuremath{\theta}}$ and quark chromo-EDMs. The equilibrium structure of ${\mathrm{AcOH}}^{+}$ in the ground and the four lowest excited electronic states was found to be linear. The calculated Franck-Condon factors and transition dipole moments indicate that the laser cooling using an optical cycle involving the first excited state is possible for the trapped ${\mathrm{AcOH}}^{+}$ ions with the Doppler limit estimated to be $\ensuremath{\sim}$4 nK. The lifetime of the ($0,{1}^{1},0$) excited vibrational state considered as a working one for MQM and $e\mathrm{EDM}$ search experiments is estimated to be $\ensuremath{\sim}0.4$ s.

Spectroscopy on the electron-electric-dipole-moment–sensitive states of ThF+

An excellent candidate molecule for the measurement of the electron's electric dipole moment (eEDM) is thorium monofluoride (ThF$^+$) because the eEDM-sensitive state, $^3\Delta_1$, is the electronic ground state, and thus is immune to decoherence from spontaneous decay. We perform spectroscopy on $X\,^3\Delta_1$ to extract three spectroscopic constants crucial to the eEDM experiment: the hyperfine coupling constant, the molecular frame electric dipole moment, and the magnetic $g$-factor. To understand the impact of thermal blackbody radiation on the vibrational ground state, we study the lifetime of the first excited vibrational manifold of $X\,^3\Delta_1$. We perform ab initio calculations, compare them to our results, and discuss prospects for using ThF$^+$ in a new eEDM experiment at JILA.

Race to find split Higgsino dark matter

Split higgsinos are a compelling class of models to explain dark matter and may be on the verge of detection by multiple current experimental avenues. The idea is based on a large split in scales between the electroweak scale and decoupled scalars, with relatively light higgsinos between the two. Such models enjoy the merit of depending on very few parameters while still explaining gauge coupling unification, dark matter, and most of the hierarchy between the Planck and electroweak scales, and they remain undetected by past experiments. We analyze split higgsinos in view of current and next generation experiments. We discuss the direct and indirect detection prospects and further demonstrate promising discovery potentials in the upcoming electron electric dipole moment experiments. The parameter space of this model is analyzed in terms of experiments expected to run in the coming years and where we should be looking for the next potential discoveries.

Towards CP -violation studies on superheavy molecules: Theoretical and experimental perspectives

Molecules containing superheavy atoms can be artificially created to serve as sensitive probes for study of symmetry-violating phenomena. Here, we provide a detailed theoretical study for diatomic molecules containing the superheavy lawrencium nuclei. The sensitivity to time-reversal violating properties was studied for different neutral and ionic molecules. The effective electric fields in these systems were found to be about 3-4 times larger than other known molecules on which electron electric dipole moment experiments are being performed. Similarly, these superheavy molecules exhibit an enhancement of more than 5 times for parity- and time-reversal-violating scalar-pseudoscalar nucleus-electron interactions. We also briefly comment on some experimental aspects by discussing the production of these systems.

Constraining CP-phases in SUSY: An interplay of muon/electron g − 2 and electron EDM

The minimal supersymmetric standard model (MSSM) with complex parameters can contribute sizably to muon/electron anomalous magnetic dipole moment (g−2) and electric dipole moment (EDM). The electron g−2 interplays with electron EDM; the muon g−2 can also interplay with electron EDM assuming the universality between smuon and selectron masses, either of which can constrain the relevant CP-phases in the MSSM. In this work, we first use such an interplay to derive an approximate analytical upper limit on the relevant CP-phase. Then we extensively scan the parameter space to obtain more accurate upper limits. We obtain the following observations: (i) The muon g−2 in the 2σ range combined with the electron EDM upper limit (assuming the universality between smuon and selectron masses) typically constrains the relevant CP-phase under 1.9×10−5(rad); (ii) The electron g−2 in the 2σ range (Berkeley) interplays with the electron EDM upper limit (without assuming the universality between smuon and selectron masses) constrains the relevant CP-phase under 3.9×10−6(rad) (also requiring muon g−2 in the allowed 2σ range). We also find some special cancellations in the parameter space which can relax the constraints by a couple of orders. Such stringent limits on CP-phases may pose a challenge for model building of SUSY, i.e., how to naturally suppress these phases.

Theoretical aspects of radium-containing molecules amenable to assembly from laser-cooled atoms for new physics searches

We explore the possibilities for a next-generation electron-electric-dipole-moment experiment using ultracold heteronuclear diatomic molecules assembled from a combination of radium and another laser-coolable atom. In particular, we calculate their ground state structure and their sensitivity to parity- and time-reversal () violating physics arising from flavor-diagonal charge-parity () violation. Among these species, the largest -violating molecular interaction constants—associated for example with the electron electric dipole moment—are obtained for the combination of radium (Ra) and silver (Ag) atoms. A mechanism for explaining this finding is proposed. We go on to discuss the prospects for an electron EDM search using ultracold, assembled, optically trapped RaAg molecules, and argue that this system is particularly promising for rapid future progress in the search for new sources of violation.