Abstract
The ACME collaboration has recently announced a new constraint on the electron EDM, |de| < 1.1 × 10−29e cm, from measurements of the ThO molecule. This is a powerful constraint on CP-violating new physics: even new physics generating the EDM at two loops is constrained at the multi-TeV scale. We interpret the bound in the context of different scenarios for new physics: a general order-of-magnitude analysis for both the electron EDM and the CP-odd electron-nucleon coupling; 1-loop SUSY, probing sleptons above 10 TeV; 2-loop SUSY, probing multi-TeV charginos or stops; and finally, new physics that generates the EDM via the charm quark or top quark Yukawa couplings. In the last scenario, new physics generates a “QULE operator” left({q}_f{overline{sigma}}^{mu nu }{overline{u}}_fright)kern0.5em cdotp kern0.5em left(ell {overline{sigma}}_{mu nu}overline{e}right) , which in turn generates the EDM through RG evolution. If the QULE operator is generated at tree level, this corresponds to a previously studied leptoquark model. For the first time, we also classify scenarios in which the QULE operator is generated at one loop through a box diagram, which include (among others) SUSY and leptoquark models. The electron EDM bound is the leading constraint on a wide variety of theories of CP-violating new physics interacting with the Higgs boson or the top quark. We argue that any future nonzero measurement of an electron EDM will provide a strong motivation for constructing new colliders at the highest feasible energies.
Highlights
The ACME collaboration has used ThO molecules to constrain the electron electric dipole moment (EDM) to be [1]|de| < 1.1 × 10−29 e cm. (1.1)This is about an order of magnitude improvement on the previous bound from ACME [2] and from studies of HfF+ at JILA [3]
We interpret the bound in the context of different scenarios for new physics: a general order-of-magnitude analysis for both the electron EDM and the CP-odd electron-nucleon coupling; 1-loop SUSY, probing sleptons above 10 TeV; 2-loop SUSY, probing multi-TeV charginos or stops; and new physics that generates the EDM via the charm quark or top quark Yukawa couplings
In the Standard Model, this symmetry is violated by a handful of parameters: the CKM phase, which generates an electron EDM only at four loops with |de| ∼ 10−44 e cm and a CP-odd electron-nucleon interaction that can mimic an EDM of size |de| ∼ 10−38 e cm [4]; the strong phase θ, which generates an electron EDM |de| 10−37 e cm [7, 8]; and phases associated with the lepton sector, which give contributions at two loops suppressed by neutrino masses [9] with an expectation that |de| 10−43 e cm or, in the presence of severe fine-tuning, at most |de| 10−33 e cm [10]
Summary
The ACME collaboration has used ThO molecules to constrain the electron electric dipole moment (EDM) to be [1]. (If the up quark is the leading coupling, the CP-odd electron-nucleon coupling plays a more important role in the ThO measurement than the electron EDM itself.) The QULE operator could be induced by scalar leptoquark exchange at tree level, as previously discussed in [41,42,43]. It could arise from a box diagram, a case that we discuss for the first time. We argue that in the latter case, these new particles would lead to a very concrete form of the hierarchy problem, motivating the construction of new colliders even if the particles directly contributing to the EDM are out of reach
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