Lorentz Violating Theories and Effects on Magnetic Dipole Moment, Electric Dipole Moment and Schiff Theorem

Seminars | Friday, June 01, 2018 | 16:30:00
Manuel Messias Ferreira

The magnetic dipole moment (MDM) of the electron is one of the physical quantities best known in nature. The electron anomalous magnetic moment, the gyromagnetic factor deviation from the value predicted by the pure Dirac equation, due to radioactive corrections, is known with precison best than 1 part in 10¹². Such experimental precision can be, obviously, used to constrain new theoretical models that yield MDM corrections. The electric dipole moment (EDM) of elementary particles is a tiny quantity compatible with parity-odd and time reversal-odd interactions. In a nonrelativistic formulation, the EDM interaction has the form d(σ·E), in which E is the electric field, σ, the spin operator and d, the EDM modulus. The EDM magnitude d, according to the Standard Model (SM), is ≈10⁻³⁸e⋅m, while the experimental measurements have reached the level ≈10⁻³¹e⋅m very recently, having a large space for new physics, beyond the Standard Model, to play a relevant role. The electron EDM, actually measured at the level ≈8×10⁻³¹e⋅m, also provides a strong tool to constrain theoretical models that correct the electron EDM. Concerning the EDM of atoms, it holds the Schiff theorem (1963), stating that for an atom with a point-like nucleus and nonrelativistic electrons that interact electrostatically only, the nuclear EDM is completely screened at first order by the atom's electrons, causing no Stark spectrum shift. For a finite-sized nucleus, however, the first order screening is no longer complete, there appearing the nuclear Schiff moment, whose interaction with the electrons generates atomic EDM. In this talk, we introduce some elements of the physics of MDM, EDM, Schiff theorem and Schiff moment, discussing how new physics can impact on the these issues and be constrained by the related experimental data.