Models for the electric dipole moment and anomalous magnetic moment of the tau lepton

The Belle II experiment and other ongoing and projected lepton facilities are expected to greatly enhance the sensitivity to the electric dipole moment (EDM) and anomalous magnetic moment ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>g</a:mi> <a:mo>−</a:mo> <a:mn>2</a:mn> </a:math> ) for the tau lepton, making it timely to explore models that predict these observables. In this work, we study a class of models in which the tau mass is generated radiatively. As a result, sizable EDM and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>g</c:mi> <c:mo>−</c:mo> <c:mn>2</c:mn> </c:math> of the tau lepton arise as a natural consequence of the radiative mass generation mechanism at the electroweak scale. We present two benchmark models with different hypercharge assignments. The first model contains neutral fermions and charged scalars. We find that the model can predict a large signal of the tau EDM, <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mrow> <e:msub> <e:mrow> <e:mi>d</e:mi> </e:mrow> <e:mrow> <e:mi>τ</e:mi> </e:mrow> </e:msub> <e:mo>=</e:mo> <e:mi mathvariant="script">O</e:mi> <e:mo stretchy="false">(</e:mo> <e:msup> <e:mrow> <e:mn>10</e:mn> </e:mrow> <e:mrow> <e:mo>−</e:mo> <e:mn>19</e:mn> </e:mrow> </e:msup> <e:mo stretchy="false">)</e:mo> <e:mi>e</e:mi> <e:mtext> </e:mtext> <e:mi>cm</e:mi> </e:mrow> </e:math> , and <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mi>g</j:mi> <j:mo>−</j:mo> <j:mn>2</j:mn> </j:math> , <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"> <l:msub> <l:mi>a</l:mi> <l:mi>τ</l:mi> </l:msub> <l:mo>=</l:mo> <l:mi mathvariant="script">O</l:mi> <l:mo stretchy="false">(</l:mo> <l:msup> <l:mn>10</l:mn> <l:mrow> <l:mo>−</l:mo> <l:mn>5</l:mn> </l:mrow> </l:msup> <l:mo stretchy="false">)</l:mo> </l:math> , which are within the reach of future updates of their measurements. In contrast, the second model, containing a charged fermion and neutral scalars, yields a similar magnitude but different sign for <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"> <q:mi>g</q:mi> <q:mo>−</q:mo> <q:mn>2</q:mn> </q:math> , and predicts a comparatively smaller EDM signal. Our models serve as well-motivated benchmarks for new physics scenarios in which radiative tau mass generation leads to sizable tau dipole moments.