Authentic Majorana versus singlet Dirac neutrino contributions to μ+μ+→ℓ+<mml:…

We revisited the computation of the cross section for the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msup><a:mrow><a:mi>μ</a:mi></a:mrow><a:mrow><a:mo>+</a:mo></a:mrow></a:msup><a:msup><a:mrow><a:mi>μ</a:mi></a:mrow><a:mrow><a:mo>+</a:mo></a:mrow></a:msup><a:mo stretchy="false">→</a:mo><a:msup><a:mrow><a:mo>ℓ</a:mo></a:mrow><a:mrow><a:mo>+</a:mo></a:mrow></a:msup><a:msup><a:mrow><a:mo>ℓ</a:mo></a:mrow><a:mrow><a:mo>+</a:mo></a:mrow></a:msup></a:mrow></a:math> <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"><d:mo stretchy="false">(</d:mo><d:msup><d:mo>ℓ</d:mo><d:mo>+</d:mo></d:msup><d:mo>=</d:mo><d:msup><d:mi>τ</d:mi><d:mo>+</d:mo></d:msup><d:mo>,</d:mo><d:msup><d:mi>e</d:mi><d:mo>+</d:mo></d:msup><d:mo stretchy="false">)</d:mo></d:math> transitions in the presence of new heavy Majorana neutrinos. We focus on scenarios where the masses of the new states are around some few TeV, the so-called low-scale seesaw models. Our analysis is set in a simple model with only two new heavy Majorana neutrinos considering the current limits on the heavy-light mixings. Our results illustrate the difference between the genuine effects of two nondegenerate heavy Majorana states and the degenerate case where they form a Dirac singlet field. Published by the American Physical Society 2024