Testing leptogenesis and seesaw in the B−L model using long-lived particle searches

We discuss the potential of using long-lived particle (LLP) searches for right-handed neutrinos (RHNs) to test resonant leptogenesis and the seesaw mechanism. This is challenging if only RHNs are added to the Standard Model, as naturally the active-sterile mixing strengths <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mo stretchy="false">|</a:mo><a:msub><a:mi>V</a:mi><a:mrow><a:mo>ℓ</a:mo><a:mi>N</a:mi></a:mrow></a:msub><a:msup><a:mo stretchy="false">|</a:mo><a:mn>2</a:mn></a:msup></a:math> are small, for <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:mn>1</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi>GeV</e:mi><e:mo>≲</e:mo><e:msub><e:mi>M</e:mi><e:mi>N</e:mi></e:msub><e:mo>≲</e:mo><e:mn>1000</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi>GeV</e:mi></e:mrow></e:math>. Instead, we consider the minimal <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>B</g:mi><g:mo>−</g:mo><g:mi>L</g:mi></g:math> gauge model, where a <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msup><i:mi>Z</i:mi><i:mo>′</i:mo></i:msup></i:math> gauge boson couples to fermions including the RHNs. During leptogenesis, this gauge coupling introduces scattering processes that washout the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>B</k:mi><k:mo>−</k:mo><k:mi>L</k:mi></k:math> asymmetry. At colliders, it can lead to abundant production of RHNs which allows probing the associated seesaw mechanism using LLP searches. We find that LLP searches at the FCC-hh can test leptogenesis and the seesaw mechanism simultaneously and probe the active-sterile mixing at or below the seesaw floor. Published by the American Physical Society 2024