Dark matter-electron scattering and freeze-in scenarios in the light of Z′ mediation

We investigate dark matter (DM-)electron scattering in a minimal <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>U</a:mi><a:mo stretchy="false">(</a:mo><a:mn>1</a:mn><a:msub><a:mo stretchy="false">)</a:mo><a:mi>X</a:mi></a:msub></a:math> extension of the Standard Model (SM), where the DM can appear as a Majorana fermion, a complex singlet scalar, or a Dirac fermion. To study bounds on the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>U</e:mi><e:mo stretchy="false">(</e:mo><e:mn>1</e:mn><e:msub><e:mo stretchy="false">)</e:mo><e:mi>X</e:mi></e:msub></e:math> gauge coupling <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mo stretchy="false">(</i:mo><i:msub><i:mi>g</i:mi><i:mi>X</i:mi></i:msub><i:mo stretchy="false">)</i:mo></i:math> and new gauge boson mass <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mo stretchy="false">(</m:mo><m:msub><m:mi>M</m:mi><m:msup><m:mi>Z</m:mi><m:mo>′</m:mo></m:msup></m:msub><m:mo stretchy="false">)</m:mo></m:math>, from DM-electron scattering, we consider several direct search experiments like CDMS, DAMIC, SENSEI, PandaX-II, DarkSide-50, and XENON1T-S2 for different <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mi>U</q:mi><q:mo stretchy="false">(</q:mo><q:mn>1</q:mn><q:msub><q:mo stretchy="false">)</q:mo><q:mi>X</q:mi></q:msub></q:math> charges. In this setup, we consider DM production via freeze-in in both radiation-dominated and modified cosmological background to project sensitivities onto <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"><u:msub><u:mi>g</u:mi><u:mi>X</u:mi></u:msub><u:mo>−</u:mo><u:msub><u:mi>M</u:mi><u:msup><u:mi>Z</u:mi><u:mo>′</u:mo></u:msup></u:msub></u:math> plane satisfying observed relic abundance. DM-electron scattering could provide comparable, or even stronger, bounds compared to those obtained from the electron/muon (<w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:mrow><w:mi>g</w:mi><w:mo>−</w:mo><w:mn>2</w:mn></w:mrow></w:math>), low-energy scattering, and intensity frontier experiments within <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:mrow><y:mn>0.01</y:mn><y:mtext> </y:mtext><y:mtext> </y:mtext><y:mi>GeV</y:mi><y:mo>≲</y:mo><y:msub><y:mi>M</y:mi><y:msup><y:mi>Z</y:mi><y:mo>′</y:mo></y:msup></y:msub><y:mo>≲</y:mo><y:mn>0.1</y:mn><y:mtext> </y:mtext><y:mtext> </y:mtext><y:mi>GeV</y:mi></y:mrow></y:math>. Constrains from freeze-in could provide stronger sensitivities for <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:msub><ab:mi>M</ab:mi><ab:msup><ab:mi>Z</ab:mi><ab:mo>′</ab:mo></ab:msup></ab:msub><ab:mo>≳</ab:mo><ab:mi mathvariant="script">O</ab:mi><ab:mo stretchy="false">(</ab:mo><ab:mn>1</ab:mn><ab:mo stretchy="false">)</ab:mo><ab:mtext> </ab:mtext><ab:mtext> </ab:mtext><ab:mi>GeV</ab:mi></ab:math>; however, these limits are comparable to those obtained from LHCb and LEP experiments for <fb:math xmlns:fb="http://www.w3.org/1998/Math/MathML" display="inline"><fb:mrow><fb:mi mathvariant="script">O</fb:mi><fb:mo stretchy="false">(</fb:mo><fb:mn>10</fb:mn><fb:mo stretchy="false">)</fb:mo><fb:mtext> </fb:mtext><fb:mtext> </fb:mtext><fb:mi>GeV</fb:mi><fb:mo>≲</fb:mo><fb:msub><fb:mrow><fb:mi>M</fb:mi></fb:mrow><fb:mrow><fb:msup><fb:mrow><fb:mi>Z</fb:mi></fb:mrow><fb:mrow><fb:mo>′</fb:mo></fb:mrow></fb:msup></fb:mrow></fb:msub><fb:mo>≲</fb:mo><fb:mn>150</fb:mn><fb:mtext> </fb:mtext><fb:mtext> </fb:mtext><fb:mi>GeV</fb:mi></fb:mrow></fb:math>. In the future, electron-muon scattering (MUonE), proton (FASER and DUNE), and electron/positron (ILC) beam-dump experiments could probe these parameters. Published by the American Physical Society 2024