Sterile neutrino dark matter from a TeV scale seesaw

In this article, we investigate the phenomenological aspects of a feebly interacting sterile neutrino dark matter candidate within a low-scale seesaw framework. The type-I seesaw model is augmented by a second complex scalar doublet ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi mathvariant="normal">Φ</a:mi> <a:mi>ν</a:mi> </a:msub> </a:math> ), which couples exclusively to the heavy right-handed neutrinos and the lepton doublet, thereby generating the neutrino Dirac mass term while the first scalar doublet is responsible for giving mass to the remaining Standard Model particles. The lightest sterile neutrino ( <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:msub> <d:mi>N</d:mi> <d:mn>1</d:mn> </d:msub> </d:math> ) acts as a feebly interacting massive particle (FIMP), produced via decays of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:msup> <f:mi>W</f:mi> <f:mo>±</f:mo> </f:msup> </f:math> , <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mi>Z</h:mi> </h:math> and extra scalars present in the setup. We point out that <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:msup> <j:mi>W</j:mi> <j:mo>±</j:mo> </j:msup> </j:math> and <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"> <l:mi>Z</l:mi> </l:math> contributions were overlooked in the previous studies, which actually dominate the <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"> <n:msub> <n:mi>N</n:mi> <n:mn>1</n:mn> </n:msub> </n:math> production by a factor of <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"> <p:mo>∼</p:mo> <p:msup> <p:mn>10</p:mn> <p:mn>13</p:mn> </p:msup> </p:math> and solely determines the relic abundance. Incorporating them leads to several novel consequences for the DM phenomenology like a new nonthermal condition which leads to smaller Yukawa couplings. We thoroughly discuss about the enhancement possibilities of <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"> <r:msub> <r:mi>N</r:mi> <r:mn>1</r:mn> </r:msub> </r:math> ’s mass which is controlled by the small vacuum expectation value ( <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"> <t:msub> <t:mi>v</t:mi> <t:mi>ν</t:mi> </t:msub> </t:math> ) of the second Higgs doublet. After incorporating the latest Lyman- <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"> <v:mi>α</v:mi> </v:math> forest observations, this setup can accommodate both warm and cold dark matter scenarios.