Astrophysical consequences of an electroweak <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:msub> <mml:mi>η</mml:mi> <mml:mi>w</mml:mi> </mml:msub> </mml:math> pseudoscalar

Recently, it has been suggested that the spectrum of physical states in the Standard Model may include an ultralight pseudoscalar, denoted by <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>η</a:mi> <a:mi mathvariant="normal">w</a:mi> </a:msub> </a:math> , in analogy with the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:msup> <d:mi>η</d:mi> <d:mo>′</d:mo> </d:msup> </d:math> state arising from the strong interactions. We find that typical expectations for the properties of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:msub> <f:mi>η</f:mi> <f:mi mathvariant="normal">w</f:mi> </f:msub> </f:math> get challenged by astrophysical constraints on the couplings of ultralight bosons. Our strongest limit sets a lower bound of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mrow> <i:mi mathvariant="script">O</i:mi> <i:mrow> <i:mo stretchy="false">(</i:mo> <i:mrow> <i:mn>100</i:mn> <i:mtext> </i:mtext> <i:mtext> </i:mtext> <i:mi>TeV</i:mi> </i:mrow> <i:mo stretchy="false">)</i:mo> </i:mrow> </i:mrow> </i:math> on the decay constant of the hypothesized pseudoscalar. We also briefly discuss whether <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"> <n:msub> <n:mi>η</n:mi> <n:mi mathvariant="normal">w</n:mi> </n:msub> </n:math> could be a dark matter candidate, or the origin of dark energy, but conclude that those identifications appear unlikely. Given the important implications of a potentially overlooked <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"> <q:msub> <q:mi>η</q:mi> <q:mi mathvariant="normal">w</q:mi> </q:msub> </q:math> state for a more complete understanding of the electroweak interactions and a fundamental description of nature, further theoretical and phenomenological investigations of this possibility and its associated physics are warranted.