Unitarity-conserving nonminimally coupled inflation and the ACT spectral index
John McDonald
Abstract
The Atacama Cosmology Telescope (ACT) Collaboration has reported a scalar spectral index <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>n</a:mi> <a:mi>s</a:mi> </a:msub> <a:mo>=</a:mo> <a:mn>0.9743</a:mn> <a:mo>±</a:mo> <a:mn>0.0034</a:mn> </a:math> . This is substantially larger than the classical prediction of nonminimally coupled inflation models such as Higgs Inflation, <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msub> <c:mi>n</c:mi> <c:mi>s</c:mi> </c:msub> <c:mo>≈</c:mo> <c:mn>0.965</c:mn> </c:math> . Here we revisit the unitarity-conserving nonminimally coupled inflation model proposed by R. N. Lerner and J. McDonald []. We show that when the inflaton is a complex nonminimally coupled gauge singlet scalar with additional interactions in the Jordan frame to maintain unitarity, the model predicts <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:msub> <e:mi>n</e:mi> <e:mi>s</e:mi> </e:msub> <e:mo>=</e:mo> <e:mn>0.9730</e:mn> </e:math> and <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>r</g:mi> <g:mo>≈</g:mo> <g:mn>9</g:mn> <g:mo>×</g:mo> <g:msup> <g:mn>10</g:mn> <g:mrow> <g:mo>−</g:mo> <g:mn>6</g:mn> </g:mrow> </g:msup> </g:math> for scalar self-coupling <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>λ</i:mi> <i:mo>=</i:mo> <i:mn>0.1</i:mn> </i:math> .