Gravitational portals with nonminimal couplings

We consider the effects of nonminimal couplings to curvature of the form <math display="inline"><mrow><msub><mrow><mi>ξ</mi></mrow><mrow><mi>S</mi></mrow></msub><msup><mrow><mi>S</mi></mrow><mrow><mn>2</mn></mrow></msup><mi>R</mi></mrow></math> for three types of scalars: the Higgs boson, the inflaton, and a scalar dark matter candidate. We compute the abundance of dark matter produced by these nonminimal couplings to gravity and compare to similar results with minimal couplings. We also compute the contribution to the radiation bath during reheating. The main effect is a potential augmentation of the maximum temperature during reheating. A model independent limit of <math display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mn>10</mn><mn>12</mn></msup><mo stretchy="false">)</mo><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> is obtained. For couplings <math display="inline"><msub><mi>ξ</mi><mi>S</mi></msub><mo>≳</mo><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></math>, these dominate over minimal gravitational interactions.