Dark dimension and decaying dark matter gravitons

Abstract

We explore the cosmology of the dark-dimension scenario taking into account perturbations in the linear regime. In the context of the dark-dimension scenario, a natural candidate for dark matter in our Universe is the excitations of a tower of massive spin-2 Kaluza-Klein (KK) gravitons. These dark gravitons are produced in the early Universe and decay to lighter KK gravitons during the course of cosmological evolution. The decay causes the average dark matter mass to decrease as the Universe evolves. In addition, the kinetic energy liberated in each decay leads to a kick velocity for the dark matter particles, leading to a suppression of structure formation. Using current cosmic microwave background (), baryon acoustic oscillation, and cosmic shear (KiDS-1000) data, we put a bound on the dark matter kick velocity today <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msub><a:mrow><a:mi>v</a:mi></a:mrow><a:mrow><a:mtext>today</a:mtext></a:mrow></a:msub><a:mo>≤</a:mo><a:mn>2.2</a:mn><a:mo>×</a:mo><a:msup><a:mrow><a:mn>10</a:mn></a:mrow><a:mrow><a:mo>−</a:mo><a:mn>4</a:mn></a:mrow></a:msup><a:mi>c</a:mi></a:mrow></a:math> at 95% CL. This leads to rather specific regions of parameter space for the dark-dimension scenario. The combination of the experimental bounds from cosmology, astrophysics, and table-top experiments leads to the range <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msub><c:mi>l</c:mi><c:mn>5</c:mn></c:msub><c:mo>∼</c:mo><c:mn>1</c:mn><c:mi>–</c:mi><c:mrow><c:mn>10</c:mn><c:mtext> </c:mtext><c:mtext> </c:mtext><c:mi mathvariant="normal">μ</c:mi><c:mrow><c:mi mathvariant="normal">m</c:mi></c:mrow></c:mrow></c:math> for the size of the dark dimension. The dark-dimension scenario is found to be remarkably consistent with current observations and provides signatures that are within reach of near-future experiments. Published by the American Physical Society 2024