Alleviating cosmological tensions with a hybrid dark sector

We investigate a cosmological model inspired by hybrid inflation, where two scalar fields representing dark energy (DE) and dark matter (DM) interact through a coupling that is proportional to the DE scalar field <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mn>1</a:mn> <a:mo>/</a:mo> <a:mi>ϕ</a:mi> </a:math> . The strength of the coupling is governed solely by the initial condition of the scalar field, <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msub> <c:mi>ϕ</c:mi> <c:mi>i</c:mi> </c:msub> </c:math> , which parametrizes deviations from the standard <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mrow> <e:mi mathvariant="normal">Λ</e:mi> </e:mrow> </e:math> cold dark matter ( <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mi mathvariant="normal">Λ</h:mi> <h:mi>CDM</h:mi> </h:math> ) model. In this model, the scalar field tracks the behavior of DM during matter domination until it transitions to DE while the DM component decays quicker than standard CDM during matter domination, and is therefore different from some interacting DM-DE models which behave like phantom dark energy. Using 2018 CMB data, Dark Energy Spectroscopic Instrument baryonic acoustic oscillations measurements and <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mrow> <k:mi>Pantheon</k:mi> <k:mo>+</k:mo> <k:mi>supernova</k:mi> </k:mrow> </k:math> observations, we find that the model allows for an increase in <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:msub> <m:mi>H</m:mi> <m:mn>0</m:mn> </m:msub> </m:math> that can help reduce the Hubble tension. In addition, we find that higher values of the coupling parameter are correlated with lower values of <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:msub> <o:mi>ω</o:mi> <o:mi>m</o:mi> </o:msub> </o:math> , and a mild decrease of the weak-lensing parameter <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"> <q:msub> <q:mi>S</q:mi> <q:mn>8</q:mn> </q:msub> </q:math> , potentially relevant to address the <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:msub> <s:mi>S</s:mi> <s:mn>8</s:mn> </s:msub> </s:math> tension. Bayesian model comparison, however, reveals inconclusive results for most datasets, unless <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"> <u:mrow> <u:mi mathvariant="normal">S</u:mi> <u:msub> <u:mrow> <u:mi>H</u:mi> </u:mrow> <u:mrow> <u:mn>0</u:mn> </u:mrow> </u:msub> <u:mi>ES</u:mi> </u:mrow> </u:math> data are included, in which case a moderate evidence in favor of the hybrid model is found.