Topological defects as effective dynamical dark energy

In this work, we consider the possibility that the dynamical dark energy hinted at by recent Dark Energy Spectroscopic Instrument data may be mimicked by the effects of additional components in the universe, potentially arising from topological defects. We find that the data does not show a particular preference for the existence of cosmic strings. However, a domain wall contribution at the percent level can improve the fit, yielding a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi mathvariant="normal">Δ</a:mi> <a:msup> <a:mi>χ</a:mi> <a:mn>2</a:mn> </a:msup> <a:mo>=</a:mo> <a:mo>−</a:mo> <a:mn>1.72</a:mn> </a:math> and <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline"> <d:mi mathvariant="normal">Δ</d:mi> <d:mi>DIC</d:mi> <d:mo>=</d:mo> <d:mo>−</d:mo> <d:mn>0.94</d:mn> </d:math> compared to the lambda-cold dark matter model ( <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi mathvariant="normal">Λ</g:mi> <g:mi>CDM</g:mi> </g:math> ). The improvement indicates that topological defects remain a viable and interesting extension to <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mi mathvariant="normal">Λ</j:mi> <j:mi>CDM</j:mi> </j:math> , meriting further investigation with future cosmological data.