EhsanZ said:Weinburg did it in his book named "Cosmology".
Weinberg's Cosmology is a theoretical framework that attempts to explain the structure and evolution of the universe. It is based on the principles of general relativity and assumes a homogeneous and isotropic universe on large scales.
In Weinberg's Cosmology, (1+z(eq)) refers to the redshift of the universe at the time of matter-radiation equality. Neglecting it in the denominator is a simplifying assumption that is often made in calculations, as it does not significantly affect the overall results.
In Weinberg's Cosmology, (1+z(eq)) is used to calculate the energy density of the universe at the time of matter-radiation equality. This is important because it marks a key point in the evolution of the universe, when matter became the dominant component and began to drive its expansion.
Neglecting (1+z(eq)) in the denominator may introduce some error in calculations, but it is considered a minor approximation in most cases. However, in more precise calculations, it may be necessary to include this term for more accurate results.
Neglecting (1+z(eq)) in the denominator does not significantly affect the overall predictions and conclusions of Weinberg's Cosmology. It is often a simplifying assumption that allows for easier calculations and does not change the overall understanding of the structure and evolution of the universe.