How is the Power Spectrum of Matter Density Field Defined?

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The power spectrum of the matter density field is defined by the equation P_{xx}(k)=(2\pi^3)\delta(k-k^\prime)<x(k)x(k^\prime)>, which incorporates a factor of (2\pi^3). An alternative definition is presented as P_{yy}(k)=\delta(k-k^\prime)<y(k)y(k^\prime)>, which raises the question of whether the (2\pi^3) factor has been absorbed into the correlation function in this context. The discussion highlights the importance of understanding the role of these constants in the definitions of power spectra. Clarifying these definitions is crucial for accurate interpretations in cosmological studies. Overall, the relationship between the two equations is central to the analysis of matter density fields.
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The definition of power spectrum of matter density field is given by eq (1). I have also seen definitions of power spectra given by eq (2) . Does this mean ##(2\pi^3)## has been absorbed in the correlation function?
Relevant Equations
##P_{xx}(k)=(2\pi^3)\delta(k-k^\prime)\langle x(k)x(k^\prime)\rangle##

##P_{yy}(k)=\delta(k-k^\prime)\langle y(k)y(k^\prime)\rangle##

<Mentor: edit latex>
The definition of power spectrum of matter density field is given by eq(1). I have also seen definitions of power spectra given by eq(2) . Does this mean (2\pi^3) has been absorbed in the correlation function?

$$P_{xx}(k)=(2\pi^3)\delta(k-k^\prime)<x(k)x(k^\prime)>$$ .. (1)
$$P_{yy}(k)=\delta(k-k^\prime)<y(k)y(k^\prime)> $$.. (2)
 
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I want to find the solution to the integral ##\theta = \int_0^{\theta}\frac{du}{\sqrt{(c-u^2 +2u^3)}}## I can see that ##\frac{d^2u}{d\theta^2} = A +Bu+Cu^2## is a Weierstrass elliptic function, which can be generated from ##\Large(\normalsize\frac{du}{d\theta}\Large)\normalsize^2 = c-u^2 +2u^3## (A = 0, B=-1, C=3) So does this make my integral an elliptic integral? I haven't been able to find a table of integrals anywhere which contains an integral of this form so I'm a bit stuck. TerryW

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