# New Cosmography

First section of → Cosmography

Problem 1

problem id: cs-1

Using the cosmographic parameters introduced above, expand the scale factor into a Taylor series in time.

Problem 2

problem id: cs-2

Using the cosmographic parameters, expand the redshift into a Taylor series in time.

Problem 3

problem id: cs-3

What is the reason for the statement that the cosmological parameters are model-independent?

Problem 4

problem id: cs-4

Obtain the following relations between the deceleration parameter and Hubble's parameter $$q(t)=\frac{d}{dt}(\frac{1}{H})-1;\,\,q(z)=\frac{1+z}{H}\frac{dH}{dz}-1;\,\,q(z)=\frac{d\ln H}{dz}(1+z)-1.$$

Problem 5

problem id: cs-5

Show that the deceleration parameter can be defined by the relation $q=-\frac{d\dot{a}}{Hda}$

Problem 6

problem id: cs-6

Classify models of Universe basing on the two cosmographic parameters -- the Hubble parameter and the deceleration parameter.

Problem 7

problem id: cs-7

Show that the deceleration parameter $q$ can be presented in the form $$q(x)=\frac{\dot{H}(x)}{H(x)}x-1;\,\,x=1+z$$

Problem 8

problem id: cs-8

Show that for the deceleration parameter the following relation holds: $$q(a)=-\left(1+\frac{dH/dt}{H^2}\right)-\left(1+\frac{adH/da}{H}\right)$$

Problem 9

problem id: "cs-9

Show that $$\frac{dq}{d\ln (1+z)}=j-q(2q+1)$$

Problem 10

problem id: cs-10

Let $C_{n} \equiv \gamma _{n} \frac{a^{(n)} }{aH^{n} } ,$ where $a^{(n)}$ is n-th time derivative of the scale factor, $n\ge 2$ , $\gamma _{2} =-1,\; \gamma _{n} =1$ äëÿ $n>2$ . Then$C_{2} =q,\; C_{3} =j,\; C_{4} =s\ldots$ Obtain $dC_{n} /d\ln (1+z)$ .

Problem 11

problem id: cs-11

Use result of the previous problem to find $dC_{n} /dt$.

Problem 12

problem id: cs-12

Use the general formula for $dC_{n} /dt$ obtained in the previous problem to obtain time derivatives of the cosmographic parameters $q,j,s,l$.

Problem 13

problem id: cs-13

Find derivatives of the cosmographic parameter w.r.t. the red shift.

Problem 14

problem id: cs-14

Let $1+z=1/a\equiv x$. Find $q(x)$ and $j(x)$.