Please help solve the equation in black hole f(R) theories

In summary, the conversation discusses trying to solve an equation from a paper, but the approach taken does not match the results in the paper. The equation being solved involves multiple variables and derivatives, and the output shows a potential mistake in the calculations.
  • #1
Boy_saber
1
0
In the paper https://arxiv.org/abs/1210.4699. How to solve this equation?

1.jpg


I've tried it, it's not same as in this paper. Even zero order still not the same.
This is what I try to do at zero order.

input

$$E=E_0\left(r_0\right)$$
$$H=H_0\left(r_0\right)$$
$$b=b\left(r_0\right)$$
$$R=R_0\left(r_0\right)$$
$$\Phi =\Phi _0\left(r_0\right)$$
$$r=r_0$$
$$g^{11}=1-\frac{b}{r}$$
$$\Box f_R=H g^{11} \left(\frac{\partial R}{\partial r_0}\right){}^2+E \left(\left(1-\frac{b}{r}\right) \left(\frac{\partial R}{\partial r_0} \left(-\frac{\partial \Phi }{\partial r_0}\right)+\frac{\frac{\partial R}{\partial r_0}}{r}+\frac{\partial }{\partial r_0}\frac{\partial R}{\partial r_0}\right)+\frac{\left(1-\frac{\partial b}{\partial r_0}\right) \frac{\partial R}{\partial r_0}}{r}\right)$$

output

$$-\frac{b\left(r_0\right) H_0\left(r_0\right) R_0'\left(r_0\right){}^2}{r_0}+\frac{b\left(r_0\right) E_0\left(r_0\right) R_0'\left(r_0\right) \Phi _0'\left(r_0\right)}{r_0}-\frac{E_0\left(r_0\right) b_0'\left(r_0\right) R_0'\left(r_0\right)}{r_0}-\frac{b\left(r_0\right) E_0\left(r_0\right) R_0'\left(r_0\right)}{r_0^2}-\frac{b\left(r_0\right) E_0\left(r_0\right) R_0''\left(r_0\right)}{r_0}+H_0\left(r_0\right) R_0'\left(r_0\right){}^2-E_0\left(r_0\right) R_0'\left(r_0\right) \Phi _0'\left(r_0\right)+\frac{2 E_0\left(r_0\right) R_0'\left(r_0\right)}{r_0}+E_0\left(r_0\right) R_0''\left(r_0\right)$$

Where did I make a mistake?
 
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  • #2


It is difficult to pinpoint the exact mistake without more context and information about the specific equation and problem being solved. However, it is possible that there may be a missing term or a sign error in the output equation. It is also important to carefully check all the inputs and their derivatives to ensure they are correct. It may also be helpful to consult with a colleague or a subject expert for further assistance in solving the equation.
 

FAQ: Please help solve the equation in black hole f(R) theories

What are black hole f(R) theories?

Black hole f(R) theories are a class of modified gravity theories where the Einstein-Hilbert action is generalized to include a function of the Ricci scalar, R. These theories aim to address various issues in cosmology and astrophysics by modifying General Relativity.

How does one derive the field equations in f(R) theories?

The field equations in f(R) theories are derived by varying the action with respect to the metric tensor. This leads to fourth-order differential equations in the metric, unlike the second-order equations in General Relativity. The resulting equations are more complex and require additional boundary conditions or constraints to solve.

What are the challenges in solving black hole equations in f(R) theories?

Solving black hole equations in f(R) theories is challenging due to the higher-order nature of the field equations. These equations often do not have closed-form solutions and require numerical methods or approximations. Additionally, ensuring the physical viability and stability of the solutions adds another layer of complexity.

Are there any known exact solutions for black holes in f(R) theories?

Yes, there are some known exact solutions for black holes in specific forms of f(R) theories. For instance, certain forms of f(R) allow for solutions that resemble the Schwarzschild or Kerr black holes of General Relativity. However, these solutions are often highly specialized and may not be applicable to all forms of f(R) functions.

What are the implications of f(R) black hole solutions for astrophysics and cosmology?

f(R) black hole solutions have significant implications for both astrophysics and cosmology. They can provide insights into the nature of dark matter and dark energy, offer alternative explanations for gravitational wave observations, and potentially resolve singularities. These solutions also help in understanding the modifications needed in General Relativity to address current observational discrepancies.

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