How is this equation solved?by Forhad3097 Tags: field theory, mathematical physics, quantum field theory 

#1
Feb113, 12:56 PM

P: 4

In this articlehttp://arxiv.org/abs/0802.3525, the authors present the inhomogeneous equation
$$\ddot{\phi}_2 + \phi_2 + g_2\phi_1^2 + \omega_1\ddot{\phi}_1 = 0\tag{11}$$ followed by its solution $$\phi_2 = p_2\cos(\tau + \alpha) + q_2\sin(\tau + \alpha) + \frac{g_2}{6}p_1^2[\cos(2\tau + 2\alpha)  3] + \frac{\omega_1}{4}p_1[2\tau\sin(\tau + \alpha) + \cos(\tau + \alpha)]\tag{14}$$ How is this solution obtained? 



#2
Feb113, 01:09 PM

Sci Advisor
Thanks
P: 3,853

You left out a crucial part of the solution: φ_{1} = p_{1} cos(τ + α). Plug that into the equation and you have a driven harmonic oscillator, solved in any calc book.




#3
Feb2013, 10:52 AM

P: 4

I have expanded the equation(9) from the paper http://arxiv.org/abs/0802.3525 . $$[1+\epsilon \omega_1+ \epsilon^2 \omega_2+\epsilon^3 \omega_4...][\epsilon \ddot\phi_1+\epsilon^2 \ddot\phi_2+\epsilon^3 \ddot\phi_3....]+\epsilon^2[\epsilon \Delta\phi_1 + \epsilon^2 \Delta\phi_2+\epsilon^3 \Delta\phi_3.....]=\epsilon \phi_1+\epsilon^2 \phi_2+\epsilon^3 \phi_3.....+[g_2 \phi^2 + g_3 \phi^3....]$$
From this equation We can write equation (10), (11) and (12) and so on. but equation (12) is not matching with the expanding equation I did. I think problem in expanding with $$[g_2 \phi^2 + g_3 \phi^3....]$$. can you please have a look, that where is the problem? 


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