Graduate Regarding Coleman's Sine-Gordon Duality

[QFT1995]

TL;DR

Confusion over perturbative series

The link to the paper is here; http://www.sbfisica.org.br/~evjaspc/xviii/images/Nunez/Jan26/AdditionalMaterial/Coleman_paper/Coleman_paper.pdf

Im confused over what exactly he is calculating on page 5 (2092) equation 4.11. Specifically what is
$$\mathcal{T} \langle 0 | \prod_i A_+ (x_i) A_-(y_i) | 0 \rangle. $$
Why aren't the $A_+ (x_i)$ and $A_-(y_i)$ at the same point and what exactly is the object above?

 

[Demystifier]

It's a time ordered correlation function. Before studying this paper, you should first learn some more basic QFT (if you haven't already).

 

[QFT1995]

I understand that its a time ordered correlation function but I'm confused on exactly what the specific perturbation series he is calculating physically means.

 

[QFT1995]

It's a time ordered correlation function. Before studying this paper, you should first learn some more basic QFT (if you haven't already).

Hi, could you help explain the specific series in the paper. I'm on a deadline and I don't have much time.
Thanks