Greetings,(adsbygoogle = window.adsbygoogle || []).push({});

I stumbled across two question that I have no idea on how to answer them.

1) The interaction term in a scalar field theory is [tex]-\frac{\lambda}{4!} \phi^4[/tex]

Why should lambda be positive? (they say look at the energy of the ground state...)

2) Write down the Feynman rules for phi^4

I have no clue as to how you get the two intersecting lines that give is -i lambda vertex. I see where the propagator comes from though.

Any thougths?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Phi^4 theory

**Physics Forums | Science Articles, Homework Help, Discussion**