Recent content by silverwhale

Yes, I do get your point. But then, I get ##a(f(\eta))## which ist not equivalent (as a function) to ## a(\eta)## That is my problem. Both are called ##a##, but they are two different functions..

Thank you martinbn for your answer. In page 59, the definition is ##d \eta = dt/a##, that I do know; from which ##a(\eta) * d\eta = dt## follows (which I wrote), right? Before I start explaining my problem (I hope this time better), We should not forget that the factor ##a(t)## depends on the...

Hello PhysicsForums-Readers, On page 59 of Birrells and Davies QFT on CS, the line element ##ds^2 = dt^2 - a(t)^2 dx^2##, where ##a(t)## is some conformal factor defined as ##a({\eta}) = dt/d{\eta}##. Then in 3.83 the equation is rewritten to ##ds^2 = a(\eta)^2 (d^2 \eta - dx^2)##. IMHO this...

Hello dear PhysicsForums attendees! I tried to solve for somebody the aforementioned problem. But I am not sure if my attempt is correct. So I am writing down what I suggested. Looking at eq 2.46 in Carrolls book; The metric is Lorentzian in General Relativity so that ##g^{\mu \nu} =...

Sometimes easy seems to be hard.. ;-)

Hi Everybody, I am trying to do the calculation of Peskin Schroeder page 14, namely the first block of equations. The author moves from: U(t) = \frac{1}{2 \pi^3} \int d^3p e^{-i(p^2/2m)t} e^{ip \cdot (x-x_0)}. to U(t) = (\frac{m}{2 \pi i t})^{3/2} e^{im(x-x_0)^2/2t}. I guess the way to go...

Mandl and Shaw is very good as an introduction to Renormalization theory for particle theorists. I checked McCombs books, it didn't help me much as it is too general, but may be helpful for later usage. I'll check Collins in the coming days.

Sounds interesting, I'll check the book!

Hello Everybody, I am searching for a book that introduces the theory of renormalization other then Peskin Schroeder, I found Peskin Schroeder cumbersome regarding this topic. Can anyone help? Thanks in advance!

If we consider an other case where the interaction term looks like c_1 \phi^3 + c_2 \phi^4, can one just sum up the feynman diagrams (for eg. tree level diagrams) for phi3 theory and phi4 theory to express the \phi \phi \to \phi \phi scattering?

I indeed got the vertex function. It is: -i \alpha (p_1 p_2 + p_1 p_3 + p_2 p_3) \delta(p_1 + p_2 + p_3) . Thank you.

Homework Statement Compute the matrix element for the scattering process \phi \phi \to \phi \phi Homework Equations The Lagrangian is given by L = \frac{1}{2} \partial_{\mu} \phi \partial^{\mu} \phi + \frac{\alpha}{2} \phi \partial_{\mu} \phi \partial^{\mu} \phi + \frac{\beta}{2} \phi^2...

Homework Statement The lagrangian is given by: L = \frac{1}{2} \partial_{\mu} \phi \partial^{\mu} \phi + \frac{\alpha}{2} \phi \partial_{\mu} \phi \partial^{\mu} \phi And the question is to find the feynman rules. Homework EquationsThe Attempt at a Solution I started by using the...

Homework Statement The Hamiltonian is given by: H = \frac{1}{2} \sum_{i=1,2}[p_i^2 + q_i^2] We define the following operators: J = \frac{1}{2} (a_1^+ a_1 + a_2^+ a_2) J_1 = \frac{1}{2} (a_2^+ a_1 + a_1^+ a_2) J = \frac{i}{2} (a_2^+ a_1 - a_1^+ a_2) J = \frac{1}{2} (a_1^+ a_1 - a_2^+...

I'll take a look at Peskin Schröder and report.