Recent content by John Greger

I can get the citation code from Inspire.net for papers. However, can I change the Bibliography settings in some way such that there are hyperlinks to the paper? I don't want to embed it manually for every reference. For instance. Now, I use the citation code @article{Hawking:2000kj...

Hi!The dot is ##\partial_\tau##. The parameters R and T are coordinates on the bubble wall as functions of proper time. Sorry for not giving more context from the paper, I believe it is not very useful, they more or less just state the norm of a bubble wall in a different spacetime background...

So say I have a bubble embedded in a spacetime with metric: $$ds^2 = -dt^2 + a(t) ( dr^2 + r^2 d\Omega^2_2) $$ how do I compute the normal vector if I assume the wall of the bubble the metric represents follows a time-like trajectory, for any ##a(t)##? Since we are interested in dynamical...

Hi! Many thanks for your answer. Yes indeed, might have abused language. I believe I expanded it in equation 1 the right way. But I feel that I am confused about how to sum the indices accordingly..

I'm trying to compute the extrinsic curvature. I have the formula and everything I need to plug into the formula. But I get confused when executing this calculation.. I have that ##ds^2_{interior} = -u(r)dt^2 + (u(r))^{-1} dr^2 + r^2 d\Omega_3^2##. This is a metric describing the interior and...

What are the units of the trigonometric functions sinus, cosinus etc? If I take say Sin(0.5), what would the units of the output be?

Hi! So I have just been studying Yang-Mills theory advanced quantum field theory. In chapter 72 of Srednicki's book Quantum Field Theory they list the Feynman rules for non-abelian gauge theory. I was asked if I could show some sample allowed diagrams but I could not.. In standard particle...

Thank you very much for clarifying. Mabye stupid question, but is it really possible to have a LHS and RHS of different matrix dimension?

Hi and thank you very much for responding. But then I will still have i's in the matrices such that they are not real? May I also ask, on the right hand side the metric is still a 3x3 matrix, but on left hand side the matrices are 2x2, can we really have that?

Hi! Is it possible to construct gamma matrices satisfying the Clifford algebra ##\{\gamma^\mu, \gamma^\nu \} = \eta^{\mu \nu}## that are *real*, for ##\eta = diag(-1,1,1)##? I know that I can construct them in principle from sigma matrices, but I don't know how to construct real gamma...

This makes sense!

I could do a Binomial expansion and argue that every ## {n \choose k}## are integers so we reduce the problem to arguing that the sum of 2 to some power of n should an integer but it does not bring me so much closer...

Sorry about that! Will try to edit the post, should be as n goes to infinity!

I came across a rather strange thing in an introductory class I still don't understand. There was a statement that $$lim_n (2+ \sqrt(2))^n $$ is an integer. I recalled that I never understood this and just recently tried to take the limit but just get that the expression diverge? Which I think...

Hi all, The killing vector equation reads: ##\nabla_{(\mu K_{\nu})} = 0## What do the parenthesis mean explicitly? Moreover, I know that ##\nabla_\mu x^\nu = \partial_\mu x^\nu+ \Gamma_{\rho \mu}^\nu x^\rho## So if the parentheses mean symmetric the Killing equation will read...