Recent content by S_klogW

What do we mean by 'Equivalent Projective representation"? I know that we say two representations R and R' of a group G is equivalent if there exists a unitary matrix U such that URU^(-1)=R'. But what do we mean by equivalent projective rerpesentations? I've heard of the theorem that the...

I have read from DJ Griffiths Quantum Mechanics that the electron-positron annihilation process will enlarge the hyperfine splitting of the positronium ground state. More precisely, the actual splitting is larger than that we calculated only considering the spin interaction between the positron...

Well, in fact this morning my teacher revealed the solution. Just think about the Wronski Determinant of the Bessel equations! This can help us get rid of the 1/x factor!

Homework Statement My teacher gave us a problem as an open question: To calculate an integral involving Bessel Functions. Homework Equations The Attempt at a Solution I've tried to convert this integral to one in which the Bessel function is in the numerator but failed. Does anyone know how to...

When I read A.Zee's QFT in a Nutshell, he asked me to do the calculation of his exercise IV.4.6: (A.Zee called these the Pontryagin Index) Let g(x) be the element of a group G. The 1-form v = gdg† is known as the Cartan-Maurer form. Then tr v^N is trivially closed on an N-dimensional manifold...

Well, i am an undergraduate at Tsinghua University. Currently A.Zee is giving a short-term lecture on Quantum Field Theory here. I've asked Zee about this equation in his book. He said that this is not exactly right if the Lagrangian is understood as an operator. He just provided a sloppy way to...

Well, i am an undergraduate at Tsinghua University. Currently A.Zee is giving a short-term lecture on Quantum Field Theory here. I've asked Zee about this equation in his book. He said that this is not exactly right if the Lagrangian is understood as an operator. He just provided a sloppy way to...

how to deduce that <k1k2| exp[iS] | k3 k4> is the propagator?

Recently i am reading A.Zee's Quantum Field Theory in a Nutshell 2nd Edition. there is a equation that i can not derive by myself. I suspect its correctness. <k1k2|exp(-iHT)|k3k4>=<k1k2|exp(i∫dxL(x))|k3k4>, where the L(x) on the RHS is an operator function of space-time. This equation...

I am reading Srednicki's Quantum Field Theory recently. I have thought over the descriptions of the Feynman Diagrams on his book in chapter 9, but I still can not understand what these diagrams mean and how do they help us to calculate the right-hand side of the equation 9.11 on the book. Is...

Nobody knows? Please help me. Thanks very much

Homework Statement Suppose we have already known these two theorems: 1.Thomson's theorem: The electrostatic energy of a system consisting of conductors reaches its minimum value relative to all the eletrostatic energy values of different charge distributions in which the total charge on or in...

Yes, I have already known that. I could not solve it because there is a typo in my Chinese Edition of the book.

Ha, I have solved this question. I got this problem from the Chinese Edition of the Zorich Analysis and it has a typo so I could not prove this. The problem in the English Edition is correct. Consider ((cos(t^2))/t)'=-2sin(t^2)-cos(t^2)/(t^2) The second part of the right side could be...

I think we could say that for every x, the series can be convergent. But it's not uniformly convergent. For all x ∈R，it's convergent. Just notice that if we assume S(x)=∑1/ [(k^x) * (2^k)] , we could find an integral number n with 1/ [(k^x) * (2^k)] ＜[(k^n) / (2^k)] . let Sn=Σ[(k^n) /...