# Tag Info

### Why are we able to compare the open and closed string perspective in AdS/CFT?

String theories have two worldsheet co-ordinates and it can often be useful to interchange which ones we regard as space and time. I think the missing link you are looking for comes from exploiting ...
1 vote

Accepted

### Does QFT Imply Strings the Same Way that String Theory Implies Branes?

When we take a good hard look at QFT, we don't see any particles (dimensionless points traveling on world lines). All we see are localized interactions. When we do our experiments to confirm these ...

### In what way is String Theory "two-dimensional"?

A string worldsheet is 2D. One space dimension (how far you are along the string), one time dimension.
Accepted

### Kaluza-Klein reducing the Chern-Simons term in 11D supergravity

$\newcommand{\d}{\mathrm{d}}\newcommand{\w}{\wedge}\newcommand{\R}{\mathbb{R}}$That integral vanishes because the differential form $\omega_i\w\omega_j\w\omega_k\in\Omega^6(S_4)$ vanishes (you cannot ...
1 vote

### Hamiltonian Open String

The orthogonality relations for sine and cosine functions should be proportional to the Kronecker $\delta$ symbol. Namely $$\int d\sigma \cos(m\sigma)\cos(n\sigma)\sim \delta_{mn}$$ \int d\sigma \...
1 vote
Accepted

### Worldsheet constraint Bosonic String

It is just a dummy variable change, from $p$ to $n:=m+p$. Since $m$ and $p$ run through all integers, $n$ also runs through all integers. $\newcommand{\ex}{\mathrm{e}^{#1}}$ Stripping off the ...

### Asymmetry of the indices in a Weyl transformation for the Polyakov action

I think the asymmetry between the indices is a convention. We chose $\sigma^{\mu}=(\sigma, \tau)$ as the integration variables. This implies that the determinant of $h_{ab}$ will be the Jacobian. So ...
The difference between string theory and quantum field theory is that QFT is the theory of point excitation whereas string theory is the theory of 1d strings. When we talk about $[X^0 , H]=-i$ and ...