8 votes
Accepted

Does String Theory predict things like Unruh effect and Hawking radiation?

Many effective field theories we know about arise as low energy limits in string theory. These include Yang-Mills in the case of open strings and Einstein gravity in the case of closed strings. Since ...
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  • 5,143
6 votes

In what sense is string theory not expected to be a QFT?

String theory is not an (algebraic) QFT because it doesn't take place on a fixed spacetime. The Haag-Kastler axioms are of the form "given a spacetime manifold $X$, then...", but string ...
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  • 108k
4 votes

Compactification in String Theory and Compactification in Topology are they the same thing?

I don't know much about compactification in string theory, but the idea is based on the compactification in (4+1) D Kaluza-Klein theory, proposed in the years after the theory of general realtivity ...
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4 votes

Compactification in String Theory and Compactification in Topology are they the same thing?

No, different concepts. The compactification in string theory is the process of taking a theory with extra infinitely extended dimensions (w.r.t. the canonical 3+1 dimensions) and modifying it so that ...
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  • 4,360
4 votes
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 ...
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  • 12.3k
4 votes
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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 ...
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4 votes

If mass in string theory is generated by string vibration, where does that leave the Higgs mechanism?

The massive states due to vibrations on the string have masses given as integer multiples of the string scale, which you should think of as a very large scale, near the Planck scale. (At least, nearer ...
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  • 35.5k
3 votes

Weyl Anomaly for Old Covariant Quantization in String Theory?

In lightcone quantization the mass of a level $N$ state is given by $m^2 \sim ( N - \frac{D-2}{24} )$. The $N=1$ transforms in a rep of $SO(D-2)$. This is because in lightcone quantization there are $...
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  • 21.4k
3 votes

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.
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  • 41.8k
3 votes

Vector $V^\mu$ vs the Lorentz contravariant components $V^a(x)$

This is just a choice of basis of vector fields in a smooth manifold really. Let $(M,g)$ be a $D$-dimensional smooth manifold with Lorentzian metric. Let $U\subset M$ be one open set and let $x:U\to \...
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  • 30.1k
3 votes

Vector $V^\mu$ vs the Lorentz contravariant components $V^a(x)$

The $e^{a}_{\mu}$ objects are called vierbein field (or tetrads, or frame fields) and connect a general frame of coordinates (in which vectors are expressed as $V^{\mu}$) to a local frame of reference....
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  • 4,360
2 votes

Compactification in String Theory and Compactification in Topology are they the same thing?

No, it is not. We compactify $\mathbb{R}$ to become a $\mathbb{S}^1$ by gluing $x\sim x+2\pi$, which is an universal covering $j:\mathbb{R}\rightarrow \mathbb{S}^1$.
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  • 5,375
1 vote
Accepted

Could the Universe have monster symmetry?

A cheap point is that there is no symmetry we can ever rule out. Just let all of the fields we've observed be singlets under that symmetry and posit that new fields transforming faithfully under it ...
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  • 5,143
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 \...
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  • 1,977
1 vote

Kalb-Ramond current fall-offs at future null infinity

This will not be an answer, as I have some counter-questions regarding your post! However, hopefully it will lead to you answering my counter-questions (presumably in the comments) and me replying ...
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  • 1,977
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. $\newcommand{\ex}[1]{\mathrm{e}^{#1}}$ Stripping off the ...
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