# Tag Info

6

One shouldn't imagine the T-duality between the two heterotic strings to be a $Z_2$ group, like in the case of type II string theories' T-duality. In type II string theory, there is only one relevant scalar field, the radius of the circle producing T-duality, and it gets reverted $R\to 1/R$ under T-duality. In the heterotic case, it's more complicated ...

6

Noncompact internal symmetries – and R-symmetry is an internal symmetry (it doesn't transform positions in the spacetime) – are unacceptable in a physical theory because they would lead to negative-norm states. Consider the $i$-th superpartner of a bosonic particle state, $|i\rangle$, where $i=1,2,\dots,N$. The inner product $\langle i|j\rangle$ of such ...

5

I would guess that the professor is explaining his/the(?) theory that dark matter is neutrinos, produced via a scattering process he calls "Witten's dog". It is funny because the neutrinos are coming out of the dog's butt. In the Standard Humor Classification, this is known as a "poop joke".

4

I've long been interested in this, but the impression I get is (speaking as a strict amateur with a reasonable understanding of QM and relativity) there is simply nothing like e.g. the Schrodinger equation or Einstein's field equation in string theory. String theory is developed by writing down the action (which is the area of the string world sheet), using ...

3

I think I got the answer now. The main idea is this: When we gauge continuous symmetries we identify all the states $$A^\mu=A^\mu+\partial^\mu\chi$$ (which are continuously many) as a unique physical state. When we gauge a discrete symmetry (let's assume it's generated by $\theta$) we identify all the states $$|\Psi\rangle=\theta^n|\Psi\rangle$$ where ...

3

The NS-NS sector is the same in type IIA and IIB, but the R-NS and NS-R sectors differ. The type IIA theory is non-chiral, so the R-NS and NS-R fields transform in $\mathbf{8}_s \otimes \mathbf{8}_v$ and $\mathbf{8}_v \otimes \mathbf{8}_s'$, where $\mathbf{8}_s$ and $\mathbf{8}_s'$ are the two eight-dimensional spinor representations of $SO(8)$. Type IIB, on ...

3

I managed to find a quasi-systematic way to do this. The idea that allowed me to do this was inspired by Noether's Theorem. Re-parameterization invariance is a symmetry of the system, a symmetry much stronger than an ordinary global symmetry. Similarly, however, a constraint is also a conserved quantity, but it is something much stronger than that. ...

3

If you spend some time looking in detail at the arguments that string theory requires supersymmetry, you'll find that they are not watertight. (How could they be, since we still can't say/don't know precisely what string theory is?) Basically, some string theorists argue that that the usual classification depends too strongly on choosing nearly trivial ...

3

Yes, gravity duals have been found for such theories. You can find at least a few examples by picking a particular rational CFT X (,e.g., a minimal model, WZW, Ising) and googling 'AdS dual of X'. For example: http://arxiv.org/abs/1011.2986 http://arxiv.org/pdf/1111.1987 http://arxiv.org/abs/1011.5900

2

There is a Feynman diagram for particle scattering which looks like a dog... imagine each of the "tubes" in that picture shrunk to zero radius. Like @dilaton says, this looks like a scattering (world sheet) diagram for closed strings. But with random (nonsensical?) particle operator insertions (maybe they're supposed to represent fleas?). And afaik, the ...

2

The symbols $\alpha,\beta$ in these toric geometry diagrams refer to the two 1-dimensional cycles of a torus, $T^2$, and the labels which are combinations of $\alpha,\beta$ correspond to the 1-cycles of the torus that degenerate at the given line of the diagram. If $c$ degenerates, so does $-c$, so all these labels are pretty much unoriented and the ...

2

Hagedorn spectrum just means that the density of states varies exponentially with the energy/mass. $m^2$ (asymptotically) given by the "level" (N) of the state (upto a sqrt). The number of states at level $N$ corresponds to the possible partitions of $N$ into different oscillator modes. That means that the number of states at level $N$ will increase ...

1

p-adic strings or the adelic approach created by B.Dragovich don't require SUSY at all. At least, not the usual SUSY symmetry... Non-critical string theory, the so-called Liouville theory, is based on the hypothesis of non-imposing the condition that critical strings with fermions (superstrings) impose on the space-time dimension due to internal ...

1

From what we understand today, p-branes are honest degrees of freedom, on equal footing with strings. Shop you have a good question. But I don't think anyone had so far managed to consistently quantize a p-brane. Loosely, a brane has much more degrees of frerdom than a string and it's difficult to get them under control. So quantizing it is a technical ...

1

An "acceptable" theory of everything is quite a matter of taste. Since all your experiences are grounded in classical physics, you feel that quantum mechanics is unnatural and seek to "understand" it, probably in terms of your classical notions. For eg: Do you ever question Newton's first law... why should objects have a property called inertia? Some ...

1

I suppose $f$ is just an arbitrary scalar function on the manifold. I'm not well-versed with the concept of Ricci flow, so I'll try to give a simple operational answer. I also don't understand what exactly you're looking for. The Ricci scalar $R$ roughly represents the amount of energy stored in spacetime (as curvature). The dilaton is a scalar field which ...

1

I would really recommend a study in QFT before going on to study SUSY. QFT has many quirks that make supersymmetry a very interesting expansion of the regular framework. You'd miss out on all that as you just had to believe the facts presented w/o following the thought that lead to the results in detail. On the Mathematical level you will need Grassmann ...

1

Glad to see enthusiasm. I'm sad to say you've been let down by the popular press. Here's the word from a real life particle physicist: I would be very much happy and grateful to know if someone can explain me a little about the relation between Higgs Boson and Force of Gravitation(Gravitons if exists). There is none. The Higgs field gives mass to some ...

1

"Falsifying supersymmetry" is a phrase that has to be properly qualified. Our ability to falsify with experiment is limited. We can rule out the existence of supersymmetry only at accessible energy/distance/density scales. LHC, for example, is not able to resolve physics at distance scales much smaller than \$\frac{\hbar c}{7\mbox{ TeV}} \simeq ...

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