New answers tagged

0

I don't believe that string theory could host possible methods of advanced communication, but there are other interesting possibilities when theorizing about higher dimensions. Here's an article that might help you: http://futurism.com/understanding-10-dimensional-universe/


2

A p-cycle is a differential form that lives in $ker(\partial_p)$ for the differential $\partial_p$ (in grading $p$), and such a form is nontrivial if it is not in the image of $\partial_{p+1}$. Mathematically we can see this as a cycle that is not the boundary of anything, picture a circle around a torus that bounds no area on the torus. If one has a ...


1

I am going to offer a small bone here. I am somewhat interested in the role of Taub-NUT spacetimes, and so contributing will help me to track this in order to read other contributions. Thanks for the Gubser paper. From a more physical perspective I will just throw out something with magnetic monopoles, which are related to Taub-NUT spacetimes that have a ...


1

Quote from "Lectures on D-branes, Constantin P. Bachas" Now within type-II perturbation theory there are no such elementary RR sources. Indeed, if a closed-string state were a source for a RR (p + 1)-form,then the trilinear coupling $$< closed| C_{(p+1)} |closed >$$ would not vanish. This is impossible because the coupling involves an ...


2

The complex world sheet (WS) coordinate $z\in\mathbb{C}$ contains a WS time and a WS space coordinate. It is important to realize that the time derivatives inside the Boltzmann factor in the path integral should respect the underlying time slicing procedure. See e.g. this & this Phys.SE answers, and my Phys.SE answer here. Thus it is implicitly ...


0

Just because the D1-string has the right dimensionality to couple to a 2-form RR potential doesn't mean that it must. The same line of reasoning could be applied to the more familiar case of electromagnetism; you could easily imagine a world with 2 different U(1) gauge fields. There could be particles that are charged under gauge field #1, particles charged ...


0

It is indeed compactly-supported Poincare duality via currents, for which the standard reference is de Rham's Differentiable Manifolds. For example, the Dirac delta function is the dual of a point! Anyway, to get to a quick understanding, see the beginning of Section 7.3 of Nicolaescu's notes http://www3.nd.edu/~lnicolae/Lectures.pdf


1

These branes are being smashed together so that once they are closer than the string length they become indistinguishable from a single brane. These branes have $U(N_c)$ gauge group, and in this space there is a vector. In a generic sense all Lie algebras are like the harmonic oscillator with $a$, $a^\dagger$ and $a^\dagger a$ in the structure of roots and ...


0

The graviton in string theory is an aspect of closed heterotic strings. The reason for closed strings is that there are two independent modes, called right and left oriented modes. This is in contrast to the open string where modes in both directions are the same, being of course reflected back and forth. We may think of these modes as $a, a^\dagger$ and ...


0

A very peculiar fact is that in a compact space THERE IS a preferred inertial system. Indeed even if locally there is no way to single out a preferred inertial system, globally you can do it. Is the topology that tells you that an observer doing a loop around a torus is topologically different from an observer moving around simply connected loops. So for ...


2

It's a bit strange because the OP basically repeats the same statement twice. First, he says that he understands it and second, he says that he doesn't. But let's try to avoid these detailed surprising aspects of the question and try to explain what's going on, anyway or again. Type I/II strings have spacetime supercharges $Q_a$ that are constructed purely ...


1

Here, $V_0(k_2)$ could have been replaced by $e^{k_2 \alpha_{-1}} e^{-k_2 \alpha_1}$ while the factors from $\alpha_{\pm n}$ for $n\gt 1$ could have been neglected because $\alpha_n$ annihilates everything that appears in the matrix element on the right side from $V_0$ (because it ultimately annihilates $|0\rangle$), and similarly for $\alpha_{-n}$ that ...


0

Physics does not predict that dimensionless constants will be anything. That would mean that nature favours one specific kind of numbers over the others. However, as user40085 indicates above, some ratios are found rational. This is probably hinting to some unknown symmetry principle fixing that ratio. On the other hand, more "fundamental" constants such ...


0

For the coupling of p-brane Gauge fields to B 2-forms and U(1) Gauge fields check the Chern-Simons effective action for Dp branes. For coupling to fermions check some SUGRA actions, for instance the D=11 SUGRA has the graviton, the gravitino and 3-form Gauge field. Coupling to scalars is omnipresent in dimensional reductions of SUGRA actions.


0

There is a confusion and misunderstanding about what "perturbative" means and its relation with the power series expansion around certain small parameter. If you state that QED/QCD is non-perturbative, because amplitudes are defined exactly, and not as a power expansion, then the same applies to string theory. Amplitudes, in any QFT, is defined a sum over ...


1

The reason is clearly given in the famous paper "Vacuum configurations for superstrings" - http://www.sciencedirect.com/science/article/pii/0550321385906029 -. Here, I am just copying the introduction of that paper. I cannot tell the reason why with better words. Recently, the discovery [6] of anomaly cancellation in a modified version of d = 10 ...


2

If there are eleven dimensions as M-Theory asserts Let us suppose it is true would that mean that the majority of what we are made from exists in the seven other dimensions? Define dimension: In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to ...


0

A simplistic answer is, 3/11ths of us exists within the normal three dimensions, and the other 8/11ths exists in the hypothetical extra dimensions. This answer does make string theory sound silly (which personally I think it is :) , but i can't see why it should not be true.



Top 50 recent answers are included