# Questions tagged [compactification]

Compactification entails changing a theory with respect to one of its space-time dimensions. Instead of this dimension ranging to infinity, the theory is changed so that this dimension has a finite range, and may be periodic. In the limit where the size of the compact dimension goes to zero, no fields depend on this extra dimension, and the theory is *dimensionally reduced*. Further use for dimensional reduction.

174 questions
Filter by
Sorted by
Tagged with
79 views

### String Theory for beginners: what is a scale?

I'm reading this introduction to string theory by Mariana Grana and Hagen Triendl and I have understanding problems around the method of compactification in string theoretical sense. The ...
42 views

### Polchinski String Theory (8.4.38) T-duality of two compactified dimensions

I am confused about a sentence in Polchinski's String theory chapter 8 p 255 when he works out the example of the full $T$-duality with two compact dimensions. He writes "A simultaneous $T$-...
42 views

### How to test extra dimensions?

It is predicted in string theory that our world has some extra dimensions. I'm wondering if we want to prove this experimentally, what should we do
51 views

### How to compute Physical Constants from given Calabi-Yau Compactification of Effective Field Theory of corresponding String Theory?

I got some interest in String Theory when I was listening to lectures of David Tong and Brian Greene. I remember them stating that the spacetime manifold is compactified to resemble our usual 3+1 ...
23 views

### Generating Fermions from Dimensional Compactification

The usual KK compactification generates additional scalar fields or gauge fields when off diagonal terms are considered in the metric. These fields have integer spin when quantized. Is it possible, ...
29 views

### Alternatives to Calabi-Yau spaces? [duplicate]

Are there alternatives to Calabi-Yau spaces describing dimensions in superstring theory? If yes, what are they? If no, why?
51 views

### Dimensional regularization and (dimension) compactification [closed]

I believe I read that "additional dimension" in dimensional regularization can be understood as spatial dimensions compactified, but I could not find resources related to this. Is this view correct? ...
39 views

### How to explain “compactification of a dimension”

The first paragraph of the wikipedia entry on "compactification (physics)" explains that it "means changing a theory with respect to one of its space-time dimensions. Instead of having a theory with ...
27 views

### Is one dimension the same as one space-time?

In this Cern article, https://home.cern/science/physics/extra-dimensions-gravitons-and-tiny-black-holes, it states: "In our everyday lives, we experience three spatial dimensions, and a fourth ...
86 views

### Four dimensional massless spectra of type IIA/B compactified on $\mathcal{M}_{4} \times {\rm CY}_3$

I am following “String Theory and M-Theory” by Becker, Becker, and Schwarz and I am currently studying chapter 9. I have a question - or better yet a point of confusion - regarding the derivation of ...
39 views

### Holomorphic 3-form on Calabi-Yau compactifications

What is the natural scale of the holomorphic 3-form on a Calabi-Yau? $\Omega=\frac{1}{3!}\Omega_{abc} ~ dz^a\wedge dz^b \wedge dz^c$ $||\Omega||^2 = \frac{1}{3!}\Omega_{abc}\bar{\Omega}^{abc}$ ...
62 views

### Did Big-Bang dimensional-expansion initially occur stepwise, i.e 1 dimension at a time?

I’ve been investigating the topological Casimir effect from compactified dimensions as a mechanism to explain dark energy, and this raised a question I was hoping someone could shed some light on. I ...
268 views

### How can extra dimensions be small?

I have a super basic gap in my understanding of the theory of extra spacial dimensions - one piece of the explanation that never felt right. As I've heard it, it's theorized that there may be extra ...
61 views

### Orientability of compactified manifolds in string theory

Calabi-Yau manifolds in string theory are orientable (topologically you can make "handed" structures in them). Non-orientable manifolds are perfectly respectable (the projective plane is a basic ...
192 views

### Why doesn't string theory predict the existence of infinitely many elementary particles?

I'm a physicist, but my knowledge of string theory is extremely minimal. My naive conceptual understanding is that the vacuum is modeled as a certain topology (and geometry?) for the spacetime, and ...
96 views

### Does string theory really associate 6 dimensions to electromagnetism & the nuclear forces?

1) I understand string (superstring) theory often ends up with 10 dimensions, 9 space-like and 1 timelike. Typically I read that these are all associated to space-time. 2) So, I was interested when I ...
83 views

### How can we demand $N=2$ supersymmetry on the worldsheet?

I have been trying to understand why one should look into $c=9, N=2$ superconformal models like the Gepner models or the Kazama-suzuki models, and I am quite confused. This is what I understood from ...
103 views

### Why is the central charge $c=9$ supersymmetry in the internal manifold?

In  (abstract [here]) (https://inspirehep.net/record/245643?ln=en) they say that, when compactifying any superstring theory, the six dimensional internal manifold must have $N=2$ supersymmetry with ...
103 views

### Are extra dimensions timelike or spacelike?

In special relativity there is a clear difference between spatial and temporal dimensions of spacetime due to the Minkowski metric diag(-1,1,1,1). In higher dimensional theories (10- and 26-...
43 views

### Toroidal compactifications of type IIB string Theory and $SO(5,5)/(SO(5)\times SO(5))$ invariant 6D sugra action

It is usually stated that the compactification of (the bosonic part of the) type IIB ($D=10$, ${\cal N}=(2,0)$) supergravity on $\mathbb{T}^4$ gives a six-dimensional ${\cal N}=(4,4)$ supergravity ...
258 views

### What is dimension? What is the size of dimension?

Recently I heard a TED talk by Brian Greene where he was speaking about String Theory working on $(10+1)$ dimensions. Plus he said that we live in only in $(3 +1)$ dimensions. So where are others? ...
382 views

### Dimensional reduction of higher-dimensional Einstein-Hilbert action

I take a spacetime of the form $\mathcal{M}_{d+1}\times \mathbb{S}^n$, with $\mathcal{M}_{d+1}$ some generic non-compact $(d+1)$-dimensional spacetime and $\mathbb{S}^n$ an $n$-dimensional sphere, so ...
173 views

### Extra Dimensions (in String Theory) - What does it mean?

I have been reading a lot about string theory and the necessity of extra dimensions (particularly as visualized in Calabi-Yau spaces), as "curling-ups" in our apparently 3-dimensional (or 4-...
123 views

### Compactification of space in Hamiltonian formulation of Yang-Mills theory

I am reading David Tong's lecture notes on Gauge Theory where he talks about Hilbert space interpretation of Yang-Mills theories in Section 2.2 of Chapter 2. When discussing the gauge dependence of ...
57 views

### Relationship between compactification moduli and generations in standard model

The situation I am describing is a $10D$ heterotic string theory which is compactified on a Calabi-Yau to get a $N=1$, $4D$ effective theory. It is mentioned in Ashoke Sen's notes on string ...
86 views

### Are the “extra dimensions” in string theory universal?

Are the extra (compactified) dimensions from string theory universal, in that any particle/field with a sufficiently small enough wavelength will be able to propagate through them? The reason I want ...
54 views

### Root weights and states in orbifold compactifications

I have the following question regarding orbifold compactifications of the heterotic string: What is the relation between a certain representation and the weights of the root lattice? I mean: take ...
64 views

### Are particles of fields that arise from compactification and strings treated differently in string theory?

I am aware that particles in string theory are different vibrating modes of strings. I am also aware that compactification leads to emergent fields from the parts of the metric of the compactified ...
90 views

### How do we assign length to dimensions in string theory?

My current understanding of the variations of string theory includes the sentence "string theory needs (at least) 6 extra spatial dimensions to work, but because our observable universe consists of 3 ...
125 views

141 views

### What generates the curvature which is necessary for curling-up extra dimensions?

To say it right away, I am not an expert in string theory, but I know well General Relativity. So I wonder how the curling up of extra-dimensions which is assumed in many "Kaluza-Klein" like theories (...
227 views

### Understanding a joke in Zwiebach - “A first course in string theory” [closed]

So fairly early on Zwiebach discusses the quantum mechanics of a one-dimensional square well. He then goes on to add an extra dimension which is compact to demonstrate how one can understand ...
75 views

### How seriously should one take the energy eigenvalues of an electron's wavefunction in a compactified space?

In chapter 2 (section 2.10) of Zwiebach's string theory book, there is a neat derivation of the energy eigenvalues for the two dimensional square well in which one dimension is compactified to a ...
126 views

### Effective action of IIB Calabi-Yau compactification

I'm currently reading K. Becker, M. Becker and John. H. Schwartz book on string theory. I have a question about Calabi-Yau compactifications of IIB string theory. In chapter 9 page 403, Why do we don'...
67 views

### Compactification of Bosonic Closed Strings on $T^2$ and $T^3$

I am looking for a text to explain compactification of bosonic closed strings on $T^2$ and $T^3$ by focusing on its gauge groups enhancement. In fact, I want to know in each case ($T^2$ and $T^3$) how ...
454 views

### What is really M-theory? (non-pertubatively)

I don´t really understand what M-theory is supposed to be. Going beyond the dualities relating different string theories (for example the common $11-D$ limit of IIA and $E_{8}\times E_{8}$) I don't ...
352 views

### Algebraic geometry and topology for string theory [duplicate]

I am looking for a comprehensive book or notes in algebraic geometry and topology techniques used in string theory compactifications covering topics like orientifolds, orbiolds, Calabi Yau manifolds ...
321 views

### The role of the Hopf Fibration in Kaluza-Klein theory

I have been learning recently about the Hopf Fibration and its relation to physics. My professor has told me that it is one of the simplest methods of dimensional reduction in Kaluza-Klein theory. ...
56 views

### Can branes obstruct complex structure deformations in string theory?

In compactifications of string theory, to preserve supersymmetry often branes need to wrap subspaces that are specified by holomorphic equations in the compactification space $X$. Additionally there ...
88 views

### For making gravity supersymmetric is a modification of Einstein's vacuum field equations necessary ( apart from adding the R-S Lagrangian)?

Upon building up supersymmetric Supergravity in 4D, is it necessary to modify the Einstein's vacuum field equations (apart from adding the Rarita-Schwinger Lagrangian for the gravitino) in order to ...
469 views

### Where are the infinite-dimensional spaces of Quantum Mechanics?

There are two questions here: One of the confusing points about String Theory is the existence of extra dimensions. These are explained by saying that the these extra dimensions are compactified. ...
118 views

### The space-time metric in string theory

I always wondered about the metric to be used in string theory. As 10-4 (11-4) or 26-4 dimensions are supposed to be curled up or being a Calabi-Yau manifold, in this part of the space-time the ...
122 views

### Can superstring theories predict our 4 dimensions? [duplicate]

Popular science literature is replete with the necessity for superstring theories to live in at least 10 dimensions, requiring at least 6 of them to be compactified so that they are not observable. ...
224 views

### Fundamental string theory questions

Can anyone answer some basic string theory questions for me? The Veneziano Amplitude is celebrated for predicting the scattering amplitude of mesons and for practically giving birth to string theory....
53 views

### Geometric interpretation of dimensional reduction of $E_8 \times E_8$ string

Following on from this question. I'm trying to get a geometric picture of what happens under dimensional reduction. Let me focus on a single $E_8$ factor, in 10 dimensions - the Lagrangian will ...
343 views

### Does String Theory predict a particle with twice the mass of the electron?

As far as I know, the spectrum of any (?) String Theory is of the form $$M^2\propto N$$ where $N$ is the number operator. The lightest known particle being the electron, I am led to think that we ...
It seems to be generally accepted (, ) that one can apply the duality between a $T^3$ compactification of heterotic string theory and a $\mathrm{K3}$ compactification of M-theory "fiberwise&...
This question is based on page 71 of Thomas Hartman's notes on Quantum Gravity and Black Holes. The Euclidean Schwarzschild black hole ds^{2} = \left(1-\frac{2M}{r}\right)d\tau^{2} + \frac{dr^{2}}{...