Questions tagged [string-theory]

A class of theories that attempt to explain all existing particles (including force carriers) as vibrational modes of extended objects, such as the 1-dimensional fundamental string. PLEASE DO NOT USE THIS TAG for non-relativistic material strings, such as, e.g., a guitar string.

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17 views

How the variation of Gauss Bonnet term is done?

I am trying to do the variation of Gauss Bonnet Invariant which is $G=R^2+R_{abcd}R^{abcd}-4R_{ab}R^{ab}$ and having problem in doing the variation of $δ(R_{abcd}R^{abcd})$. Can anyone please give ...
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48 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 ...
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The use of Ramanujan Summation [duplicate]

What is the real life significance of the famous Ramanujan summation $1+2+3+\cdots = -\frac{1}{12}$ in string theory? How this is coming into play?
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Could dark matter actually be matter which resides in a different spatial dimension? [on hold]

I have at best a rudimentary understanding of the math in this side of physics, so bear with me. I am also aware of this question, but it was asked and answered 4 years ago and I don't want to ...
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Why D-brane can be attached to NS5 branes?

What is NS5 brane? Is it possible (in analogy with D-brane) understand appearance of NS5 brane in perturbative string spectrum? Why D-brane can be attached to NS5 branes?
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What does it mean to have different CFTs in AdS/CFT?

1) In AdS/CFT, what does a different CFT mean in gravity? 2) Also, if the background metric is curved in CFT, how does it appear in the corresponding gravity side? In the gauge/gravity duality (a.k.a....
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Computation with bispinors for a compatible pair of pure spinors in N=1 supersymmetric vacua compactified down to 4-dimension

I ask this question basically because I need help, just an hint, for a computation with bispinors. The background is string theory / supergravity, where many data of a supersymmetric vacuum can be ...
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48 views

Critical dimension from the symmetries of the string action

(Related: This post and this post.) In this thesis it is said (on page 13) that just by assuming that we have some general action with the same symmetries as the Polyakov action (Poincare invariance, ...
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6D (2,0) superconformal field theory

I'm looking for a good reference book or textbook to study on 6D (2,0) superconformal field theory as a part of string theory.
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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 ...
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67 views

How can I show that the inverse of the induced metric $h_{\alpha \beta}$ is $h^{\alpha \beta}$?

So I was reading through Becker, Becker, Schwarz and there is a line in the second chapter that states that $h^{\alpha \beta} = (h_{\alpha \beta})^{-1}$ where $h_{\alpha \beta}$ is defined as: $$h_{\...
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$(0,2)$ worldsheet SUSY implies ${\cal N}=1$ spacetime SUSY (reference request)

In [1] they write that "Boucher et al. [14] found quite generally that $(0, 2)$ world-sheet SUSY ensures the existence of $N = 1$ spacetime SUSY." But this reference "[14]" they cite just says: "...
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How one goes to derive equation (2.4.19) from Polchinski's String Theory Volume 1?

Equation (2.4.19) states that an exponential times a general product of derivatives $$:(\Pi_i \partial^{m_i}X^{\mu_i})(\Pi_j \bar{\partial}^{n_j}X^{\nu_j})\exp(i k \cdot X ):\tag{2.4.18}$$ has weight ...
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114 views

Why are worldsheets of strings _holomorphic_?

Disclaimer. I am a mathematician (algebraic geometer) who knows nothing about physics. Even worse, I might have major misconceptions about the objects I'll ask about. The level of the question is pop-...
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Conceptional question about Quintic 3-fold and Calabi–Yau 3-fold

Has anyone an idea if I’m studying CY 3-fold in the context of string theory decomposition, for instance, from 10 dimensions to 4 dimensions supergravity , can I take the metric of the complex ...
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Could the Universe have monster symmetry?

The Monster Group is the largest "sporadic simple group" with order: 808,017,424,794,512,875,886,459,904,961,710,757,005,754,368,000,000,000 I read that if you compactify 26D bosonic string theory ...
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How Quintic 3-fold is a Calabi–Yau manifold and has non-vanishing Ricci scalar?

It’s well known that quintic 3-fold is a Calabi-Yau manifold in the complex projective space $\mathbb{CP}^{n+1}$ , see for instance: https://en.wikipedia.org/wiki/Quintic_threefold Now the main ...
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Why is the central charge $c=9$ supersymmetry in the internal manifold?

In [2] (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 ...
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58 views

How I can get the numerical factor in the relation between string coupling and YM coupling?

I'm trying to understand some references about Wilson loops being used to test AdS/CFT. Some of them are Nadav Drukker, David J. Gross: An Exact Prediction of N=4 SUSYM Theory for String Theory ...
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When exactly is a dimension spatial?

I every so often hear claims like: M-Theory predicts that there are 10 spatial dimensions! Now I'm not really sure what these claims mean. There are three spatial dimensions that I normally ...
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How do we know the laws of physics remain the same in different dimensions?

Section on Wikipedia dealing with the possibility of different dimensions. When reading this section it feels like there's a giant elephant in the room that is not addressed. For example, here's a ...
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Deriving and plotting Quintic 3-fold metric

In this reference: https://people.maths.ox.ac.uk/delaossa/LecturesQuad.pdf Any help to know how the metric in figure 5 has been plotted ? Following the last equations in page ( 143) ? I don’t get ...
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Is there a way to make this simple “derivation” of the Trace Anomaly correct?

I think I came up with a simple yet sketchy almost-proof of the trace anomaly (A.K.A. Weyl anomaly) in 2D CFT, but it has the wrong prefactor. I was wondering if anyone could assess whether this "...
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Twin Paradox in String Theoretical Backgrounds / Compactifications

It is a common exercise while learning special relativity to work out the resolution to the twin paradox. As an extension, I have looked at the twin paradox with compact dimensions, i.e. having an ...
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Describing Calabi–Yau 3-fold

Background: In Calabi-Yau 3-fold, the Kähler metric is given in terms of the Kähler potential $\kappa$ : $ g_{i\bar{j}} = \partial_i \partial_{\bar{j}} \kappa$, where $i, \bar{j}$ = 1,2,3 $ ( the ...
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Explicit form for Calabi–Yau’s Kähler potential

Is this paper: Hierarchies from Fluxes in String Compactifications equ: A.9 $ \partial_\alpha \kappa = - k_\alpha$, where $\alpha =1, ..., h_{2,1} $ What are $ k_\alpha$ ? I’m trying to find an ...
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67 views

If there exists a universe with other than 3+1 dimensions, could we quantum tunnel to it?

Section of Wikipedia article on the possibility of universes with space & time dimensions other than 3 and 1 respectively. If one of these other universes exist, could we in principle quantum ...
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Symmetry of Polyakov action

In every literature and lecture notes on Bosonic String theory I have found that the authors tend to show the diffoemorphism symmetry in terms of definite symmetry i.e. they take an arbitrary ...
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Gauge fixing of Polyakov Action

In the Gauge fixing of Polyakov action we do general coordinate transformation where we take the transformation stated below $$h_{\alpha\beta} = e^{\phi(\sigma)}\eta_{\alpha\beta}.$$ But here the ...
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Relationship between boundary states and primary states of a Kazama-Suzuki model

In [1] and [2] the authors claim that the boundary states (not just the Ishibashi states) of a Kazama-Suzuki model are labelled in the same way as the primary states of the model, so that the boundary ...
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58 views

Gauge anomaly in Polyakov string and Faddeev-Popov method

I am currently trying to gain a better understanding of the gauge fixing procedure used in chapter 5 of David Tong's notes. Since the central charge of the Polyakov action for, say, the bosonic ...
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How to get the Nambu-Goto action from the Polyakov action by lagrangian multiplier? [duplicate]

I consulted some textbooks about string theory, but they only told me that the Nambu-Goto action and the Polyakov action is equivalent. So I searched relevant questions here and got some ways of ...
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42 views

How can a non-expert think of Black Hole microstates?

For someone familiar with basic QFT and GR and semi-classical physics but doesn't know string theory nor AdS/CFT is there some intuitive way to think about what the microstate of a black hole means? ...
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114 views

How is there no hierarchy problem without UV cutoff?

I can understand the quadratic divergent corrections to Higgs bare mass which is referred to as the hierarchy problem. But I don't understand how there won't be any hierarchy problem if we do not ...
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75 views

Clifford algebra formulation of the Nambu-goto action

Using the wedge product one can pair the generators the Clifford algebra $Cl_{1,3}(\mathbb{R})$ to produce 2-vectors (area elements). The Nambu-Goto action is a statement on the evolution of ...
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Understanding the statement “orbifold theories are QFTs with finite gauge group”

I'd like to understand the equivalence of orbifold theories in string theory and (2D worldsheet) QFTs with finite gauge group, using the path integral. Suppose my action is $$S= \frac{1}{2\pi \alpha'...
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Intuitive way to get 10 dimensions in string theory?

To get the 26 dimensions is sort of intuitive (in a handwavey sort of way). Basically we solve: $$(D-2)\frac{1}{2}(1+2+3+4+...)=-1$$ Where $1+2+3+..$ times $\frac{1}{2}\hbar$ are the ground energy ...
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Neumann Boundary Conditions for the Open string and the energy momentum tensor

I read in Polchinski's book, "String Theory", page 56, that for the open string the energy momentum tensor satisfies equation (2.6.26) at a boundary $$ T_{ab}n^a t^b=0 \,, $$ where $n^a$ and $t^a$ are ...
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Almost complex structure $J_i^j$ from covariantly constant spinor $\eta$

In the context of superstring compactification on a 6-manifold which admits a covariantly conserved spinor $\eta$, which we normalize so that $\eta^{\dagger} \eta = 1$, I am trying to show that the ...
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Can a person from different universe which has its “own different laws of nature”, can go into our past in our Universe? [closed]

Suppose There is a Universe, which has different laws of nature than ours galaxy and they have much greater speed of light than $3* 10^8 $ m/s ,so some person from their universe visits our universe ...
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Why don't strings have a Planck mass? (version 2)

The Energy $E$ of a fundamental string due to its length $L$ goes like $$E\sim TL$$ where string tension $T$ is given by $$T \sim \frac{1}{l_P^2}$$ (Using natural units $\hbar=c=1$ with planck ...
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Why don't strings have a Planck mass?

I understand that strings have a size of roughly the Planck length $l_P$ of $10^{-35}$ m. If that is the case then one would expect that their mass would be roughly the Planck mass which is an ...
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$bc$-system energy momentum tensor

I have a (maybe silly) question regarding the expression of the energy momentum tensor of the $bc$-system in equations $(2.5.11a)$ and $(2.5.11b)$ in Polchinski's String Theory, page 50. I know that ...
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Why strings, and confusion about string coupling constant

Source: Brian Greene's Elegant Universe 1) I finally understand why string theory is a theory of quantum gravity after reading chapter 6 - the quantum fluctuations/foam that made a mess of the ...
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How does it make sense to talk about the size of a string if the string action is conformally invariant?

From what I understand the Polyakov action in string theory is essentially something like $$S(\xi, g, G)=\kappa \int_{\Sigma} d \mu_{g} \operatorname{Tr}_{g} \xi^{*} G$$ where $\Sigma$ is a given ...
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Polchinski Vol.2 P58 projection under a twist with a discrete torsion in E8$\times$E8 superstring

I don't know how to get the projection Equation (11.3.15) in the book. In the $E_8$$\times$$E_8$ superstring theory, one can introduce the following twist, $$(h_1,h_2)=(\exp[\pi i(k_1F_1+l_1\tilde{F}...
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$\alpha_n^{i}$ excitations in superstring vs $\psi_r^{i}$ excitations

Perhaps due to a gap in my learning I don't know why I don't see bosonic excitations $\alpha_n^{i}$ discussed in superstring theory, only fermionic excitations $\psi_r^i$. I know the NS sector ...
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Why worldsheet current associated to spacetime supersymmetry is the integral of the vertex opertor?

Sorry, I just haven't enough reputations for adding a comment in that post. @MISC {389179, TITLE = {Polchinski equation 11.2.7}, AUTHOR = {Nogueira (https://physics.stackexchange.com/users/...
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Point particles as the limit of a short string

There's a common saying in the domain of the study of classical relativistic strings, that in the limit of a very short string, the action reduces to that of a point particle (there is for instance a ...
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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-...