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.

Filter by
Sorted by
Tagged with
2
votes
1answer
72 views

OPE of stress tensor in CFT

I come aross an OPE between stress tensor components in CFT which is \begin{equation} T(z)\bar{T}(\bar{w})\sim -\frac{\pi c}{12}\partial_{z}\partial_{\bar{w}}\delta^{(2)}(z-w)+... \end{equation} I am ...
2
votes
0answers
33 views

Spin of higher string excitations

I am trying to better understand spin in string theory. There is already a good post here: Ssecond and third level excitations of open string But I have these questions: 1) Why would the second ...
2
votes
0answers
47 views

Can string theory explain why the charge of the positron and of the proton are equal? [duplicate]

There is not much more to elaborate. Can string theory say why electrons and protons have exactly opposite charge? And thus why hydrogen atoms are neutral? I guess that the answer is no, because ...
4
votes
1answer
70 views

Casimir Force and bosonic String Theory dimensions

I was reading the lecture notes on Quantum field theory by David Tong. In the section on Casimir force he derived the force of attraction felt by the plates due to the field vacuum energy in $1+1$ ...
3
votes
1answer
43 views

What are the necessary conditions for a CFT to have a holographic dual? [duplicate]

The number of degrees of freedom of a CFT is given by its central charge $c$. From the bootstrap point of view, any CFT is characterized by the knowledge of its "CFT data", i.e. the scaling dimensions ...
2
votes
1answer
71 views

How does the $D$-brane geometry influence the gauge symmetries?

I am trying to understand why the $D$-brane structure of a string theory matters for string phenomenology. From what I understood from Wikipedia, the $D$-brane structure determines the gauge ...
1
vote
0answers
35 views

On the use of the Cauchy-product in deriving the stress-energy tensor constraint for a string in light-cone coordinates

I shall be following the notation used in David Tong's String Theory notes. In bosonic string theory, after fixing the gauge of the Polyakov action using Diff/Weyl invariance to make the two-...
2
votes
0answers
18 views

Can supersymmetry be extended to include anyons for 3+1D superstrings?

Are there no-go theorems and the like proving that there is no generalization of supersymmetry to fractional spins either in general or for superstrings in four dimensions? If so, are there ...
1
vote
2answers
45 views

Polchinski's String theory Green's function on $RP_2$; eq. (6.2.38) p. 176

Is there an error in Polchinski's String Theory Equation (6.2.38) p 176 that is not on the Errata's page https://www.kitp.ucsb.edu/joep/links/joes-big-book-string/errata ? He write for the Green's ...
1
vote
1answer
39 views

Unitarity/Hermiticity condition for $osp(m,n|\mathbb{C})$ superalgebra

According to Dictionary on Lie Superalgebras (page 82), the compact form of $OSP(m,n|\mathbb C)$ Lie superalgebra must satisfy $M^{\text st}H\,M=1$ and $M^{\ddagger}M=1$ (is this the unitarity ...
1
vote
0answers
37 views

Holographic AdS/CFT intepretation of Cosmological Constant

I'm trying to understand how the value of AdS cosmological constant (or, equivalently, of AdS radius) affects the boundary CFT in AdS/CFT correspondence. I'd be glad of discovering something about the ...
6
votes
1answer
174 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 ...
1
vote
3answers
94 views

If extra dimensions are out there, why don't/can't we see them? [duplicate]

String theory proposes the existence of extra space dimensions. Very brilliant minds believe in their existence. Of course, I could appreciate that they are consequences of mathematical ...
-1
votes
1answer
64 views

Explanation of the Nambu-Goto action and calculus needed for a beginner to learn [closed]

I have recently started trying to learn String Theory, but haven't learnt calculus - I know this probably isn't a good idea, but I decided to learn each part as I go. I'm partly using Brilliant, and ...
0
votes
0answers
41 views

AdS/CFT phenomenology and realistic FRW model building

Are there any examples of realistic holography (likely as a de Sitter type Universe: as it approximates FRW / is an FRW solution without baryonic and dark matter). I don’t see why one wouldn’t be ...
0
votes
0answers
99 views

Basic problem with String Theory

String theory turns the page on the standard description of the universe by replacing all matter and force particles with just one element: Tiny vibrating strings that twist and turn in complicated ...
1
vote
1answer
41 views

What sets the AdS radius $\ell$ in the CFT dual description?

In the context of AdS/CFT there should be a mapping between parameters for any given duality. But AdS has at least one dimensionful parameter, $\ell$: $$ds^2 = \frac{\ell^2}{z^2} ( -dt^2 + d\vec x^2 +...
0
votes
0answers
20 views

Branes ending on branes

From Polchinski book, I know that a one-dimensional brane can end on a higher dimensional brane. However, I was wondering if an even more generic picture could be developed, where a $(p+1)$-...
2
votes
0answers
30 views

Is there a black hole information paradox in string theory?

In string theory there is, for several black hole-like objects, a precise way to account for the microstates which make up the macroscopic Bekenstein-Hawking entropy. For instance for the black brane ...
1
vote
2answers
54 views

Travel and locate extra dimensions

I'm a newbie to String Theory. String Theory says there are extra dimensions apart from the 4 known ones (space and time). Even if the extra dimensions are very small, what makes the theory say they ...
0
votes
0answers
35 views

String Landscape and Extremal / SUSY Black Holes

I should preface this question that I am new to understanding the string landscape and swampland program and F-theory, so I apologize if my question is obvious / unclear! Recently I was reading some ...
1
vote
0answers
55 views

D7-brane in Type IIB and axio-dilaton

In the context of Type IIB string theory with one D7-brane we have the following situation. The axio-dilaton complex scalar is defined by $\tau:= C_0+i e^{-\phi}$ where $C_0$ is the axion and $\phi$ ...
1
vote
0answers
71 views

Non-linear sigma-models on curved worldsheet

I am studying nonlinear sigma-models and topological twists using E.Witten's article "Mirror manifolds and topological field theory" (https://arxiv.org/abs/hep-th/9112056), as well as "Mirror symmetry"...
-1
votes
1answer
81 views

Understanding quantum mechanics [closed]

Forgive me for this dumb question but what are matter waves of particles? are they particles being spread out in a space like waves or the particles are still "particles" but matter waves are ...
0
votes
0answers
27 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 ...
0
votes
0answers
60 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 ...
1
vote
0answers
91 views

Could dark matter actually be matter which resides in a different spatial dimension? [closed]

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 ...
1
vote
0answers
30 views

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?
1
vote
0answers
57 views

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....
0
votes
0answers
50 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, ...
1
vote
0answers
30 views

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.
0
votes
0answers
52 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 ...
2
votes
1answer
74 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_{\...
0
votes
0answers
31 views

$(0,2)$ 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: "...
1
vote
1answer
56 views

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 ...
3
votes
1answer
117 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-...
0
votes
0answers
65 views

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 ...
-2
votes
1answer
75 views

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 ...
3
votes
1answer
85 views

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 ...
3
votes
1answer
61 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 ...
4
votes
3answers
1k views

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 ...
8
votes
1answer
172 views

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 ...
0
votes
0answers
42 views

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 "...
3
votes
0answers
44 views

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 ...
0
votes
0answers
37 views

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 ...
0
votes
0answers
30 views

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 ...
0
votes
1answer
68 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 ...
0
votes
0answers
28 views

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 ...
2
votes
1answer
41 views

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 ...
2
votes
1answer
70 views

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 ...