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
0answers
59 views

Holographic dual of a star?

In AdS/CFT, we know that the AdS-Schwarzschild black hole is dual to a thermal state (or the thermofield double for the two-sided case). Suppose, instead of a black hole, we have a star in the bulk ...
6
votes
1answer
78 views

How can you make mechanics invariant under inversion of length? [closed]

I read that in some string theories they are invariant under a change of distance from $r$ to $1/r$. I wondered what is the simplest theory or lagrangian in 4 dimensions that could have this property. ...
1
vote
1answer
76 views

Why there are only two manifold in 1d?

I'm following Witten's essay and he writes: Let us try to make such a theory with one spacetime dimension instead of four. The choices for a one-manifold are quite limited: and then gives this ...
0
votes
1answer
151 views

What is "one-loop cosmological constant"?

I'm following Witten's essay and I'm trying to understand the UV divergence. When he writes: In quantum field theory, this Feynman diagram with a single proper-time parameter τ, underlies the one-...
3
votes
1answer
146 views

Two perturbative expansions in String Theory

In my String Theory course we learned about the two perturbative expansions of the theory: the one in $g_s$ and the one in $\alpha'$, but I can't picture the difference between the two of them. I was ...
-2
votes
2answers
120 views

Are we looking at the CERN Supercollider's results the wrong way? [closed]

As some background, I really don't know all that much about physics except what I study in school. So, this question might make me sound like a noob, but I hope I can be beared with. Anyway, I watched ...
1
vote
0answers
48 views

Chiral zero modes in type IIB matrix model

I have seen many articles in which the authors consider various modifications of IKKT matrix model (non-perturbative regularization of type IIB string theory) such as (Orbifolds, fuzzy spheres, ...
2
votes
0answers
100 views

AdS/CFT spacetime visualization

I was inspired by comments under this answer to ask this question. In the context of AdS/CFT, one often finds an embedding diagram of the $10d$ spacetime that I don't find particularly enlightening, ...
2
votes
1answer
92 views

Zwiebach String theory text - Why is the $(R-, R+)$ sector fermionic?

On Page 323 of Zwiebach 2ed, he says the state $$ (R_-,R_+): |R_a\rangle_L \otimes |R_{\bar b}\rangle_R \otimes |p^+, \vec{p}_T\rangle, $$ 'include the product of two $R$ ground states, they are "...
1
vote
0answers
55 views

Which ideas from String Theory are useful in other fields? [closed]

I hear sometimes that ideas in String Theory (ST) turned useful in other fields. I am curious, what are these ideas, and what insights or tools did they provide (that otherwise would not be discovered ...
1
vote
1answer
78 views

How is the $d=2$ Weyl invariance different from the generic Conformal $SO(2,d)$ invariance?

First of all, I read this answer and I understand that Weyl transformations are transformations of the metric and Conformal transformations are transformations of the coordinates that "Weyl-...
1
vote
0answers
37 views

Where is the warped throat in Klebanov-Strassler geometry?

In string theory, it is common to work in the Klebanov-Strassler geometry to find AdS and dS vacua. Applications are that anti-branes can be placed at the tip of this deformed/warped conifold to ...
3
votes
1answer
111 views

Absence of negative-norm states in old covariant quantization of the bosonic string

This question is about the discussion about the absence of negative-norm states in the old covariant quantization of the bosonic string as presented e.g. in Becker Becker & Schwarz (BBS). Their ...
2
votes
1answer
69 views

Question on the IR and UV regions in the bulk?

As the AdS/CFT correspondence is known, there is a correspondence between the quantum field theory and the string theory. Where do the duals of IR and UV place in the bulk? Are there the UV on the ...
2
votes
1answer
54 views

$D0$ brane and open string bound state radiating a closed string

I had this quite vague picture in my head of how a bound state of two $D0$ branes and an open string might "radiate" a closed string when the open string forms a cusp. I know the idea is ...
1
vote
1answer
100 views

What is the determinant of the induced metric $h_{ab}$ of the NG action?

In the introductory section of Polchinski String Theory: An introduction to the bosonic string we are given the induced metric which reads $$ h_{ab} = \partial_a X^{\mu}\partial_b X_{\mu}\tag{1.2.8} $$...
3
votes
0answers
129 views

Graviton-graviton scattering in tree level. Based on a talk by Bryce DeWitt

In this talk given by Bryce DeWitt, at page 6 he mentions a problem he gave to one of his PhD students. The problem is to compute the graviton-graviton scattering amplitude in tree level approximation....
1
vote
0answers
59 views

Gaussian Matrix Integral

I couldn't quite understand how we calculate the Gaussian Matrix Integral $$\mathcal{Z}=\int dM\ e^{-N\text{tr}\left(\frac{1}{2}M^2+JM\right)},$$ where the integration measure $dM$ over the $N$ by $N$ ...
4
votes
0answers
98 views

Dualities in Physics and Fourier Transforms

In many articles, authors compare physical dualities to Fourier transforms. For example: Joseph Polchinski, in his article "String Duality" (hep-th/9607050v2), writes: "Weak/strong ...
2
votes
1answer
105 views

Why for the closed string we need to take both left and right moving modes into account when deriving the mass?

In the closed bosonic string we have both left and right moving sectors with modes $\alpha_m^\mu$ and $\tilde{\alpha}_m^\mu$ respectively where $m\in \mathbb{Z}$ and where we have $\alpha_0^\mu = \...
3
votes
2answers
131 views

Poisson brackets of bosonic string oscillators

I'm reading string theory books and I'm stuck at the moment when we consider a Hamiltonian version of the classical string. Namely I don't understand how to derive the Poisson brackets for string ...
1
vote
0answers
68 views

Is Supergravity just Super String Theory without open strings?

I'm trying to understand the elements of the AdS-CFT correspondence. The definition I have in mind is a correspondence between: (A) a Super String Theory of $D_p$-branes and closed strings in a $10$d ...
1
vote
1answer
53 views

Derivative of OPEs in conformal field theory

Suppose you have the following OPE of a free theory: $$\partial X(z)\partial X(w) = \frac{\alpha'}{2}\frac{1}{(z-w)^2}+...$$ Then $X(z) \partial^2X(w)$ is given by $$X(z) \partial^2X(w) = +\frac{\...
2
votes
1answer
79 views

OPE in linear dilaton theory

I'm trying to do the following question from David Tong's problem sheets on string theory: A theory of a free scalar field has OPE $$\partial X(z)\partial X(w) = \frac{\alpha'}{2}\frac{1}{(z-w)^2}+......
1
vote
1answer
52 views

Operator Product Expansions using the stress energy tensor

I'm reading "String Theory Demystified" by David McMahon. On p.111 of the book, it is asserted that: One operator product expansion of particular interest involves the energy-momentum ...
1
vote
0answers
55 views

$bc$ CFT commutator of Virasoro and modes of ghost number current

Given the ghost current $j(z)=-:b(z)c(z):$ and the stress tensor $T(z) = \colon \partial b c \colon - \lambda \partial \colon b c \colon$, one may obtain the following commutation relation (via the ...
3
votes
1answer
139 views

On the spectrum of a quantised open string

I'm learning string theory from the book by Zwiebach and others. I'm trying to understand the quantisation of the open string and its mass spectrum. In light-cone gauge the mass-shell condition of an ...
1
vote
0answers
55 views

Physical origin of coisotropic branes

The paper "Remarks on A-branes, Mirror Symmetry, and the Fukaya category" develops the possibility of A-model open strings ending on a coisotropic submanifold equipped with a holomorphic ...
3
votes
0answers
88 views

Free field realisation for Vertex Operators

I wanted to know if for a generic CFT (in weak coupling limit) there exists free field realisation of the vertex operators. This seems like it should exist but I want to know a generic algorithm to ...
10
votes
2answers
241 views

Is there a description of D-branes from the worldsheet CFT perspective?

D-branes are best known as hypersurfaces in spacetime on which open strings with Dirichlet boundary conditions can end. Furthermore, they have several geometric properties associated with them, such ...
3
votes
0answers
65 views

Mass deformations in D-brane systems

It is well known that the worldvolume theory of $N$ coincident D$p$-branes is given by the $U(N)$ Yang-Mills theory in $(p+1)$-dimensions. One important feature of this setup is the possibility of ...
1
vote
1answer
82 views

Is Weyl transformation part of diffeomorphism? Does a gravitational anomaly capture also the anomaly due to Weyl transformation? [duplicate]

Weyl transformation is a local rescaling of the metric tensor $$ g_{ab}\rightarrow e^{-2\omega(x)}g_{ab} $$ Diffeomorphism maps to a theory under arbitrary differentiable coordinate transformations (...
2
votes
0answers
86 views

Trying to understand the conformal gauge "derivation" in Polyakov action symmetries

In section 2.3 of the book "Basic Concepts of String Theory" by Blumenhagen, Lüst, Theisen, 3 symmetries of Polyakov action are discussed: Poincarè invariance, diffeomorphism invariance and ...
4
votes
2answers
164 views

Action dimensions in string theory

Disclaimer: I'm tagging this as "string theory" because the doubts came to me studying the actions in string theory, but the underlying problem could be about the concept of the action ...
3
votes
0answers
50 views

At what coordinate is the D-brane located in the T dual world?

I have a simple question on the geometrical intuition of D branes. I am currently reading the TASI notes by Polchinski. Say one has a bosonic open string with all Neumann boundary conditions and ...
3
votes
1answer
76 views

Usage of Lagrangian not Lagrangian density for quantum string in Polchinski

In section 1.3 p. 18 while working out the energy spectrum of quantum string Polchinski uses Lagrangian instead of Lagrangian density while in QFT the usual convention is to use Lagrangian density (to ...
2
votes
1answer
89 views

Low energy effective action of bosonic string different in GSW and Polchinski/Tong?

In Superstring Theory vol.1 by Green, Schwarz and Witten (GSW) the low energy effective action of the bosonic string is given by: $$S=-\frac{1}{2k_0^2}\int d^{26}x\sqrt{-g}e^{-2\Phi}({\cal R}-4\...
4
votes
3answers
191 views

Identity of dynamical D$p$-branes

In my String Theory course, we introduced D$p$-branes, and I'm having trouble picturing them as dynamical objects. We analyzed the open and closed bosonic strings, found the EoM, quantized them, and ...
-2
votes
2answers
73 views

Twistor and Calabi-Yau spaces

The twistor space of Penrose's twistor theory is a projective space of three complex dimensions. This can be understood as six orthogonal dimensions, three with real metric and three with imaginary ...
4
votes
0answers
75 views

Error of $-i$ factor in light cone indices in conformal field theory in Becker's book

In Becker's book of String theory Ch-$3$ I'm getting an error of factor $-i$ in the definition of lightcone indicies after Wick rotation. The convention of the book is following $\sigma_{\pm}=\tau\pm\...
5
votes
1answer
231 views

Why do we have residual symmetry when we already used all symmetry in gauge fixing of the worldsheet metric?

In Becker, Becker and Schwarz' book about string theory, the following symmetries are listed for the $\sigma$-model of the string: Poincaré transformations Reparametrizations $\sigma^{\alpha}\...
1
vote
0answers
49 views

Super Virasoro Algerbra in string theory [closed]

I'd like to calculate the algebra ${G_r,G_s}$ for the Ramond sector, or Neuveu-Schwarz Sector for super Strings. The problem is that I don't know how to evaluate the anti-commutator relation between ...
4
votes
1answer
112 views

Critical dimension of ${\cal N}=2$ strings

In "A tour through ${\cal N}=2$ strings" by Neil Marcus (https://arxiv.org/abs/hep-th/9211059) the following problem - among others - is noted: The critical dimension of the ${\cal N}=2$ ...
7
votes
0answers
94 views

Low-energy effective actions in string theory: agreement between beta-function vs. scattering-based derivations?

In string theory, in my limited understanding, starting with the worldsheet theory, we have at least two methods for deriving the low-energy effective action on the target spacetime. We can either ...
0
votes
0answers
50 views

Can the string coupling constant be written in Planck units?

The relationship between string units and Planck units can be written as $l_p^{24} = l_s^{24}g_s^2$, where $g_s$ is the string coupling constant. It then seems like the $g_s$ always must be a mix ...
0
votes
1answer
90 views

What is $\mu_5$ in string theory?

I have come across the quantity $\mu_5$ in string theory quite a lot but I have not found it explicitly defined anywhere. The bosonic worldvolume action reads [1] \begin{equation} S = \frac{\mu_5}{g_s}...
2
votes
2answers
92 views

Detecting space-filling $D$-Branes in string theory

I am currently studying Zweibach's "A First Course in String Theory" CH:9 and I have managed to understand mode expansion in the light-cone gauge, at the classical level. Right before ...
2
votes
1answer
77 views

How do I go from Planck units to string units?

I am not sure exactly what "string units" are. I know that $\alpha' = l_{string}^2 = \frac{1}{M_{string}^2}.$ But these are not units per see, I still need values for $l_{string}$ and $M_{...
3
votes
0answers
63 views

How do you find the projector appearing in $\kappa$-symmetry for Green-Schwarz formulation of superstring?

I am trying to study the Green-Schwarz formulation of the superstring and I am following the string theory book by Becker, Becker, Schwarz. In there, they consider the action $$ S = S_1 + S_2 = -\frac{...
0
votes
1answer
71 views

Why do we integrate up to the invariances

Following Witten's essay What every physicist should know about string theory I understood that in the Hilbert-Einstein action is invariant under diffeomorphism in 1D and under conformal mapping in 2D....

1 2 3
4
5
48