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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52 views

Is string theory physics or not? [on hold]

duality /no duality free will/no free will. supersymmetry/no supersymmetry, extra dimension/no extra dimension. multiple universes/no multiple universes.
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Is Randall-Sundrum model background independent?

Randall-Sundrum model (https://en.wikipedia.org/wiki/Randall%E2%80%93Sundrum_model) is based on string theory. String theory can be background independent (https://en.wikipedia.org/wiki/...
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Evolution of theories in physics [closed]

I am searching for a book on the theories of (high energy) physics to gain insight, why they are so powerful. Namely, I would like to find a book that uses the evolution of physics from classical ...
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Dirichlet boundary conditions Polyakov action

The most general solution for the equations of motion for Dirichlet is given by: $$ X^{\mu}=a^{\mu}+\frac{1}{\pi}\left(b^{\mu}-a^{\mu}\right) \sigma+\sqrt{2 \alpha^{\prime}} \sum_{n \neq 0} \frac{\...
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Has the conjecture of Guillemin-Sternberg been proven for relevant physics cases?

From a working physicist's perspective, the conjecture of Guillemin-Sternberg (and its generalisations) seems to state in a highly technical manner that quantization commutes with gauge-fixing. In ...
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Boundary term in the holographic circular Wilson loop

Our professor has given us the holographic circular wilson loop as homework. He gave us the following reference https://arxiv.org/abs/hep-th/9904191 https://arxiv.org/abs/hep-th/0501109 and told us ...
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32 views

Factor of $1/2$ in $TT$-OPE

I'm trying to calculate the TT OPE in a bosonic theory. I'm missing a factor of 1/2 in the least-singular term. We have (following Di Francesco) $$\langle \partial \phi(z) \partial \phi(0) \rangle = \...
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Quantum corrections to metric on non-linear sigma model target space

I am trying to make sense of what physicists mean when they talk of quantum corrections to the metric on the target spaces of nonlinear sigma models, for example [GHL99]. First some quick notation. ...
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Polchinski Vol.2 10.6.4 mutual locality condition

I'm reading String Theory Vol.2 by Polchinski. In the book, Polchinski claimed that to define a consistent superstring theory, we need to impose several constraints. One of them is the mutual locality ...
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38 views

Diffeomorphisms on Polyakov action

The Polyakov action is invariant under arbitrary transformations of the sort: $$ \sigma^{\alpha} \rightarrow \tilde{\sigma}^{\alpha}(\sigma). $$ How do I show that the metric will transform like a ...
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Wheeler-deWitt equation as a renormalization group flow

I recently heard a comment that Wheeler-deWitt equation can be interpreted as RG flow equations. However, I haven't been able to find appropriate references for the same. Could someone suggest any ...
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1answer
58 views

Is the gauge/gravity (or AdS/CFT) duality believed to be exact?

I was wondering about the implications of the gauge/gravity (or AdS/CFT in a more restrictive sense) duality for the way we deal with physical theories, and I was wondering if the duality was believed ...
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95 views

What's the connection between cosmic strings and the strings hypothesized in string theory?

I read somewhere that Edward Witten, the (once) big hotshot of string theory, said that the discovery of cosmic strings (at the beginning of this Wikipedia article it is written: "Not to be confused ...
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Why is so much work spent on String Theory (despite lack of evidence), contrary to the Rishon Model? [closed]

I read this interview with Nathan Seiberg, one of the most outspoken physicists of String Theory. In this interview he writes: There are two correct statements. One is that at the moment there is ...
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1answer
59 views

Supercurrent of the $bc$-$\beta\gamma$ SCFT

In Polchinksi's Sec. 10.1, the $bc$-$\beta\gamma$ SCFT is introduced with action $$S_{BC} = \frac{1}{2\pi} \int d^2z (b \bar \partial c + \beta \bar \partial \gamma)$$ and supercurrent $$T_F = -\...
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1answer
113 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? ...
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3answers
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Why the full conformal symmetry is $Vir\otimes \overline{Vir}$ instead of $Vir\oplus \overline{Vir}$

In 2D CFT, we have the Virasoro generators $L_m$ and the generators $\bar L_m$, which are such that $[L_m,\bar L_n]=0$. Hence I thought that the full conformal algebra was $Vir\oplus \overline{Vir}$. ...
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Tachyon mode in Brane-Antibrane system (Type II)

Lets First start with coincident $D3$ brane- $D3$ Brane system. Superstring stretch between these two contain a Tachyon mode But GSO projection removes this. For open string, $D$ branes serve just as ...
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Which AdS/CFT correspondences have been found so far?

When I read about AdS/CFT correspondence, there always comes the most famous example of conjectured correspondence, which is the one between type IIB string theory (AdS side) and $\mathcal{N}=4$ ...
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25 views

Will string theory ever be provable? [duplicate]

Some time ago I saw a documentary in which they said that to have the experimental certainty of the existence of a string we would need a particle accelerator with the same diameter of the milky way. ...
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32 views

A simple question about equation of motion in polchinski's String theory?

In page 14 to get the equation of motion, it takes the variation of the action $$ S_P[X,\gamma]=-\frac{1}{4\pi\alpha'}\int_Md\tau d\sigma(-\gamma)^{1/2}\gamma^{ab}\partial_a X^\mu\partial_b X_\mu $$ ...
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String theory question

If string theory proposes that the point like particles observed are actually different vibrations of a string. Is the way the see them equivalent to various harmonics and fundamental frequencies? So ...
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3answers
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Motivation behind action when deriving ''Strings as Harmonic oscillators" in Zwiebach's book on String theory

Page 248 gives us this action and he simply says that we will assume it correct. $$ S=\int d \tau d \sigma ~\mathcal{L}=\frac{1}{4 \pi \alpha^{\prime}} \int d \tau \int_{0}^{\pi} d \sigma\left(\dot{X}...
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154 views

How to derive the Hamilton-Jacobi equation for the area of a minimal surface on a Riemannian manifold?

The action for a string in this background $$G_{IJ}\tag{1}$$ can be written as the Nambu-Goto action $$S_{NG}=\int d\sigma^1d\sigma^2\sqrt{g}\quad\quad\Rightarrow\quad\mathcal{L}=\sqrt{g}\tag{2}$$ ...
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Finite size energy levels

I am reading this paper. In section 5 they consider a 2d QFT in finite size geometry (cylinder of radius $R$). They say that the energy levels of stationary states ($|n \rangle$) therein will behave ...
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1answer
27 views

Can we ignore the scalar field (dilaton) term in the Polyakov sigma-model action when deriving the classical equations of motion?

I have the full Polyakov sigma model action: \begin{equation} \begin{split} &S=S_P + S_B + S_\Phi = \\ &- {1 \over 4 \pi \alpha'} \Big[ \int_\Sigma d^2\sigma \sqrt{-g} g^{ab} \partial_a X^\mu ...
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Idea behind boundary states in BCFT

In Blumenhagen's book on CFT, in the BCFT chapter he introduces the concept of a boundary state. TO do this, he first explains how there is a duality between the one-loop open string worldsheet and ...
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1answer
35 views

Does the string theory landscape apply to M-theory?

I had read about "string theory" having a large number of solutions (~$10^{500}$). Does this apply to the 11 dimensional M-theory or only to it's five 10-dimensional limiting cases?
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Minimal area for circular Wilson loops in these coordinates

In all references you can see that the Poincare coordinates are used to get the minimal area for the circular wilson loop. I want to use the metric that is used also for the D3-brane (e.g. see ...
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Nambu-Goto action using ADM metric

I start from the Nambu-Goto action:$$ S=-\frac{T_{0}}{c} \int_{\tau_{i}}^{\tau_{f}} d \tau \int_{0}^{\sigma_{1}} d \sigma \sqrt{\left(\dot{X} \cdot X^{\prime}\right)^{2}-(\dot{X})^{2}\left(X^{\prime}\...
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Veneziano amplitude from 3-point constants

Consider an open bosonic string in the critical dimension at $g_s = 0$ (only the sphere contributes to the string amplitude). The scattering of 4 tachyons is given by the Veneziano amplitude. I'm ...
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51 views

Systematic way of calculating 3-point worldsheet amplitudes

I'm looking for a systematic way of deriving the 3-point functions $\left< V_1(z_1, \bar{z}_1) V_2(z_2, \bar{z}_2)V_3(z_3, \bar{z}_3)\right>$ of the worldsheet CFT of a closed bosonic string. ...
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1answer
47 views

Mobius invariance of the worldsheet 3-point function

Consider the CFT that corresponds to a gauge-fixed closed bosonic string. Ground level string states are described by vertex operators such as $$V(p) = :\exp(i p_{\mu} X^{\mu}(z, \bar{z})):$$ which ...
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66 views

Are there other theories (apart from string theory) that combined with inflation, would produce universes with different laws?

In chaotic inflation, space would stop expanding in some points, creating hubble volumes that could experience different spontaneous symmetry breaking, which would result in different properties, such ...
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Book with explanation of Kazama-Suzuki models

The book "Introduction to Conformal Field Theory" by Blumenhagen and Plauschinn (BP) covers coset construction and minimal models, but it stops there. The original papers by Kazama and Suzuki seem to ...
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String Theory with a background B-Field

i was reading some articles about open string theory with a background B-Field, and i was wondering if this B-field can carry a mass or not? i mean, can we find in the expression of the mass operator ...
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String topology in string theory

How do string topology, string field theory and topological strings interact? Does anybody see a global picture? By string topology I mean the TQFT based on the homology of the space of loops ...
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1answer
51 views

Are the factors in the de Broglie identities operators, scalar real numbers, or both? Or something else?

I understand that $\hbar$ is an honest element of $\mathbb{R}$. But I am trying to understand how the de Broglie wavelength is related to the wave function mathematically. In the identity $p = \hbar k$...
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1answer
59 views

Are particles of the same type identical in string theory?

Things that oscillate have a phase. Does it allow two electrons in string theory to be different from each other (different phases, while everything else except position is the same)? Would that ...
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4answers
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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-...
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2answers
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Can gamma matrices be real in 6 dimensions?

I'm trying to find the really real representation of 6D gamma matrices. The problem is that "do they really exist?" If yes, then how am I supposed to construct them? Thank you!
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1answer
51 views

How to get the mass squared for the Green-Schwarz string?

Im following the GSW book. Specifically equations (5.2.39), (5.2.40) $$H=\frac{1}{2p^-}((p^i)^2+2N)$$ $$N=\sum_{m=1}^\infty(\alpha_{-m}^i\alpha_m^i+mS_{-m}^aS_{m}^a)$$ are not clear for me. I know, ...
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Is string theory self-consistent? (Conformal anomaly)

Recently I attended a very short course on string theory. We went through the standard presentation in light-cone gauge for brevity. We ‘derived’ the Einstein field equation in the following manner. ...
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Variation under infinitesimal reparametrization

Say that under the infinitesimal reparametrization $\sigma \rightarrow \sigma' = \sigma-\xi(\sigma)$, $x^\mu$ transforms as a scalar, i.e. $x'^\mu(\sigma')=x^\mu(\sigma)$. I would like to show the ...
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47 views

How does AdS/CFT enact and not just be static geometry?

I understand the duality between the two regions of phase space (as Maldacena described it) that are Anti-de Sitter geometry and conformal field theory as an asymptotic grafting on of scale-invariant ...
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86 views

Two-dimensional bosonic field theory

I'm struggeling with the following question: Consider a two-dimensional bosonic field theory defined by the following action $$S =\frac{k}{2} \int dx_{1}dx_2 [(∂x_1 φ(x_1, x_2))^2 + (∂x_2 φ(x_1, ...
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1answer
72 views

IIB Supergravity from worldsheet (super)conformal invariance of Green-Schwarz string

After reading this question How are low energy effective actions derived in string theory? I began to wonder what is the coupling of the string to the other sugra fields. In almost all textbooks ...
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2answers
106 views

Role of AdS/CFT correspondence in the context of integrability

I was wondering how the AdS/CFT correspondence fits in the context of integrability. As I understand, the AdS/CFT correspondence postulates a duality between gravity theories and CFT's. If one theory ...
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1answer
49 views

Stress-Energy Tensor and Conformal Invariance in String Theory

Since the Euler-Lagrange Equations corresponding to the Polyakov Action implies no dependance on the auxillary metric we arrive at the constraint $T_{ab}=0$. We then change to lightcone coordinates $++...
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In M-Theory are membranes excited states of a field? [duplicate]

Are M2 and M5 membranes in M-Theory excited states of some underlying field, or are they fundamental? In what sense are membranes solitonic? In the reference question, someone made a comment that had ...