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
1 vote
1 answer
40 views

How many massless particles are there in closed bosonic string theory?

How many massless particles are there for closed strings in bosonic string theory? Page 53 of String Theory and $M$-Theory by Becker and Schwarz states that there are 576 massless states for the $N = ...
user avatar
4 votes
2 answers
94 views

What experiments could be done *in principle* to help down-select between different versions of string theory?

I understand that string theory (broadly defined) is a solution to quantum gravity. That is, it is a unified theory the explains both quantum phenomena (such as the particles of the standard model ...
user avatar
  • 9,134
-1 votes
0 answers
31 views

Help in understanding string theory? [closed]

0 I am a high school student trying to understand string theory for a physics project and I wonder if someone here would like to help me. I know the basics of the theory and with that I mean that I ...
user avatar
-2 votes
0 answers
50 views

Is superstring (M-theory) an effective theory from higher spin theory?

In the proceedings of the 2003 conference to celebrate Stephen Hawking's 60th birthday Hawking writes: String theorists have long used the term, effective theory, as a pejorative description of ...
user avatar
  • 5,363
4 votes
0 answers
84 views

Is Planck length constant in String Theory? Does it have a renormalization flow?

Is Planck length constant? Planck length $l_p$ is dependent on Newton constant $G_N$ which is related to coupling constant of interaction of gravitons, but from field theory point of view, we know ...
user avatar
1 vote
0 answers
35 views

String theory coset-space theories in the text book by Becker, Becker and Schwarz (BBS)

I am reading the string theory and M-theory by Becker, Becker and Schwarz (BBS). And I came across a section in chapter 3 called coset-space theories (after equation 3.58) At the beginning of this ...
user avatar
0 votes
0 answers
31 views

Can we say tension is the ability to generate interference by this paper?

https://arxiv.org/abs/1206.2021 Abstract : We propose a method for measuring the string tension in gauge theories, by considering an interference effect of mesons, which is governed by a space-time ...
user avatar
1 vote
0 answers
66 views

Can any other manifold be used for compactifying the 6 extra dimensions of string theory? [duplicate]

I'm a layman interested in string theory. I read about how the 6 extra dimensions of superstring theory are compactified into 3-dimensional complex manifolds (so real dimension 6?) called Calabi-yau ...
user avatar
5 votes
1 answer
123 views

Why is (1,1) worldsheet SUSY enhanced to (2,2) SUSY after compactification of type II string theory on a CY threefold?

I have a quick question. In case of compactification on an Calabi Yau cutting off 3/4th SUSY from the type-II string in 10D leads to an enhancement of worldsheet SUSY. It has been claimed since time ...
user avatar
0 votes
1 answer
47 views

String partition function

Hey I am a bit confused because when reading physics papers I encounter the free energy as a generating function of topological invariants as integrals over certain compactified moduli spaces. For ...
user avatar
  • 141
6 votes
1 answer
234 views

String theory: Conformal invariance and Conformal Killing Vectors

I am confused by the relation between the invariance of the Polyakov action under conformal transformations and the Conformal Killing Vectors (CKVs) appearing during the process of quantization. Let ...
user avatar
  • 165
4 votes
1 answer
63 views

How to calculate the OPE of the $X_L(z_1)X_L(z_2)$ in the free boson theory from the mode expansion?

From the polchinski page 238, given \begin{equation} [x_L,p_L] =[x_R,p_R]=i\tag{8.2.14} \end{equation} and the mode expansion $$\begin{equation} \begin{split} X_L(z) = x_L -i\frac{\alpha'}{2}p_L \ln z ...
user avatar
7 votes
1 answer
112 views

How to Wick rotate differential forms?

The bosonic sector of the Cremmer-Julia-Sherk (CJS) 11D supergravity action is $$ eR-\frac12 F\wedge *F-\frac16 A\wedge F\wedge F,$$ where $F=dA$ is a 4-form field strength. How would one perform a ...
user avatar
1 vote
0 answers
23 views

Wave equation for lightcone coordinate $X^-$

A quick question from Polchinski volume.1 : He claims in p.20 that the worldsheet lightcone coordinates $X^\pm$ also (i.e. in addition to the transverse coordinates $X^i$) satisfy the wave-equation. ...
user avatar
  • 93
1 vote
1 answer
82 views

String Compactification on a Circle Results in a Moduli Space?

I have been reviewing some string theory for a project I'm working on and I have some questions regarding string compactifications on a circle and the precise definition/origin of the moduli space ...
user avatar
2 votes
0 answers
91 views

Are dualities necessarily quantum mechanical?

What happens to dualities in a certain limit where quantum mechanics is turned off? Like sending $\hbar/S$ $\rightarrow0$ where $S$ is the action of each side of the duality. Does the duality have a ...
user avatar
4 votes
1 answer
197 views

Bosonic closed string effective action

Neil Lambert in his lecture notes https://nms.kcl.ac.uk/neil.lambert/SBQG.pdf in section 3.9 states that imposing conformal invariance at one-loop imposes the following equations on the spacetime ...
user avatar
  • 583
1 vote
0 answers
38 views

Strings: Neumann and Dirichlet boundary conditions

As I understand it there are two possible boundary conditions for open strings. The Neumann boundary condition implies that the ends of an open string move freely with the velocity of light. The ...
user avatar
3 votes
0 answers
72 views

Emergent spacetime from a web of string world sheets?

Like many, I have deep conceptual difficulty understanding how an enormous amount of closed strings can become an effective classical spacetime that satisfies Einstein's equations. I appreciate that ...
user avatar
4 votes
1 answer
130 views

Stückelberg mechanism and the axion

In the so-called Stückelberg mechanism we have the BF term $$ \sim \int m\; B_2\wedge F ~, $$ where the field $B_2$ is a 2-form and $F$ is the field strength arising from a $U(1)$. The Stückelberg ...
user avatar
1 vote
0 answers
42 views

Confusion about the definition of negative angles between two D-branes

I have a conceptual question regarding a paper I am reading. More precisely, the first appendix starting on page 29. In this paper, schematically, the classical oriented open strings get quantised ...
user avatar
6 votes
1 answer
95 views

Computing the DBI action on $S^5$

I've been looking at this paper (arXiv: 1103.4079). On page 7, from the metric of the giant gravtiton on $AdS_5 \times S^5$, $$ds^2 = -\cosh^2\rho \, dt^2 + d\rho^2 + \sinh^2 \rho \, d\tilde \Omega_3^...
user avatar
2 votes
0 answers
41 views

How to show that the low energy effective bosonic sigma model is consistent : $\beta^G=\beta^B=0 \Rightarrow \beta^\phi=cnst$

I am totally stuck at an exercise regarding the consistency of nonlinear sigma model... Let \begin{equation} \beta^G_{ab}=R_{ab}+2D_a D_b \phi-\frac{1}{4}H_{acd}H^{bcd}\text{, }\beta^H_{ab}=-\frac{1}{...
user avatar
  • 987
0 votes
0 answers
28 views

Number of dimensions of the universe according to the string theory [duplicate]

I am not a physicist, but what is the current idea of the number of dimensions of the universe according to the string theory?
user avatar
  • 1
1 vote
0 answers
40 views

Can wrapped D-branes change the cycle they wrap, by quantum effects?

Suppose the internal manifold in a string compactification of type II, say, contains a D-brane wrapped around a given cycle. Is there an obstruction to the brane changing its wrapping cycle via a sort ...
user avatar
  • 11
7 votes
1 answer
97 views

Open strings and branes

In string theory, open strings are attached to branes. What does "attached" mean? Do they just interact with the branes, or are they related to them in some other way?
user avatar
2 votes
0 answers
46 views

Does compactification of a Nambu-Goto string in one direction break Diff invariance?

Assume we have a Nambu-Goto action, in phase space, for a closed string. If I compactify one coordinate of the target space, do I reduce the diff invariance of the system. We have $$S=\int d^2\sigma \...
user avatar
  • 1,183
1 vote
0 answers
72 views

One-Loop Fayet-Iliopoulos term in heterotic string

I'm having problems computing the coefficient of the Fayet-Iliopoulos term, following the book of Kiritsis. With the term in the effective action in the Einstein Frame $$- \frac{\zeta}{2}M_s ^2 \int \...
user avatar
-2 votes
2 answers
203 views

In the history of the development of the standard model was there a version in which quark-antiquark pairs or flux tubes were the fundamental particle [closed]

Based on the observations of color confinement and no free quarks, I'm wondering if instead of a having quarks as fundamental particles, during development of the Standard Model was there ever a ...
user avatar
  • 336
3 votes
0 answers
86 views

Why string theory action needs to be manifestly diffeomorphism invariant?

A typical QFT action is obviously not diff invariant, in other words, the integration parameters have physical significance as time and position. For example action for massless free scalar field on ...
user avatar
  • 1,183
3 votes
1 answer
128 views

How does string theory get around the argument in Weinberg's QFT?

In Weinberg's The Quantum Theory of Fields Vol. 1, an argument is presented that the three postulates of Lorentz invariance quantum mechanics cluster decomposition principle leads to quantum field ...
user avatar
  • 767
1 vote
1 answer
70 views

Conformal weights of space-time and ghosts

I'm studying the paper of Kaplunovsky https://arxiv.org/abs/hep-th/9205070 In particular in page 12 he says Hamiltonians $H$ and ̄$\bar{H}$ are totals of space-time, ghost and internal components; ...
user avatar
1 vote
0 answers
32 views

Doubt for open string toroidal compactification

Let $(\tau,\sigma)$ be our coordinate system on a local path of worldsheet. For open string $\sigma \in [0,\pi]$ and the end points are different. Now if we do compactification on this string in $26$...
user avatar
  • 2,815
3 votes
0 answers
78 views

Utility of Topological Data Analysis in Theoretical Physics

I audited a lecture on Topological Data Analysis, and I found it really interesting, primarily because of the connection to algebraic topology. I asked the professor if there are any connections to (...
user avatar
2 votes
1 answer
64 views

Conformal transformations problem in flat worldsheet

In section 2.2 of David Tong's String Theory lecture notes, he claims that conformal transformations on the flat worldsheet are such that $$\sigma^\pm \to \tilde{\sigma}^\pm(\sigma^\pm).\tag{2.10}$$ I'...
user avatar
0 votes
1 answer
65 views

Variation of induced metric in Nambu-Goto action

I'm working with the Nambu-Goto action $$ S=-\mu\int d^2\zeta\sqrt{\gamma} $$ with $\gamma$ the determinant of the pull-back metric $$ \gamma_{ab}= \begin{pmatrix} \dot{X}^2 & \dot{X}\cdot X' \\ \...
user avatar
1 vote
1 answer
45 views

Misconception about closed string worldsheet definition

I'm a little confused about the precise way to define the worldsheet $\Sigma$ of a closed string. Its parametrization must be of the form $X: \Sigma \longrightarrow \mathbb{R}^{1,D-1}$ and one of its ...
user avatar
0 votes
0 answers
28 views

What are the energies (in eV) that we need to reach to create 'strings', gravitons and a 'Theory of Everything' (quantum gravity)?

Somehow, I cannot find an answer on the Web.... Possibly because nobody knows, of course, but I would still like to find a 'ballpark' answer... Creating the particles or whatever (and whatever they ...
user avatar
  • 3,421
3 votes
1 answer
77 views

Conformal transformations that preserves the string boundary condition

I am currently reading 't Hooft's lecture notes on string theory [1]. I am trying to show that given the world sheet metric $h_{ab}(\tau,\sigma)$ and the boundary condition for closed string $$ X^\mu(\...
user avatar
5 votes
1 answer
227 views

Propagator of four-dimensional Chern-Simons theory

In https://arxiv.org/abs/1903.03601, on page 13, the propagator of 4d Chern-Simons theory is computed, in the gauge $D^iA_i=0$, where $D^i = (\partial_x,\partial_y,4\partial_z)$. The gauge-fixed ...
user avatar
  • 1,129
0 votes
1 answer
48 views

Is Polyakov action in a fixed conformal gauge, diff invariant?

The polyakov action in fixed gauge is given as $$S[X]=-\frac{1}{4\pi\alpha}\int d^2\sigma\partial_\alpha X\cdot\partial^\alpha X$$ is this invariant under diff transformations? Intuitively I think it ...
user avatar
  • 1,183
2 votes
0 answers
61 views

D0, D1, D2... DN branes consist of D0 branes?

In BFSS Matrix theory, D0-branes connect the ends of open strings. Do other D-branes (D1, D2... DN) consist of D0-branes?
user avatar
3 votes
0 answers
36 views

Semi-classical spinning strings and AdS-CFT

I'm trying to understand how the AdS/CFT correspondence is precisely formulated when on the bulk side people are working with the string theory as a sigma model on the worldsheet expanded about some ...
user avatar
  • 7,472
2 votes
1 answer
75 views

Coordinates on a compactified dimension in bosonic string theory

In the simple case of compactification on the circle of radius $R$, $S^1_R$, most sources on string theory, e.g. here (Kevin Wray, An Introduction to String Theory, page 197), it is stated that the ...
user avatar
  • 130
1 vote
0 answers
43 views

Why don't strings have a Planck mass of vibrational energy?

It is claimed that strings have a length $l_S$ within an order of magnitude of the Planck length $l_{Pl}=10^{-35}$ m. If they oscillate at the speed of light, $c=10^8$ m/s, then their natural ...
user avatar
1 vote
0 answers
32 views

What is the meaning of region momentum (or dual momenta) variables in the worldsheet?

In scattering amplitudes, we deal with usual momentum variables which flow across any edge in a Feynman diagram. For a colour ordered amplitude, we can further designate region momenta to the planes ...
user avatar
0 votes
1 answer
91 views

Implications of M-Theory on the correctness of String Theory

So we know that there are 5 types of string theories (Type 1, Type IIA, Type IIB, $SO(32)$ heterotic, and $E_8 \times E_8$ heterotic). It was shown that these 5 types are just limits of something ...
user avatar
0 votes
0 answers
52 views

What are the basic building blocks in M-Theory?

In particle theory, the basic building blocks are particles (okay... perhaps I should say quantum fields). In string theory, the basic building blocks are strings. I heard that there's something ...
user avatar
1 vote
0 answers
77 views

What does M-theory predict at the singularity of a black hole?

how does M-theory avoid problems like infinite density and geodesic incompleteness. like, is there a fundamental limit to where matter can collapse or simply does matter decay and form a condensate of ...
user avatar
2 votes
0 answers
43 views

Quantum computing and string theory: which path should I pursue first? [closed]

I'm an undergraduate physics student waiting for responses from graduate programs I applied to. I apologize if this question is slightly off-topic for physics SE, but I really want to hear some advice ...
user avatar
  • 399

1
2 3 4 5
49