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

What are the known ways to model baryons in string theory?

As I understand, string theory models baryons by including a so called "baryon vertex". Is this right? It seems that baryon vertex's are usually D/M branes. Is that always the case?
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Is the target space metric a dynamic field in the Polyakov action?

In Quantum Fields and String, A Course For Mathematicians in the lecture on string theory (volume II), the Polyakov action is described: $$S(\xi, g, G) = \kappa\int_\Sigma d\mu_g \text{Tr}_g\,\xi^\...
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117 views

Hagedorn transitions in 10 D and 11 D string/M-theories?

Are there Hagedorn transitions in 10D superstrings and 11D M-theory?
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Questions about the landscape in string theory

If I understand correctly, the string theory landscape is the totality of possible Calabi-Yau manifolds to make up the compact factor of space in string theory, in which there are of the order of $10^{...
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Is there overcounting states in string theory?

Say you are trying to find the amplitude for a particular state $A$ to a particular state $B$ of the Universe. For the final state you pick a spacial slice given by a 3-manifold $M$ (say a space-like ...
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What do string theorists mean when they say that little is known about M theory? [closed]

It’s often said that we don’t know what M theory is, but what does that actually mean? And how long until M theory becomes somewhat of an understood theory? Where are we at now with M theory?
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101 views

Wrapped M2 brane gauge field coupling?

An M2 brane is coupled to the C3 field of SUGRA. And as you all know, a wrapped M2 brane gives us the fundamental string. My question is, does the wrapped M2 brane (fundamental string) still couple ...
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1answer
237 views

String theory and one idea of “quantum structure of spacetime”

First of all, I do recognize that I haven't studied string theory up to this point. I'm actualy just getting started with it. So my question here is as follows: Einstein's theory of General ...
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401 views

What is a wavefunction, in the context of String Theory?

I have to admit that I don't know much about String Theory (or QFT, for that matter ..), but, if we assume that String Theory is the correct description of fundamental particles, what is the correct ...
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Conformal invariance and Diffeo - Weyl invariance

Consider a 2d Conformal Field Theory, with the metric of the underlying spacetime being $\gamma_{ab}$. I understand that we have the freedom to set $\gamma_{ab}$ to a flat form (either Euclidean or ...
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On String Theory, Supersymmetry and prospects of a theory of everything

The fundamental postulate of string theory is that matter is composed of tiny vibrating loops of string, and each vibrational mode of the string corresponds to a different fundamental particle. Now, ...
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In Cardy-Verlinde generalized uncertainty principle (GUP), how we know that the alpha is a constant of order one?

The GUP equation [1] is, $$\Delta x_i\geq\frac{\hbar}{\Delta p_i}+\alpha^2l_p^2\frac{\Delta p_i}{\hbar},$$ where $l_p$ is the Planck length. How do we know that $\alpha$ has a order of unity [1]? What'...
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In what sense are solutions to the Dirac equation and solutions to the Laplace equation equivalent in string theory?

I have come across statements like elementary particles on a Calabi-Yau correspond to harmonic forms (or to cohomology classes, which is equivalent for a compact Kähler manifold, since every ...
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178 views

On the boundary conditions for closed and open strings

In the process of finding the equations of motion for a string from the Polyakov action (say in the conformal gauge), we have to implement some boundary conditions on the target spacetime coordinates $...
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Non-local field theory (of Jaffe type) vs strings

As it is well known expectation values of fields are distributions. One usually works with tempered distributions or even with Jaffe fields (https://doi.org/10.1103/PhysRev.158.1454), all defining ...
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The electric charge of the M2 brane come from Kaluza Klein theory?

I'm curious if the electric charge of the M2 brane comes from the Kaluza Klein theory. As you all know, if something is going around the circular dimension it looks like electric charge. So is this ...
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How does magnetic charge in string theory arise?

In string theory, all of the standard model charges (electric, color, and weak hypercharge) arise from Kaluza Klein theory and through the interactions between strings and branes. But little is said ...
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Do 11D SUGRA fields exist at the fundamental level of M theory?

The M branes in M theory are a configuration of the fields of 11D sugra, but sugra is a low energy limit of M theory. So do these fields exist at the fundamental level of the theory, and if not, what ...
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Equations of motion from Polyakov action, before choosing the conformal gauge

My question is the following: It is usual in the standard textbooks to firstly choose a gauge (usually the conformal gauge) and then extract the equations of motion from the Polyakov action by ...
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71 views

In M theory, are strings and branes made of fields or are they fundamental objects?

Are strings and branes made of underlying quantum fields, just like particles in QFT. Or are they really the fundamental entities of nature and not made out of fields?
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Is this a correct non-technical description of mirror symmetry for Calabi-Yau manifolds arising from string theory?

In string theory there are physical reasons why the space we live in must locally be the product of Minkowski space with a Calabi-Yau manifold. The general theory doesn't say which Calabi-Yau manifold....
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81 views

Have string theory and brane cosmology the same landscape?

Has any of these hypothetical theories a "higher" number of possible universes or has string theory landscape the same type of possible universes than brane cosmology?
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Are internal string states analogues of internal particle states?

It is sometimes said that in string theory elementary particles correspond to modes of vibration of a string. Likewise in QFT, several particle fields take their values in a higher dimensional space,...
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Derivation of Born-Infeld (BI) for D-brane

I am trying to reproduce derivation of the Born-Infeld (BI) action for D-branes as it is presented in R.J. Szabo, BUSSTEPP Lectures on String Theory, arXiv:hep-th/0207142. In particular, I don't ...
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“$\theta$-$\phi$ duality” and $T$-duality

When bosonizing an interacting spinless Luttinger liquid, the action can be written as \begin{equation} S=\frac{K}{2\pi}\int dx d\tau\ (\partial_\mu\phi)^2 = \frac{1}{2\pi K}\int dx d\tau\ (\partial_\...
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1answer
214 views

Is Superstring Theory fundamentally flawed?

I suspect that i'm missing some fundamental concept here, so please kindly help me figure it out (if any). Suppose that superstring theory is a valid theory of nature. That is, every fundamental ...
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What is U-duality? and Why U-duality is important?

In string theory, we know three dualities. S-duality: Extension of Electric-magnetic duality, Duality between strongly coupled qft and weakly coupled qft. (One of the typical example is Seiberg ...
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About ghost D-branes and wrong statistics

I'm currently reading this article, which is about Ghost D-branes in string theory. The authors define these objects as something that cancels the effects of an ordinary D-brane. However, there is ...
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Strings 2018 takeaways [closed]

What are the main takeaways from the Strings 2018 conference? What are the main announcements, discoveries or directions emerging from this event? To my knowledge, one is the result by Vafa and ...
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D-brane worldvolume actions: Where are the Fermions?

I am studying D$p$-brane polarization (Myer's effect https://arxiv.org/abs/hep-th/9910053) and brane-flux annihilation (KPV mechanism, https://arxiv.org/abs/hep-th/0112197). There is little to no ...
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Anomalous curvature coupling corrections for $Dp$-branes worldvolume actions

The Chern-Simons term of an (abelian brane) is commonly written as $$ \sim\int_{\mathcal M_{p+1}}\sum_iC_{i}[e^{2\pi\alpha'F+B}], $$ where $C_i$ is the background Ramond-Ramond $i$-form, $F$ is the ...
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Are there any “Problems and Solutions” books or notes for advanced Quantum Field theory or/and String theory or/and Supersymmetry?

I was wondering whether or not there are any good resources of the type "Problems and Solutions" on String theory, on Supersymmetry and on advanced Quantum Field theory (separately). [I am aware ...
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How to understand the non-abelian DBI action?

I'm reading chapter 7 in "String Theory and M-theory, A Modern Introduction" by Becker, Becker and Schwarz. It says that the understanding of the square root of the determinant is to compute the ...
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What is meant by this variant of the euclidean plane: $\mathbb{R}^2_{\hbar}$?

I am reading some papers in mathematical physics (https://arxiv.org/abs/1006.0977) and I came across the following symbol $\mathbb{R}^2_{\hbar}$ I don't recognize nor could I find any background ...
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Is is true Superstring theory does not satisify diffeomorphism invariance?

So it is well known that string theory contains General Relativity in the classical limit. And assuming the spin-2 fields all couple correctly to the other fields this means it is diffeomorphism ...
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Why all deformations of the string background come from vertex operators?

It is possible to ask for deformations of the string action that preserve conformal (or superconformal) symmetry. These are the integrated vertex operators. Two questions: Is there a reason -- ...
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Fuzzy sphere of polarized D0 branes, non-abelian worldvolume action regime validity

I am studying Myer's paper "Dielectric Branes" (https://arxiv.org/abs/hep-th/9910053v2), where it is shown that a stack of D0 branes polarizes into a spherical D0-D2 bound state. The stack of $N$ D0 ...
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120 views

Chern-Simons action for non-abelian brane worldvolume and Tsetlyn's symmetric trace prescription

I am trying to reproduce the results of the (famous) Myer's paper "Dielectric Branes" https://arxiv.org/abs/hep-th/9910053. I am struggling a bit to obtain the numerical factors in the equations. When ...
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1answer
66 views

DBI action expansion for non-abelian brane worldvolume

I am trying to reproduce the results of the (famous) Myer's paper "Dielectric Branes" https://arxiv.org/abs/hep-th/9910053. In eq (33), when he expands the determinant factor for a flat-space ...
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Phase transition between two CFTs

If we start with a CFT (say CFT$_1$) and deform it by some relevant operator, in the IR we can get another CFT (say CFT$_2$). This is flowing from one CFT to another. I was wondering whether there ...
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Can you explain the background Independence of String Theory?

Is it possible to prove background independence of string theory? I've seen a few things about it but not really sure how it works. I seems to involve the action: $$S = \int \sqrt{G}G^{\mu\nu}(X)\eta^...
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127 views

How is Casimir effect related to String theory?

I'm looking at the Casimir effect calculation. As I understand it, it says that because wavelengths can only take on discrete values between two sheets there is a difference in the energy of the ...
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How many types of Singularities has string theory successfully resolved?

Except for proposing the fuzzball as a solution for black hole singularity, has string theory successfully explained/dealt with any other form of spacelike or timelike singularities? Kindly explain
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Definition of Sigma Model Path Integral

All references I have consulted have been extremely sketchy about this point. The (2 dimensional) nonlinear sigma model in some Riemannian manifold $M$ with metric $g_{\mu\nu}$ has action $$S = \frac{...
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What are the theoretical puzzles and/or experimental results that superstring theory can explain, but Standard Models can't?

From what I understand by reading this answer and this answer, Superstring theory can't directly explain all of the arbitrary "input parameters" in the Standard Model much like how Newtonian Laws of ...
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109 views

Pick a specific solution of string theory?

This is a conceptual question. One popular criticism against String Theory is its high number of solutions, around $ 10^{500} $. Is it true that each solution is corresponding to a specific possible ...
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396 views

Is the operator-state correspondence an axiom or a theorem?

The operator-state correspondence – the statement that the states of a theory are in one-to-one correspondence with its (local) operators – always seemed like a working-principle to me, rather than a ...
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About the Lagrangian for Chern-Simons-Matter theories

I am particularly thinking of the theory described in section $6$ (starting page 31) of this paper, https://arxiv.org/abs/1104.0680. The exact Lagrangian has never been explicitly stated here but ...
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1answer
327 views

Diffeomorphism & Weyl transformations in the 2D worldsheet of string theory and the existence of conformal gauge

D. Tong's notes on string theory, chapter 5 (PDF), feature the following in introducing the symmetries used in the Faddeev-Popov method: We have two gauge symmetries: diffeomorphisms and Weyl ...
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On the Schwarzchild black hole metric:

I've been going through the introduction on Ads/CFT by Horatiu Nastase (https://arxiv.org/abs/0712.0689). In chapter 5, "Black holes and p branes", in Eq. 5.2, it is mentioned the schwarzchild metric ...