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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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How could we conclude this relationship? [closed]

Facing a problem in Katrin Becker, Melanie Becker, John Schwarz's String Theory. A state $\left| \psi \right>$ is called spurious if it satisfies the mass-shell condition and is orthogonal to ...
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1answer
174 views

What is a theory of gravity?

Let me introduce this question by noting that my training is in condensed matter physics, and my familiarity with gravity is superficial at best. Hence, this question may be somewhat naive. In ...
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58 views

Does string theory need operator formalism to quantize?

Can we really use path integral approach to quantize for (first-quantized) string theory? This question is motivated from the following fact: even though we can establish exact correspondence between ...
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1answer
52 views

Why do we consider solitons as a composite object?

Can someone explain why do we consider solitons as a composite object? I know that there are dual theories which the role of fundamental and solitonic objects can be mapped to each other, but I can't ...
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1answer
39 views

Equation of motion for a massless scalar in 2 dimensions

I'm working through Polchinski's String Theory (Volume 1, Chapter 2, page 34), with $D$ scalar fields: The action is given by $$ S = \frac{1}{2 \pi \alpha'}\int d^{2}z \partial X^{\mu} \overline{\...
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1answer
46 views

Can holography be applied to every model?

Can all models have a holographic representation? I was talking with a physicist and he told me: "Holography is not a property you can just apply to any model of the universe willy-nilly. It either ...
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1answer
117 views

Should all black holes have Bekenstein-Hawking entropy especially in string theory?

There are so many confusing descriptions of how Bekenstein-Hawking entropy binds black holes, and thus the question. I previously asked similar questions, but I realized questions were misleading and ...
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29 views

Conformal transformation of a vertex operator before normal ordering

Let us consider a free scalar boson $\varphi(z,\bar{z})$ on the complex plane and assume the following two-point correlation function \begin{eqnarray} \langle\varphi(z,\bar{z})\varphi(w,\bar{w})\...
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2answers
48 views

Dual of Kalb Ramond field [closed]

i've been studying string theory for 4 days, i have a Kalb Ramond $B_{(2)}$ of this kind (from a $5^2 _2$ solution [1]) and i want evaluate its dual but i don't obtain the right result: The variables ...
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Hierarchy problem and loop quantum gravity

According to https://en.wikipedia.org/wiki/Hierarchy_problem#Finite_Groups. Hierarchy problem can be theoretically solved using symmetry of certain bosonic string theory on the Leech lattice (though ...
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Paper similar to Loop quantum gravity (Living review) by Rovelli but for string theory

So basically I want to know whether there exist any paper similar to the above mentioned one but for string theory which discusses the central achievement, main idea and open problems of the theory. ...
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1answer
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Are particles of fields that arise from compactification and strings treated differently in string theory?

I am aware that particles in string theory are different vibrating modes of strings. I am also aware that compactification leads to emergent fields from the parts of the metric of the compactified ...
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Why didn't Gravitational waves from neutron star passed into extra dimensions? [duplicate]

String theory is most prominent candidate for theory of everything but it defines our universe correctly through higher dimensions, precisely 11 dimensions. We know that gravity can pass through ...
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Loop-loop propagator in bosonic string theory

I have been searching for information on how to compute (or at least partially compute) the propagator of a string given an initial and a final loop in bosonic string theory. I have found several ...
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1answer
70 views

How do we assign length to dimensions in string theory?

My current understanding of the variations of string theory includes the sentence "string theory needs (at least) 6 extra spatial dimensions to work, but because our observable universe consists of 3 ...
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0answers
38 views

s-wave radial equation for minimally coupled scalar field

I am trying to work through the calculations from the following article. I need to find the s-wave radial wave equation for a minimally coupled scalar field, given by $\partial_{\mu}( \sqrt {-g} g^{\...
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1answer
74 views

Tension of String Connecting Two Objects [closed]

I believe the way you find tension in a string connecting 2 objects is by using Newton's Second Law on the object which the tension points to. But I am not completely sure how you would find the ...
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1answer
65 views

Pilot-Wave vs. Quantum Mechanics vs. String Theory [closed]

I wanted to know that are the main shortcomings of contemporary Pilot-Wave theory which is holding it back from dominating physics departments? To what extent is the facukty biase, do you think, ...
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1answer
103 views

In string theory, what replaces the black hole singularity?

In string theory, what replaces the black hole singularity? I know that it is possible for a single string to have arbitrarily large energy. Is a black hole just a single string?
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How cold does Something need to be for String Theory to be relevant?

I’ve often read casually that in order for modern string theory and other competing quantum gravity theories to be tested absolutely enormous temperatures (or rather energy densities) are required. ...
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1answer
69 views

What is a fuzzy space?

Can someone give a down-to-earth explanation of what is a fuzzy space? (As known from M-theory and noncommutative geometry)
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1answer
51 views

Polyakov Lagrangian and Lagrange multipliers

I'm reading Polchinski's Introduction to String Theory (volume I) and something got me quite puzzled in the beginning (At the top of page 19 to be precise). This part is about the open string and the ...
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1answer
72 views

Background for understanding the holographic principle?

I'm really fascinated by the wikipedia page on the Holographic Principle - "the description of a volume of space can be thought of as encoded on a lower-dimensional boundary to the region" seems ...
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Is there any reason why the moduli and axion fields are not observable in string theory?

One of the biggest criticisms put forth by the common skeptics of string theory is that we don't observe the moduli and axion fields that the theory predicts, and so we have to hide these fields so ...
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Why can't we apply the same rationale behind string theory and go down further?

I understand that string theory proposes to unify the four fundamental forces of nature by positing that there are these so-called vibrating strings at the core of all quants in the universe. I'm ...
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What is the spectrum of two open strings attached to a d0 brane?

The spectrum of a closed string is a tower of particles of spin 2N. With a massless spin 2 particle. (And a tachyon) The spectrum of an open string is a tower of particles of spin N. With a massless ...
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2answers
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How can 0-dimensional particles or 1-dimensional strings be 3D matter? [closed]

According to the latest information we got String theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings....
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In String Theory, does the geometry of the vibrating string cause a particle's behavior?

Apologies for the beginner-like question, but I've been thinking about this for a few weeks now, and I thought this was the best place to ask it. I know that, according to String Theory, particles ...
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How can string theory produce a globally Lorentz non-invariant theory like GR?

Locally, General Relativity is Lorentz invariant. Globally, it is not. e.g. Galaxy's sufficiently far apart are travelling more than the speed of light relative to each other. Although no particles in ...
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115 views

Physical examples of log CFTs

There are examples of CFTs having correlators with logarithms. What are the examples of physical systems exhibiting such logarithmic behaviour (particularly in $d>2$ dimensions)?
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63 views

What role does SUSY play in gauge/gravity duality?

This question arises in my project of finding the conformal field theory dual to the bosonic part of the Yang-Mills theory, i.e. non-supersymmetric large $N$ YM theory. Supersymmetry is a constant ...
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2answers
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What is meant by “non-perturbative” string theory?

I often hear people talk about finding a non-perturbative formulation of string theory. What does this mean exactly? To my knowledge string theory is a perturbative method. Just like Feynman graphs ...
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1answer
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Are the nonphysical degrees of freedom in Yang-Mills theory analogous to the worldsheet metric in the Polyakov formalism?

The Polyakov string action on a flat background (in the Euclidean signature) $$S_{P}[X,\gamma]\propto\int_{\Sigma}\mathrm{d}^2\sigma\,\sqrt{\text{det}\gamma}\,\gamma^{ab}\delta_{\mu\nu}\partial_{a}X^{...
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3answers
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String theory and background independence

I have read that string theory assumes strings live in spacetime defined by general relativity which make the theory background dependent (although general relativity is a background independent ...
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1answer
62 views

Is it possible to test the physical reality of extra dimensions predicted by string theory?

I have no business asking this question since I am not a string scientist but I like to follow science news in phys.org and I read an article dated today Gravitational waves provide dose of reality ...
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World-volume (higher) gauge theory on D-branes

It is well known that if one constructs ordinary WZW type sigma model for string action, it is possible whenever they find a cocycle in appropriate Chevalley-Eilenberg algebra. If I understand it ...
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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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Are strings capable of information processing? If so would string computers be more powerful than quantum computers?

A deterministic computer is weaker than quantum computer at least quadratically for (almost) all kinds of tasks. This is proved and the difference arises from Grover's search algorithm, which allows ...
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String theory: what are strings made of? [duplicate]

In my very limited understanding of string theory, put in extremely simplified layman's terms, it states that elementary particles (quarks, leptons, bosons) are all vibrating strings. And the ...
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3answers
115 views

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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1answer
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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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1answer
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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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1answer
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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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1answer
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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
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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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2answers
235 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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1answer
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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'...