# 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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### 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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### From Freshman Mechanics to String Theory: A Comprehensive Textbook Sequence in Physics [duplicate]

If a student with no background in physics and an understanding of only single variable calculus wanted to learn string theory, what sequence of textbooks would most succinctly, clearly, and ...
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### Electroweak Hierarchy Problem (Softball Question)

My question is two-fold: 1) if i recall correctly, the hierarchy problem was initially appreciated by GUT model builders from the 80s onward. if the only valid solution is susy, would this suggest (...
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### Is String Theory formulated in flat or curved spacetime?

String Theory is formulated in 10 or 11 (or 26?) dimensions where it is assumed that all of the space dimensions except for 3 (large) space dimensions and 1 time dimension are a compact manifold with ...
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### 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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### Why T-duality only work when the background has isometries?

I have been studying from some textbooks and papers about the T-dality topic. In particular for the Buscher rules it seems that they claim that in order to have T-duality in certain direction we need ...
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### OPE of stress tensor in CFT

I come aross an OPE between stress tensor components in CFT which is \begin{equation} T(z)\bar{T}(\bar{w})\sim -\frac{\pi c}{12}\partial_{z}\partial_{\bar{w}}\delta^{(2)}(z-w)+... \end{equation} I am ...
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### Polchinski's String theory Green's function on $RP_2$; eq. (6.2.38) p. 176

Is there an error in Polchinski's String Theory Equation (6.2.38) p 176 that is not on the Errata's page https://www.kitp.ucsb.edu/joep/links/joes-big-book-string/errata ? He write for the Green's ...
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### How does the $D$-brane geometry influence the gauge symmetries?

I am trying to understand why the $D$-brane structure of a string theory matters for string phenomenology. From what I understood from Wikipedia, the $D$-brane structure determines the gauge ...
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### Casimir Force and bosonic String Theory dimensions

I was reading the lecture notes on Quantum field theory by David Tong. In the section on Casimir force he derived the force of attraction felt by the plates due to the field vacuum energy in $1+1$ ...
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### Can string theory explain why the charge of the positron and of the proton are equal? [duplicate]

There is not much more to elaborate. Can string theory say why electrons and protons have exactly opposite charge? And thus why hydrogen atoms are neutral? I guess that the answer is no, because ...
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### Spin of higher string excitations

I am trying to better understand spin in string theory. There is already a good post here: Ssecond and third level excitations of open string But I have these questions: 1) Why would the second ...
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### Which CFTs have AdS/CFT duals?

The AdS/CFT correspondence states that string theory in an asymptotically anti-De Sitter spacetime can be exactly described as a CFT on the boundary of this spacetime. Is the converse true? Does any ...
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### What are the necessary conditions for a CFT to have a holographic dual? [duplicate]

The number of degrees of freedom of a CFT is given by its central charge $c$. From the bootstrap point of view, any CFT is characterized by the knowledge of its "CFT data", i.e. the scaling dimensions ...
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### Equation of motion from Polyakov action

If I write (my understanding of) how to derive the equations of motion from the Polyakov action, I come up missing a term. Beginning with the basic Polyakov action \begin{equation} S = -\frac{T}{2}...
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### About the duality when embedding Gopakumar-Vafa into superstring theory

Vafa proposed a duality when embedding the Gopakumar-Vafa duality into superstring theory. Vafa's duality is about a correspondence N=1 supersymmetric gauge theory and superstring propagating on ...
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### Conformal weights in Laurent expansions

Currently I am taking an introductory class in conformal field theory and ran into some confusion. Everywhere I run into Laurent expansions of several important quantities, and (mostly) all of them ...
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### Matrix Model in AdS/CFT & exact results

Matrix models appeared in the context of AdS/CFT while trying to calculate the Circular Wilson Loop. It was first noted by Erickson, Semenoff & Zarembo [hep-th/0003055] that the 2-loop ...
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### Polchinski equation 11.2.7

In Polchinski's string theory volume 2, when discussing the GSO projection for the heterotic string he says: In the IIA and IIB superstrings the GSO projection acted separately on the left- and ...
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### Supersymmetry beyond $D=11$ spacetime dimensions

Taking into account the higher spin theories, from which string theory is an effective field theory, I just wondering if there is something to do to extend supersymmetry to any dimension without any ...
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### Are the possible universes in brane cosmology embedded in string theory landscape?

String theory has a landscape of possible universes. Brane cosmology is related to string theory because it needs extra dimensions, but are the possible different universes of brane cosmology ...
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### Could an holographic universe consist of 3d embedded in 4d instead of 3d embedded in 2d?

In the holographic model, information about a given dimension can be embedded in a lower dimension, so our 3d universe could be considered as a 2d one. Could it happen the other way? I mean, could the ...
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### Why doesn't string theory predict the existence of infinitely many elementary particles?

I'm a physicist, but my knowledge of string theory is extremely minimal. My naive conceptual understanding is that the vacuum is modeled as a certain topology (and geometry?) for the spacetime, and ...
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### How to calculate the free energy in curved space?

To study the Hagedorn temperature of string near a black hole, we need to calculate the free energy in curved space. This is can be done calculating a torus path integral, but I want to know if an ...
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### If extra dimensions are out there, why don't/can't we see them? [duplicate]

String theory proposes the existence of extra space dimensions. Very brilliant minds believe in their existence. Of course, I could appreciate that they are consequences of mathematical ...
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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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### Explanation of the Nambu-Goto action and calculus needed for a beginner to learn [closed]

I have recently started trying to learn String Theory, but haven't learnt calculus - I know this probably isn't a good idea, but I decided to learn each part as I go. I'm partly using Brilliant, and ...