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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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71 views

How does Alain Connes NCG compare phenomenologically with superstring theory?

In Veltmans book on QFT, diagrammatica, the full SM Lagrangian is published. There are more than a hundred terms and it looks pretty uninspiring and not quite the kind of equation one would want to ...
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181 views

Free Field Realization of Current Algebras and its Hilbert space

I have some conceptual confusion regarding the interplay between current algebras, their free field representation and the Hilbert space generated from it. Let's sketch a simple example, $\mathfrak{...
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68 views

If strings of matter are of the same substance how can matter carry differing charges?

Considering that a string is a loop of energy composed of the same underlying material how is it possible for it to be either positively or negatively charged? For that matter, how is it possible for ...
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56 views

Generalization of Chern-Simons Wilson Line

The Wilson line in Abelian Chern-Simons theory is $$\langle\exp\left(i\int dt\dot{x}^{\mu}A_{\mu}\right)\rangle=\int\mathcal{D}A\exp\left(i\int dt\dot{x}^{\mu}A_{\mu}+\frac{i}{4\pi}\int A\wedge F\...
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46 views

Root weights and states in orbifold compactifications

I have the following question regarding orbifold compactifications of the heterotic string: What is the relation between a certain representation and the weights of the root lattice? I mean: take ...
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66 views

Question about Mode expansion of free compact boson

$(1+1)$-Dim free compact boson, Lagrangian is $$\mathcal{L}= \frac{1}{2}(\partial_\mu\phi(\sigma,t))^2$$ with $\phi(x,t)\sim\phi(x,t)+2\pi r$ and periodic boundary condition along $x$, i.e. $\phi(\...
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21 views

Branes without Fayet-Iliopoulos term

Often D-brane effective actions are given as (let's take D3-branes) $$ S=-T\int d^4x \sqrt{-det(g_{mn}+2\pi\alpha'F_{mn})}. $$ After expansion in $2\pi\alpha'$ there is a constant Fayet-Iliopoulos ...
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88 views

What happens to the $U(1)$ factor in the $U(N)$ SYM gauge group of the AdS/CFT correspondence?

I'm learning about the AdS/CFT correspondence. I know that from the open string perspective, the dynamics on a stack of $N$ coincident $D3$-branes is given by a $\mathcal{N} = 4$ Super Yang Mills ...
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37 views

Differentiating D3 brane worldvolume theories with NS5 brane and NS5 antibrane boundary conditions

In 'Supersymmetric Boundary Conditions in N=4 Super Yang-Mills Theory', Gaiotto and Witten derive boundary conditions for the worldvolume theory of the D3 brane. In particular the boundary conditions (...
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68 views

Transformation algebra of supersymmetry transformation

Given supersmmetry transformation: $$δX^\mu = i\barξψ^\mu.δψ^\mu = ξγ^a(∂_aX^\mu-\frac i2\barχ_a ψ^\mu). δχ_a = 2 D_aξ.$$ How to calculate the transformation algebra of $X^\mu$ and $\psi^\mu$? ...
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31 views

A generalized Veneziano formula for p-branes?

The rise of string theory as a theory of quantum gravity is in debt to G. Veneziano and his formula for the string scattering in terms of Euler beta function. Could a generalization of that formula, ...
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Lattice model realization of $SU(2)$ WZW model at level $k$?

Is there any lattice model realization of the following model: $c=1$ boson at the self-dual radius, or the $SU(2)$ WZW model at $k=1$. This is a question inspired by: Orbifolds of the $c =1$ ...
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1answer
73 views

Number of strings? [duplicate]

Is each particle associated with an unique string and where exactly is the string located, if it's vibration produces the appearance of a particle? What I mean is if I see an electron, does it have an ...
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59 views

Symmetries on String theory

Recently I was watching and reading about String theory, M-theory and the supersymmetry, when I remembered one question that I had while reading 'The Elegant Universe' by Brian Greene that is: why do ...
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Partition function computation on a Riemannian Manifold

This discussion comes from Chapter 10, Mirror Symmetry. I am given a Riemannian manifold $M$, and a classical (Euclidean) theory: $$(1)\quad S_E={\int}_0^\beta d\tau\space\Bigl(\frac{1}{2}g_{ij}{\dot{...
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Superstrings and supermembranes withouth the maximal spin constraint

Can supermembranes exist in higher dimensional superspaces if we admit higher spin fields?
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46 views

Are there any practical implications of string theory? [duplicate]

In my understanding, Strings theory tries to establish a functional model explaining how the world works. What are some practical applications of string theory? Would a solution to one of the ...
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155 views

Diffeomorphism invariance of scattering amplitude in bosonic string theory

It is mentioned in Polchinski's book (vol 1) that the diffeomorphism invariance of the scattering amplitude (see Polchinski, vol 1, eq 5.3.9) follows from the equation of motion of $b_{ab}$ (see ...
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76 views

Emergent physics in the gap between the Planck scale and the “size” of quarks [closed]

The smallest probed length scale to date is around $\Delta x \approx 10^{-18} m$ (see here). If we compare this to the Planck scale of $\Delta x \approx 10^{-35} m$ we are left with almost 20 orders ...
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306 views

String behavior in electron orbitals?

It feels like this should be a incredibly easy question to find an answer to, but I’m coming up zeroes in my search - if I’ve overlooked a parallel question please feel free to close this. ...
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Weyl anomaly in 2d CFT (string theory lectures by D.Tong)

In his lectures on String Theory (http://www.damtp.cam.ac.uk/user/tong/string.html), Tong gives a proof of the Weyl anomaly, using equation $(4.36)$. It seems wrong to me. Here he uses the OPE ...
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Effective low energy actions in string cosmology

I wonder why can SUGRA actions be used in string cosmology, since in some cases they are used to model big bang scenarios (for example the pre big bang scenario in chapter 4 of Gasperini's "Elements ...
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224 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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82 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
84 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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56 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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71 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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379 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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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
93 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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47 views

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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1answer
59 views

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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1answer
84 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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47 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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173 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
184 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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211 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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174 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
118 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
150 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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39 views

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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26 views

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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154 views

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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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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160 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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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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343 views

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
72 views

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
404 views

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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87 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 ...