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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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Is string theory inconsistent with the Standard Model of Elementary Particles?

According to (super)string theory, each fundamental particle represents a different vibrational mode of a relativistic string and each type of vibration pattern represents a different particle. But ...
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1answer
21 views

Mass formula for open string with mixed boundary conditions

I want to give an expression for the mass formula of an open string with has Neumannn condtion in $m$ directions and Dirichlet in $n$ directions $X^{i}(\sigma ^{1}=0)=x_{0}^{i}, X^{i}(\sigma ^{1}=\pi)=...
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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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63 views
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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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1answer
58 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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1answer
28 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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1answer
23 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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1answer
33 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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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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1answer
43 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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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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1answer
55 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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160 views

Supersymmetry and reparametrization invariance of superstring action

Section $4.3.5$ Superstring action and its symmetries, Page$229$ Superstring theory by Green, Schwarz and Witten. $S_1=-\frac1{2π} ∫d^2σ\ eh^{αβ}∂_αX^μ∂_βX_μ.\quad S_2=\frac i{2π}∫d^2σ\ e\barψ^μρ^α∇...
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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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40 views

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
68 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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39 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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What is so special about strings in string theory? [duplicate]

I mean to say that why have we kept ourselves stuck at strings. If strings explained stuff that particles couldn't a membrane explain more physical phenomena? I have just started learning about string ...
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0answers
34 views

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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16 views

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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40 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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2answers
98 views

Where did the idea that there *might* be magnetic monopoles come from?

I know that we declare that there exist no magnetic monopoles. I see it all the time in my E&M class. $$\vec{\nabla}\cdot\vec{B}=0$$ So there exists no point for $\vec{B}$ to originate from and no ...
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0answers
70 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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1answer
60 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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1answer
210 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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2answers
190 views

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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1answer
30 views

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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1answer
201 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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0answers
73 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
68 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
43 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
58 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
188 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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0answers
60 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
66 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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0answers
35 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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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
49 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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0answers
19 views

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
74 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
41 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
81 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
76 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
123 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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30 views

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
79 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
60 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
109 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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0answers
34 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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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 ...