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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46 views

Why is energy minimized over the string landscape?

As understand it, the 4D string landscape is a function that assigns an energy to every possible compactification of the 6 small spatial dimensions. We expect our universe to lie in a local energy ...
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0answers
57 views

Conformal group in 2D being a subgroup of Diff/Weyl - Polchinksi's 'String Theory' [on hold]

In the appendix on page 364 of 'String Theory', Polchinski defines the conformal group (Conf) in two dimensions to be the set of all holomorphic maps. On page 85 he explains how Conf is a subgroup of ...
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0answers
18 views

What does “Field theory limit” means in D/M-branes or supergravity theories? [on hold]

What does "Field theory limit" means in D/M-branes or supergravity theories? Reading some papers related with D/M-branes, they often mention field theory limit, $i.e$, limit of $\alpha\rightarrow 0$,...
1
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1answer
61 views

String Theory Vs. Holographic Theory of the Universe. Compatibility [on hold]

String Theory claims strings to be one dimensional objects vs. dimensionless point particles of the Standard Model. String Theory also needs 10 or possibly more spatial dimensions to operate in. ...
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0answers
122 views
+50

Zeno effect in quantum gravity?

Given that "the quantum zeno effect can "freeze" the evolution of the system by measuring it frequently enough in its known initial state." Is there any equivalent/similar Zeno effect in quantum ...
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0answers
37 views

Force and dimension is the same? [on hold]

I read somewhere that maybe we have 10 dimensions. We know that we have four dimensions (3 dimensions of space plus one of time). There are also four forces: gravity, electromagnetism, the strong ...
6
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1answer
58 views

What keeps strings in their proper “shape” despite their enormous inherent tension?

Here is an extract from a great answer by Luboš Motl to this question: Tension in Strings Because the string tension is not far from the Planck tension - one Planck energy per one Planck length 10$...
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1answer
51 views

Spectral covers and a specific exact short sequence

I have a question about the spectral cover construction of Friedman, Morgan, and Witten (typically used to map a description in heterotic string theory into F-theory). I realise this is a highly ...
2
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2answers
356 views

What's smaller: a neutrino, or a string from string theory [on hold]

I've recently read an article that stated "If an atom were as big as the solar system, a neutrino would be the size of a golf ball". I watch the science channel, and on (I believe) the show How the ...
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1answer
57 views

Doesn't quantum uncertainty disprove string theory? [duplicate]

String theory states that the oscillations of little strings are responsible for all the particles in and the evolution of the universe. The specific type of particle created by a string depends on ...
8
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2answers
283 views

Why are the Nambu-Goto action and Polyakov action equivalent at quantum level?

It's a well known elementary fact that the Nambu-Goto action $$S_{NG} = T \int d \tau d \sigma \sqrt{ (\partial_{\tau} X^{\mu})^2 (\partial_{\sigma} X^{\mu})^2 - (\partial_{\sigma} X^{\mu} \partial_{\...
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1answer
92 views

AdS/CFT-duality: How does the $U(1)$ decouple form the $U(N)$?

A stack of N coincident D3-branes on its world-volume describe, at the lowest order in $\alpha'$ and in absence of non-trivial background fields, a supersymmetric $U(N)$ gauge theory as explained in ...
5
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1answer
242 views

Has Sen quantized superstring fields?

Today I saw a paper by Ashoke Sen titled "BV Master Action for Heterotic and Type II String Field Theories". Is it really the "quantization" of superstring fields for the first time? What can be its ...
2
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1answer
129 views

Normal Ordering in String Theory: Polchinsky vs. all others

Polchinsky defines normal ordering in string theory as: $$:X^\mu(z,\bar z)X^\nu(w,\bar w): = X^\mu(z,\bar z) X^\nu(w, \bar w) + \frac{\alpha'}{2} \eta^{\mu\nu} \log |z-w|^2$$ and for more ...
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0answers
22 views

Moduli space of torus compactifications

I am trying to understand some general statements made in the lecture notes by Vafa entitled "Lectures on Strings and Dualities" concerning toroidal compactifications (arXiv:hep-th/9702201). Question ...
6
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2answers
323 views

Why does the non-linearity of the string action prohibit stretching due to strong excitations?

From 't Hooft's String Theory lecture notes on page 8 (paraphrased): To understand hadronic particles as excited states of strings, we have to study the dynamical properties of these strings, and ...
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0answers
65 views

Connection between Veneziano amplitude and Regge amplitude

I have tried to read about Regge theory, and I continue to run my head against the Veneziano formula, which is said to produce correct Regge trajectories by eg. t'Hooft at page 6 here: http://www....
3
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0answers
83 views

Clarification on the 11 dimension in the M-theory [closed]

In the book the Grand Design by Stephen Hawking, he wrote about the M-theory, and how in that theory it has 11 dimensions. I do not quite get that, so can someone explain it to me a little bit. I ...
2
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2answers
67 views

Does M theory have open strings?

M theory combines all string theories, however, some contain open strings but other do not. So what does M theory have to say about this?
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2answers
135 views

How exactly does string theory make general relativity and quantum mechanics compatible?

Correct me if I'm wrong, but the reason that quantum mechanics and general relativity are incompatible is because the quantum foam at Planck scales renders space-time discontinuous and doesn't allow ...
7
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5answers
9k views

Why does string theory require 9 dimensions of space and one dimension of time?

String theorists say that there are many more dimensions out there, but they are too small to be detected. However, I do not understand why there are ten dimensions and not just any other number? ...
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0answers
47 views

Why do strings need 9+1=10 spacetime dimensions to exist? [duplicate]

Why do strings need 9+1=10 spacetime dimensions according to previous theory, or equivalently, 11 dimensions as per M-theory? Why cannot they exist in the 4-dimensional world?
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2answers
46 views

Given a metric of a torus can we measure it's thickness?

What I mean is, if you have a metric of a torus $T_2$, and you want to distinguish between say very thin stringy tori and very thick tori with the same surface area, is there a nice formula for this ...
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4answers
1k views

Space-time in String Theory

I would like to understand how Physicists think of space-time in the context of String Theory. I understand that there are $3$ large space dimensions, a time dimension, and $6$ or $7$ (or $22$) extra ...
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2answers
711 views

S-Matrix in $\mathcal{N}=4$ Super-Yang Mills

This is a general question, but what is meant when people refer to the S-Matrix of $\mathcal{N}=4$ Super Yang Mills? The way I understood it is the S-Matrix is only well defined for theories with a ...
6
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2answers
516 views

Sparticles: Relationship to supersymmetry and dark matter?

I was attempting to read this paper after watching a show with Brian Greene. As I understand it, sparticles are a prediction of supersymetry, so I was wondering: Wouldn't the discovery of ...
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1answer
139 views

Review of String Field Theory

Could anybody suggest the comprehensive review of String Field Theory? Original papers are lengthy and it would take quite a long time to read them all.
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1answer
169 views

Generalized spin connection and dreibein in higher spin gravity

I am studying 3D higher spin gravity and I would like to know the mathematical and physical meaning of generalized spin connection and generalized dreibein that appear in this theory. It is well known ...
2
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1answer
50 views

Nambu-Goto and Polyakov Actions

This might be a little bit of a technical question, so bear with me. Ok, so from string theory we know that the action for a relativistic string is found from the worldsheet when we embed the string ...
5
votes
3answers
134 views

Does string theory explain the existence of 3 generations of quarks/leptons?

I am wondering whether string theory explains the existence of 3 families of quarks/leptons or not. I have a very limited understanding of string theory, as of now, and I have a mathematical ...
2
votes
1answer
56 views

Exchanging a local operator with a path integral

I am reading a paper by J. Polchinski, called "What is string theory", hep-th/9411028. In eq. 1.1.9, and the line before it, the author seems to have used: $$\langle \partial_z \partial_{\bar{z}} X(z,...
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0answers
62 views

Does string theory predict QFT? [duplicate]

Does string theory predict QFT? Or is it only consistent with it? Or is it build-in from the start?
3
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1answer
384 views

Reduction of Nambu Goto action to true degrees of freedom

First consider the particle $$S=m\int\sqrt{-\dot{X}^2}d\tau$$ if you choose the static gauge $\tau=X^0$ and replace it in the action you get $$=m\int\sqrt{1-\dot{X}^j\dot{X}^j}d\tau$$ So now, you ...
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0answers
106 views

Are strings in string theory actually little black holes? [closed]

I sometimes read that strings in string theory are actually little black holes, or can be interpreted that way. Is this true? How is that consistent with that the particle that a string represents ...
6
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1answer
156 views

Theories that predict the number of space-time dimensions

My impression in that most theories assume three spatial dimensions and one temporal dimension, though could in principle be formulated in others numbers of dimensions without inconsistencies. I know, ...
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1answer
69 views

What is the difference between worldsheet supersymmetry and spacetime supersymmetry?

What is the difference between worldsheet supersymmetry and spacetime supersymmetry? For worldline formulation of fermions quantum mechanics, there is a supersymmetry. But the corresponding spacetime ...
3
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0answers
25 views

Multi-Cut Matrix Models

I have a question pertaining specifically to a one-matrix model with a multi-cut solution. The standard procedure is to take a polynomial superpotential $W(x)$. In the classical limit (analogous to $...
5
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2answers
147 views

What does string theory predict for the singularity inside a black hole?

The usual explanation for what's going on inside a black hole goes something like "General Relativity predicts a singularity with infinite curvature, but when matters gets so tightly compressed we ...
6
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2answers
254 views

From Quantum Mechanics to Quantum field theory to String theory?

Today during a very "unique" study session, I might have internalized why Quantum mechanics was not enough, and Quantum field theory makes sense. It seems the reasons are that When a potential is ...
0
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1answer
62 views

About the non-locality of gravitational energy 2

Gravitational energy is non-local which is essentially because of the equivalence principle. The equivalence principle says that you can always transform your frame so that you feel like in a ...
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0answers
38 views

OPE coefficents and commutation relations, and OPE with stress tensor

Basic question about conformal field theory: In a conformal field theory in $d\geq 3$ dimensions, what is the relation between commutation relations and OPE coefficients? In particular, because ...
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0answers
28 views

T-duality between $E_8 \times E_8$ and $\text{Spin(}32)/\mathbb{Z}_2$ heterotic strings at the $\sigma$-model level

I would like to understand how T-duality between the heterotic $E_8 \times E_8$ (HE) and heterotic $\textrm{Spin}(32)/\mathbb{Z}_2$ (HO) theories works, at the level of the worldsheet $\sigma$-model. ...
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votes
1answer
36 views

Do Quark confinement prevents proving strings? [closed]

In baryons like protons,neutrons;isolated quark doesn't exist due to quark confinement. We will need an infinite energy to pull quarks apart.Even if we try to pull them apart there will be pair ...
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0answers
35 views

Ramond-Ramond potential and field strenght

I have a doubt about R-R potential in Superstring theory. The known facts are (according many books, for example "Basic Concepts in String Theory" by R. Blumenhagen, D. Lüst and S. Theisen): in the ...
2
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0answers
37 views

Which supersymmetry principles make the axio-dilaton field in F-theory holomorphic?

I am following the lecture notes on F-theory by T. Weigand . On page 7 he states that when considering F-theory as the strong coupling limit of type IIB orientifolds with D-branes, the axio-dilaton ...
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1answer
49 views

How do comparatively larger particles arise from vibrations of infinitely smaller strings?

In String Theory, how can a string as infinitesimally small as the Planck length, manifest itself as a much larger and massive particle?
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1answer
92 views

What particles are closed strings? [closed]

In String Theory, I understand that gravitons are particles that are closed strings. Are there other particles that are manifested from closed strings?
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1answer
155 views

Superconformal approach to supergravity

In the book (Supergravity - Daniel Z.Freedman & Antoine Van Proeyen - Cambridge), there is (Chapters 16-17) a presentation of pure supergravity or supergravity with matter, from a superconformal ...
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1answer
53 views

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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1answer
42 views

What is the spin of the Kalb-Ramond field?

In bosonic string theory the massless states of the closed string are given by a rank 2 tensor, which is divided into its three irreducible spherical tensors: symmetric traceless, antisymmetric and ...