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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3answers
452 views

Is there any intuitive interpretation of compactification?

Obviously the question's title has an unspecified subtext: intuitive to me. Some background to pitch the discussion appropriately: I have a broad understanding, more qualitative than quantitative, of ...
7
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1answer
143 views

What is the concept of cosmic strings?

What is the concept of cosmic strings? Is it related to the strings in the string theory, and if it is, then how?
7
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1answer
137 views

Is the LEP B meson asymmetry evidence for higher dimensions and/or string theory?

According to this blog, new standard model calculations have changed the 3 sigma B meson forward and backward production asymmetry observed at LEP into two anomolies: A 2.5 sigma B meson production ...
7
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1answer
38 views

Low-energy gluodynamics as a string

Does anyone know of a (most likely heuristic) derivation of the use of the string sigma model action to model the soft gluonic interactions between color charges? I'm familiar with the classic ...
7
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1answer
366 views

Why does string theory (in case it is true ) have NO divergencies?

Why is string theory in 10 or 26 dimension not divergent? Due to the high number of spacetime dimension (10 or 26) it should have a lot of UV divergencies of the form $ \int k^{n}dk $ and gravity ...
7
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1answer
378 views

Graviton Emission from D-Branes

I'm working through Polchinski's book on string theory, and I ran into something that I don't think I understand. I'm hoping that someone who knows this stuff can help me out. Before calculating the ...
7
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1answer
227 views

Statistics and macrolocality in string theory

Take two identical closed strings, both tracing out exactly the same path in space. These two strings are coincident everywhere. Call this state I. Take a single closed string following exactly the ...
7
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1answer
88 views

Connection beween infinite gauge symmetries and UV finiteness

In e.g., http://arxiv.org/abs/arXiv:0712.3526 the author claims: Since the massless higher-spin field theories involve infinite-dimensional gauge symmetries, one expects that such theories may be ...
7
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1answer
254 views

Could string theory be an effective theory?

I know that many quantum field theories could be low-energy effective theories in String Theory (ST), but I've also read and heard that ST cannot itself be an effective theory. I suppose this has ...
7
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0answers
341 views

Duality between Euclidean time and finite temperature, QFT and quantum gravity, and AdS/CFT

The thoughts below have occurred to me, several years ago (since 200x), again and again, since I learn quantum field theory(QFT) and statistical mechanics, and later AdS/CFT. It is about the duality ...
7
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0answers
109 views

Topology-dependent groud state degeneracy of $B \wedge F + B \wedge B$ and $B \wedge F + B \wedge B \wedge B$

There are some examples of topological BF theory with extra terms allow it still being topological. See this Ref. paper In 4d (3+1D), we have the trace of: $$ \int\frac{k}{2\pi}\text{Tr}[B \wedge F + ...
7
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0answers
131 views

Moduli Stabilization in 6D Einstein-Maxwell theory - Fluxes and O3 planes

I'd like to do the maths for the moduli stabilization of 6D Einstein-Maxwell Gravity $$ S= \int d^6X \sqrt{-G_6}(M_6^4R_6[G_6]-M_6^2|F_2|^2), $$ where the 6D metric is specified by $$ ds^2 = ...
7
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0answers
149 views

Why is it hard to give a lattice definition of string theory?

In Polyakov's book, he explains that one possible way to compute the propagator for a point particle is to compute the lattice sum $\sum_{P_{x,x'}}\exp(-m_0L[P_{x,x'}])$, where the sum goes over all ...
7
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0answers
469 views

Can the laws of quantum mechanics be derived from a more fundamental theory? [closed]

String theory takes quantum mechanics and tries to make it compatible with gravity. If it turns out to be a theory of everything then would it explain why our world is described by the laws of quantum ...
7
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0answers
133 views

What is the state-of-the-art on spacelike singularities in string theory?

What lessons do we have from string theory regarding the fate of singularities in general relativity? What happens to black hole singularities? What happens to cosmological singularities? Which ...
7
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2answers
849 views

Global symmetries in quantum gravity

In several papers (including a recent one by Banks and Seiberg) people mention a "folk-theorem" about the impossibility to have global symmetries in a consistent theory of quantum gravity. I remember ...
7
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1answer
676 views

String theory and trace anomaly in semiclassical gravity?

what does string theory have to say about the trace anomaly in the expectation value of the stress energy tensor of massless quantum fields on a curved background and its interpretation as the ...
6
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1answer
3k views

Gabriele Veneziano, strong nuclear force and beta-function

Background to the question: From The History of String Theory: Gabriele Veneziano, a research fellow at CERN (a European particle accelerator lab) in 1968, observed a strange coincidence - many ...
6
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4answers
667 views

Measuring extra-dimensions

I have read and heard in a number of places that extra dimension might be as big as $x$ mm. What I'm wondering is the following: How is length assigned to these extra dimensions? I mean you can ...
6
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2answers
359 views

How does the full string theory potential look?

Is the full stringy potenetial (for which it is claimed to be 10^500 vacua) written down explicitly somewhere? Any references? Thanks, Dave
6
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1answer
90 views

Are there stable string theory vacua with non-minimal cosmological constant?

Naive reasoning suggests that a string theory vacuum with cosmological constant Lambda1 is always unstable as long as there is a string theory vacuum with cosmological constant Lambda2 < Lambda1 ...
6
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3answers
614 views

Is there a maximum number of types of elementary particles?

Doing a Google search i found a paper called The maximum number of elementary particles in a super symmetric extension of the standard model. It claims in the abstract that the upper bound is 84 (i ...
6
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2answers
340 views

How relevant is LHC to quantum gravity?

Premise: the LHC is obviously mapping unseen territory in high energies, and therefore it's always possible to imagine far out results. Excluding completely unexpected outcomes - is the LHC ...
6
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2answers
539 views

Why is a stack of N D-branes equivalent to an extremal black brane?

A stack of N D-branes can have open strings ending on them. There is a U(N) brane gauge field, and r adjoint Higgs fields, with r equal to the number of transverse spatial dimensions. The eigenvalues ...
6
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1answer
170 views

Decomposition of Representation Multiplication

How can the multiplication of spinor representations (of $SO(8)$) $8_+ \otimes 8_-$ be decomposed into $8_v \oplus 56_v$? Where can I read more about the decomposition rule of different ...
6
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3answers
450 views

Extending General Relativity with Kahler Manifolds?

Standard general relativity is based on Riemannian manifolds. However, the simplest extension of Riemannian manifolds seems to be Kahler manifolds, which have a complex (hermitian) structure, a ...
6
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2answers
1k views

Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon?

Does String theory say that spacetime is not fundamental but should be considered an emergent phenomenon? If so, can quantum mechanics describe the universe at high energies where there is no ...
6
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1answer
743 views

Why is E6 favored over E8 for GUT building?

What is the simplest explanation on why is E6 gauge group more favored as a group for Grand unified theory builders, while E8 is not? What about other exceptional groups? Which of them originate from ...
6
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3answers
423 views

SUSY's Critical role in String Theory

In many popsci articles it is claimed that String Theory (ST) birthed SUSY. Yet ST was originally invented as a bosons-only theory, that later on brought fermions into the fold. This was only ...
6
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1answer
276 views

Why are the even and odd Regge trajectories degenerate?

This is an old classic which I don't think ever got a clear answer. The Gribov-Froissart projection that gives the relativistic version of Regge trajectories treats even angular momentum differently ...
6
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1answer
388 views

Is integrability necessary for the Amplituhedron?

It is well known that there exist mappings between operators in N = 4 Super Yang–Mills and spin chain states making the theory Bethe Ansatz integrable. Is integrability a necessity for the ...
6
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1answer
183 views

A question about conformal transformation in Polchinski's string theory

I have one more stupid question in Polchinski's string theory book. P. 46, it is said It is convenient to take a basis of local operators that are eigenstates under rigid transformation (2.4.9) ...
6
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2answers
677 views

The General Relativity from String Theory Point of View [duplicate]

I have a hard time understand the statement that When you only look at the classical limit or classical physics, string theory exactly agrees with general relativity Because from what I know, ...
6
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2answers
251 views

Does the lack of modular nuclearity in string theory mean anything?

Nuclearity is a postulate in algebraic quantum field theory (AQFT). Basically, it says thermal states at any temperature always have a thermodynamic limit with extensive quantities. This is violated ...
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6answers
2k views

How is the double slit experiment modeled in contemporary physical theories?

Suppose I have the following double split experiment set up: a monochromatic electron source of low intensity, which we can model as emitting a single electron at a time with energy $T$. a ...
6
votes
2answers
264 views

How to check Einstein-like equations on their correspondence with the real world?

Physicists studying the grounds of physics and some mathematicians often come to a theories which are like a general-relativity, but do not coincide with it. Often these theories contradict the real ...
6
votes
2answers
343 views

Seiberg-Witten theory and Superconductivity

There seems to have some (deep) relation between Seiberg-Witten theory and superconductivity. e.g. this Witten paper. Q: Could someone introduce the relations between the twos both physically in ...
6
votes
1answer
249 views

How exactly are Calabi-Yau compactifications done?

To compactify 2 open dimensions to a torus, the method of identification written down for this example as $$ (x,y) \sim (x+2\pi R,y) $$ $$ (x,y) \sim (x, y+2\pi R) $$ can be applied. What are the ...
6
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1answer
476 views

Energy-momentum tensor of Bosonic Ghost Action in String Theory

When quantizing bosonic string theory by means of the path integral, one inverts the Faddeev-Popov determinant by going to Grassmann variables, yielding: $$ S_{\mathrm{ghosts}} = ...
6
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1answer
118 views

About Vanishing of BRST commutator in path integral

In Witten's paper Topological Quantum Field Theory, about formula (3.2), the property $<\{Q,\mathcal{O}\}>=0$ depends on the assertion that $Z_{\varepsilon}(\mathcal{O})= \int \mathcal{D}X ...
6
votes
4answers
1k views

What is background independence and how important is it?

What is background independence and how important is it? In order to be a theory of everything, will the final string-theory/m-theory have to be background independent? Does the current lack of ...
6
votes
1answer
114 views

“gauge fixed world-sheet action”

My question is in reference to the action in equation 4.130 of Becker, Becker and Schwartz. It reads as, $S_{matter}= \frac{1}{2\pi}\int (2\partial X^\mu \bar{\partial}X_\mu + \frac{1}{2}\psi^\mu ...
6
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3answers
966 views

Does string theory and preons exclude each other?

Does string theory contradict the theory of preons, especially the Harari-Shupe one?
6
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1answer
206 views

Can long strings always snap?

In quantum chromodynamics, long flux tubes will always snap because a quark-antiquark pair gets created from the vacuum, and hadronization results with a quark attached to each new end. In string ...
6
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1answer
1k views

Can/has string theory solved cosmological constant problem?

Can someone explain to me what the KKLT paper says, and what has and hasn't it achieved regarding the ability to construct solutions with a small positive or negative cosmological constant in string ...
6
votes
1answer
122 views

How do I deal with a quantum field in the denominator?

I am wondering how to deal with an expression like $$ \int d^4\theta \frac{1}{T + T^\dagger} \big( \dots \big) $$ If the denominator was of the form $1 + T + T^\dagger$, I could assume that $T \ll 1$ ...
6
votes
2answers
231 views

What happens if the holonomy group lies in $SU(2)$ for a CY 3-fold?

I am a mathematician and reading a physics paper about the holonomy group of Calabi-Yau 3-folds. In that paper, a Calabi-Yau 3-fold $X$ is defined as a compact 3-dimensional complex manifold with ...
6
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2answers
2k views

Is anti-gravity possible in theoretical physics?

Is anti-gravity possible in string theory? I have read some articles about scientists making assumptions about the existence of anti-gravity, but is it possible in string theory?
6
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1answer
368 views

Scherk-Schwarz and other compactifications?

I have been thinking about various types of compactifications and have been wondering if I have been understanding them, and how they all fit together, correctly. From my understanding, if we want ...
6
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1answer
131 views

Why is there no double counting of $s$- and $t$-channels in string theory?

In string theory for the four particle tree diagram exchange, why is there some mysterious crossing duality between the $s$- and $t$- and $u$-channels? Why isn't there a double counting in the Feynman ...