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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590 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
335 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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2answers
590 views

Derivation of the Polyakov Action

As is usually done when first presenting string theory, the Nambu-Goto Action, $$ S_{\text{NG}}:=-T\int d\tau d\sigma \sqrt{-g} $$ ($g:=\det (g_{\alpha \beta})$ is the induced metric on the ...
6
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1answer
85 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
567 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
329 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
2k views

Does String Theory disagree with General Relativity?

I would like to expand on what I mean by the title of this question to focus the answers. Normally whenever a theory (e.g. General Relativity) replaces another (e.g. Newtonian Gravity) there is a ...
6
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1answer
398 views

Topological ground state degeneracy of SU(N), SO(N), Sp(N) Chern-Simons theory

We know that level-k Abelian 2+1D Chern-Simons theory on the $T^2$ spatial torus gives ground state degeneracy($GSD$): $$GSD=k$$ How about $GSD$ on $T^2$ spatial torus of: SU(N)$_k$ level-k ...
6
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1answer
152 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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2answers
432 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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3answers
401 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
268 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
326 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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2answers
799 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
369 views

Conformal transformation equation

I am currently reading Kiritsis's string theory book, and something bugs in the CFT (fourth) chapter. He derives the equation that should satisfy an infinitesimal conformal transformation $x^{\mu} ...
6
votes
2answers
237 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 ...
6
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3answers
472 views

Why (in relatively non-technical terms) are Calabi-Yau manifolds favored for compactified dimensions in string theory?

I was hoping for an answer in general terms avoiding things like holonomy, Chern classes, Kahler manifolds, fibre bundles and terms of similar ilk. Simply, what are the compelling reasons for ...
6
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2answers
258 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
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2answers
290 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
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1answer
207 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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2answers
518 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
votes
1answer
108 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
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1answer
104 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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2answers
809 views

On black holes, Hawking radiation and gravitational atoms

Over the past hour or so I've been following one of my standard physics-based, wanders-through-the-internet. Specifically, I began by reviewing some details of dark energy theory but soon found myself ...
6
votes
1answer
200 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 ...
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1answer
849 views

Is Poincare recurrence relevant to our universe?

If the theory of everything indicates a singularity-free and finite universe, will Poincare recurrence be relevant to the universe? If so, is there any interesting physical consequence, e.g. in ...
6
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2answers
205 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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1answer
358 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
397 views

Vector and Spinor Representation in Ramond-Neveu-Schwarz Superstring Theory

I am learning Ramnond-Neveu-Schwarz Superstring theory (RNS theory). I often find the following notation, especially in the closed string spectrum etc.: $$\mathbf{8}_s,\mathbf{8}_v $$ And it is ...
6
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3answers
1k views

What should a physics undergrad aspiring to be a string theorist learn before grad school?

The question I guess is pretty clear. I am a physics undergrad wishing to pursue research in quantum gravity(string theory?). What are the subjects I should learn other than the usual compulsory ...
6
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1answer
277 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
votes
1answer
113 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 ...
6
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1answer
228 views

Why aren't D-branes and strings independent degrees of freedom?

A condensate of open strings with both ends attached to the same D-brane can be equivalent to a displacement of the D-brane with no open string condensate. A solution to the D-brane Born-Infeld ...
6
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1answer
232 views

The double-trace deformation effect in AdS/CFT

Let me use this paper as the reference for this. I want to understand better the argument at the bottom of page 6. If the bulk $AdS$ metric is written as $\frac{1}{r^2}(dr^2 + ...
6
votes
1answer
374 views

What does it mean to renormalize an effective field theory?

This is in reference to slide 19 of this talk "As always in Effective Field Theory, the theory becomes predictive when there are more observables than parameters" Can one explain what this exactly ...
6
votes
1answer
280 views

Light Front Dynamics and Infinite Momentum Frame

What is the the relationship between Light Front Dynamics (One of the forms of dynamics pioneered by Dirac), and the infinite momentum frame? In the literature, it is claimed that the two are very ...
6
votes
1answer
1k views

What is the essence of BCFW recursion techniques?

I have recently briefly read about new methods as the Britto-Cachazo-Feng-Witten (BCFW) on-shell recursion method. Can anybody please tell me about the essence of it? What does it mean for the ...
6
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1answer
274 views

Uniqueness of the 5 string theories

This question combines several sub-questions, the common theme being: why the known 5 string theories are unique? Firstly, regarding heterotic theory. I understand the only allowed gauge groups are ...
6
votes
1answer
125 views

Poisson structure on moduli space of CFTs

The moduli space of CFTs with central charge 26 forms the classical phase space of bosonic string theory, in some sense. Similarily the moduli space of SCFTs with central charge 10 forms the classical ...
6
votes
1answer
510 views

Is Weyl invariance absolutely necessary for string worldsheets?

The Polyakov action for a string worldsheet has Weyl invariance. In the conformal gauge augmented with Weyl gauge-fixing, we can always impose a flat worldsheet metric in Minkowski coordinates. The ...
6
votes
2answers
245 views

Decoupling of Holomorphic and Anti-holomorphic parts in 2D CFT

This maybe a very naive question. I have just started studying CFT, and I am confused by why we have two separate parts of everything in CFT (operator algebras and hilbert space), the holomorphic ...
6
votes
1answer
182 views

A question about Lorentz invariance of the Polyakov action

I have a super basic and stupid question about the Lorentz invariance of the Polyakov action (cannot skip the disclaimer..) $$S_p[X,\gamma]=-\frac{1}{4 \pi \alpha'} \int_{-\infty}^{\infty} d \tau ...
6
votes
4answers
536 views

Is String Theory a Field Theory?

Is String Theory a Field or Quantum Mechanical Theory of the String rather than a Particle? I should know this having studied this for a term, but we jumped into the deep end, without really ...
6
votes
1answer
74 views

References for phase-transitions in supersymmetric field theory

Apart from other reasons, recently my interest in this area got piqued when I heard an awesome lecture by Seiberg on the idea of meta-stable-supersymmetry-breaking. I am looking for references on ...
6
votes
1answer
386 views

Some questions about the BCFW reduction

I am trying to give a fast sketch of what the BCFW reduction does and embed within it some questions at the steps which I don't seem to understand clearly. The first bullet point is sort of a very ...
6
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1answer
111 views

Quantized coefficients of Chern-Simons action and F $\wedge$ F $\wedge \dots$

We know that for U(1) gauge field Chern-Simons action in 2+1 Dim(ension), we have an action $$ S=\alpha \int A \wedge dA $$ with $\alpha=k/(4\pi)$ for a proper level quantization. Here $k$ is the ...
6
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1answer
509 views

bc CFT Energy-momentum tensor from Noether's theorem

Following Polchinski's book (String Theory 1), we have the bc action : $$S = \frac{1}{2 \pi}\int~d^2z ~b\bar \partial c\tag{2.5.4}$$ where $b$ and $c$ have holomorphic weights $\lambda$ and $1- ...
6
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1answer
178 views

Critical dimension in quantization of p-branes

So I have what might be a fairly basic question, but my understanding that in the quantization of the the string, or the 1-brane, there are conditions on the number of spacetime dimensions to ensure ...
6
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1answer
366 views

Gravity duals to Navier Stokes and interpretation of non linear contributions

I have been reading the paper The Incompressible Non-Relativistic Navier-Stokes Equation from Gravity. In it they state, "An instability, if it occurs, must necessarily break a symmetry ... ...
6
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1answer
170 views

If a fundamental theory exibits e.g. a mirror symmetry, in what sense it the underlying geometry real?

Are the more recently discovered symmetries in string theory such that the theories based on mirroring geometries are absolutely the same from an observable point of view? I have mirror symmetry ...