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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2
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3answers
190 views

What is the reason/significance of using $ \sum\limits_{n=1}^{\infty}n\rightarrow-\frac{1}{12}$?

What is the reason/significance of using a trick equation in the Volume I - String Theory - Joseph Polchinsky? I have no doubts at all that the author knows extremely well the subject and that this ...
0
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1answer
93 views

What are susy transformations for N=2 sugra?

Killing spinor equations are equations that result from supersymmetric transformations. One example of those is for example is in $N=2$ Supergravity theories. As suggested by some books and papers on ...
4
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0answers
42 views

Brane interactions?

In particle physics, in QFT's, interactions come from the interaction piece in the Lagrangian (action). In string theory, waiting for a complete formulation of SFT, we have to add "by hand" ...
3
votes
1answer
69 views

What is the relationship between a brane, a manifold, and a space?

I've read many ways to define manifold; one way is to define it as a type of mathematical space (a type of topological space to be exact). All of the definitions that I've seen for brane, on the ...
1
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0answers
52 views

What sorts of problems does asymptotically safe gravity face as a potential quantum gravity solution?

I've recently read an article by Ethan Siegel over at Forbes (he also blogs at Starts with a Bang) on asymptotically safe gravity as a possible alternative to string theory. I read the author's blog ...
1
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1answer
43 views

$n=0$ mode Fourier expansion on string theory

I am quite baffled at what the $n=0$ mean in compactification, why is this mode important? I mean if $n=0$ was applied here we'd just be left with I know that (39) holds from (37), but I can't ...
0
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1answer
77 views

In M theory, what size are the branes/D branes?

In string theory strings are around Planck length, but how big are the D branes in M theory? Can we see them with the LHC?
1
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1answer
49 views

Globally defined solutions in bc CFT system

Consider $bc$-system which is 2-dimensional CFT of fermions: $S = \int_\Sigma d^2 z \ b \bar{\partial} c + h.c. $ where $\Sigma$ - 2-dimensional manifold of genus $p$, fields $b, c$ have ...
3
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0answers
82 views

Confusion on Polchinski P.67

I am reading Polchinski's String Theory Volume I. While I am learning the basics of string scatterings in Ch.3, I went back to chapter 2 and review the part of vertex operators. However, I found that ...
2
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0answers
74 views

How to find explicit QFT particles from a heterotic String theorie partition function

Starting with a SUSY $E_8$ x $E_8$ heterotic partition function: $ Z = - \frac{1}{8} \sum Z^8_x Z_4[^s_{s'}] Z_8[^t_{t'}] Z_8[^u_{u'}] $ where the sum is over all spin structures $s,t,u,s',t',u' = ...
0
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0answers
40 views

Why is the formulation of M(embrane) theory so hard? [duplicate]

The formulation of String theory is fairly straight forward in that the action is just the world-sheet area of a string. Then you can add supersymmetry in various ways. Finally you add some ghosts to ...
0
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0answers
26 views

String spreading?

What is 'string spreading' (in the context of string theory)? Does it have implications for the observability of post-classical effective field theory of gravity terms near macroscopic black hole ...
0
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1answer
62 views

Multiparticle States in String Theory

I am new to string theory and I hope that the following question, if not actually deep, may provoke answers that might not only be useful to me but also to other newcomers: I believe to have ...
1
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0answers
49 views

How to visualize a sphere bundle?

In the paper ``Gravitational Anomaly Cancellation for M Theory Fivebranes", the authors consider removing a tubular region of radius $\epsilon$ around the M5 brane (in order to make sense of the three ...
2
votes
1answer
144 views

Is M-Theory and 11D Supergravity the same thing?

Is M-Theory and 11D Supergravity the same thing? Reading Hawking, he uses 11D Supergravity and M-Theory interchangeably. ...
3
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1answer
61 views

Different OPE channels in bootstrap

Can someone quickly explain what exactly are those different channels (namely s,t,u) in OPE expansions frequently used in conformal bootstrap. Explanation with a simple example will be really helpful. ...
1
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0answers
38 views

Boundary condition for holographic Green's function

I understand that to obtain retarded Green's function using AdS/CFT one needs to put ingoing wave boundary condition at the horizon, when one is considering a finite temperature system. For system ...
2
votes
1answer
78 views

What exactly is a fundamental string as opposed to a D-string?

What exactly is a "fundamental string" in string theory? For bosonic string theory we have the bosonic string inside a 26-dimensional target space. Introducing supersymmetry, we have the ...
3
votes
1answer
112 views

What is the meaning of the UV =? IR statement in String theory

I was looking through these notes http://www.damtp.cam.ac.uk/user/tong/string/six.pdf and on page 146 it says "This corresponds to the fact that any putative UV divergence of string theory can always ...
5
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4answers
7k 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? ...
1
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1answer
27 views

Why will a Fourier transform of a pickup placed at the middle of a string only result in odd harmonics?

My physics teacher explained a lot of information about strings but he never went in depth with my question. What happens to the even harmonics and why are the odd ones the only ones picked up?
2
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0answers
40 views

What are the definitions and the differences between string “background” and string “vacuum”?

In cosmology one studies perturbations around FRW metric classically (pure GR, we say that we perturbe the FWR "background"). In QFT we have perturbation theory quantistically (we expand around a ...
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?
1
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3answers
347 views

The size of extra dimensions

Supposing we have a model, like the String one, which predicts (or requires) $N$ spacetimes dimensions, for the precision let's talk only about space dimensions. What is the process, the rule or the ...
3
votes
0answers
48 views

Fluctuating string in AdS black hole

People frequently use fluctuating string in AdS black hole (see 1,2,3 etc) to study dynamics of a "free external quark" in quark-gluon-plasma (QGP) at finite temperature. The background black hole ...
1
vote
2answers
94 views

Is it possible to calculate the shape of extra dimensions?

According to Brian Greene it is possible to calculate the physical constants from the shape of the extra dimensions. Is it possible to do the inverse, so predict the shape of these dimensions from the ...
1
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0answers
17 views

Target space Lorentz symmetry of superstrings in noncritical dimensions

Is the target space Lorentz symmetry of noncritical strings ($D \neq 26$) or superstrings ($D \neq 10$) broken or is it not? Naive arguments suggest that the mentioned anomaly does not exist, since ...
1
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0answers
45 views

Where does E8 come from in M-Theory?

Where does the E8 symmetry comes from in M-Theory? For example when you compactify one of the dimensions on a line you get E8xE8 heterotic string theory. Or if you compactify 11D Supergravity ...
1
vote
1answer
42 views

Why did the inflation era not produce decompactification of the extra dimensions of string theory?

My question is undoubtedly naive, due to lack of background, but any answers, or simply comments with short explanations of my incorrect assumptions, would be appreciated. I must point out this ...
1
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1answer
30 views

Constant in Regge trajectory

The Regge trajectory in QCD is given by $$m=\sqrt{\frac{J}{\alpha}-\alpha_0},$$ where $m$ is the mass and $J$ is the angular momentum of the hadrons, $\alpha=(4\pi\sigma)^{-1}$ is the inverse QCD ...
2
votes
1answer
568 views

General Relativity - Einstein field equation and quantum field theory

Einstein field equation has many solutions. Out of them, is there any solution that is incompatible with quantum field theory? Also, what solutions of Einstein field equation would be incompatible ...
2
votes
2answers
64 views

Orbifold with discrete torsion

I'm trying to understand some of the early works of Vafa and Witten [1-3]. The way I look at orbifolds is they are the quotient space $M/G$. This is simply a quotient manifold when the action of $G$ ...
0
votes
0answers
40 views

Could the gauged six-dimensional chiral supergravity model explain dark matter, as well as gravity?

I was reading a paper on 6-dimensional supergravity http://www.math.ist.utl.pt/~strings/MTST2/audio/pope1.pdf after watching a sixty symbols video on it https://www.youtube.com/watch?v=O4eXU8VHM2g ...
1
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1answer
78 views

What's between the branes?

So I'm doing my best to explain M Theory to some friends... Mind you, I'm no expert... When we finally got past the obstacle of more than three dimensions... which can be difficult for folks who ...
2
votes
0answers
92 views

Undergrad in QFT/GR looking to do string theory Ph.D [closed]

I am currently a third year undergrad in physics who is currently taking QFT and GR. I took these classes just out of pure interest in the subjects but I find that my mind is being blown almost every ...
1
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0answers
46 views

Naked Singularity and AdS/CFT

I am a bit confused about the status of naked singularities that appear in black hole physics and more so in the context of AdS/CFT. Here is what I know about this in brief. For a charged ...
0
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1answer
33 views

Modes of a quantum string

It has been said that particle identity relates to vibrational modes of its quantum string. However, I have not seen the identification of a particle related to a specific vibrational mode. At a ...
21
votes
1answer
4k views

Introduction to AdS/CFT

AdS/CFT seems like a really hot topic and I'd like to start reading about. I am looking for the best introduction at my level, i.e. I have a background in QFT, CFT and general relativity at the level ...
1
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0answers
35 views

Supersymmetry breaking and normalizable zero modes

Why does supersymmetry always lead to normalizable zero modes? For example, it is stated in the paper by Michelson and Kaplan (http://arxiv.org/abs/hep-th/9510053) that we can assume, without loss of ...
3
votes
0answers
142 views

Estimating volume of moduli space of genus-g Riemann surface with n marked points

I wanted to know how can I estimate the volume of the moduli space of a Riemann surface of genus $g$ and having $n$ marked points. I am reading some old string theory papers which discuss divergences ...
2
votes
0answers
35 views

Near horizon limit of near-extreamal black brane

It is known that the near horizon limit of a ($d+1$) dimensional extremal charged black hole (BH) is $AdS_2\times S^{d-1}$. I was looking at this paper by Faulkner et al. They consider a ($d+1$) ...
1
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1answer
52 views

What would happen if two branes collided and stuck together?

There is a theory that the universe began when two "branes" bumped each other, creating the energy that sparked the beginning of our universe. What if instead of separating, they actually stuck, ...
7
votes
3answers
594 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 ...
1
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0answers
54 views

Linear Dilaton CFT

I´m doing the exercises on the Tong lectures of String Theory, in particular Problem Sheet 2: Consider the tensor: $T(z) = \frac{-1}{\alpha '} :\partial X(z) \partial X(z): - Q \partial^2 X$. By ...
-1
votes
2answers
74 views

How many dimensions our universe consists of?

Omnibus science convinces us in that we live within three-dimensional space. The coordinate measuring units XYZ. Quite controversial, but there are some legitimate theories clarifying why we live in ...
3
votes
0answers
55 views

Can two closed strings in string theory be tangled?

Can two closed strings in string theory be tangled? Like two elements in an iron chain linked together by one going through the other.
0
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0answers
40 views

DBI action with Weyl Invariance

The DBI action, given by $S_{Dp}=-T_p\int d^{p+1}\xi e^{-\phi(\xi)}\sqrt{-\textrm{det}\left(G_{ab}(\xi)+B_{ab}(\xi)+2\pi{\alpha}'F_{ab}(\xi)\right)}$ is diff and Poincaré invariant. I want to ...
9
votes
3answers
966 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 ...
173
votes
11answers
24k views

What experiment would disprove string theory?

I know that there's big controversy between two groups of physicists: those who support string theory (most of them, I think) and those who oppose it. One of the arguments of the second group is ...
1
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0answers
37 views

M-theory compactified on $S^4$

I am trying to understand what happens to the 32 supersymmetries of M-theory when it is compactified on $S^4$, with the other seven dimensions being flat, e.g., $\mathbb{R^7}$, $\mathbb{R^6} \times ...