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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Geometry of spacetime and spinor bilinears

In this paper (http://arxiv.org/abs/0704.0247) p.20, the author says in the section titled Geometry of spacetime the following: In order to obtain the spacetime geometry, we consider the spinor ...
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112 views

Orbifold actions and twist operators

A twist operator $\sigma$ is the operator that acts on the untwisted vacuum $|0\rangle$ to create a twisted vacuum $\sigma|0\rangle$. States belonging to the twisted sector of an orbifold are built on ...
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on fundamental 2D conductivity equation boundary value problem

Consider the following homogeneous boundary value problem for a function/potential $u(x,y)$ on the infinite strip $[-\infty,\infty]\times[0,\pi/4]$ w/positive periodic coefficient/nductivity ...
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51 views

Squashed spheres in general dimension

The point of this question is to help me find references regarding squashed spheres in general dimension. I am interested in the general theory of squashing for arbitrary dimension. All of the ...
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100 views

How to understand the relationship between these two geometrical structures?

During my study of quantum information processing, I occasionally meet two different geometrical structures: (a) The geometry of the Hilbert space of quantum state, where the superposition and ...
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47 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" ...
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101 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 ...
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94 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 ...
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59 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 ...
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47 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 ...
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57 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 ...
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98 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 ...
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73 views

Reparameterization invariance of strings

I'm working through Zweibach's First Course In String Theory. I'm stuck on a problem (16.1) where I need to show that the coupling Kalb-Ramond field to a worldsheet have the following transformation: ...
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44 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 ...
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77 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' = ...
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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 ...
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72 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 ...
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50 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 ...
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43 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 ...
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123 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 ...
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28 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?
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73 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. ...
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44 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 ...
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370 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 ...
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52 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 ...
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127 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 ...
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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 ...
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48 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 ...
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48 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 ...
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34 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 ...
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136 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 ...
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46 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 ...
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83 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 ...
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102 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 ...
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2answers
98 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 $G$ ...
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65 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 ...
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36 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 ...
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38 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 ...
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39 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 ($d+1$) ...
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169 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. ...
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56 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, ...
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74 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 ...
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56 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.
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61 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 ...
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91 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 ...
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3answers
204 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 ...
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41 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 ...
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326 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 ...
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3answers
250 views

Wick Theorem, ordering & CFT

I'm having a little trouble with correlation functions wick theorem and ordering in the context of OPE and CFT, for string theory. (1) My first question, the propagator is: $$<X(z) X(w)> = ...
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39 views

How are fermions describes by M theory?

How are particles like electrons described by M theory? Are they closed strings like gravitons, or are they open strings connected to an M2 or M5 brane?