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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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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52 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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45 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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1answer
127 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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77 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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3answers
382 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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54 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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138 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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21 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 ...
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52 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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49 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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36 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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1answer
158 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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48 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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1answer
87 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 aren'...
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108 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
105 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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71 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 Reissner-...
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39 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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39 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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42 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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181 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. http://www.hawking.org.uk/quantum-cosmology-m-theory-and-the-anthropic-...
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58 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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82 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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74 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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100 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
208 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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42 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 S^...
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332 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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271 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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40 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?
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In M theory, is a baryon a D4 brane with three strings attached?

I've read in a few string theory documents, with 10d space time, that a baryon is a D4 brane with 3 strings attached (each being a quark), but what about in 11d M theory?
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92 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?
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49 views

M5 brane zero modes

The Euclidean M5 brane worldvolume has an anti self-dual 3-form and two negative chirality spinors. The spinors can couple to the SO(5) gauge fields of the normal bundle, but the 3-form cannot couple ...
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60 views

Trouble proving $\frac{1}{4\pi}\int_Md\tau\,d\sigma\,\sqrt{-\gamma}\,R$ is Weyl invariant

Consider the Polyakov action $$S[x^{\mu},\gamma_{ab}]=-\frac{1}{4\pi\alpha'}\int_M d\tau\,d\sigma\,\sqrt{-\gamma}\gamma^{ab}\partial_ax^{\mu}\partial_ax_{\mu}$$ Consider the case of a closed string. ...
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46 views

Why don't closed strings's world-sheets have boundaries?

I have been told that the world-sheet described by a closed string is a world-sheet without boundaries. On the contrary, the world-sheet described by an open string has boundaries. I do see why the ...
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264 views

Is electron/positron annihilation to two gravitons forbidden?

This follows from the question Can stress energy tensor vanish in general relativity?. What I'm really asking is whether electron/positron annihilation to two gravitons is allowed, but the obvious ...
3
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1answer
105 views

Regularization of the 1-dimensional Laplacian

Disclaimer: this is a technical question about regularization of functional determinants which comes from a person with (relatively) strong background in QFT, string theory and path integrals, who ...
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1answer
94 views

Physical interpretation of the creation operators in string theory?

Is there any way to describe phsycially which each creation operator $a^{(i)+}_{n}$ in string theory does to the ground state string? Here would be my guess (although it is likely to be totally wrong)...
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56 views

How to derive the effective action or Vertex generating functional of complex scalar field?

I am studying-self QFT. Recently, I am studying and trying to follow the calculation of the Ginzburg-Landau free energy functional of superconductor in this paper:http://arxiv.org/abs/hep-ph/0108256. ...
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47 views

In M theory, can a fundamental open string attach to a M5 brane?

I only saw a couple of pages online that showed this so i guess I'll ask on here, can fundamental open 1 string end on an M5 brane?
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1answer
53 views

Euler density of two-dimensional manifolds

I am asking this question after reading this post: What is Euler Density?. For a two dimensional manifold, the Euler density is given by: \begin{equation} E_2=2R_{1212} \end{equation} (note that $...
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1answer
178 views

In M Theory, what does the M5 brane look like?

In M theory, the fundamental 1 strings are made out of the compactification of an M2 brane. In String Theory: Volume 2, Superstring Theory and Beyond By Joseph Polchinski Pg. 204 He states that ...
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63 views

In M-theory, are strings created by membranes?

In M-theory there are 2- and 5-branes, but where are the one-dimensional strings which are responsible for all the particles? Can 5-branes turn into 1-dimensional strings due to compactification?
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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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213 views

Are virtual exchange particles real or just mathematical? [duplicate]

When an electron exchanges a virtual photon with another electron or proton, is the virtual photon a real particle or just a mathematical construct? In string theory, the force carrier particles of ...
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144 views

Sources that explain strings between two branes, where one brane ends on the other

I can't seem to find a source that explains what happens when there are strings between one brane and another brane, where one brane ends on the other brane. For example, consider a D3-brane ending on ...