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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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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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 ...
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76 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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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 ...
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76 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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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 ...
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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 $G$ ...
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44 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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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 ...
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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 ...
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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 ($d+1$) ...
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143 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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51 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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52 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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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.
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38 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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73 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
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 ...
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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 ...
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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 ...
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3answers
179 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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32 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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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?
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47 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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50 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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1answer
39 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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225 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 ...
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1answer
100 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
80 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 ...
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0answers
41 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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1answer
42 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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50 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
97 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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1answer
55 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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57 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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167 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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137 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 ...
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71 views

Background independent string theory

I don't really understand what one actually means when one says about doing string theory in a background independent way. Apparently B. Sathiapalan is the only person (as far as I know from ...
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1answer
50 views

Why does the Weyl transformation preserve angles in string theory?

The Weyl invariance symmetry of the Polyakov action is said to be considered as the invariance of the theory under a local change of scale which preserves the angles between all lines. However, why ...
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33 views

Mathematics involved in string theory [duplicate]

As an amateur mathematician and lover of the sciences I have a well working knowledge of classical mechanics, quantum mechanics, general relativity, quantization, and so on... But recently I've been ...
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1answer
156 views

Is string theory really science? [closed]

According to Karl Popper's theory of demarcation, science should be falsifiable but string theory is yet to be tested experimentally as It will require at least 19 TeV of energy to prove it which is ...
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32 views

Diiference between three squashed sphere and three sphere and number of susy

First I know that three sphere $S^3$ and squashed sphere $S_b^3$ \begin{align} S_{b}^{3} = \begin{array} & R^2 \times S_{r}, \quad r=b, \quad b\rightarrow 0 \\ R^2 \times S_{r}, \quad ...
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70 views

Why are WZW models interesting?

I realise this is a very broad question, but when I was studying for my thesis I randomly came across WZW models for a few times and I never quit understood them. So I understand that these models ...
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0answers
45 views

Hypermultiplet as BPS particles

In the third paragraph of page 7 of the paper arxiv:1112.3984 it mentions that we form a basis out of hypermultiplets on the charge lattice $\Gamma$. My questions are: In what sense do we form such ...
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1answer
95 views

M-theory and Mathematics [closed]

If the framework of M-theory is the right path for a unification of gravity with quantum mechanics, is it obligatory to believe that, at a certain level, reality is not just easily describable by ...
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54 views

Concerning topology of BPS states of the M5-brane

My question is about the M5-brane in M-theory. I would like to know whether the BPS states of the M5-brane worldvolume theory (especially the 1/2 BPS and 1/4 BPS ones) are independent of the topology ...
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17 views

Toroidal compactification and number of susy

In case of Tordial compactification, reference states page 13, A.Font et al, Introduction to string compactification, it does not reduce the number of real supercharges. I wonder why this happens. ...
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65 views

Fayet-Iliopolous Parameters from Separation of NS5-branes in $(x_{7}, x_{8}, x_{9})$: An ambiguity as to which gauge group the FI parameter belongs

hep-th/9611230v3, page 12 explains how, for a configuration of D3s along $(x_{1}, x_{2}, x_{6})$, and NS5's along $(x_{1}, x_{2}, x_{3}, x_{4}, x_{5})$, the Fayet-Iliopolous D-term coefficient $\zeta$ ...
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109 views

Can someone explain about M-theory? [closed]

Can someone explain about M-theory? I am very new to M-theory and string theory. I am very through with classical physics and little bits of quantum mechanics. Will you be able to explain why ...