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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100 views

What is meant by open-string tachyon scattering amplitude?

It was said here that Veneziano derived: open-string tachyon scattering amplitude from principles of Regge theory and S-matrix theory and used the Euler beta-function to make all the critical ...
2
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0answers
27 views

Kalb-Ramond in T-duality

I'm working through a particular problem (Problem 17.4) in Zweibach's "A first course in string theory", because I'm trying to understand how the Kalb-Ramond field affects T-duality. The question ...
3
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1answer
78 views

Semi-infinite forms?

I am reading Vafa's paper 'Topological Mirros and Quantum Strings'. In this paper, the author says the Hilbert Space of a fermionic string theory corresponds to the space of semi-infinite forms on the ...
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0answers
25 views

Generally speaking, given two CFTs, how can we check that they are equivalent?

We can calculate their central charges. And beyond this, are there some other general approaches? Or we must find an isomorphism of operators between the two theories?
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2answers
234 views

Symmetry of the Polyakov action?

Let us look at the Polyakov action for a string moving in a spacetime with metric $g_{\mu \nu}(X)$:$$S_P = -{1\over{4\pi \alpha'}} \int d^2 \sigma \sqrt{-\gamma} \gamma^{ab} \partial_a X^\mu ...
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1answer
84 views
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86 views

Poincare Symmetry of Nambu-Goto action

How do I show invariance under the Poincare transformations of the action for a relativistic string, $$S=-\frac{1}{2 \pi \alpha'} \int{\text{d}^2 ...
3
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0answers
46 views

Tension of string-theory string

Can the tension of a given string in string theory be increased (by say interaction with other strings), or is it always fixed. I am trying to figure out if the energy of a string can be increased. ...
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0answers
29 views

What does black hole temperature mean? [duplicate]

From the title, the question is a bit open ended. Let me make it a bit simpler. 1. What region of the black hole has temperature? Is it the surface space? the region outside? . . . etc , any precise ...
5
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0answers
140 views

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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6answers
2k views

How is the double slit experiment modeled in contemporary physical theories?

Suppose I have the following double split experiment set up: a monochromatic electron source of low intensity, which we can model as emitting a single electron at a time with energy $T$. a ...
0
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1answer
51 views

What happens when an open string start to stretch in a full Neumann boundary scenario?

I'm only reading about string theory. I'm an undergraduate. I see that for a full Neumann boundary condition the ends of a relativist string travel at the speed of light. If they travel in opposite ...
5
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1answer
104 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 ...
4
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0answers
310 views

750 GeV diphoton resonance: KK graviton?

As everybody of you may know at LHC they found this probable resonance (https://cds.cern.ch/record/2114808, https://cds.cern.ch/record/2114853?ln=en). It may be a scalar or a KK graviton mode. Now, ...
2
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0answers
40 views

What are the difference between a black holes and a black branes? [closed]

I want to know the fundamental difference between a black hole and a black brane? What is the planar limit?
2
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1answer
39 views

Why are only certain fluxes allowed in 11D SUGRA?

In Type IIA/IIB string theory we can have various fluxes, such as the 3-form H-flux, and the various Ramond-Ramond fluxes in even/odd dimensions. In 11D SUGRA, however, the field content seems to ...
3
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0answers
83 views

Projective superspace: why extra bosonic coordinates

I'm studying the projective superspace formalism for N = 4 supersymmetric $\sigma$-models in two dimensions. My question is: why do we need the extra bosonic coordinates for the manifest action? I ...
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0answers
50 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 ...
2
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0answers
99 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 ...
4
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0answers
1k views

holographic principle and Wheeler's bag of gold

How is it possible to explain "bag of gold" spacetimes (see Marlof) such that the ideas are compatible with AdS/CFT and the holographic principle?
2
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3answers
202 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
99 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
45 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
91 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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0answers
58 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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1answer
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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1answer
88 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
56 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
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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0answers
75 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
votes
0answers
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 ...
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
votes
1answer
70 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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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
165 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. ...
2
votes
1answer
72 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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0answers
42 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
116 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
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 ...
6
votes
4answers
8k 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
vote
1answer
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?
2
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0answers
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 ...
7
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2answers
3k 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?
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vote
3answers
366 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
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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vote
2answers
121 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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0answers
20 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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0answers
47 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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1answer
47 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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1answer
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 ...