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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15 views

Low-energy “effective measure” from superstrings?

There is obviously a gap in my knowledge of the origin of effective actions in string theory. As far as I understand it, the strategy is straightforward (at least in principle): Write down the ...
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1answer
25 views

Curvature of Weyl-rescaled metric from curvature of original metric

I'm trying to go from the low-energy effective action in the string-frame to the corresponding action in the Einstein frame. The action in the string frame has the form $$S = \frac{1}{(2\pi)^7 ...
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2answers
69 views

What does the “T” stand for in T-duality?

First of all, I am not a physicist. I'm a graduate math student and recently I came across the concept of T-duality. Actually I'm studying generalized complex geometry, which according to this paper ...
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53 views

1 + 2 + 3 … = -1/12 appears in bosonic string theory. Is this regularization method also used in superstring theories?

I found two previous posts on this, but no specific answer to my question. How does the sum of the series “1 + 2 + 3 + 4 + 5 + 6…” to infinity = “-1/12”? What areas of physics depend on the sum $1 + ...
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1answer
113 views

Calculus of variations and string theory

In Polchinski's String theory book, Vol 1., in chapter 1, p. 18, he is deriving the Lagrangian in the light cone gauge (that's not necessary to know in order to answer this question), and he gets ...
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52 views

Polyakov equation in the strings theory

In the equation of Polyakov there wouldn't be in our universe 10 or 11 dimensions but more (26) because it is referred to the bosonic theory. Are there any connections between this equation and the ...
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1answer
28 views

Why is the torus important for compactification in string theory? (aka much ado about the torus)

Why is the torus important in string theory and supergravity? To be specific, why does one care about something like compactification of Type IIB or IIA supergravity on a torus $T^5$, as opposed to ...
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1answer
33 views

Basic question about curved and flat indices, and the Dirac matrices on $S^5$

In discussing the Kaluza-Klein formalism for Type IIB Supergravity on $S^5$, or the AdS5xS5 compactification, one requires Killing spinors on $S^5$. I read that the Dirac matrices on $S^5$ satisfy ...
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2answers
93 views

Idea behind Compactified Boson

On p. 167 of his Conformal Field Theory, Di Francesco introduces "Compactified Boson". He says: The invariance of the free-boson Lagrangian [...] with respect to translations $\varphi(x) ...
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21 views

The low dimensional end of the brane scan

Common wisdom says that only the top dimensional part of the brane scan of Green-Schwarz super p-brane sigma models is quantum consistent (the critical strings and the M-branes). But by the results in ...
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1answer
69 views

$SO(p,1)$ transformation on black p-branes

I'm working on Blackfolds at the moment and I'm trying to boost-rotate( $SO(1,p)$ ) the p-brane $$ds^2=ds^2_{Sch}+\sum_{i=1}^p dz_i^2$$ Where $ds^2_{Sch}$ is the Schwarzschild metric in $N$ ...
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1answer
82 views

How to make a string theory without gravity?

Is there a way to take a string theory, and produce from it a string theory which does not contain gravity? I.e., effectively remove the graviton and it's states from the theory.
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1answer
45 views

What does it mean to “uplift” a supergravity solution to higher dimensions?

What does it mean to "uplift" a supergravity solution to higher dimensions? This is a common term used in the literature but I cannot understand it. A very common example is "uplifting d-dimensional ...
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1answer
62 views

Why is the universe 3D if the holographic principle says it's encoded in a its surface?

The way I understand the holographic principle is that everything in a 3D space can be thought of as living on the 2D boundary of that space. If that is the case, why does everything in the universe ...
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0answers
50 views

How does the sum of natural numbers arise in the derivation of critical string dimensions?

In the standard treatment of bosonic string theory the “heuristic” argument for the critical dimension goes as follows (see Ref. 1-4). Upon quantization the mass-squared operator becomes normal ...
3
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1answer
58 views

What is meant by the following divergent formula?

I have encountered the following formula a couple of times (in different physics contexts which I do not have a good understanding of) $$\int_{0}^\infty \frac{dt}{t}e^{-tx}=-\log x$$ Formally one ...
3
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1answer
59 views

Type IIB string theory is chiral. Do there exist non-chiral II SUGRA theories?

Type IIB string theory is chiral. Do there exist non-chiral $\mathcal{N}=2$ II SUGRA theories? The answer is apparently yes. Additionally how do we understand the fact that Type IIB SUGRA is chiral ...
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0answers
74 views

Why are there only 11 dimensions in M-theory? [duplicate]

Why is it that there are only 11 dimensions in M-theory?
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1answer
106 views

Why are right hand neutrinos unaffected by all forces except gravity

I'm curious as to something I read on Berkeley's website. Does anyone happen to know why, according to this model,right hand neutrinos are unaffected by all forces except gravity? (Model taken from ...
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0answers
17 views

How do we use the Killing spinors to determine the resulting supersymmetry conserved?

How do we exactly use the Killing spinors to determine the resulting supersymmetry conserved? Is there some nice "toy" example you could provide me with to see this and convince my self? And is there ...
2
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1answer
37 views

Decomposition of the gravitino into helicity $\pm \frac{3}{2}$ and $\pm \frac{1}{2}$ components

I'm reading this book on string theory. When they decompose two dimensional gravitino (formula 7.16) $$ \chi_\alpha = \frac{1}{2}\rho^\beta \rho_\alpha \chi_\beta + \frac{1}{2}\rho_\alpha \rho^\gamma ...
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0answers
16 views

What is the significance of self-duality and anti self-duality in supergravity?

So I see the terms "self-dual" and "anti self-dual" appear routinely in supergravity/string thery, e.g. the fact that Type IIB supergravity contains a real self-dual rank-5 antisymmetric tensor ...
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1answer
67 views
+50

Why does the non-linearity of the string action prohibit stretching due to strong excitations?

From 't Hooft's String Theory lecture notes (paraphrased): To understand hadronic particles as excited states of strings, we have to study the dynamical properties of these strings, and then ...
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1answer
59 views

D branes Ns brane and p-branes

It is now a common knowledge that "D-p branes are equivalent to p-branes" due to Polchinski's work. Note that D-p branes are objects in string theory and p-branes are objects in blackhole theory. So ...
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17 views

Correlation functions on $S^2$ (from OPE singularities)

Consider a closed string scattering (worldsheet topology $S^2$ sphere). Given that the OPE: $i \partial X^\mu(z) e^{ik X(w)} \sim \frac{k^\mu}{z - w} e^{ik X (w)} + ... \ \ , \ \ i \partial X^\mu (z) ...
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31 views

Fermion counting operator for open superstring

In Barton Zwiebach's A First Course in String Theory, in section 14.4, there's a fermion counting operator $(-1)^F$ which is supposed to give you $+1$ if the state is bosonic, or $-1$ if the state is ...
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1answer
42 views

How can extra (non-curled up) dimensions be hidden from us?

Wikipedia says: If extra dimensions exist, they must be hidden from us by some physical mechanism. One well-studied possibility is that the extra dimensions may be "curled up" at such tiny ...
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1answer
68 views

Compactified extra dimensions and symmetry

It's my understanding that M-Theory necessitates 11 space-time dimensions (10 spatial dimensions plus 1 time dimension) in order work mathematically. This appears to jar with reality, which only ...
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0answers
32 views

The limited Computing Capabilities of Space, Increased quantized info leads to time-dilation?

Are there any approaches to Special and General Relativity using space as a computing medium? With space having a maximum computing capability and time dilation as lag? Could this idea describe the ...
4
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3answers
471 views

Does the need for renormalization in QFT vanish once you use a more fundamental theory (e.g., string theory)?

It is often explained that renormalization arises in QFT because QFT is a low-energy effective theory that needs to be replaced by a more fundamental theory at higher energies/smaller distances. While ...
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0answers
30 views

SUSY preserved by an extended D-brane

There's a nice way to prove that for an extended D-brane half of SUSY is preserved, from perturbative string argument with SUSY Ward identities and the doubling trick (at least, at tree-level and ...
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0answers
25 views

Tadpole-free condition

Tadpole-free is a very important condition for perturbative string theory (which is equivalent to the theory to be expanded around the "right" vacuum). For simplicity, let's consider closed string ...
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25 views

What information do quiver gauge diagrams provide?

I am struggling to understand what the information one can extract by looking a quiver diagram for a quiver gauge theory is. I understand what quivers are but I cannot get some physical intuition and ...
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0answers
21 views

T-Duality for closed bosonic string: what is the difference between a graviphoton and a B-vector?

Consider the closed bosonic string in 26 dimensions, of which one physical dimension, say $X^{24}$ is compactified into a circle of radius $R$. The lowest lying massless states are the graviton, the ...
2
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0answers
63 views

What exactly does it mean to wrap a D-brane or a M-brane in a Riemann surface $\Sigma_g$?

What exactly does it mean to wrap a D-brane or an M-brane in a Riemann surface $\Sigma_g$ ($g$ is the genous)? Is there some mathematical statement? And why do we get various supersymmetric gauge ...
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0answers
70 views

Why string theorist use the following result? [duplicate]

$1+2+3.......$so on $ = -1/12.$ I have seen a few proofs of this result. And I hope most of you are familiar with them. Why string theorist use this ambiguous result in string theory, when assigning ...
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1answer
33 views

What exactly are the ADE type of gauge theories?

What exactly are the ADE type of (susy) gauge theories? What exactly we mean, intuitively, the ADE singularities? What are their relation to brane constructions and do you have any references one ...
4
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2answers
167 views

Why M-theory has only M2 and M5 branes?

Why M-theory has only M2 and M5 branes? In string theory, depending on the type one considers, you get all kind of D-branes. What is so special in M-theory that only allows 2 and 5 branes?
2
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1answer
26 views

Branes on a tip of a conifold; how to understand it?

I am not sure if this question makes sense "intuitively" but here it is. In Klebanov-Witten theory one puts branes on the tip of a cone over a Calabi-Yau manifold. My question is what does it mean to ...
3
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1answer
108 views

States in light cone string theory

Currently I'm trying to understand string theory in the light cone quantization. I just have had a look into Polchinski (Vol. 1, Introduction to the bosonic string), because – as far as I could see – ...
3
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0answers
37 views

Is the $\alpha'$ expansion in string theory an asymptotic expansion?

The low-energy bosonic effective actions of string theory lead to Einstein-Hilbert gravity, along with scalars and $p$-form Maxwell fields. For example, the action for type IIA string theory is $S = ...
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1answer
26 views

What does it mean the term “probe brane”?

What does it exactly mean the term "probe brane"? People say for example: We put a stack of N branes at some point and then a probe brane ..." How do they appear in AdS/CFT? Can you give me an ...
2
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1answer
51 views

How is a string different from a harmonic oscillator or a point?

I am reading String Theory and M-Theory: A Modern Introduction by Becker, Becker and Schwartz. I've tried to read this book before but not succeeded because I didn't know enough math or physics. This ...
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2answers
92 views

If a theory gets two predictions right, how likely it is that the rest of the predictions are true too? [closed]

The question lucidly defines what I am trying to inquire, so there is no need to elucidate it any further. Another question would be, General/Special Relativity has gotten some predictions right as ...
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0answers
51 views

What does string theory and loop quantum gravity say about the Planck Epoch and anything before the Big Bang?

General Relativity is known to commit suicide exuberantly at the planck epoch, and is unable to say anything further, whereas string theory and loop quantum gravity breathe well under these ...
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42 views

Lorentz violation in String theory

First of all, why are there so many researches to find Lorentz violation? Are there some models of (super-)string theory that include Lorentz violation at some scale?
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1answer
46 views

Extended SuSy from the kappa-Symmetry WZW terms

In José de Azcárraga, Jerome Gauntlett, J.M. Izquierdo, Paul Townsend, Topological Extensions of the Supersymmetry Algebra for Extended Objects, Phys.Rev.Lett. 63 (1989) 2443 (spire) it was ...
3
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0answers
37 views

Supergravity prerequisites for branes in string theory [duplicate]

I have a one-semester background in string theory (bosonic string theory, the NSR string, conformal field theory), but I have not taken any full length courses on supersymmetry and supergravity. I'm ...
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26 views

Available material on Giant Gravitons

I am looking for a pedagogical introduction to giant gravitons (if one exists!). I have basic string theory/SUSY knowledge but no introduction to AdS/CFT. (Do I need to do some reading on AdS/CFT ...
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1answer
247 views

Noether currents in QFT

I am trying to organize my knowledge of Noether's theorem in QFT. There are several questions I would like to have an answer to. In classical field theory, Noether's theorem states that for each ...