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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5
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1answer
107 views

Where do $X_0^{-d}$ and $G'_r$ come from in Polchinski Eq. (6.2.13)?

I have a question about deriving Eq. (6.2.13) in Polchinski's string theory book volume I. It is claimed that Now consider the path integral with a product of tachyon vertex operators, ...
2
votes
0answers
48 views

Problem with OPE (from Polchinski) [on hold]

I was reading Polchinski, Vol. 2 pag 12, while I found (10.3.12a): $$ e^{iH(z)}e^{-iH(z)}=\frac{1}{2z} + i\partial H(0) + 2zT^H_B(0) + O(z^2).\tag{10.3.12a} $$ Now I tried to do the OPE, what I ...
0
votes
0answers
6 views

Superstring NS tachyon vertex operator

After reading some confusing chapter of various string theory book I'm trying to construct the Tachyon vertex operator for superstring theory. I know that this is removed after GSO projection, but for ...
1
vote
0answers
18 views

Correlator $bc$ system

I have da doubt with bc system. Polchinski says (2.5.10) $$ b(z)b(0)~=~O(z). \tag{2.5.10} $$ I tried to compute the correlation function With eom, using eq (2.5.6b) by Polchinki, removing the ...
1
vote
1answer
48 views

Polchinski Equation (10.4.7)

I'm having a problem to interpret eq. (10.4.7) in Polchinski: $$ \gamma(z)\delta(\gamma(0)) = O(z), \qquad \beta(z)\delta(\gamma(0)) = O(z^{-1}). $$ What does he mean by $\delta$? He tries to ...
2
votes
0answers
15 views

Connection between the M5 brane and (2, 0) superconformal field theory

I have read that the worldvolume theory of the M5 brane is a $(2, 0)$ superconformal field theory (SCFT). But I have also learnt from talks that the $(2, 0)$ theory lacks a Lagrangian description. ...
5
votes
3answers
917 views

Does string theory and preons exclude each other?

Does string theory contradict the theory of preons, especially the Harari-Shupe one?
2
votes
1answer
100 views

How is a string in string theory 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 ...
1
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0answers
15 views

Quantum corrections to holographic entanglement entropy

I was looking at this paper by Faulkner-Lewkowycz-Maldacena. They give a very interesting proposal of calculating one loop (i.e, 1/N) correction to EE from computing the EE between the bulk regions. ...
2
votes
0answers
22 views

Type I string theory on $K3 \times \mathbb T^2/\mathbb Z_2$ and the K3 orbifold limit

Consider Type IIB string theory with 4 O7-planes and 32 D7-branes on $K3 \times \mathbb T^2/\mathbb Z_2$. The K3 induces D3-charge on their world-volumes which can be cancelled by the introduction of ...
1
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0answers
21 views

D-brane tension of type I D9-branes after T-duality

Type I contains branes with a brane tension which is $\frac{1}{\sqrt 2}$ times that of type II branes. The reason is that, e.g., in the computation of the D9-D9 amplitude the open string is ...
1
vote
1answer
38 views

Conformal blocks in 2D CFTs

I have studied conformal field theories in two dimensions and I understand the basic idea behind conformal blocks too. But I never completely realized what they are when it comes to computing them. ...
6
votes
1answer
50 views

Polchinski Exercise 2.2, can I show that a function is harmonic by applying $\partial\bar{\partial}$?

I'm working on the following exercise: Exercise 2.2: Work out explicitly the expression $$:X^{\mu_1}(z_1, \overline{z}_1) \dots X^{\mu_n}(z_n, \overline{z}_n): \qquad \qquad\qquad $$ $$ ...
0
votes
3answers
3k views

Relation between quarks and strings

In string theory, are quarks just individual strings, or are they made of multiple strings? Are the heavier quarks made of heavier or longer strings? Are there red, blue, and green strings ...
4
votes
0answers
34 views

Target Space Lorentz Invariance vs. World Sheet Weyl Invariance

The Polyakov action, $S\sim \int d^2\sigma\sqrt{\gamma}\, \gamma_{ab}\partial^a X^\mu \partial ^b X_\mu$, has the well known classical symmetries of world sheet diffeomorphism invariance, world ...
2
votes
2answers
369 views

Black hole entropy

Bekenstein and Hawking derived the expression for black hole entropy as, $$ S_{BH}={c^3 A\over 4 G \hbar}. $$ We know from the hindsight that entropy has statistical interpretation. It is a measure ...
1
vote
1answer
45 views

What is the definition of the duality group $E_{7(7)}$?

What is the definition of the duality group $E_{7(7)}$ that appears in ${\cal N}=8$ Supergravity and what are the basics properties? Moreover what is the relation with the Lie Algebra $E_7$? ...
3
votes
1answer
64 views

Maldacena's decoupling argument

I am a bit confused about Maldacena's original decoupling argument. There are two different low energy (i.e, $\alpha^\prime \to 0$) descriptions of the stack of D3-branes: $\mathcal{N}=4$ SYM and ...
9
votes
1answer
624 views

String theory from a mathematical point of view

I have a great interest in the area of string theory, but since I am more focused on mathematics, I was wondering if there is any book out there that covers mathematical aspects of string theory. I ...
2
votes
1answer
46 views

D-branes in type II string theory

D-branes, as I currently understand them, are submanifolds of spacetime on which open strings can end with Dirichlet boundary conditions. On the other hand, type II string theory is a theory of ...
1
vote
1answer
40 views

Dimensional reduction of SUSY theories

I know that if one reduces 10 dimensional $\mathcal{N}=1$ SYM theory to 4 dimensions one gets $\mathcal{N}=4$ SYM. There are other examples also. I have two related questions regarding this fact. ...
4
votes
2answers
137 views

Where and how is the entropy of a black hole stored?

Where and how is the entropy of a black hole stored? Is it around the horizon? Most of the entanglement entropy across the event horizon lies within Planck distances of it and are short lived. Is ...
2
votes
0answers
46 views

Amplitude for a string to propagate from one point to another

In Zwiebach’s book sections 12.6 and 12.7 interesting aspects of the wave function of the string are discussed. In order to introduce my question first recall what happens with the relativistic ...
-5
votes
1answer
75 views

In string theory, are strings really just one dimensional? [duplicate]

Is it possible that they are 3 dimensional? Or what if they are 10 dimensional? Is it allowed that they are more than just one dimensional?
2
votes
2answers
83 views

Mathematics needed for string theory [duplicate]

I'm interested in cutting edge string theory studied by research physicist. I'm wonder what mathematics is needed and how far am I in terms of mathematics background needed and how much more ...
0
votes
0answers
25 views

Compactification and $S^1/Z_2$ orbifold in Randall-Sundrum (RS) model [closed]

In the Randall-Sundrum model we have a finite fifth dimension, with simplest periodic geometry as that of a circle, $S^1$ of radius $R$ where $y\mapsto y+2\pi R$ is identified. But to describe the ...
3
votes
2answers
78 views

How can one calculate the central term of the conformal field theory algebra (and show it's really the virasoro algebra)?

So I'm following Szabo's book "An Introduction to String Theory and D-brane Dynamics (2nd ed, 2011); still on the canonical treatment in chapter 3. After doing a mode expansion, we get (up to a ...
-3
votes
0answers
51 views

How is it physically possible for strings to only be one-dimensional? [duplicate]

How can something have length, but no width or height? If something is one-dimensional, does it even exist? By one-dimensional, do they mean that the height and width of the strings are so small ...
1
vote
1answer
132 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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0answers
47 views

Instantons and Fivebranes

What is the general relationship between instantons and fivebranes? In the paper ``Magnetic Monopoles in String Theory'' by Gauntlett, Harvey and Liu, the authors state the fivebrane ansatz of ...
-1
votes
1answer
37 views

Superstrings in the 10th Dimension [closed]

Physicists say that the superstrings vibrating in the 10th dimension are what create the subatomic particles that make up our universe and all other possible universes as well. If that is true, ...
10
votes
5answers
4k views

Can Loop Quantum Gravity connect in any way with string theory?

The one difficulty I see with LQG is that it requires an enormous number of degrees of freedom, e.g. these spin variables in the net. This is in contrast to stringy holographic theory where the ...
0
votes
0answers
36 views

Resource for (String) Symmetry Breaking in Terms of Roots and Weights?

I'm currently searching, for quite a while now, for a paper/book that discusses symmetry breaking in terms of roots and weights. Any suggestions would be much appreciated!
0
votes
2answers
50 views

Dirichlet boundary conditions in space-time?

In the context of string theory, and world sheets the Dirichlet boundary conditions can be written as: $$\frac{\partial X^\mu(\tau,\sigma_1)}{\partial \tau}=0$$ where $\sigma_1$ is the value of the ...
1
vote
3answers
82 views

The Nambu-Goto action how do we know the Hamilton's principle applies?

I am reading 'A first course in string theory' by Barton Zwiebach (2ed) on page 112 he comes up (after a small derivation) the action formula: $$S=-\frac{T_0}{c} \int d\tau d \sigma \sqrt{-\gamma}.$$ ...
1
vote
0answers
96 views

Calculating euler number of disk [migrated]

I'm trying to do exercise 3.1 from Polchinski, which should be a rather easy differential geometry problem. I have to calculate the euler number defined by $$\chi = \frac{1}{4\pi}\int_{M}d^{2}\sigma ...
0
votes
0answers
30 views

Decoupling of Weyl factor in critical dimension

In his paper called "Quantum geometry of bosonic strings", A.M.Polyakov quantizes a bosonic string using path integrals over the space of all metrics on the worldsheet. A critical dimension renders $D ...
4
votes
2answers
215 views

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

From 't Hooft's String Theory lecture notes on page 8 (paraphrased): To understand hadronic particles as excited states of strings, we have to study the dynamical properties of these strings, and ...
2
votes
1answer
116 views

Proper way to quantize the string in the light-cone gauge

In many books like Polchinski and Green-Schwarz-Witten the light cone quantization is carried out in a fast way. They just use the virasoro constraint in the light-cone gauge to get the ligh-cone ...
1
vote
1answer
82 views

Why does a certain covariant derivative of the stress-energy tensor vanish due to diffeomorphism invariance?

In Polchinski's string theory volume 1, at chap 1.2, after equation 1.2.22, he says $$\nabla_{a}T^{ab}=0$$ as a consequence of diffeomorphism invariance. But I cannot derive it. My derivation is ...
3
votes
1answer
139 views

Closed strings = open ones attached to a D0-brane?

I decided recently (to try) to learn String Theory, however from the beginning some newbie questions came up, which haven't given me a break. For this reason, I decided to ask some of them. I'd prefer ...
3
votes
0answers
53 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 ...
3
votes
1answer
111 views

Estimating volume of moduli space of genus-g Riemann surface with n marked points

I wanted to know how can I estimate the volume of the moduli space of a Riemann surface of genus $g$ and having $n$ marked points. I am reading some old string theory papers which discuss divergences ...
6
votes
4answers
1k views

What is background independence and how important is it?

What is background independence and how important is it? In order to be a theory of everything, will the final string-theory/m-theory have to be background independent? Does the current lack of ...
1
vote
0answers
42 views

Calculating OPE of Graviton Vertex Operator [duplicate]

Consider Exercise 2.8 in Polchinski's String Theory book. We are asked to compute the weight of $$f_{\mu \nu}:\partial X^{\mu} \bar{\partial}X^{\nu}e^{ik\cdot X}:$$ I have carried out the usual ...
15
votes
1answer
1k views

Do neutrinos refract?

The most benign of interactions is refraction. While neutrinos rarely interact with matter in a sense like the photoelectric effect, does that mean that they don't refract either?
2
votes
1answer
50 views

What is $\mathcal{N}=2$ QED?

I would like to know is $\mathcal{N}=2$ QED is simply a $\mathcal{N}=2$ theory with gauge group $U(1)$ like in normal QED? If not, exactly what theory is it? Is there some reference for it?
1
vote
0answers
34 views

Effect of orbifolding on gauge fields

A paper by Lalak et al, entitled "Soliton Solutions of M-theory on an orbifold", considers the brane solutions of 11 dimensional supergravity on a space of the form $R^{10} \times S^1/\mathbb{Z}_2$. ...
2
votes
0answers
79 views

Mathematician learning theoretical physics [duplicate]

EDIT: I was aware of the supposed duplicate. But I'm interested in a clear and focused path through the basics to advanced theoretical physics such as string theory - a path that avoids studying ...
1
vote
0answers
30 views

Fourier transformation and mode expansions [duplicate]

Sorry as this is a rather trivial question, but I'm stuck with a certain implication. I'm working on exercise 1.7 from Polchinski where we are given an open string with boundary conditions ...