Questions tagged [string-theory]

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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String Theory and extra dimentions [closed]

I have watched a lot about relativity and quantum mechanics growing up, and while I am not an expert in any regard to quantum mechanics I feel like I might be onto something big, accounting for the ...
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Holomorphic anomaly at genus 1

Partition function on torus can be defined using a generalized Witten like index as given below: $$F_1=\int_\mathbb{T}\frac{d^2\tau}{\tau_2} Tr(-1)^F F_LF_R \;q^{L_0} \bar{q}^{\bar{L_0}},$$ where $\...
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Symmetry generating commutator in Witten's treatment of WZW model

In 'Non-abelian Bosonization in Two Dimensions', Witten writes down the commutation relations between currents and fields of the WZW model in equation (33): \begin{equation} \bigg[\frac{1}{2\pi}\bigg(\...
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Is it realistic for an unstable vacuum to have an infinite past, but a finite future?

Is it realistic for an unstable vacuum to have an infinite past, but a finite future? In other words, can there be a plausible scenario in which an unstable vacuum did not have a beginning, but ...
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String theory assumes that strings are complex geometric objects

In string theory, a string is a one-dimensional space that can be closed on itself as a circle (closed string) or open as a linear interval (open string), but does a string have one real dimension or ...
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Polchinski “String theory” (B.2.8)

The $\mathcal N = 1$ algebra \begin{equation} \{Q_\alpha,\overline Q_\beta\} = -2P_\mu\Gamma^\mu_{\alpha\beta} \end{equation} is in a frame where $k_1 = k_0$ \begin{equation} \{Q_\alpha, Q_\beta^\...
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Why does Witten not include higher order quantum corrections when quantizing Poisson brackets in the WZW model?

In 'Non-abelian Bosonization in Two Dimensions', Witten argues that the Poisson brackets of the currents that generate the $G\times G$ symmetry of the WZW model give rise to a Kac-Moody algebra upon ...
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Different symmetries or no symmetries in string theory?

I was reading the book "A Fortunate Universe" by Geraint Lewis and Luke Barnes and something caught my attention: At page 195 the authors say that universes with different symmetries could ...
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Textbook reference: Superstring Theory

I have almost finished reading the basics of Bosonic String Theory from Becker, Becker and Schwartz as well as Tong's notes. What is the best book to start reading about Superstring theory (something ...
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On the number of spacetime atoms in a Calabi-Yau crystal

This question is about an application of crystallography to topological string theory. Plane partitions are discrete models of the Planck scale geometry of Calabi-Yau manifolds in the A-model ...
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Chemical potentials for $D$-brane bound states

This question is about a mathematical subtlety arising in the computation of the partition function of a supersymmetric ensemble of some lower dimensional $D$-branes attached to a stack of higher ...
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Fuzzballs vs. black holes

Now I am trying understand: What are fuzzballs? What is the difference between fuzzballs and black holes? According to this presentation, one can construct fuzzball solution from ordinary BH solution ...
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Physical open string state problem

This is a basic question in bosonic String Theory. Can someone explain what is the interpretation of the coefficients? Since this is like the first quantized version of String theory, I would guess ...
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Commutation relations of derivatives of fermionic fields from the commutation relations of the original fields

I have a general question regarding such type of calculations, but let me start with a concrete question. Consider the $bc$- free fermion CFT so that $b(z)$ and $c(z)$ are free fermions with OPE, $$b(...
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Does the Kalb-Ramond field lead to electroweak force?

String theory predicts the following massless fields: $G_{\mu\nu}(X)$, $B_{\mu\nu}(X)$ and $\Phi(X)$. I understand that when one reduces to $4$-D then the $G_{\mu\nu}(X)$ is the spin-$2$ field of the ...
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1answer
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Angular momenta of closed bosonic string

Say we have the standard mode expansion of the closed bosonic string in conformal gauge. We compute the angular momenta which has an integration over the co-ordinate along the string. We get a zero-...
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What is more fundamntal? Fields, the excitations of which are particles, or particles, from which fields are formed? [duplicate]

I'll try to ask a naive question. In quantum field theory, which is more fundamental, fields or particles? And in string theory?
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Where do virtual particles come from?

Do I understand correctly that for the existence of virtual particles, a single physical object is needed - a quantum field? And virtual particles are excitations of this field that fills all space. ...
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1answer
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References on mathematical stacks for a string theory student

This question was posted on mathoverflow (here) without too much success. I'm hoping to read the famous Kapustin-Witten Paper "Electric-magnetic duality and the geometric Langlands program" ...
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Show that a system of intersecting $D4$-$D6$ branes is supersymmetric

The paper "Supersymmetric Gauge Theories, Intersecting Branes and Free Fermions" asserts (first paragraph, page 12,section 2.4) that a system of $N$ $D4$-branes intersecting with $k$ $D6$ ...
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What is brane inflation, and can it be eternal?

What is Brane Inflation and how does it describe inflation process? Can it be eternal?
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Quantum String action

If we have an action of the form: $$ S^{(0)} =\int d^Dx\sqrt{-G}\left(R+\alpha (\partial \phi)^2 + \frac{1}{6} e^{2 \alpha \phi}H_{mnp}H^{mnp}\right).$$ where $H_{mnp}=\partial_m B_{np}+\partial_n B_{...
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1answer
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Supersymmetry infinitesimal variation

In Wess & Bagger, chapter 3, the infinitesimal supersymmetric transformation is defined as: $$ \delta_\xi \psi = i\sqrt{2} \ \sigma^m \bar{\xi}\partial_m A + \sqrt{2} \ \xi F$$ and $$\delta_\xi A =...
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Cosmological time in the Milne region of Misner space

I refer to this paper. In the Milne regions of Misner space, the coordinates $x^{\pm}$ are defined as \begin{equation*}x^{\pm} = \frac{T\mathbb{e}^{\pm \beta \theta}}{\sqrt{2}}, x^{+}x^{-} > 0. \...
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Cyclic identity of $\gamma$-matrices in 3D and 4D

Reading the book on Supergravity from Freedman & van Proeyen I was very bewildered by the so called cyclic identity of $\gamma$-matrices of the Clifford-algebra(eq. 3.67) important in string ...
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STU supergravity

Tghere are a lot of different papers about STU supergravity, for example see this. As I understand, STU supergravity is N = 2 supergravity coupled to three vector multiplets. Could someone explain, ...
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Born-Infeld term for $D$-brane low energy effective action

I am trying to reproduce the Born-Infeld term for the $D$-brane action as explained in Szabo's BUSSTEP Lectures and must admit I am utterly confused by some of the steps. This is a long and technical ...
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Why string amplitude could be computed by path integral of string field theory?

I am trying to understand BCOV's paper: Kodaira-Spencer theory of gravity and exact results for quantum string amplitudes. In this paper, it was shown that the higher genus string amplitude for B-...
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1answer
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Non-extended and extended SUSY

What are the distinctions between Non-extended SUSY and Extended SUSY? (Is that just a non-extended SUSY has $\mathcal{N}=1$ while the extended SUSY has $\mathcal{N}>1$ ? Then there is no ...
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The Interaction between the fundamental gravitational strings

In string theory, do fundamental gravitational strings interact with each other constantly, or can they interact and then cease to interact?
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String theory and birth of the universe

Am I correct in understanding that in string theory before the birth of the universe, fundamental strings did not interact with each other, and when the strings began to interact, space-time appeared?
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Gravitational radiation in M theory and super string theory [closed]

Hey I'm trying to build a toy model of gravitational radiation for fun from M theory. I need some general help with selecting thru the ideas I have. My first "model" is to make a M2 brane ...
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1answer
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Superalgebra and BRST supersymmetry 2: why Lie algebra and groups?

This follows a comment to split to a 2nd question Superalgebra and BRST supersymmetry 1: odd vs even It is said that most of theories, the even elements of the superalgebra correspond to bosons and ...
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1answer
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Superalgebra and BRST supersymmetry 1: odd vs even

It is said that most of theories, the even elements of the superalgebra correspond to bosons and odd elements to fermions (but this is not always true; for example, the BRST supersymmetry is the other ...
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1answer
76 views

Prerequisites for IAS volumes on Quantum Fields and Strings [closed]

I'm a physics grad student interested in pursuing physics in a mathematically rigorous manner. However, I've hit a roadblock with the two volume book, Quantum Fields and Strings: A Course For ...
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1answer
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Perturbative non-renormalizability of brane action

In the second chapter of string theory book by Green-Schwarz-Witten, the advantages of string theory over others is discussed. It is stated that the higher-dimensional analogs, with the action ...
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What would it mean if symmetries are not fundamental at all?

In this paper 1 written by Joseph Polchinski, he seems to indicate that all symmetries of nature may not be fundamental: From more theoretical points of view, string theory appears to allow no exact ...
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$(p,q)$-5 webs from $M$-Theory

The authors of the paper "Webs of (p,q) 5-branes, Five Dimensional Field Theories and Grid Diagrams" consider type $IIB$ superstring theory compactified on a circle $S^{1}$ and claim (in ...
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Static fields described by coherent states of photons/gravitons with longitudinal/timelike polarization

There are formulations of QED where electrostatic Coulomb fields around a charge are expressed as coherent states of photons with longitudinal/timelike polarization.  See for example chapter 3 of ...
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If string theory is inconsistent with observations, why hasn't it been rejected yet?

I'm no expert on string theory, but I've been reading about it. I've been quite surprised because of how it appears to be inconsistent with observations, but hasn't been rejected yet. Examples: On the ...
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Anomalies in the self-dual Yang-Mills theory and $\mathcal{N}=2$ open-string theory

I am reading a paper, written by G. Chalmers and W. Siegel - https://arxiv.org/abs/hep-th/9606061, where they discuss the action of self-dual Yang-Mills theory, which in light-cone formalism is ...
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D-brane, and SUSY charges

The following results summarize the relation between orientifold and D-brane, and SUSY charge $$ \begin{array}{l||c|c|c|c|c|c}\text{orientifold} &\text{O4} & \text{O3} & \text{O2} &\...
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1answer
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String theory allows chiral gauge coupling

In Polchinski String Vol 1: Chiral gauge couplings. The gauge interactions in nature are parity asymmetric (chiral). This has been a stumbling block for a number of previous unifying ideas: they ...
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Supersymmetry $\mathcal{N}$ constrained by spacetime dimensions $D$

Given some spacetime dimensions $D$, are there only certain allowed supersymmetry charge nunbers $\mathcal{N}$? What are the relations of $\mathcal{N}$ and $D$ for the following cases: When the ...
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1answer
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Does one ever need infinitely many cohomologies?

In a theory containing gauge fields or higher-form gauge fields, if the background spacetime is a complicated manifold, a nice way to represent the configuration of the gauge field mathematically is ...
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What is matter really made up of?

We know matter is made up atoms, and atoms are made up of protons, neutrons, and electrons. And we know that protons and neutrons are made up of smaller particles known as quarks. Would probing deeper ...
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A discrepancy between the usual interpretation of Bell's theorem and a full theory of quantum gravity

**** This question has been modified following the discussion below. **** Bell’s theorem says, in a nutshell, that “local hidden-variable theories (HVT) cannot exist” (since they contradict QM in Bell ...
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Causality: Why can't things move backwards in time, within past lightcone?

My question Why can't effects propagate backwards in time, within the backwards light cone of a cause? For example, when I turn on a flashlight, why doesn't the light travel backwards in time just ...
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Is superstrings on the $E_8$ torus dual to bosonic string theory on the Leech lattice torus?

Two important unimodular lattices are $E_8$ and the Leech lattice. One can take 10D superstring theory and compactify it over the $E_8$ torus. One can also take 26D bosonic string theory and ...
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Supersymmetry v.s. BRST symmetry: QFT examples

Questions: Can any expert contrast the differences and similarities of Supersymmetry (SUSY) v.s. BRST (global) symmetry? (Question 1) What are the RULES and CRITERIA that having one symmetry implies ...

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