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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1answer
73 views

Worldsheet SCFT on a lattice

My question is clear from the title. I'm curious whether it is possible to put the string world sheet SCFT on a lattice. I expect when the world sheet theory is chiral, then it's not possible. But I ...
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Background knowledge needed to read the book "Holographic Quantum Matter" by Hartnoll, Lucas, Sachdev?

I want to start going through the book "Holographic Quantum Matter" by Hartnoll, Lucas, Sachdev but it seems that my background in basic solid state physics and basic quantum field theory (1-...
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Thermodynamics Relevance to String Theory, Advice

Please help me make a very important decision! I only need to hear a bit from a String Theorist or Quantum Field Theorist (or anyone close to such people and areas of research) to tell me about how ...
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Is it possible to bound a single D0-brane to a D4-brane?

I'm studying the Jafferis solution for twisted $N=4$ Yang-Mills theory in four dimensions from the paper Crystals and intersecting branes. Consider the problem of computing the charges of the allowed ...
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Compactification of additional dimensions [duplicate]

The extra dimensions in string theory are supposed to close in on themselves to form circles. Are there other possibilities for compactification? For example a compactification in segment.
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BRST invariant vertex operator

I'm trying to compute the commutator $\left[Q_{BRST}(z), V^{-1/2}_{v}(w)\right]$, where $V^{-1/2}_{v}(w)$ is the vertex operator corresponding to a massive fermion state. The vertex reads $$ V_{v}^{-\...
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2answers
133 views

Vacuum in string theory

How is vacuum described in string theory? The same as in the QFT? Does string theory have quantum fluctuations of the vacuum, are the processes of creation and destruction of virtual strings ...
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2answers
231 views

Inconsistency in the normal ordered Virasoro algebra

I seem to have found a basic contradiction when it comes to the commutation relations of the Virasoro algebra with normal ordered operators and I am not sure what the resolution is. If we have a ...
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1answer
69 views

Does the new measurement of the fine structure constant rule out string theory?

I am no expert in either string theory or experimental physics, but I was reading this article by Nature, where it is quoted: This result confirms, for example, that the electron has no substructure ...
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1answer
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Simplifying Equation - Quantum String

In this post Quantum String action , the user does the following manipulation : $$\delta (H_{mnp})H^{mnp} =\partial_m\delta(B_{np})[H^{mnp}+H^{pmn}+H^{npm}] $$ I can't quite understand how he does ...
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Open string as intermediate state in closed string propagator

I'm a freshman in string theory. My question is: when we compute the full closed string propagator in a theory that contains both closed and open string, do we need to include open string as the ...
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2answers
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Can string theory be background independent?

Are there any models in string theory which are background independent? If there are, would this mean that these models could be built in any number of dimensions? (Instead of assuming a fixed number ...
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Zero-point energy? (D-branes C.Johnson's book)

In Johnson's Book about D-branes (11.2) gives the zero point energy. This is given using (2.80) \begin{equation} +\frac12\omega: \text{for boson and}\;\; -\frac12\omega: \text{for fermion}. \end{...
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1answer
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How does one get rid of tachyonic fields in string theory?

I've been watching Susskind's lectures on string theory and M-theory. He mentioned in video 3 that string theory initially had tachyons but that this was fixed early on in string theory's development. ...
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1answer
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Can strings exist along time in spacetime (aka. target space)?

I have had this question for quite some time: As I understand it, in string theory there is tension along the strings such that this tension is between different elements of the string in space. Thus, ...
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Extra term in E.O.M. for Nambu-Goto action with general targetspace metric

Strangely I haven't found a derivation of the E.O.M. of a string in an arbitrary background metric $G_{\mu \nu}$ from the Nambu-Goto action. (Many places present it for the Polyakov action.) Upon ...
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1answer
152 views

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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1answer
81 views

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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1answer
107 views

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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1answer
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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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2answers
201 views

Textbook reference: Superstring Theory [closed]

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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1answer
107 views

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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1answer
74 views

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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1answer
118 views

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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70 views

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
45 views

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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3answers
768 views

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
247 views

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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2answers
134 views

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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2answers
272 views

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
96 views

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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1answer
88 views

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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57 views

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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0answers
47 views

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-...
2
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1answer
53 views

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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2answers
120 views

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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168 views

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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1answer
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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
45 views

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
56 views

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 ...
2
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1answer
230 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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