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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65 views

Hierarchy problem and loop quantum gravity

According to https://en.wikipedia.org/wiki/Hierarchy_problem#Finite_Groups. Hierarchy problem can be theoretically solved using symmetry of certain bosonic string theory on the Leech lattice (though ...
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758 views

From Freshman Mechanics to String Theory: A Comprehensive Textbook Sequence in Physics [duplicate]

If a student with no background in physics and an understanding of only single variable calculus wanted to learn string theory, what sequence of textbooks would most succinctly, clearly, and ...
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Electroweak Hierarchy Problem (Softball Question)

My question is two-fold: 1) if i recall correctly, the hierarchy problem was initially appreciated by GUT model builders from the 80s onward. if the only valid solution is susy, would this suggest (...
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Is String Theory formulated in flat or curved spacetime?

String Theory is formulated in 10 or 11 (or 26?) dimensions where it is assumed that all of the space dimensions except for 3 (large) space dimensions and 1 time dimension are a compact manifold with ...
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2answers
153 views

Role of AdS/CFT correspondence in the context of integrability

I was wondering how the AdS/CFT correspondence fits in the context of integrability. As I understand, the AdS/CFT correspondence postulates a duality between gravity theories and CFT's. If one theory ...
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1answer
207 views

Why T-duality only work when the background has isometries?

I have been studying from some textbooks and papers about the T-dality topic. In particular for the Buscher rules it seems that they claim that in order to have T-duality in certain direction we need ...
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1answer
73 views

OPE of stress tensor in CFT

I come aross an OPE between stress tensor components in CFT which is \begin{equation} T(z)\bar{T}(\bar{w})\sim -\frac{\pi c}{12}\partial_{z}\partial_{\bar{w}}\delta^{(2)}(z-w)+... \end{equation} I am ...
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Polchinski's String theory Green's function on $RP_2$; eq. (6.2.38) p. 176

Is there an error in Polchinski's String Theory Equation (6.2.38) p 176 that is not on the Errata's page https://www.kitp.ucsb.edu/joep/links/joes-big-book-string/errata ? He write for the Green's ...
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1answer
71 views

How does the $D$-brane geometry influence the gauge symmetries?

I am trying to understand why the $D$-brane structure of a string theory matters for string phenomenology. From what I understood from Wikipedia, the $D$-brane structure determines the gauge ...
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1answer
70 views

Casimir Force and bosonic String Theory dimensions

I was reading the lecture notes on Quantum field theory by David Tong. In the section on Casimir force he derived the force of attraction felt by the plates due to the field vacuum energy in $1+1$ ...
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Can string theory explain why the charge of the positron and of the proton are equal? [duplicate]

There is not much more to elaborate. Can string theory say why electrons and protons have exactly opposite charge? And thus why hydrogen atoms are neutral? I guess that the answer is no, because ...
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Spin of higher string excitations

I am trying to better understand spin in string theory. There is already a good post here: Ssecond and third level excitations of open string But I have these questions: 1) Why would the second ...
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Which CFTs have AdS/CFT duals?

The AdS/CFT correspondence states that string theory in an asymptotically anti-De Sitter spacetime can be exactly described as a CFT on the boundary of this spacetime. Is the converse true? Does any ...
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What are the necessary conditions for a CFT to have a holographic dual? [duplicate]

The number of degrees of freedom of a CFT is given by its central charge $c$. From the bootstrap point of view, any CFT is characterized by the knowledge of its "CFT data", i.e. the scaling dimensions ...
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405 views

Equation of motion from Polyakov action

If I write (my understanding of) how to derive the equations of motion from the Polyakov action, I come up missing a term. Beginning with the basic Polyakov action \begin{equation} S = -\frac{T}{2}...
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157 views

Orientifold plane and twisted sector of bosonic string

Consider a bosonic string theory where we truncate the Hilbert space to states that are invariant under an orientifold action $\Omega$, which acts as a worldsheet parity + a space-time reflection, $$\...
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On the use of the Cauchy-product in deriving the stress-energy tensor constraint for a string in light-cone coordinates

I shall be following the notation used in David Tong's String Theory notes. In bosonic string theory, after fixing the gauge of the Polyakov action using Diff/Weyl invariance to make the two-...
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606 views

Why are there no branes in heterotic string theory?

Why does the heterotic string (or heterotic supergravity) have no brane solutions? According to David Tong's notes: the heterotic string doesn’t have (finite energy) D-branes. This is due to an ...
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986 views

Reduction of Nambu-Goto action to true degrees of freedom

I) First consider the point particle $$S=m\int\sqrt{-\dot{X}^2}d\tau.$$ If you choose the static gauge $$\tau=X^0$$ and replace it in the action you get $$=m\int\sqrt{1-\dot{X}^j\dot{X}^j}d\tau.$$ ...
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Can supersymmetry be extended to include anyons for 3+1D superstrings?

Are there no-go theorems and the like proving that there is no generalization of supersymmetry to fractional spins either in general or for superstrings in four dimensions? If so, are there ...
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1answer
184 views

Einstein Field Equation for a Garfinkle-Horowitz-Strominger theory

Consider a gravitational theory with a dilaton field and the action being given by Charged black holes in string theory (this link contains an erratum in the original paper) \begin{align} S = \int d^...
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3answers
375 views

Is the number of dimensions predicted by String Theory related to the Poincare group?

The Poincare group represents the isometries of Minkowski spacetime and is a ten-dimensional manifold. String theories predict that the universe is a ten-dimensional manifold. Question: Is this a ...
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333 views

Massive states of the closed bosonic string fitting into a representation of $SO(D-1)$

It is usually shown in the literature that massive light-cone gauge states for a closed bosonic string combine at mass level $N=\tilde{N}=2$ into representations of the little group $SO(D-1)$ and then ...
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1answer
40 views

Unitarity/Hermiticity condition for $osp(m,n|\mathbb{C})$ superalgebra

According to Dictionary on Lie Superalgebras (page 82), the compact form of $OSP(m,n|\mathbb C)$ Lie superalgebra must satisfy $M^{\text st}H\,M=1$ and $M^{\ddagger}M=1$ (is this the unitarity ...
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Holographic AdS/CFT intepretation of Cosmological Constant

I'm trying to understand how the value of AdS cosmological constant (or, equivalently, of AdS radius) affects the boundary CFT in AdS/CFT correspondence. I'd be glad of discovering something about the ...
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Supercurrent of the $bc$-$\beta\gamma$ SCFT

In Polchinksi's Sec. 10.1, the $bc$-$\beta\gamma$ SCFT is introduced with action $$S_{BC} = \frac{1}{2\pi} \int d^2z (b \bar \partial c + \beta \bar \partial \gamma)$$ and supercurrent $$T_F = -\...
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1answer
177 views

About the duality when embedding Gopakumar-Vafa into superstring theory

Vafa proposed a duality when embedding the Gopakumar-Vafa duality into superstring theory. Vafa's duality is about a correspondence N=1 supersymmetric gauge theory and superstring propagating on ...
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1answer
123 views

Conformal weights in Laurent expansions

Currently I am taking an introductory class in conformal field theory and ran into some confusion. Everywhere I run into Laurent expansions of several important quantities, and (mostly) all of them ...
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116 views

Matrix Model in AdS/CFT & exact results

Matrix models appeared in the context of AdS/CFT while trying to calculate the Circular Wilson Loop. It was first noted by Erickson, Semenoff & Zarembo [hep-th/0003055] that the 2-loop ...
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1answer
192 views

Polchinski equation 11.2.7

In Polchinski's string theory volume 2, when discussing the GSO projection for the heterotic string he says: In the IIA and IIB superstrings the GSO projection acted separately on the left- and ...
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1answer
160 views

Supersymmetry beyond $D=11$ spacetime dimensions

Taking into account the higher spin theories, from which string theory is an effective field theory, I just wondering if there is something to do to extend supersymmetry to any dimension without any ...
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Are the possible universes in brane cosmology embedded in string theory landscape?

String theory has a landscape of possible universes. Brane cosmology is related to string theory because it needs extra dimensions, but are the possible different universes of brane cosmology ...
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138 views

Could an holographic universe consist of 3d embedded in 4d instead of 3d embedded in 2d?

In the holographic model, information about a given dimension can be embedded in a lower dimension, so our 3d universe could be considered as a 2d one. Could it happen the other way? I mean, could the ...
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Why doesn't string theory predict the existence of infinitely many elementary particles?

I'm a physicist, but my knowledge of string theory is extremely minimal. My naive conceptual understanding is that the vacuum is modeled as a certain topology (and geometry?) for the spacetime, and ...
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1answer
171 views

How to calculate the free energy in curved space?

To study the Hagedorn temperature of string near a black hole, we need to calculate the free energy in curved space. This is can be done calculating a torus path integral, but I want to know if an ...
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3answers
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If extra dimensions are out there, why don't/can't we see them? [duplicate]

String theory proposes the existence of extra space dimensions. Very brilliant minds believe in their existence. Of course, I could appreciate that they are consequences of mathematical ...
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4answers
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Extra Dimensions (in String Theory) - What does it mean?

I have been reading a lot about string theory and the necessity of extra dimensions (particularly as visualized in Calabi-Yau spaces), as "curling-ups" in our apparently 3-dimensional (or 4-...
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1answer
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Explanation of the Nambu-Goto action and calculus needed for a beginner to learn [closed]

I have recently started trying to learn String Theory, but haven't learnt calculus - I know this probably isn't a good idea, but I decided to learn each part as I go. I'm partly using Brilliant, and ...
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AdS/CFT phenomenology and realistic FRW model building

Are there any examples of realistic holography (likely as a de Sitter type Universe: as it approximates FRW / is an FRW solution without baryonic and dark matter). I don’t see why one wouldn’t be ...
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155 views

Schwarzschild radius in matrix models

The Schwarzschild radius for 11D BHs is given by $l_{11}(l_{11}m)^{1/8}$, which is the special case ($D=11$) of the general dimensional case of $(G_Dm)^{\frac{1}{D-3}}$. Here $m$ is the BH mass and $...
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1answer
250 views

Supergroup action on $AdS_5\times S^5$

In the context of the AdS/CFT correspondence I was trying to understand how the symmetry group of the underlying space $AdS_5 \times S^5$ comes out to be the supergroup $SU(2,2|4)$. I can see how the ...
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216 views

In string theory, what replaces the black hole singularity?

In string theory, what replaces the black hole singularity? I know that it is possible for a single string to have arbitrarily large energy. Is a black hole just a single string?
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OPE of Lorentz current with tachyon vertex

This is a question related to chapter 2 in Polchinski's string theory book. On page 43 Polchinski calculates the Noether current from spacetime translations and then calculates its OPE with the ...
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Basic problem with String Theory

String theory turns the page on the standard description of the universe by replacing all matter and force particles with just one element: Tiny vibrating strings that twist and turn in complicated ...
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What sets the AdS radius $\ell$ in the CFT dual description?

In the context of AdS/CFT there should be a mapping between parameters for any given duality. But AdS has at least one dimensionful parameter, $\ell$: $$ds^2 = \frac{\ell^2}{z^2} ( -dt^2 + d\vec x^2 +...
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Branes ending on branes

From Polchinski book, I know that a one-dimensional brane can end on a higher dimensional brane. However, I was wondering if an even more generic picture could be developed, where a $(p+1)$-...
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2answers
628 views

M-theory and many-worlds interpretation

I am getting some confusion on whether M-theory accepts many-worlds interpretation. Can anyone show me the reasons or rebuttals for the possibility of the many-worlds interpretation in M-theory? ...
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Is there a black hole information paradox in string theory?

In string theory there is, for several black hole-like objects, a precise way to account for the microstates which make up the macroscopic Bekenstein-Hawking entropy. For instance for the black brane ...
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2answers
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Travel and locate extra dimensions

I'm a newbie to String Theory. String Theory says there are extra dimensions apart from the 4 known ones (space and time). Even if the extra dimensions are very small, what makes the theory say they ...
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1answer
159 views

Diffeomorphism invariance of scattering amplitude in bosonic string theory

It is mentioned in Polchinski's book (vol 1) that the diffeomorphism invariance of the scattering amplitude (see Polchinski, vol 1, eq 5.3.9) follows from the equation of motion of $b_{ab}$ (see ...